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	diff --git a/doc/gpgme.texi b/doc/gpgme.texi
	index 7f178158..a616e335 100644
	--- a/doc/gpgme.texi
	+++ b/doc/gpgme.texi
	@@ -1,8445 +1,8446 @@
	\input texinfo @c -- mode: texinfo; coding: utf-8; --
	@documentencoding UTF-8
	@setfilename gpgme.info
	@include defs.inc
	@settitle The `GnuPG Made Easy' Reference Manual

	@dircategory GNU Libraries
	@direntry
	* @acronym{GPGME}: (gpgme). Adding support for cryptography to your program.
	@end direntry

	@c Unify some of the indices.
	@syncodeindex tp fn
	@syncodeindex pg fn

	@copying
	Copyright @copyright{} 2002--2008, 2010, 2012--2018 g10 Code GmbH.

	@quotation
	Permission is granted to copy, distribute and/or modify this document
	under the terms of the GNU General Public License as published by the
	Free Software Foundation; either version 3 of the License, or (at your
	option) any later version. The text of the license can be found in the
	section entitled ``Copying''.
	@end quotation

	This document is distributed in the hope that it will be useful, but
	WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	General Public License for more details.
	@end copying

	@c Macros used by the description of the UI server protocol
	@macro clnt{string}
	@sc{c:} \string\
	@end macro
	@macro srvr{string}
	@sc{s:} \string\
	@end macro

	@c API version.
	@macro since{string}
	@sc{Since:} \string\
	@end macro


	@c
	@c T I T L E P A G E
	@c
	@ifinfo
	This file documents the @acronym{GPGME} library.

	This is Edition @value{EDITION}, last updated @value{UPDATED}, of
	@cite{The `GnuPG Made Easy' Reference Manual}, for Version
	@value{VERSION}.

	@c NOTE: Don't forget to update the year for the TeX version, too.
	@insertcopying

	@end ifinfo

	@c We do not want that bastard short titlepage.
	@c @iftex
	@c @shorttitlepage The `GnuPG Made Easy' Reference Manual
	@c @end iftex
	@titlepage
	@center @titlefont{The `GnuPG Made Easy'}
	@sp 1
	@center @titlefont{Reference Manual}
	@sp 6
	@center Edition @value{EDITION}
	@sp 1
	@center last updated @value{UPDATED}
	@sp 1
	@center for version @value{VERSION}
	@page
	@vskip 0pt plus 1filll
	Published by The GnuPG Project@* c/o g10 Code GmbH@* Hüttenstr. 61@* 40699 Erkrath, Germany

	@insertcopying
	@end titlepage
	@page

	@summarycontents
	@contents

	@ifnottex
	@node Top
	@top Main Menu
	This is Edition @value{EDITION}, last updated @value{UPDATED}, of
	@cite{The `GnuPG Made Easy' Reference Manual}, for Version
	@value{VERSION} of the @acronym{GPGME} library.
	@end ifnottex

	@menu
	* Introduction:: How to use this manual.
	* Preparation:: What you should do before using the library.
	* Protocols and Engines:: Supported crypto protocols.
	* Algorithms:: Supported algorithms.
	* Error Handling:: Error numbers and their meanings.
	* Exchanging Data:: Passing data to and from @acronym{GPGME}.
	* Contexts:: Handling @acronym{GPGME} contexts.

	Appendices

	* UI Server Protocol:: The GnuPG UI Server Protocol.
	* Debugging:: How to solve problems.
	* Deprecated Functions:: Documentation of deprecated functions.

	* Library Copying:: The GNU Lesser General Public License says
	how you can copy and share `GnuPG Made Easy'.
	* Copying:: The GNU General Public License says how you
	can copy and share this manual.

	Indices

	* Concept Index:: Index of concepts and programs.
	* Function and Data Index:: Index of functions, variables and data types.

	@detailmenu
	--- The Detailed Node Listing ---

	Introduction

	* Getting Started:: Purpose of the manual, and how to use it.
	* Features:: Reasons to install and use @acronym{GPGME}.
	* Overview:: Basic architecture of the @acronym{GPGME} library.

	Preparation

	* Header:: What header file you need to include.
	* Building the Source:: Compiler options to be used.
	* Largefile Support (LFS):: How to use @acronym{GPGME} with LFS.
	* Using Automake:: Compiler options to be used the easy way.
	* Using Libtool:: Avoiding compiler options entirely.
	* Library Version Check:: Getting and verifying the library version.
	* Signal Handling:: How @acronym{GPGME} affects signal handling.
	* Multi-Threading:: How @acronym{GPGME} can be used in an MT environment.

	Protocols and Engines

	* Engine Version Check:: Verifying the engine version.
	* Engine Information:: Obtaining more information about the engines.
	* Engine Configuration:: Changing the engine configuration.
	* OpenPGP:: Support for the OpenPGP protocol.
	* Cryptographic Message Syntax:: Support for the CMS.

	Algorithms

	* Public Key Algorithms:: A list of all public key algorithms.
	* Hash Algorithms:: A list of all hash algorithms.

	Error Handling

	* Error Values:: The error value and what it means.
	* Error Codes:: A list of important error codes.
	* Error Sources:: A list of important error sources.
	* Error Strings:: How to get a descriptive string from a value.

	Exchanging Data

	* Creating Data Buffers:: Creating new data buffers.
	* Destroying Data Buffers:: Releasing data buffers.
	* Manipulating Data Buffers:: Operations on data buffers.

	Creating Data Buffers

	* Memory Based Data Buffers:: Creating memory based data buffers.
	* File Based Data Buffers:: Creating file based data buffers.
	* Callback Based Data Buffers:: Creating callback based data buffers.

	Manipulating Data Buffers

	* Data Buffer I/O Operations:: I/O operations on data buffers.
	* Data Buffer Meta-Data:: Meta-data manipulation of data buffers.
	* Data Buffer Convenience:: Convenience function for data buffers.

	Contexts

	* Creating Contexts:: Creating new @acronym{GPGME} contexts.
	* Destroying Contexts:: Releasing @acronym{GPGME} contexts.
	* Result Management:: Managing the result of crypto operations.
	* Context Attributes:: Setting properties of a context.
	* Key Management:: Managing keys with @acronym{GPGME}.
	* Crypto Operations:: Using a context for cryptography.
	* Miscellaneous:: Miscellaneous operations.
	* Run Control:: Controlling how operations are run.

	Context Attributes

	* Protocol Selection:: Selecting the protocol used by a context.
	* Crypto Engine:: Configuring the crypto engine.
	* Setting the Sender:: How to tell the engine the sender.
	* ASCII Armor:: Requesting @acronym{ASCII} armored output.
	* Text Mode:: Choosing canonical text mode.
	* Offline Mode:: Choosing offline mode.
	* Included Certificates:: Including a number of certificates.
	* Key Listing Mode:: Selecting key listing mode.
	* Passphrase Callback:: Getting the passphrase from the user.
	* Progress Meter Callback:: Being informed about the progress.
	* Status Message Callback:: Status messages received from gpg.
	* Locale:: Setting the locale of a context.

	Key Management

	* Key objects:: Description of the key structures.
	* Listing Keys:: Browsing the list of available keys.
	* Information About Keys:: Requesting detailed information about keys.
	* Manipulating Keys:: Operations on keys.
	* Generating Keys:: Creating new key pairs.
	* Signing Keys:: Adding key signatures to public keys.
	* Exporting Keys:: Retrieving key data from the key ring.
	* Importing Keys:: Adding keys to the key ring.
	* Deleting Keys:: Removing keys from the key ring.
	* Changing Passphrases:: Change the passphrase of a key.
	* Changing TOFU Data:: Changing data pertaining to TOFU.
	* Advanced Key Editing:: Advanced key edit operation.

	Crypto Operations

	* Decrypt:: Decrypting a ciphertext.
	* Verify:: Verifying a signature.
	* Decrypt and Verify:: Decrypting a signed ciphertext.
	* Sign:: Creating a signature.
	* Encrypt:: Encrypting a plaintext.

	Sign

	* Selecting Signers:: How to choose the keys to sign with.
	* Creating a Signature:: How to create a signature.
	* Signature Notation Data:: How to add notation data to a signature.

	Encrypt

	* Encrypting a Plaintext:: How to encrypt a plaintext.

	Miscellaneous

	* Running other Programs:: Running other Programs.
	* Using the Assuan protocol:: Using the Assuan protocol.
	* Checking for updates:: How to check for software updates.

	Run Control

	* Waiting For Completion:: Waiting until an operation is completed.
	* Using External Event Loops:: Advanced control over what happens when.
	* Cancellation:: How to end pending operations prematurely.

	Using External Event Loops

	* I/O Callback Interface:: How I/O callbacks are registered.
	* Registering I/O Callbacks:: How to use I/O callbacks for a context.
	* I/O Callback Example:: An example how to use I/O callbacks.
	* I/O Callback Example GTK+:: How to integrate @acronym{GPGME} in GTK+.
	* I/O Callback Example GDK:: How to integrate @acronym{GPGME} in GDK.
	* I/O Callback Example Qt:: How to integrate @acronym{GPGME} in Qt.

	@end detailmenu
	@end menu

	@node Introduction
	@chapter Introduction

	`GnuPG Made Easy' (@acronym{GPGME}) is a C language library that
	allows to add support for cryptography to a program. It is designed
	to make access to public key crypto engines like GnuPG or GpgSM easier
	for applications. @acronym{GPGME} provides a high-level crypto API
	for encryption, decryption, signing, signature verification and key
	management.

	@acronym{GPGME} uses GnuPG and GpgSM as its backends to support
	OpenPGP and the Cryptographic Message Syntax (CMS).

	@menu
	* Getting Started:: Purpose of the manual, and how to use it.
	* Features:: Reasons to install and use @acronym{GPGME}.
	* Overview:: Basic architecture of the @acronym{GPGME} library.
	@end menu


	@node Getting Started
	@section Getting Started

	This manual documents the @acronym{GPGME} library programming
	interface. All functions and data types provided by the library are
	explained.

	The reader is assumed to possess basic knowledge about cryptography in
	general, and public key cryptography in particular. The underlying
	cryptographic engines that are used by the library are not explained,
	but where necessary, special features or requirements by an engine are
	mentioned as far as they are relevant to @acronym{GPGME} or its users.

	This manual can be used in several ways. If read from the beginning
	to the end, it gives a good introduction into the library and how it
	can be used in an application. Forward references are included where
	necessary. Later on, the manual can be used as a reference manual to
	get just the information needed about any particular interface of the
	library. Experienced programmers might want to start looking at the
	examples at the end of the manual, and then only read up those parts
	of the interface which are unclear.

	The documentation for the language bindings is currently not included
	in this manual. Those languages bindings follow the general
	programming model of @acronym{GPGME} but may provide some extra high
	level abstraction on top of the @acronym{GPGME} style API. For now
	please see the README files in the @file{lang/} directory of the
	source distribution.


	@node Features
	@section Features

	@acronym{GPGME} has a couple of advantages over other libraries doing
	a similar job, and over implementing support for GnuPG or other crypto
	engines into your application directly.

	@table @asis
	@item it's free software
	Anybody can use, modify, and redistribute it under the terms of the GNU
	Lesser General Public License (@pxref{Library Copying}).

	@item it's flexible
	@acronym{GPGME} provides transparent support for several cryptographic
	protocols by different engines. Currently, @acronym{GPGME} supports
	the OpenPGP protocol using GnuPG as the backend, and the Cryptographic
	Message Syntax using GpgSM as the backend.

	@item it's easy
	@acronym{GPGME} hides the differences between the protocols and
	engines from the programmer behind an easy-to-use interface. This way
	the programmer can focus on the other parts of the program, and still
	integrate strong cryptography in his application. Once support for
	@acronym{GPGME} has been added to a program, it is easy to add support
	for other crypto protocols once @acronym{GPGME} backends provide them.

	@item it's language friendly
	@acronym{GPGME} comes with languages bindings for several common
	programming languages: Common Lisp, C++, Python 2, and Python 3.
	@end table

	@node Overview
	@section Overview

	@acronym{GPGME} provides a data abstraction that is used to pass data
	to the crypto engine, and receive returned data from it. Data can be
	read from memory or from files, but it can also be provided by a
	callback function.

	The actual cryptographic operations are always set within a context.
	A context provides configuration parameters that define the behaviour
	of all operations performed within it. Only one operation per context
	is allowed at any time, but when one operation is finished, you can
	run the next operation in the same context. There can be more than
	one context, and all can run different operations at the same time.

	Furthermore, @acronym{GPGME} has rich key management facilities
	including listing keys, querying their attributes, generating,
	importing, exporting and deleting keys, and acquiring information
	about the trust path.

	With some precautions, @acronym{GPGME} can be used in a multi-threaded
	environment, although it is not completely thread safe and thus needs
	the support of the application.


	@node Preparation
	@chapter Preparation

	To use @acronym{GPGME}, you have to perform some changes to your
	sources and the build system. The necessary changes are small and
	explained in the following sections. At the end of this chapter, it
	is described how the library is initialized, and how the requirements
	of the library are verified.

	@menu
	* Header:: What header file you need to include.
	* Building the Source:: Compiler options to be used.
	* Largefile Support (LFS):: How to use @acronym{GPGME} with LFS.
	* Using Automake:: Compiler options to be used the easy way.
	* Using Libtool:: Avoiding compiler options entirely.
	* Library Version Check:: Getting and verifying the library version.
	* Signal Handling:: How @acronym{GPGME} affects signal handling.
	* Multi-Threading:: How @acronym{GPGME} can be used in an MT environment.
	@end menu


	@node Header
	@section Header
	@cindex header file
	@cindex include file

	All interfaces (data types and functions) of the library are defined
	in the header file `gpgme.h'. You must include this in all programs
	using the library, either directly or through some other header file,
	like this:

	@example
	#include <gpgme.h>
	@end example

	The name space of @acronym{GPGME} is @code{gpgme_*} for function names
	and data types and @code{GPGME_*} for other symbols. Symbols internal
	to @acronym{GPGME} take the form @code{_gpgme_} and @code{_GPGME_}.

	Because @acronym{GPGME} makes use of the GPG Error library, using
	@acronym{GPGME} will also use the @code{GPG_ERR_*} name space
	directly, and the @code{gpg_err}, @code{gpg_str}, and @code{gpgrt_*}
	name space indirectly.


	@node Building the Source
	@section Building the Source
	@cindex compiler options
	@cindex compiler flags

	If you want to compile a source file including the `gpgme.h' header
	file, you must make sure that the compiler can find it in the
	directory hierarchy. This is accomplished by adding the path to the
	directory in which the header file is located to the compilers include
	file search path (via the @option{-I} option).

	However, the path to the include file is determined at the time the
	source is configured. To solve this problem, gpgme ships with a small
	helper program @command{gpgme-config} that knows about the path to the
	include file and other configuration options. The options that need
	to be added to the compiler invocation at compile time are output by
	the @option{--cflags} option to @command{gpgme-config}. The following
	example shows how it can be used at the command line:

	@example
	gcc -c foo.c `gpgme-config --cflags`
	@end example

	Adding the output of @samp{gpgme-config --cflags} to the compiler
	command line will ensure that the compiler can find the
	@acronym{GPGME} header file.

	A similar problem occurs when linking the program with the library.
	Again, the compiler has to find the library files. For this to work,
	the path to the library files has to be added to the library search
	path (via the @option{-L} option). For this, the option
	@option{--libs} to @command{gpgme-config} can be used. For
	convenience, this option also outputs all other options that are
	required to link the program with @acronym{GPGME} (in particular, the
	@samp{-lgpgme} option). The example shows how to link @file{foo.o}
	with the @acronym{GPGME} library to a program @command{foo}.

	@example
	gcc -o foo foo.o `gpgme-config --libs`
	@end example

	Of course you can also combine both examples to a single command by
	specifying both options to @command{gpgme-config}:

	@example
	gcc -o foo foo.c `gpgme-config --cflags --libs`
	@end example

	If you need to detect the installed language bindings you can use list
	them using:

	@example
	gpgme-config --print-lang
	@end example

	or test for the availability using

	@example
	gpgme-config --have-lang=python && echo 'Bindings for Pythons available'
	@end example


	@node Largefile Support (LFS)
	@section Largefile Support (LFS)
	@cindex largefile support
	@cindex LFS

	@acronym{GPGME} is compiled with largefile support by default, if it
	is available on the system. This means that GPGME supports files
	larger than two gigabyte in size, if the underlying operating system
	can. On some systems, largefile support is already the default. On
	such systems, nothing special is required. However, some systems
	provide only support for files up to two gigabyte in size by default.
	Support for larger file sizes has to be specifically enabled.

	To make a difficult situation even more complex, such systems provide
	two different types of largefile support. You can either get all
	relevant functions replaced with alternatives that are largefile
	capable, or you can get new functions and data types for largefile
	support added. Those new functions have the same name as their
	smallfile counterparts, but with a suffix of 64.

	An example: The data type @code{off_t} is 32 bit wide on GNU/Linux PC
	systems. To address offsets in large files, you can either enable
	largefile support add-on. Then a new data type @code{off64_t} is
	provided, which is 64 bit wide. Or you can replace the existing
	@code{off_t} data type with its 64 bit wide counterpart. All
	occurrences of @code{off_t} are then automagically replaced.

	As if matters were not complex enough, there are also two different
	types of file descriptors in such systems. This is important because
	if file descriptors are exchanged between programs that use a
	different maximum file size, certain errors must be produced on some
	file descriptors to prevent subtle overflow bugs from occurring.

	As you can see, supporting two different maximum file sizes at the
	same time is not at all an easy task. However, the maximum file size
	does matter for @acronym{GPGME}, because some data types it uses in
	its interfaces are affected by that. For example, the @code{off_t}
	data type is used in the @code{gpgme_data_seek} function, to match its
	@acronym{POSIX} counterpart. This affects the call-frame of the
	function, and thus the ABI of the library. Furthermore, file
	descriptors can be exchanged between GPGME and the application.

	For you as the user of the library, this means that your program must
	be compiled in the same file size mode as the library. Luckily, there
	is absolutely no valid reason for new programs to not enable largefile
	support by default and just use that. The compatibility modes (small
	file sizes or dual mode) can be considered an historic artefact, only
	useful to allow for a transitional period.

	On POSIX platforms @acronym{GPGME} is compiled using largefile support
	by default. This means that your application must do the same, at
	least as far as it is relevant for using the @file{gpgme.h} header
	file. All types in this header files refer to their largefile
	counterparts, if they are different from any default types on the
	system.

	On 32 and 64 bit Windows platforms @code{off_t} is declared as 32 bit
	signed integer. There is no specific support for LFS in the C
	library. The recommendation from Microsoft is to use the native
	interface (@code{CreateFile} et al.) for large files. Released binary
	versions of @acronym{GPGME} (libgpgme-11.dll) have always been build
	with a 32 bit @code{off_t}. To avoid an ABI break we stick to this
	convention for 32 bit Windows by using @code{long} there.
	@acronym{GPGME} versions for 64 bit Windows have never been released
	and thus we are able to use @code{int64_t} instead of @code{off_t}
	there. For easier migration the typedef @code{gpgme_off_t} has been
	defined. The reason we cannot use @code{off_t} directly is that some
	toolchains (e.g. mingw64) introduce a POSIX compatible hack for
	@code{off_t}. Some widely used toolkits make use of this hack and in
	turn @acronym{GPGME} would need to use it also. However, this would
	introduce an ABI break and existing software making use of libgpgme
	might suffer from a severe break. Thus with version 1.4.2 we
	redefined all functions using @code{off_t} to use @code{gpgme_off_t}
	which is defined as explained above. This way we keep the ABI well
	defined and independent of any toolchain hacks. The bottom line is
	that LFS support in @acronym{GPGME} is only available on 64 bit
	versions of Windows.

	On POSIX platforms you can enable largefile support, if it is
	different from the default on the system the application is compiled
	on, by using the Autoconf macro @code{AC_SYS_LARGEFILE}. If you do
	this, then you don't need to worry about anything else: It will just
	work. In this case you might also want to use @code{AC_FUNC_FSEEKO}
	to take advantage of some new interfaces, and @code{AC_TYPE_OFF_T}
	(just in case).

	If you do not use Autoconf, you can define the preprocessor symbol
	@code{_FILE_OFFSET_BITS} to 64 @emph{before} including any header
	files, for example by specifying the option
	@code{-D_FILE_OFFSET_BITS=64} on the compiler command line. You will
	also want to define the preprocessor symbol @code{LARGEFILE_SOURCE} to
	1 in this case, to take advantage of some new interfaces.

	If you do not want to do either of the above, you probably know enough
	about the issue to invent your own solution. Just keep in mind that
	the @acronym{GPGME} header file expects that largefile support is
	enabled, if it is available. In particular, we do not support dual
	mode (@code{_LARGEFILE64_SOURCE}).


	@node Using Automake
	@section Using Automake
	@cindex automake
	@cindex autoconf

	It is much easier if you use GNU Automake instead of writing your own
	Makefiles. If you do that you do not have to worry about finding and
	invoking the @command{gpgme-config} script at all. @acronym{GPGME}
	provides an extension to Automake that does all the work for you.

	@c A simple macro for optional variables.
	@macro ovar{varname}
	@r{[}@var{\varname\}@r{]}
	@end macro
	@defmac AM_PATH_GPGME (@ovar{minimum-version}, @ovar{action-if-found}, @ovar{action-if-not-found})
	@defmacx AM_PATH_GPGME_PTH (@ovar{minimum-version}, @ovar{action-if-found}, @ovar{action-if-not-found})
	@defmacx AM_PATH_GPGME_PTHREAD (@ovar{minimum-version}, @ovar{action-if-found}, @ovar{action-if-not-found})
	Check whether @acronym{GPGME} (at least version @var{minimum-version},
	if given) exists on the host system. If it is found, execute
	@var{action-if-found}, otherwise do @var{action-if-not-found}, if
	given.

	Additionally, the function defines @code{GPGME_CFLAGS} to the flags
	needed for compilation of the program to find the @file{gpgme.h}
	header file, and @code{GPGME_LIBS} to the linker flags needed to link
	the program to the @acronym{GPGME} library. If the used helper script
	does not match the target type you are building for a warning is
	printed and the string @code{libgcrypt} is appended to the variable
	@code{gpg_config_script_warn}.

	@code{AM_PATH_GPGME_PTHREAD} checks for the version of @acronym{GPGME}
	that can be used with the native pthread implementation, and defines
	@code{GPGME_PTHREAD_CFLAGS} and @code{GPGME_PTHREAD_LIBS}. Since
	version 1.8.0 this is no longer required to GPGME_PTHREAD as
	@acronym{GPGME} itself is thread safe.

	This macro searches for @command{gpgme-config} along the PATH. If
	you are cross-compiling, it is useful to set the environment variable
	@code{SYSROOT} to the top directory of your target. The macro will
	then first look for the helper program in the @file{bin} directory
	below that top directory. An absolute directory name must be used for
	@code{SYSROOT}. Finally, if the configure command line option
	@code{--with-gpgme-prefix} is used, only its value is used for the top
	directory below which the helper script is expected.

	@end defmac

	You can use the defined Autoconf variables like this in your
	@file{Makefile.am}:

	@example
	AM_CPPFLAGS = $(GPGME_CFLAGS)
	LDADD = $(GPGME_LIBS)
	@end example


	@node Using Libtool
	@section Using Libtool
	@cindex libtool

	The easiest way is to just use GNU Libtool. If you use libtool, and
	link to @code{libgpgme.la}, @code{libgpgme-pth.la} or
	@code{libgpgme-pthread.la} respectively, everything will be done
	automatically by Libtool.


	@node Library Version Check
	@section Library Version Check
	@cindex version check, of the library

	@deftypefun {const char } gpgme_check_version (@w{const char @var{required_version}})
	The function @code{gpgme_check_version} has four purposes. It can be
	used to retrieve the version number of the library. In addition it
	can verify that the version number is higher than a certain required
	version number. In either case, the function initializes some
	sub-systems, and for this reason alone it must be invoked early in
	your program, before you make use of the other functions in
	@acronym{GPGME}. The last purpose is to run selftests.

	As a side effect for W32 based systems, the socket layer will get
	initialized.


	If @var{required_version} is @code{NULL}, the function returns a
	pointer to a statically allocated string containing the version number
	of the library.

	If @var{required_version} is not @code{NULL}, it should point to a
	string containing a version number, and the function checks that the
	version of the library is at least as high as the version number
	provided. In this case, the function returns a pointer to a
	statically allocated string containing the version number of the
	library. If @var{REQUIRED_VERSION} is not a valid version number, or
	if the version requirement is not met, the function returns
	@code{NULL}.

	If you use a version of a library that is backwards compatible with
	older releases, but contains additional interfaces which your program
	uses, this function provides a run-time check if the necessary
	features are provided by the installed version of the library.

	If a selftest fails, the function may still succeed. Selftest errors
	are returned later when invoking @code{gpgme_new} or
	@code{gpgme-data_new}, so that a detailed error code can be returned
	(historically, @code{gpgme_check_version} does not return a detailed
	error code).
	@end deftypefun


	@deftypefun {int} gpgme_set_global_flag @
	(@w{const char *@var{name}}, @
	@w{const char *@var{value}})

	@since{1.4.0}

	On some systems it is not easy to set environment variables and thus
	hard to use @acronym{GPGME}'s internal trace facility for debugging.
	This function has been introduced as an alternative way to enable
	debugging and for a couple of other rarely used tweaks. It is
	important to assure that only one thread accesses @acronym{GPGME}
	functions between a call to this function and after the return from
	the call to @code{gpgme_check_version}.

	All currently supported features require that this function is called
	as early as possible --- even before @code{gpgme_check_version}. The
	features are identified by the following values for @var{name}:

	@table @code
	@item debug
	To enable debugging use the string ``debug'' for @var{name} and
	@var{value} identical to the value used with the environment variable
	@code{GPGME_DEBUG}.

	@item disable-gpgconf
	Using this feature with any @var{value} disables the detection of the
	gpgconf program and thus forces GPGME to fallback into the simple
	OpenPGP only mode. It may be used to force the use of GnuPG-1 on
	systems which have both GPG versions installed. Note that in general
	the use of @code{gpgme_set_engine_info} is a better way to select a
	specific engine version.

	@item gpgconf-name
	@itemx gpg-name
	Set the name of the gpgconf respective gpg binary. The defaults are
	@code{GNU/GnuPG/gpgconf} and @code{GNU/GnuPG/gpg}. Under Unix the
	leading directory part is ignored. Under Windows the leading
	directory part is used as the default installation directory; the
	@code{.exe} suffix is added by GPGME. Use forward slashed even under
	Windows.

	@item require-gnupg
	Set the minimum version of the required GnuPG engine. If that version
	is not met, GPGME fails early instead of trying to use the existent
	version. The given version must be a string with major, minor, and
	micro number. Example: "2.1.0".

	@item w32-inst-dir
	On Windows GPGME needs to know its installation directory to find its
	spawn helper. This is in general no problem because a DLL has this
	information. Some applications however link statically to GPGME and
	thus GPGME can only figure out the installation directory of this
	application which may be wrong in certain cases. By supplying an
	installation directory as value to this flag, GPGME will assume that
	that directory is the installation directory. This flag has no effect
	on non-Windows platforms.

	@end table

	This function returns @code{0} on success. In contrast to other
	functions the non-zero return value on failure does not convey any
	error code. For setting ``debug'' the only possible error cause is an
	out of memory condition; which would exhibit itself later anyway.
	Thus the return value may be ignored.
	@end deftypefun


	After initializing @acronym{GPGME}, you should set the locale
	information to the locale required for your output terminal. This
	locale information is needed for example for the curses and Gtk
	pinentry. Here is an example of a complete initialization:

	@example
	#include <locale.h>
	#include <gpgme.h>

	void
	init_gpgme (void)
	@{
	/* Initialize the locale environment. */
	setlocale (LC_ALL, "");
	gpgme_check_version (NULL);
	gpgme_set_locale (NULL, LC_CTYPE, setlocale (LC_CTYPE, NULL));
	#ifdef LC_MESSAGES
	gpgme_set_locale (NULL, LC_MESSAGES, setlocale (LC_MESSAGES, NULL));
	#endif
	@}
	@end example

	Note that you are highly recommended to initialize the locale settings
	like this. @acronym{GPGME} can not do this for you because it would
	not be thread safe. The conditional on LC_MESSAGES is only necessary
	for portability to W32 systems.


	@node Signal Handling
	@section Signal Handling
	@cindex signals
	@cindex signal handling

	The @acronym{GPGME} library communicates with child processes (the
	crypto engines). If a child process dies unexpectedly, for example
	due to a bug, or system problem, a @code{SIGPIPE} signal will be
	delivered to the application. The default action is to abort the
	program. To protect against this, @code{gpgme_check_version} sets the
	@code{SIGPIPE} signal action to @code{SIG_IGN}, which means that the
	signal will be ignored.

	@acronym{GPGME} will only do that if the signal action for
	@code{SIGPIPE} is @code{SIG_DEF} at the time
	@code{gpgme_check_version} is called. If it is something different,
	@code{GPGME} will take no action.

	This means that if your application does not install any signal
	handler for @code{SIGPIPE}, you don't need to take any precautions.
	If you do install a signal handler for @code{SIGPIPE}, you must be
	prepared to handle any @code{SIGPIPE} events that occur due to
	@acronym{GPGME} writing to a defunct pipe. Furthermore, if your
	application is multi-threaded, and you install a signal action for
	@code{SIGPIPE}, you must make sure you do this either before
	@code{gpgme_check_version} is called or afterwards.


	@node Multi-Threading
	@section Multi-Threading
	@cindex thread-safeness
	@cindex multi-threading

	The @acronym{GPGME} library is mostly thread-safe, and can be used
	in a multi-threaded environment but there are some requirements
	for multi-threaded use:

	@itemize @bullet
	@item
	The function @code{gpgme_check_version} must be called before any
	other function in the library, because it initializes the thread
	support subsystem in @acronym{GPGME}. To achieve this in
	multi-threaded programs, you must synchronize the memory with respect
	to other threads that also want to use @acronym{GPGME}. For this, it
	is sufficient to call @code{gpgme_check_version} before creating the
	other threads using @acronym{GPGME}@footnote{At least this is true for
	POSIX threads, as @code{pthread_create} is a function that
	synchronizes memory with respects to other threads. There are many
	functions which have this property, a complete list can be found in
	POSIX, IEEE Std 1003.1-2003, Base Definitions, Issue 6, in the
	definition of the term ``Memory Synchronization''. For other thread
	packages other, more relaxed or more strict rules may apply.}.

	@item
	Any @code{gpgme_data_t} and @code{gpgme_ctx_t} object must only be
	accessed by one thread at a time. If multiple threads want to deal
	with the same object, the caller has to make sure that operations on
	that object are fully synchronized.

	@item
	Only one thread at any time is allowed to call @code{gpgme_wait}. If
	multiple threads call this function, the caller must make sure that
	all invocations are fully synchronized. It is safe to start
	asynchronous operations while a thread is running in gpgme_wait.

	@item
	The function @code{gpgme_strerror} is not thread safe. You have to
	use @code{gpgme_strerror_r} instead.
	@end itemize


	@node Protocols and Engines
	@chapter Protocols and Engines
	@cindex protocol
	@cindex engine
	@cindex crypto engine
	@cindex backend
	@cindex crypto backend

	@acronym{GPGME} supports several cryptographic protocols, however, it
	does not implement them. Rather it uses backends (also called
	engines) which implement the protocol. @acronym{GPGME} uses
	inter-process communication to pass data back and forth between the
	application and the backend, but the details of the communication
	protocol and invocation of the backend is completely hidden by the
	interface. All complexity is handled by @acronym{GPGME}. Where an
	exchange of information between the application and the backend is
	necessary, @acronym{GPGME} provides the necessary callback function
	hooks and further interfaces.

	@deftp {Data type} {enum gpgme_protocol_t}
	@tindex gpgme_protocol_t
	The @code{gpgme_protocol_t} type specifies the set of possible protocol
	values that are supported by @acronym{GPGME}. The following protocols
	are supported:

	@table @code
	@item GPGME_PROTOCOL_OpenPGP
	@itemx GPGME_PROTOCOL_OPENPGP
	This specifies the OpenPGP protocol.

	@item GPGME_PROTOCOL_CMS
	This specifies the Cryptographic Message Syntax.

	@item GPGME_PROTOCOL_GPGCONF
	Under development. Please ask on @email{gnupg-devel@@gnupg.org} for help.

	@item GPGME_PROTOCOL_ASSUAN
	@since{1.2.0}

	This specifies the raw Assuan protocol.

	@item GPGME_PROTOCOL_G13
	@since{1.3.0}

	Under development. Please ask on @email{gnupg-devel@@gnupg.org} for help.

	@item GPGME_PROTOCOL_UISERVER
	Under development. Please ask on @email{gnupg-devel@@gnupg.org} for help.

	@item GPGME_PROTOCOL_SPAWN
	@since{1.5.0}

	Special protocol for use with @code{gpgme_op_spawn}.

	@item GPGME_PROTOCOL_UNKNOWN
	Reserved for future extension. You may use this to indicate that the
	used protocol is not known to the application. Currently,
	@acronym{GPGME} does not accept this value in any operation, though,
	except for @code{gpgme_get_protocol_name}.
	@end table
	@end deftp


	@deftypefun {const char *} gpgme_get_protocol_name (@w{gpgme_protocol_t @var{protocol}})
	The function @code{gpgme_get_protocol_name} returns a statically
	allocated string describing the protocol @var{protocol}, or
	@code{NULL} if the protocol number is not valid.
	@end deftypefun

	@menu
	* Engine Version Check:: Verifying the engine version.
	* Engine Information:: Obtaining more information about the engines.
	* Engine Configuration:: Changing the engine configuration.
	* OpenPGP:: Support for the OpenPGP protocol.
	* Cryptographic Message Syntax:: Support for the CMS.
	* Assuan:: Support for the raw Assuan protocol.
	@end menu


	@node Engine Version Check
	@section Engine Version Check
	@cindex version check, of the engines

	@deftypefun @w{const char } gpgme_get_dirinfo (@w{cons char @var{what}})
	@since{1.5.0}

	The function @code{gpgme_get_dirinfo} returns a statically allocated
	string with the value associated to @var{what}. The returned values
	are the defaults and won't change even after
	@code{gpgme_set_engine_info} has been used to configure a different
	engine. @code{NULL} is returned if no value is available. Commonly
	supported values for @var{what} are:

	@table @code
	@item homedir
	Return the default home directory.

	@item sysconfdir
	Return the name of the system configuration directory

	@item bindir
	Return the name of the directory with GnuPG program files.

	@item libdir
	Return the name of the directory with GnuPG related library files.

	@item libexecdir
	Return the name of the directory with GnuPG helper program files.

	@item datadir
	Return the name of the directory with GnuPG shared data.

	@item localedir
	Return the name of the directory with GnuPG locale data.

	@item agent-socket
	Return the name of the socket to connect to the gpg-agent.

	@item agent-ssh-socket
	Return the name of the socket to connect to the ssh-agent component of
	gpg-agent.

	@item dirmngr-socket
	Return the name of the socket to connect to the dirmngr.

	@item uiserver-socket
	Return the name of the socket to connect to the user interface server.

	@item gpgconf-name
	Return the file name of the engine configuration tool.

	@item gpg-name
	Return the file name of the OpenPGP engine.

	@item gpgsm-name
	Return the file name of the CMS engine.

	@item g13-name
	Return the name of the file container encryption engine.

	@item keyboxd-name
	Return the name of the key database daemon.

	@item agent-name
	Return the name of gpg-agent.

	@item scdaemon-name
	Return the name of the smart card daemon.

	@item dirmngr-name
	Return the name of dirmngr.

	@item pinentry-name
	Return the name of the pinentry program.

	@item gpg-wks-client-name
	Return the name of the Web Key Service tool.

	@end table

	@end deftypefun


	@deftypefun gpgme_error_t gpgme_engine_check_version (@w{gpgme_protocol_t @var{protocol}})
	The function @code{gpgme_engine_check_version} verifies that the
	engine implementing the protocol @var{PROTOCOL} is installed in the
	expected path and meets the version requirement of @acronym{GPGME}.

	This function returns the error code @code{GPG_ERR_NO_ERROR} if the
	engine is available and @code{GPG_ERR_INV_ENGINE} if it is not.
	@end deftypefun


	@node Engine Information
	@section Engine Information
	@cindex engine, information about

	@deftp {Data type} {gpgme_engine_info_t}
	@tindex gpgme_protocol_t
	The @code{gpgme_engine_info_t} type specifies a pointer to a structure
	describing a crypto engine. The structure contains the following
	elements:

	@table @code
	@item gpgme_engine_info_t next
	This is a pointer to the next engine info structure in the linked
	list, or @code{NULL} if this is the last element.

	@item gpgme_protocol_t protocol
	This is the protocol for which the crypto engine is used. You can
	convert this to a string with @code{gpgme_get_protocol_name} for
	printing.

	@item const char *file_name
	This is a string holding the file name of the executable of the crypto
	engine. Currently, it is never @code{NULL}, but using @code{NULL} is
	reserved for future use, so always check before you use it.

	@item const char *home_dir
	This is a string holding the directory name of the crypto engine's
	configuration directory. If it is @code{NULL}, then the default
	directory is used. See @code{gpgme_get_dirinfo} on how to get the
	default directory.

	@item const char *version
	This is a string containing the version number of the crypto engine.
	It might be @code{NULL} if the version number can not be determined,
	for example because the executable doesn't exist or is invalid.

	@item const char *req_version
	This is a string containing the minimum required version number of the
	crypto engine for @acronym{GPGME} to work correctly. This is the
	version number that @code{gpgme_engine_check_version} verifies
	against. Currently, it is never @code{NULL}, but using @code{NULL} is
	reserved for future use, so always check before you use it.
	@end table
	@end deftp

	@deftypefun gpgme_error_t gpgme_get_engine_info (@w{gpgme_engine_info_t *@var{info}})
	The function @code{gpgme_get_engine_info} returns a linked list of
	engine info structures in @var{info}. Each info structure describes
	the defaults of one configured backend.

	The memory for the info structures is allocated the first time this
	function is invoked, and must not be freed by the caller.

	This function returns the error code @code{GPG_ERR_NO_ERROR} if
	successful, and a system error if the memory could not be allocated.
	@end deftypefun

	Here is an example how you can provide more diagnostics if you receive
	an error message which indicates that the crypto engine is invalid.

	@example
	gpgme_ctx_t ctx;
	gpgme_error_t err;

	[...]

	if (gpgme_err_code (err) == GPG_ERR_INV_ENGINE)
	@{
	gpgme_engine_info_t info;
	err = gpgme_get_engine_info (&info);
	if (!err)
	@{
	while (info && info->protocol != gpgme_get_protocol (ctx))
	info = info->next;
	if (!info)
	fprintf (stderr, "GPGME compiled without support for protocol %s",
	gpgme_get_protocol_name (info->protocol));
	else if (info->file_name && !info->version)
	fprintf (stderr, "Engine %s not installed properly",
	info->file_name);
	else if (info->file_name && info->version && info->req_version)
	fprintf (stderr, "Engine %s version %s installed, "
	"but at least version %s required", info->file_name,
	info->version, info->req_version);
	else
	fprintf (stderr, "Unknown problem with engine for protocol %s",
	gpgme_get_protocol_name (info->protocol));
	@}
	@}
	@end example


	@node Engine Configuration
	@section Engine Configuration
	@cindex engine, configuration of
	@cindex configuration of crypto backend

	You can change the configuration of a backend engine, and thus change
	the executable program and configuration directory to be used. You
	can make these changes the default or set them for some contexts
	individually.

	@deftypefun gpgme_error_t gpgme_set_engine_info (@w{gpgme_protocol_t @var{proto}}, @w{const char @var{file_name}}, @w{const char @var{home_dir}})
	@since{1.1.0}

	The function @code{gpgme_set_engine_info} changes the default
	configuration of the crypto engine implementing the protocol
	@var{proto}.

	@var{file_name} is the file name of the executable program
	implementing this protocol, and @var{home_dir} is the directory name
	of the configuration directory for this crypto engine. If
	@var{home_dir} is @code{NULL}, the engine's default will be used.

	The new defaults are not applied to already created GPGME contexts.

	This function returns the error code @code{GPG_ERR_NO_ERROR} if
	successful, or an error code on failure.
	@end deftypefun

	The functions @code{gpgme_ctx_get_engine_info} and
	@code{gpgme_ctx_set_engine_info} can be used to change the engine
	configuration per context. @xref{Crypto Engine}.


	@node OpenPGP
	@section OpenPGP
	@cindex OpenPGP
	@cindex GnuPG
	@cindex protocol, GnuPG
	@cindex engine, GnuPG

	OpenPGP is implemented by GnuPG, the @acronym{GNU} Privacy Guard.
	This is the first protocol that was supported by @acronym{GPGME}.

	The OpenPGP protocol is specified by @code{GPGME_PROTOCOL_OpenPGP}.


	@node Cryptographic Message Syntax
	@section Cryptographic Message Syntax
	@cindex CMS
	@cindex cryptographic message syntax
	@cindex GpgSM
	@cindex protocol, CMS
	@cindex engine, GpgSM
	@cindex S/MIME
	@cindex protocol, S/MIME

	@acronym{CMS} is implemented by GpgSM, the S/MIME implementation for
	GnuPG.

	The @acronym{CMS} protocol is specified by @code{GPGME_PROTOCOL_CMS}.


	@node Assuan
	@section Assuan
	@cindex ASSUAN
	@cindex protocol, ASSUAN
	@cindex engine, ASSUAN

	Assuan is the RPC library used by the various @acronym{GnuPG}
	components. The Assuan protocol allows one to talk to arbitrary
	Assuan servers using @acronym{GPGME}. @xref{Using the Assuan
	protocol}.

	The ASSUAN protocol is specified by @code{GPGME_PROTOCOL_ASSUAN}.


	@node Algorithms
	@chapter Algorithms
	@cindex algorithms

	The crypto backends support a variety of algorithms used in public key
	cryptography.@footnote{Some engines also provide symmetric only
	encryption; see the description of the encryption function on how to use
	this.} The following sections list the identifiers used to denote such
	an algorithm.

	@menu
	* Public Key Algorithms:: A list of all public key algorithms.
	* Hash Algorithms:: A list of all hash algorithms.
	@end menu


	@node Public Key Algorithms
	@section Public Key Algorithms
	@cindex algorithms, public key
	@cindex public key algorithms

	Public key algorithms are used for encryption, decryption, signing and
	verification of signatures.

	@deftp {Data type} {enum gpgme_pubkey_algo_t}
	@tindex gpgme_pubkey_algo_t
	The @code{gpgme_pubkey_algo_t} type specifies the set of all public key
	algorithms that are supported by @acronym{GPGME}. Possible values
	are:

	@table @code
	@item GPGME_PK_RSA
	This value indicates the RSA (Rivest, Shamir, Adleman) algorithm.

	@item GPGME_PK_RSA_E
	Deprecated. This value indicates the RSA (Rivest, Shamir, Adleman)
	algorithm for encryption and decryption only.

	@item GPGME_PK_RSA_S
	Deprecated. This value indicates the RSA (Rivest, Shamir, Adleman)
	algorithm for signing and verification only.

	@item GPGME_PK_DSA
	This value indicates DSA, the Digital Signature Algorithm.

	@item GPGME_PK_ELG
	This value indicates ElGamal.

	@item GPGME_PK_ELG_E
	This value also indicates ElGamal and is used specifically in GnuPG.

	@item GPGME_PK_ECC
	@since{1.5.0}

	This value is a generic indicator for ellipic curve algorithms.

	@item GPGME_PK_ECDSA
	@since{1.3.0}

	This value indicates ECDSA, the Elliptic Curve Digital Signature
	Algorithm as defined by FIPS 186-2 and RFC-6637.

	@item GPGME_PK_ECDH
	@since{1.3.0}

	This value indicates ECDH, the Eliptic Curve Diffie-Hellmann
	encryption algorithm as defined by RFC-6637.

	@item GPGME_PK_EDDSA
	@since{1.7.0}

	This value indicates the EdDSA algorithm.

	@end table
	@end deftp

	@deftypefun {const char *} gpgme_pubkey_algo_name (@w{gpgme_pubkey_algo_t @var{algo}})
	The function @code{gpgme_pubkey_algo_name} returns a pointer to a
	statically allocated string containing a description of the public key
	algorithm @var{algo}. This string can be used to output the name of
	the public key algorithm to the user.

	If @var{algo} is not a valid public key algorithm, @code{NULL} is
	returned.
	@end deftypefun

	@deftypefun {char *} gpgme_pubkey_algo_string (@w{gpgme_subkey_t @var{key}})
	@since{1.7.0}

	The function @code{gpgme_pubkey_algo_string} is a convenience function
	to build and return an algorithm string in the same way GnuPG does
	(e.g. ``rsa2048'' or ``ed25519''). The caller must free the result
	using @code{gpgme_free}. On error (e.g. invalid argument or memory
	exhausted), the function returns NULL and sets @code{ERRNO}.
	@end deftypefun


	@node Hash Algorithms
	@section Hash Algorithms
	@cindex algorithms, hash
	@cindex algorithms, message digest
	@cindex hash algorithms
	@cindex message digest algorithms

	Hash (message digest) algorithms are used to compress a long message
	to make it suitable for public key cryptography.

	@deftp {Data type} {enum gpgme_hash_algo_t}
	@tindex gpgme_hash_algo_t
	The @code{gpgme_hash_algo_t} type specifies the set of all hash algorithms
	that are supported by @acronym{GPGME}. Possible values are:

	@table @code
	@item GPGME_MD_MD5
	@item GPGME_MD_SHA1
	@item GPGME_MD_RMD160
	@item GPGME_MD_MD2
	@item GPGME_MD_TIGER
	@item GPGME_MD_HAVAL
	@item GPGME_MD_SHA256
	@item GPGME_MD_SHA384
	@item GPGME_MD_SHA512
	@item GPGME_MD_SHA224
	@since{1.5.0}

	@item GPGME_MD_MD4
	@item GPGME_MD_CRC32
	@item GPGME_MD_CRC32_RFC1510
	@item GPGME_MD_CRC24_RFC2440
	@end table
	@end deftp

	@deftypefun {const char *} gpgme_hash_algo_name (@w{gpgme_hash_algo_t @var{algo}})
	The function @code{gpgme_hash_algo_name} returns a pointer to a
	statically allocated string containing a description of the hash
	algorithm @var{algo}. This string can be used to output the name of
	the hash algorithm to the user.

	If @var{algo} is not a valid hash algorithm, @code{NULL} is returned.
	@end deftypefun


	@node Error Handling
	@chapter Error Handling
	@cindex error handling

	Many functions in @acronym{GPGME} can return an error if they fail.
	For this reason, the application should always catch the error
	condition and take appropriate measures, for example by releasing the
	resources and passing the error up to the caller, or by displaying a
	descriptive message to the user and cancelling the operation.

	Some error values do not indicate a system error or an error in the
	operation, but the result of an operation that failed properly. For
	example, if you try to decrypt a tempered message, the decryption will
	fail. Another error value actually means that the end of a data
	buffer or list has been reached. The following descriptions explain
	for many error codes what they mean usually. Some error values have
	specific meanings if returned by a certain functions. Such cases are
	described in the documentation of those functions.

	@acronym{GPGME} uses the @code{libgpg-error} library. This allows to
	share the error codes with other components of the GnuPG system, and
	thus pass error values transparently from the crypto engine, or some
	helper application of the crypto engine, to the user. This way no
	information is lost. As a consequence, @acronym{GPGME} does not use
	its own identifiers for error codes, but uses those provided by
	@code{libgpg-error}. They usually start with @code{GPG_ERR_}.

	However, @acronym{GPGME} does provide aliases for the functions
	defined in libgpg-error, which might be preferred for name space
	consistency.

	@menu
	* Error Values:: The error value and what it means.
	* Error Sources:: A list of important error sources.
	* Error Codes:: A list of important error codes.
	* Error Strings:: How to get a descriptive string from a value.
	@end menu


	@node Error Values
	@section Error Values
	@cindex error values
	@cindex error codes
	@cindex error sources

	@deftp {Data type} {gpgme_err_code_t}
	The @code{gpgme_err_code_t} type is an alias for the @code{libgpg-error}
	type @code{gpg_err_code_t}. The error code indicates the type of an
	error, or the reason why an operation failed.

	A list of important error codes can be found in the next section.
	@end deftp

	@deftp {Data type} {gpgme_err_source_t}
	The @code{gpgme_err_source_t} type is an alias for the
	@code{libgpg-error} type @code{gpg_err_source_t}. The error source
	has not a precisely defined meaning. Sometimes it is the place where
	the error happened, sometimes it is the place where an error was
	encoded into an error value. Usually the error source will give an
	indication to where to look for the problem. This is not always true,
	but it is attempted to achieve this goal.

	A list of important error sources can be found in the next section.
	@end deftp

	@deftp {Data type} {gpgme_error_t}
	The @code{gpgme_error_t} type is an alias for the @code{libgpg-error}
	type @code{gpg_error_t}. An error value like this has always two
	components, an error code and an error source. Both together form the
	error value.

	Thus, the error value can not be directly compared against an error
	code, but the accessor functions described below must be used.
	However, it is guaranteed that only 0 is used to indicate success
	(@code{GPG_ERR_NO_ERROR}), and that in this case all other parts of
	the error value are set to 0, too.

	Note that in @acronym{GPGME}, the error source is used purely for
	diagnostical purposes. Only the error code should be checked to test
	for a certain outcome of a function. The manual only documents the
	error code part of an error value. The error source is left
	unspecified and might be anything.
	@end deftp

	@deftypefun {static inline gpgme_err_code_t} gpgme_err_code (@w{gpgme_error_t @var{err}})
	The static inline function @code{gpgme_err_code} returns the
	@code{gpgme_err_code_t} component of the error value @var{err}. This
	function must be used to extract the error code from an error value in
	order to compare it with the @code{GPG_ERR_*} error code macros.
	@end deftypefun

	@deftypefun {static inline gpgme_err_source_t} gpgme_err_source (@w{gpgme_error_t @var{err}})
	The static inline function @code{gpgme_err_source} returns the
	@code{gpgme_err_source_t} component of the error value @var{err}. This
	function must be used to extract the error source from an error value in
	order to compare it with the @code{GPG_ERR_SOURCE_*} error source macros.
	@end deftypefun

	@deftypefun {static inline gpgme_error_t} gpgme_err_make (@w{gpgme_err_source_t @var{source}}, @w{gpgme_err_code_t @var{code}})
	The static inline function @code{gpgme_err_make} returns the error
	value consisting of the error source @var{source} and the error code
	@var{code}.

	This function can be used in callback functions to construct an error
	value to return it to the library.
	@end deftypefun

	@deftypefun {static inline gpgme_error_t} gpgme_error (@w{gpgme_err_code_t @var{code}})
	The static inline function @code{gpgme_error} returns the error value
	consisting of the default error source and the error code @var{code}.

	For @acronym{GPGME} applications, the default error source is
	@code{GPG_ERR_SOURCE_USER_1}. You can define
	@code{GPGME_ERR_SOURCE_DEFAULT} before including @file{gpgme.h} to
	change this default.

	This function can be used in callback functions to construct an error
	value to return it to the library.
	@end deftypefun

	The @code{libgpg-error} library provides error codes for all system
	error numbers it knows about. If @var{err} is an unknown error
	number, the error code @code{GPG_ERR_UNKNOWN_ERRNO} is used. The
	following functions can be used to construct error values from system
	errnor numbers.

	@deftypefun {gpgme_error_t} gpgme_err_make_from_errno (@w{gpgme_err_source_t @var{source}}, @w{int @var{err}})
	The function @code{gpgme_err_make_from_errno} is like
	@code{gpgme_err_make}, but it takes a system error like @code{errno}
	instead of a @code{gpgme_err_code_t} error code.
	@end deftypefun

	@deftypefun {gpgme_error_t} gpgme_error_from_errno (@w{int @var{err}})
	The function @code{gpgme_error_from_errno} is like @code{gpgme_error},
	but it takes a system error like @code{errno} instead of a
	@code{gpgme_err_code_t} error code.
	@end deftypefun

	Sometimes you might want to map system error numbers to error codes
	directly, or map an error code representing a system error back to the
	system error number. The following functions can be used to do that.

	@deftypefun {gpgme_err_code_t} gpgme_err_code_from_errno (@w{int @var{err}})
	The function @code{gpgme_err_code_from_errno} returns the error code
	for the system error @var{err}. If @var{err} is not a known system
	error, the function returns @code{GPG_ERR_UNKNOWN_ERRNO}.
	@end deftypefun

	@deftypefun {int} gpgme_err_code_to_errno (@w{gpgme_err_code_t @var{err}})
	The function @code{gpgme_err_code_to_errno} returns the system error
	for the error code @var{err}. If @var{err} is not an error code
	representing a system error, or if this system error is not defined on
	this system, the function returns @code{0}.
	@end deftypefun


	@node Error Sources
	@section Error Sources
	@cindex error codes, list of

	The library @code{libgpg-error} defines an error source for every
	component of the GnuPG system. The error source part of an error
	value is not well defined. As such it is mainly useful to improve the
	diagnostic error message for the user.

	If the error code part of an error value is @code{0}, the whole error
	value will be @code{0}. In this case the error source part is of
	course @code{GPG_ERR_SOURCE_UNKNOWN}.

	The list of error sources that might occur in applications using
	@acronym{GPGME} is:

	@table @code
	@item GPG_ERR_SOURCE_UNKNOWN
	The error source is not known. The value of this error source is
	@code{0}.

	@item GPG_ERR_SOURCE_GPGME
	The error source is @acronym{GPGME} itself. This is the default for
	errors that occur in the @acronym{GPGME} library.

	@item GPG_ERR_SOURCE_GPG
	The error source is GnuPG, which is the crypto engine used for the
	OpenPGP protocol.

	@item GPG_ERR_SOURCE_GPGSM
	The error source is GPGSM, which is the crypto engine used for the
	CMS protocol.

	@item GPG_ERR_SOURCE_GCRYPT
	The error source is @code{libgcrypt}, which is used by crypto engines
	to perform cryptographic operations.

	@item GPG_ERR_SOURCE_GPGAGENT
	The error source is @command{gpg-agent}, which is used by crypto
	engines to perform operations with the secret key.

	@item GPG_ERR_SOURCE_PINENTRY
	The error source is @command{pinentry}, which is used by
	@command{gpg-agent} to query the passphrase to unlock a secret key.

	@item GPG_ERR_SOURCE_SCD
	The error source is the SmartCard Daemon, which is used by
	@command{gpg-agent} to delegate operations with the secret key to a
	SmartCard.

	@item GPG_ERR_SOURCE_KEYBOX
	The error source is @code{libkbx}, a library used by the crypto
	engines to manage local keyrings.

	@item GPG_ERR_SOURCE_USER_1
	@item GPG_ERR_SOURCE_USER_2
	@item GPG_ERR_SOURCE_USER_3
	@item GPG_ERR_SOURCE_USER_4
	These error sources are not used by any GnuPG component and can be
	used by other software. For example, applications using
	@acronym{GPGME} can use them to mark error values coming from callback
	handlers. Thus @code{GPG_ERR_SOURCE_USER_1} is the default for errors
	created with @code{gpgme_error} and @code{gpgme_error_from_errno},
	unless you define @code{GPGME_ERR_SOURCE_DEFAULT} before including
	@file{gpgme.h}.
	@end table


	@node Error Codes
	@section Error Codes
	@cindex error codes, list of

	The library @code{libgpg-error} defines many error values. Most of
	them are not used by @code{GPGME} directly, but might be returned by
	@acronym{GPGME} because it received them from the crypto engine. The
	below list only includes such error codes that have a specific meaning
	in @code{GPGME}, or which are so common that you should know about
	them.

	@table @code
	@item GPG_ERR_EOF
	This value indicates the end of a list, buffer or file.

	@item GPG_ERR_NO_ERROR
	This value indicates success. The value of this error code is
	@code{0}. Also, it is guaranteed that an error value made from the
	error code @code{0} will be @code{0} itself (as a whole). This means
	that the error source information is lost for this error code,
	however, as this error code indicates that no error occurred, this is
	generally not a problem.

	@item GPG_ERR_GENERAL
	This value means that something went wrong, but either there is not
	enough information about the problem to return a more useful error
	value, or there is no separate error value for this type of problem.

	@item GPG_ERR_ENOMEM
	This value means that an out-of-memory condition occurred.

	@item GPG_ERR_E...
	System errors are mapped to GPG_ERR_FOO where FOO is the symbol for
	the system error.

	@item GPG_ERR_INV_VALUE
	This value means that some user provided data was out of range. This
	can also refer to objects. For example, if an empty
	@code{gpgme_data_t} object was expected, but one containing data was
	provided, this error value is returned.

	@item GPG_ERR_UNUSABLE_PUBKEY
	This value means that some recipients for a message were invalid.

	@item GPG_ERR_UNUSABLE_SECKEY
	This value means that some signers were invalid.

	@item GPG_ERR_NO_DATA
	This value means that a @code{gpgme_data_t} object which was expected
	to have content was found empty.

	@item GPG_ERR_CONFLICT
	This value means that a conflict of some sort occurred.

	@item GPG_ERR_NOT_IMPLEMENTED
	This value indicates that the specific function (or operation) is not
	implemented. This error should never happen. It can only occur if
	you use certain values or configuration options which do not work,
	but for which we think that they should work at some later time.

	@item GPG_ERR_DECRYPT_FAILED
	This value indicates that a decryption operation was unsuccessful.

	@item GPG_ERR_BAD_PASSPHRASE
	This value means that the user did not provide a correct passphrase
	when requested.

	@item GPG_ERR_CANCELED
	This value means that the operation was canceled.

	@item GPG_ERR_INV_ENGINE
	This value means that the engine that implements the desired protocol
	is currently not available. This can either be because the sources
	were configured to exclude support for this engine, or because the
	engine is not installed properly.

	@item GPG_ERR_AMBIGUOUS_NAME
	This value indicates that a user ID or other specifier did not specify
	a unique key.

	@item GPG_ERR_WRONG_KEY_USAGE
	This value indicates that a key is not used appropriately.

	@item GPG_ERR_CERT_REVOKED
	This value indicates that a key signature was revoced.

	@item GPG_ERR_CERT_EXPIRED
	This value indicates that a key signature expired.

	@item GPG_ERR_NO_CRL_KNOWN
	This value indicates that no certificate revocation list is known for
	the certificate.

	@item GPG_ERR_NO_POLICY_MATCH
	This value indicates that a policy issue occurred.

	@item GPG_ERR_NO_SECKEY
	This value indicates that no secret key for the user ID is available.

	@item GPG_ERR_MISSING_CERT
	This value indicates that a key could not be imported because the
	issuer certificate is missing.

	@item GPG_ERR_BAD_CERT_CHAIN
	This value indicates that a key could not be imported because its
	certificate chain is not good, for example it could be too long.

	@item GPG_ERR_UNSUPPORTED_ALGORITHM
	This value means a verification failed because the cryptographic
	algorithm is not supported by the crypto backend.

	@item GPG_ERR_BAD_SIGNATURE
	This value means a verification failed because the signature is bad.

	@item GPG_ERR_NO_PUBKEY
	This value means a verification failed because the public key is not
	available.

	@item GPG_ERR_USER_1
	@item GPG_ERR_USER_2
	@item ...
	@item GPG_ERR_USER_16
	These error codes are not used by any GnuPG component and can be
	freely used by other software. Applications using @acronym{GPGME}
	might use them to mark specific errors returned by callback handlers
	if no suitable error codes (including the system errors) for
	these errors exist already.
	@end table


	@node Error Strings
	@section Error Strings
	@cindex error values, printing of
	@cindex error codes, printing of
	@cindex error sources, printing of
	@cindex error strings

	@deftypefun {const char *} gpgme_strerror (@w{gpgme_error_t @var{err}})
	The function @code{gpgme_strerror} returns a pointer to a statically
	allocated string containing a description of the error code contained
	in the error value @var{err}. This string can be used to output a
	diagnostic message to the user.

	This function is not thread safe. Use @code{gpgme_strerror_r} in
	multi-threaded programs.
	@end deftypefun


	@deftypefun {int} gpgme_strerror_r (@w{gpgme_error_t @var{err}}, @w{char *@var{buf}}, @w{size_t @var{buflen}})
	The function @code{gpgme_strerror_r} returns the error string for
	@var{err} in the user-supplied buffer @var{buf} of size @var{buflen}.
	This function is, in contrast to @code{gpgme_strerror}, thread-safe if
	a thread-safe @code{strerror_r} function is provided by the system.
	If the function succeeds, 0 is returned and @var{buf} contains the
	string describing the error. If the buffer was not large enough,
	ERANGE is returned and @var{buf} contains as much of the beginning of
	the error string as fits into the buffer.
	@end deftypefun


	@deftypefun {const char *} gpgme_strsource (@w{gpgme_error_t @var{err}})
	The function @code{gpgme_strerror} returns a pointer to a statically
	allocated string containing a description of the error source
	contained in the error value @var{err}. This string can be used to
	output a diagnostic message to the user.
	@end deftypefun

	The following example illustrates the use of @code{gpgme_strerror}:

	@example
	gpgme_ctx_t ctx;
	gpgme_error_t err = gpgme_new (&ctx);
	if (err)
	@{
	fprintf (stderr, "%s: creating GpgME context failed: %s: %s\n",
	argv[0], gpgme_strsource (err), gpgme_strerror (err));
	exit (1);
	@}
	@end example


	@node Exchanging Data
	@chapter Exchanging Data
	@cindex data, exchanging

	A lot of data has to be exchanged between the user and the crypto
	engine, like plaintext messages, ciphertext, signatures and
	information about the keys. The technical details about exchanging
	the data information are completely abstracted by @acronym{GPGME}.
	The user provides and receives the data via @code{gpgme_data_t} objects,
	regardless of the communication protocol between @acronym{GPGME} and
	the crypto engine in use.

	@deftp {Data type} {gpgme_data_t}
	The @code{gpgme_data_t} type is a handle for a container for generic
	data, which is used by @acronym{GPGME} to exchange data with the user.
	@end deftp

	@code{gpgme_data_t} objects do not provide notifications on events.
	It is assumed that read and write operations are blocking until data
	is available. If this is undesirable, the application must ensure
	that all GPGME data operations always have data available, for example
	by using memory buffers or files rather than pipes or sockets. This
	might be relevant, for example, if the external event loop mechanism
	is used.

	@deftp {Data type} {gpgme_off_t}
	@since{1.4.1}

	On POSIX platforms the @code{gpgme_off_t} type is an alias for
	@code{off_t}; it may be used interchangeable. On Windows platforms
	@code{gpgme_off_t} is defined as a long (i.e. 32 bit) for 32 bit
	Windows and as a 64 bit signed integer for 64 bit Windows.
	@end deftp

	@deftp {Data type} {gpgme_ssize_t}
	The @code{gpgme_ssize_t} type is an alias for @code{ssize_t}. It has
	only been introduced to overcome portability problems pertaining to
	the declaration of @code{ssize_t} by different toolchains.
	@end deftp


	@menu
	* Creating Data Buffers:: Creating new data buffers.
	* Destroying Data Buffers:: Releasing data buffers.
	* Manipulating Data Buffers:: Operations on data buffers.
	@end menu


	@node Creating Data Buffers
	@section Creating Data Buffers
	@cindex data buffer, creation

	Data objects can be based on memory, files, or callback functions
	provided by the user. Not all operations are supported by all
	objects.


	@menu
	* Memory Based Data Buffers:: Creating memory based data buffers.
	* File Based Data Buffers:: Creating file based data buffers.
	* Callback Based Data Buffers:: Creating callback based data buffers.
	@end menu


	@node Memory Based Data Buffers
	@subsection Memory Based Data Buffers

	Memory based data objects store all data in allocated memory. This is
	convenient, but only practical for an amount of data that is a
	fraction of the available physical memory. The data has to be copied
	from its source and to its destination, which can often be avoided by
	using one of the other data object

	@deftypefun gpgme_error_t gpgme_data_new (@w{gpgme_data_t *@var{dh}})
	The function @code{gpgme_data_new} creates a new @code{gpgme_data_t}
	object and returns a handle for it in @var{dh}. The data object is
	memory based and initially empty.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, @code{GPG_ERR_INV_VALUE} if
	@var{dh} is not a valid pointer, and @code{GPG_ERR_ENOMEM} if not
	enough memory is available.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_new_from_mem (@w{gpgme_data_t @var{dh}}, @w{const char @var{buffer}}, @w{size_t @var{size}}, @w{int @var{copy}})
	The function @code{gpgme_data_new_from_mem} creates a new
	@code{gpgme_data_t} object and fills it with @var{size} bytes starting
	from @var{buffer}.

	If @var{copy} is not zero, a private copy of the data is made. If
	@var{copy} is zero, the data is taken from the specified buffer as
	needed, and the user has to ensure that the buffer remains valid for
	the whole life span of the data object.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, @code{GPG_ERR_INV_VALUE} if
	@var{dh} or @var{buffer} is not a valid pointer, and
	@code{GPG_ERR_ENOMEM} if not enough memory is available.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_new_from_file (@w{gpgme_data_t @var{dh}}, @w{const char @var{filename}}, @w{int @var{copy}})
	The function @code{gpgme_data_new_from_file} creates a new
	@code{gpgme_data_t} object and fills it with the content of the file
	@var{filename}.

	If @var{copy} is not zero, the whole file is read in at initialization
	time and the file is not used anymore after that. This is the only
	mode supported currently. Later, a value of zero for @var{copy} might
	cause all reads to be delayed until the data is needed, but this is
	not yet implemented.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, @code{GPG_ERR_INV_VALUE} if
	@var{dh} or @var{filename} is not a valid pointer,
	@code{GPG_ERR_NOT_IMPLEMENTED} if @var{code} is zero, and
	@code{GPG_ERR_ENOMEM} if not enough memory is available.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_new_from_filepart (@w{gpgme_data_t @var{dh}}, @w{const char @var{filename}}, @w{FILE *@var{fp}}, @w{off_t @var{offset}}, @w{size_t @var{length}})
	The function @code{gpgme_data_new_from_filepart} creates a new
	@code{gpgme_data_t} object and fills it with a part of the file specified
	by @var{filename} or @var{fp}.

	Exactly one of @var{filename} and @var{fp} must be non-zero, the other
	must be zero. The argument that is not zero specifies the file from
	which @var{length} bytes are read into the data object, starting from
	@var{offset}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, @code{GPG_ERR_INV_VALUE} if
	@var{dh} and exactly one of @var{filename} and @var{fp} is not a valid
	pointer, and @code{GPG_ERR_ENOMEM} if not enough memory is available.
	@end deftypefun


	@node File Based Data Buffers
	@subsection File Based Data Buffers

	File based data objects operate directly on file descriptors or
	streams. Only a small amount of data is stored in core at any time,
	so the size of the data objects is not limited by @acronym{GPGME}.

	@deftypefun gpgme_error_t gpgme_data_new_from_fd (@w{gpgme_data_t *@var{dh}}, @w{int @var{fd}})
	The function @code{gpgme_data_new_from_fd} creates a new
	@code{gpgme_data_t} object and uses the file descriptor @var{fd} to read
	from (if used as an input data object) and write to (if used as an
	output data object).

	When using the data object as an input buffer, the function might read
	a bit more from the file descriptor than is actually needed by the
	crypto engine in the desired operation because of internal buffering.

	Note that GPGME assumes that the file descriptor is set to blocking
	mode. Errors during I/O operations, except for EINTR, are usually
	fatal for crypto operations.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, and @code{GPG_ERR_ENOMEM} if not
	enough memory is available.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_new_from_stream (@w{gpgme_data_t @var{dh}}, @w{FILE @var{stream}})
	The function @code{gpgme_data_new_from_stream} creates a new
	@code{gpgme_data_t} object and uses the I/O stream @var{stream} to read
	from (if used as an input data object) and write to (if used as an
	output data object).

	When using the data object as an input buffer, the function might read
	a bit more from the stream than is actually needed by the crypto
	engine in the desired operation because of internal buffering.

	Note that GPGME assumes that the stream is in blocking mode. Errors
	during I/O operations, except for EINTR, are usually fatal for crypto
	operations.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, and @code{GPG_ERR_ENOMEM} if not
	enough memory is available.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_new_from_estream (@w{gpgme_data_t *@var{dh}}, @w{gpgrt_stream_t @var{stream}})
	The function @code{gpgme_data_new_from_estream} creates a new
	@code{gpgme_data_t} object and uses the gpgrt stream @var{stream} to read
	from (if used as an input data object) and write to (if used as an
	output data object).

	When using the data object as an input buffer, the function might read
	a bit more from the stream than is actually needed by the crypto
	engine in the desired operation because of internal buffering.

	Note that GPGME assumes that the stream is in blocking mode. Errors
	during I/O operations, except for EINTR, are usually fatal for crypto
	operations.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, and @code{GPG_ERR_ENOMEM} if not
	enough memory is available.
	@end deftypefun


	@node Callback Based Data Buffers
	@subsection Callback Based Data Buffers

	If neither memory nor file based data objects are a good fit for your
	application, you can implement the functions a data object provides
	yourself and create a data object from these callback functions.

	@deftp {Data type} {ssize_t (gpgme_data_read_cb_t) (@w{void @var{handle}}, @w{void @var{*buffer}}, @w{size_t @var{size}})}
	@tindex gpgme_data_read_cb_t
	The @code{gpgme_data_read_cb_t} type is the type of functions which
	@acronym{GPGME} calls if it wants to read data from a user-implemented
	data object. The function should read up to @var{size} bytes from the
	current read position into the space starting at @var{buffer}. The
	@var{handle} is provided by the user at data object creation time.

	Note that GPGME assumes that the read blocks until data is available.
	Errors during I/O operations, except for EINTR, are usually fatal for
	crypto operations.

	The function should return the number of bytes read, 0 on EOF, and -1
	on error. If an error occurs, @var{errno} should be set to describe
	the type of the error.
	@end deftp

	@deftp {Data type} {ssize_t (gpgme_data_write_cb_t) (@w{void @var{handle}}, @w{const void @var{*buffer}}, @w{size_t @var{size}})}
	@tindex gpgme_data_write_cb_t
	The @code{gpgme_data_write_cb_t} type is the type of functions which
	@acronym{GPGME} calls if it wants to write data to a user-implemented
	data object. The function should write up to @var{size} bytes to the
	current write position from the space starting at @var{buffer}. The
	@var{handle} is provided by the user at data object creation time.

	Note that GPGME assumes that the write blocks until data is available.
	Errors during I/O operations, except for EINTR, are usually fatal for
	crypto operations.

	The function should return the number of bytes written, and -1 on
	error. If an error occurs, @var{errno} should be set to describe the
	type of the error.
	@end deftp

	@deftp {Data type} {off_t (gpgme_data_seek_cb_t) (@w{void @var{handle}}, @w{off_t @var{offset}}, @w{int @var{whence}})}
	@tindex gpgme_data_seek_cb_t
	The @code{gpgme_data_seek_cb_t} type is the type of functions which
	@acronym{GPGME} calls if it wants to change the current read/write
	position in a user-implemented data object, just like the @code{lseek}
	function.

	The function should return the new read/write position, and -1 on
	error. If an error occurs, @var{errno} should be set to describe the
	type of the error.
	@end deftp

	@deftp {Data type} {void (gpgme_data_release_cb_t) (@w{void @var{handle}})}
	@tindex gpgme_data_release_cb_t
	The @code{gpgme_data_release_cb_t} type is the type of functions which
	@acronym{GPGME} calls if it wants to destroy a user-implemented data
	object. The @var{handle} is provided by the user at data object
	creation time.
	@end deftp

	@deftp {Data type} {struct gpgme_data_cbs}
	This structure is used to store the data callback interface functions
	described above. It has the following members:

	@table @code
	@item gpgme_data_read_cb_t read
	This is the function called by @acronym{GPGME} to read data from the
	data object. It is only required for input data object.

	@item gpgme_data_write_cb_t write
	This is the function called by @acronym{GPGME} to write data to the
	data object. It is only required for output data object.

	@item gpgme_data_seek_cb_t seek
	This is the function called by @acronym{GPGME} to change the current
	read/write pointer in the data object (if available). It is optional.

	@item gpgme_data_release_cb_t release
	This is the function called by @acronym{GPGME} to release a data
	object. It is optional.
	@end table
	@end deftp

	@deftypefun gpgme_error_t gpgme_data_new_from_cbs (@w{gpgme_data_t @var{dh}}, @w{gpgme_data_cbs_t @var{cbs}}, @w{void @var{handle}})
	The function @code{gpgme_data_new_from_cbs} creates a new
	@code{gpgme_data_t} object and uses the user-provided callback functions
	to operate on the data object.

	The handle @var{handle} is passed as first argument to the callback
	functions. This can be used to identify this data object.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, and @code{GPG_ERR_ENOMEM} if not
	enough memory is available.
	@end deftypefun


	@node Destroying Data Buffers
	@section Destroying Data Buffers
	@cindex data buffer, destruction

	@deftypefun void gpgme_data_release (@w{gpgme_data_t @var{dh}})
	The function @code{gpgme_data_release} destroys the data object with
	the handle @var{dh}. It releases all associated resources that were
	not provided by the user in the first place.
	@end deftypefun

	@deftypefun {char } gpgme_data_release_and_get_mem (@w{gpgme_data_t @var{dh}}, @w{size_t @var{length}})
	The function @code{gpgme_data_release_and_get_mem} is like
	@code{gpgme_data_release}, except that it returns the data buffer and
	its length that was provided by the object.

	The user has to release the buffer with @code{gpgme_free}. In case
	the user provided the data buffer in non-copy mode, a copy will be
	made for this purpose.

	In case an error returns, or there is no suitable data buffer that can
	be returned to the user, the function will return @code{NULL}. In any
	case, the data object @var{dh} is destroyed.
	@end deftypefun


	@deftypefun void gpgme_free (@w{void *@var{buffer}})
	@since{1.1.1}

	The function @code{gpgme_free} releases the memory returned by
	@code{gpgme_data_release_and_get_mem} and
	@code{gpgme_pubkey_algo_string}. It should be used instead of the
	system libraries @code{free} function in case different allocators are
	used by a program. This is often the case if gpgme is used under
	Windows as a DLL.
	@end deftypefun


	@node Manipulating Data Buffers
	@section Manipulating Data Buffers
	@cindex data buffer, manipulation

	Data buffers contain data and meta-data. The following operations can
	be used to manipulate both.


	@menu
	* Data Buffer I/O Operations:: I/O operations on data buffers.
	* Data Buffer Meta-Data:: Meta-data manipulation of data buffers.
	* Data Buffer Convenience:: Convenience function for data buffers.
	@end menu


	@node Data Buffer I/O Operations
	@subsection Data Buffer I/O Operations
	@cindex data buffer, I/O operations
	@cindex data buffer, read
	@cindex data buffer, write
	@cindex data buffer, seek

	@deftypefun ssize_t gpgme_data_read (@w{gpgme_data_t @var{dh}}, @w{void *@var{buffer}}, @w{size_t @var{length}})
	The function @code{gpgme_data_read} reads up to @var{length} bytes
	from the data object with the handle @var{dh} into the space starting
	at @var{buffer}.

	If no error occurs, the actual amount read is returned. If the end of
	the data object is reached, the function returns 0.

	In all other cases, the function returns -1 and sets @var{errno}.
	@end deftypefun

	@deftypefun ssize_t gpgme_data_write (@w{gpgme_data_t @var{dh}}, @w{const void *@var{buffer}}, @w{size_t @var{size}})
	The function @code{gpgme_data_write} writes up to @var{size} bytes
	starting from @var{buffer} into the data object with the handle
	@var{dh} at the current write position.

	The function returns the number of bytes actually written, or -1 if an
	error occurs. If an error occurs, @var{errno} is set.
	@end deftypefun

	@deftypefun off_t gpgme_data_seek (@w{gpgme_data_t @var{dh}}, @w{off_t @var{offset}}, @w{int @var{whence}})
	The function @code{gpgme_data_seek} changes the current read/write
	position.

	The @var{whence} argument specifies how the @var{offset} should be
	interpreted. It must be one of the following symbolic constants:

	@table @code
	@item SEEK_SET
	Specifies that @var{offset} is a count of characters from the
	beginning of the data object.

	@item SEEK_CUR
	Specifies that @var{offset} is a count of characters from the current
	file position. This count may be positive or negative.

	@item SEEK_END
	Specifies that @var{offset} is a count of characters from the end of
	the data object. A negative count specifies a position within the
	current extent of the data object; a positive count specifies a
	position past the current end. If you set the position past the
	current end, and actually write data, you will extend the data object
	with zeros up to that position.
	@end table

	If successful, the function returns the resulting file position,
	measured in bytes from the beginning of the data object. You can use
	this feature together with @code{SEEK_CUR} to read the current
	read/write position.

	If the function fails, -1 is returned and @var{errno} is set.
	@end deftypefun


	@node Data Buffer Meta-Data
	@subsection Data Buffer Meta-Data
	@cindex data buffer, meta-data
	@cindex data buffer, file name
	@cindex data buffer, encoding

	@deftypefun {char *} gpgme_data_get_file_name (@w{gpgme_data_t @var{dh}})
	@since{1.1.0}

	The function @code{gpgme_data_get_file_name} returns a pointer to a
	string containing the file name associated with the data object. The
	file name will be stored in the output when encrypting or signing the
	data and will be returned to the user when decrypting or verifying the
	output data.

	If no error occurs, the string containing the file name is returned.
	Otherwise, @code{NULL} will be returned.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_data_set_file_name (@w{gpgme_data_t @var{dh}}, @w{const char *@var{file_name}})
	@since{1.1.0}

	The function @code{gpgme_data_set_file_name} sets the file name
	associated with the data object. The file name will be stored in the
	output when encrypting or signing the data and will be returned to the
	user when decrypting or verifying the output data.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{dh} is not a valid pointer and @code{GPG_ERR_ENOMEM} if not
	enough memory is available.
	@end deftypefun


	@deftp {Data type} {enum gpgme_data_encoding_t}
	@tindex gpgme_data_encoding_t
	The @code{gpgme_data_encoding_t} type specifies the encoding of a
	@code{gpgme_data_t} object. For input data objects, the encoding is
	useful to give the backend a hint on the type of data. For output
	data objects, the encoding can specify the output data format on
	certain operations. Please note that not all backends support all
	encodings on all operations. The following data types are available:

	@table @code
	@item GPGME_DATA_ENCODING_NONE
	This specifies that the encoding is not known. This is the default
	for a new data object. The backend will try its best to detect the
	encoding automatically.

	@item GPGME_DATA_ENCODING_BINARY
	This specifies that the data is encoding in binary form; i.e. there is
	no special encoding.

	@item GPGME_DATA_ENCODING_BASE64
	This specifies that the data is encoded using the Base-64 encoding
	scheme as used by @acronym{MIME} and other protocols.

	@item GPGME_DATA_ENCODING_ARMOR
	This specifies that the data is encoded in an armored form as used by
	OpenPGP and PEM.

	@item GPGME_DATA_ENCODING_MIME
	@since{1.7.0}

	This specifies that the data is encoded as a MIME part.

	@item GPGME_DATA_ENCODING_URL
	@since{1.2.0}

	The data is a list of linefeed delimited URLs. This is only useful with
	@code{gpgme_op_import}.

	@item GPGME_DATA_ENCODING_URL0
	@since{1.2.0}

	The data is a list of binary zero delimited URLs. This is only useful
	with @code{gpgme_op_import}.

	@item GPGME_DATA_ENCODING_URLESC
	@since{1.2.0}

	The data is a list of linefeed delimited URLs with all control and space
	characters percent escaped. This mode is is not yet implemented.

	@end table
	@end deftp

	@deftypefun gpgme_data_encoding_t gpgme_data_get_encoding (@w{gpgme_data_t @var{dh}})
	The function @code{gpgme_data_get_encoding} returns the encoding of
	the data object with the handle @var{dh}. If @var{dh} is not a valid
	pointer (e.g. @code{NULL}) @code{GPGME_DATA_ENCODING_NONE} is
	returned.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_set_encoding (@w{gpgme_data_t @var{dh}, gpgme_data_encoding_t @var{enc}})
	The function @code{gpgme_data_set_encoding} changes the encoding of
	the data object with the handle @var{dh} to @var{enc}.
	@end deftypefun

	@deftypefun {gpgme_error_t} gpgme_data_set_flag @
	(@w{gpgme_data_t @var{dh}}, @
	@w{const char *@var{name}}, @
	@w{const char *@var{value}})

	@since{1.7.0}

	Some minor properties of the data object can be controlled with flags
	set by this function. The properties are identified by the following
	values for @var{name}:

	@table @code
	@item size-hint
	The value is a decimal number with the length gpgme shall assume for
	this data object. This is useful if the data is provided by callbacks
	or via file descriptors but the applications knows the total size of
	the data. If this is set the OpenPGP engine may use this to decide on
	buffer allocation strategies and to provide a total value for its
	progress information.

	@item io-buffer-size
	The value is a decimal number with the length of internal buffers to
	used for internal I/O operations. The value is capped at 1048576 (1
	MiB). In certain environments large buffers can yield a performance
	boost for callback bases data object, but the details depend a lot on
	the circumstances and the operating system. This flag may only be set
	once and must be set before any actual I/O happens ion the data
	objects.

	@item sensitive
	If the numeric value is not 0 the data object is considered to contain
	sensitive information like passwords or key material. If this is set
	the internal buffers are securely overwritten with zeroes by
	gpgme_data_release.


	@end table

	This function returns @code{0} on success.
	@end deftypefun


	@node Data Buffer Convenience
	@subsection Data Buffer Convenience Functions
	@cindex data buffer, convenience
	@cindex type of data
	@cindex identify

	@deftp {Data type} {enum gpgme_data_type_t}
	@tindex gpgme_data_type_t
	@since{1.4.3}

	The @code{gpgme_data_type_t} type is used to return the detected type
	of the content of a data buffer.
	@end deftp

	@table @code
	@item GPGME_DATA_TYPE_INVALID
	This is returned by @code{gpgme_data_identify} if it was not possible
	to identify the data. Reasons for this might be a non-seekable stream
	or a memory problem. The value is 0.
	@item GPGME_DATA_TYPE_UNKNOWN
	The type of the data is not known.
	@item GPGME_DATA_TYPE_PGP_SIGNED
	The data is an OpenPGP signed message. This may be a binary
	signature, a detached one or a cleartext signature.
	@item GPGME_DATA_TYPE_PGP_ENCRYPTED
	@since{1.7.0}

	The data is an OpenPGP encrypted message.
	@item GPGME_DATA_TYPE_PGP_SIGNATURE
	@since{1.7.0}

	The data is an OpenPGP detached signature.
	@item GPGME_DATA_TYPE_PGP_OTHER
	This is a generic OpenPGP message. In most cases this will be
	encrypted data.
	@item GPGME_DATA_TYPE_PGP_KEY
	This is an OpenPGP key (private or public).
	@item GPGME_DATA_TYPE_CMS_SIGNED
	This is a CMS signed message.
	@item GPGME_DATA_TYPE_CMS_ENCRYPTED
	This is a CMS encrypted (enveloped data) message.
	@item GPGME_DATA_TYPE_CMS_OTHER
	This is used for other CMS message types.
	@item GPGME_DATA_TYPE_X509_CERT
	The data is a X.509 certificate
	@item GPGME_DATA_TYPE_PKCS12
	The data is a PKCS#12 message. This is commonly used to exchange
	private keys for X.509.
	@end table

	@deftypefun gpgme_data_type_t gpgme_data_identify (@w{gpgme_data_t @var{dh}})
	@since{1.4.3}

	The function @code{gpgme_data_identify} returns the type of the data
	with the handle @var{dh}. If it is not possible to perform the
	identification, the function returns zero
	(@code{GPGME_DATA_TYPE_INVALID}). Note that depending on how the data
	object has been created the identification may not be possible or the
	data object may change its internal state (file pointer moved). For
	file or memory based data object, the state should not change.
	@end deftypefun


	@c
	@c Chapter Contexts
	@c
	@node Contexts
	@chapter Contexts
	@cindex context

	All cryptographic operations in @acronym{GPGME} are performed within a
	context, which contains the internal state of the operation as well as
	configuration parameters. By using several contexts you can run
	several cryptographic operations in parallel, with different
	configuration.

	@deftp {Data type} {gpgme_ctx_t}
	The @code{gpgme_ctx_t} type is a handle for a @acronym{GPGME} context,
	which is used to hold the configuration, status and result of
	cryptographic operations.
	@end deftp

	@menu
	* Creating Contexts:: Creating new @acronym{GPGME} contexts.
	* Destroying Contexts:: Releasing @acronym{GPGME} contexts.
	* Result Management:: Managing the result of crypto operations.
	* Context Attributes:: Setting properties of a context.
	* Key Management:: Managing keys with @acronym{GPGME}.
	* Crypto Operations:: Using a context for cryptography.
	* Miscellaneous:: Miscellaneous operations
	* Run Control:: Controlling how operations are run.
	@end menu


	@node Creating Contexts
	@section Creating Contexts
	@cindex context, creation

	@deftypefun gpgme_error_t gpgme_new (@w{gpgme_ctx_t *@var{ctx}})
	The function @code{gpgme_new} creates a new @code{gpgme_ctx_t} object
	and returns a handle for it in @var{ctx}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	context was successfully created, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and @code{GPG_ERR_ENOMEM} if not
	enough memory is available. Also, it returns
	@code{GPG_ERR_NOT_OPERATIONAL} if @code{gpgme_check_version} was not
	called to initialize GPGME, and @code{GPG_ERR_SELFTEST_FAILED} if a
	selftest failed. Currently, the only selftest is for Windows MingW32
	targets to see if @code{-mms-bitfields} was used (as required).
	@end deftypefun


	@node Destroying Contexts
	@section Destroying Contexts
	@cindex context, destruction

	@deftypefun void gpgme_release (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_release} destroys the context with the handle
	@var{ctx} and releases all associated resources.
	@end deftypefun


	@node Result Management
	@section Result Management
	@cindex context, result of operation

	The detailed result of an operation is returned in operation-specific
	structures such as @code{gpgme_decrypt_result_t}. The corresponding
	retrieval functions such as @code{gpgme_op_decrypt_result} provide
	static access to the results after an operation completes. Those
	structures shall be considered read-only and an application must not
	allocate such a structure on its own. The following interfaces make
	it possible to detach a result structure from its associated context
	and give it a lifetime beyond that of the current operation or
	context.

	@deftypefun void gpgme_result_ref (@w{void *@var{result}})
	@since{1.2.0}

	The function @code{gpgme_result_ref} acquires an additional reference
	for the result @var{result}, which may be of any type
	@code{gpgme_*_result_t}. As long as the user holds a reference, the
	result structure is guaranteed to be valid and unmodified.
	@end deftypefun

	@deftypefun void gpgme_result_unref (@w{void *@var{result}})
	@since{1.2.0}

	The function @code{gpgme_result_unref} releases a reference for the
	result @var{result}. If this was the last reference, the result
	structure will be destroyed and all resources associated to it will be
	released.
	@end deftypefun

	Note that a context may hold its own references to result structures,
	typically until the context is destroyed or the next operation is
	started. In fact, these references are accessed through the
	@code{gpgme_op_*_result} functions.


	@node Context Attributes
	@section Context Attributes
	@cindex context, attributes

	@menu
	* Protocol Selection:: Selecting the protocol used by a context.
	* Crypto Engine:: Configuring the crypto engine.
	* Setting the Sender:: How to tell the engine the sender.
	* ASCII Armor:: Requesting @acronym{ASCII} armored output.
	* Text Mode:: Choosing canonical text mode.
	* Offline Mode:: Choosing offline mode.
	* Pinentry Mode:: Choosing the pinentry mode.
	* Included Certificates:: Including a number of certificates.
	* Key Listing Mode:: Selecting key listing mode.
	* Passphrase Callback:: Getting the passphrase from the user.
	* Progress Meter Callback:: Being informed about the progress.
	* Status Message Callback:: Status messages received from gpg.
	* Context Flags:: Additional flags for a context.
	* Locale:: Setting the locale of a context.
	* Additional Logs:: Additional logs of a context.
	@end menu


	@node Protocol Selection
	@subsection Protocol Selection
	@cindex context, selecting protocol
	@cindex protocol, selecting

	@deftypefun gpgme_error_t gpgme_set_protocol (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_protocol_t @var{proto}})
	The function @code{gpgme_set_protocol} sets the protocol used within
	the context @var{ctx} to @var{proto}. All crypto operations will be
	performed by the crypto engine configured for that protocol.
	@xref{Protocols and Engines}.

	Setting the protocol with @code{gpgme_set_protocol} does intentionally
	not check if the crypto engine for that protocol is available and
	installed correctly. @xref{Engine Version Check}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	protocol could be set successfully, and @code{GPG_ERR_INV_VALUE} if
	@var{protocol} is not a valid protocol.
	@end deftypefun

	@deftypefun gpgme_protocol_t gpgme_get_protocol (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_get_protocol} retrieves the protocol currently
	use with the context @var{ctx}.
	@end deftypefun


	@node Crypto Engine
	@subsection Crypto Engine
	@cindex context, configuring engine
	@cindex engine, configuration per context

	The following functions can be used to set and retrieve the
	configuration of the crypto engines of a specific context. The
	default can also be retrieved without any particular context.
	@xref{Engine Information}. The default can also be changed globally.
	@xref{Engine Configuration}.

	@deftypefun gpgme_engine_info_t gpgme_ctx_get_engine_info (@w{gpgme_ctx_t @var{ctx}})
	@since{1.1.0}

	The function @code{gpgme_ctx_get_engine_info} returns a linked list of
	engine info structures. Each info structure describes the
	configuration of one configured backend, as used by the context
	@var{ctx}.

	The result is valid until the next invocation of
	@code{gpgme_ctx_set_engine_info} for this particular context.

	This function can not fail.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_ctx_set_engine_info (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_protocol_t @var{proto}}, @w{const char @var{file_name}}, @w{const char @var{home_dir}})
	@since{1.1.0}

	The function @code{gpgme_ctx_set_engine_info} changes the
	configuration of the crypto engine implementing the protocol
	@var{proto} for the context @var{ctx}.

	@var{file_name} is the file name of the executable program
	implementing this protocol, and @var{home_dir} is the directory name
	of the configuration directory for this crypto engine. If
	@var{home_dir} is @code{NULL}, the engine's default will be used.

	Currently this function must be used before starting the first crypto
	operation. It is unspecified if and when the changes will take effect
	if the function is called after starting the first operation on the
	context @var{ctx}.

	This function returns the error code @code{GPG_ERR_NO_ERROR} if
	successful, or an error code on failure.
	@end deftypefun


	@node Setting the Sender
	@subsection How to tell the engine the sender.
	@cindex context, sender
	@cindex sender
	@cindex From:

	Some engines can make use of the sender’s address, for example to
	figure out the best user id in certain trust models. For verification
	and signing of mails, it is thus suggested to let the engine know the
	sender ("From:") address. @acronym{GPGME} provides two functions to
	accomplish that. Note that the esoteric use of multiple "From:"
	addresses is not supported.

	@deftypefun gpgme_error_t gpgme_set_sender @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{int @var{address}})

	@since{1.8.0}

	The function @code{gpgme_set_sender} specifies the sender address for
	use in sign and verify operations. @var{address} is expected to be
	the ``addr-spec'' part of an address but my also be a complete mailbox
	address, in which case this function extracts the ``addr-spec'' from
	it. Using @code{NULL} for @var{address} clears the sender address.

	The function returns 0 on success or an error code on failure. The
	most likely failure is that no valid ``addr-spec'' was found in
	@var{address}.

	@end deftypefun

	@deftypefun @w{const char *} gpgme_get_sender @
	(@w{gpgme_ctx_t @var{ctx}})

	@since{1.8.0}

	The function @code{gpgme_get_sender} returns the current sender
	address from the context, or NULL if none was set. The returned
	value is valid as long as the @var{ctx} is valid and
	@code{gpgme_set_sender} has not been called again.

	@end deftypefun



	@c FIXME: Unfortunately, using @acronym here breaks texi2dvi.
	@node ASCII Armor
	@subsection @acronym{ASCII} Armor
	@cindex context, armor mode
	@cindex @acronym{ASCII} armor
	@cindex armor mode

	@deftypefun void gpgme_set_armor (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{yes}})
	The function @code{gpgme_set_armor} specifies if the output should be
	@acronym{ASCII} armored. By default, output is not @acronym{ASCII}
	armored.

	@acronym{ASCII} armored output is disabled if @var{yes} is zero, and
	enabled otherwise.
	@end deftypefun

	@deftypefun int gpgme_get_armor (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_get_armor} returns 1 if the output is
	@acronym{ASCII} armored, and @code{0} if it is not, or if @var{ctx} is
	not a valid pointer.
	@end deftypefun


	@node Text Mode
	@subsection Text Mode
	@cindex context, text mode
	@cindex text mode
	@cindex canonical text mode

	@deftypefun void gpgme_set_textmode (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{yes}})
	The function @code{gpgme_set_textmode} specifies if canonical text mode
	should be used. By default, text mode is not used.

	Text mode is for example used for the RFC2015 signatures; note that
	the updated RFC 3156 mandates that the mail user agent does some
	preparations so that text mode is not needed anymore.

	This option is only relevant to the OpenPGP crypto engine, and ignored
	by all other engines.

	Canonical text mode is disabled if @var{yes} is zero, and enabled
	otherwise.
	@end deftypefun

	@deftypefun int gpgme_get_textmode (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_get_textmode} returns 1 if canonical text
	mode is enabled, and @code{0} if it is not, or if @var{ctx} is not a
	valid pointer.
	@end deftypefun


	@node Offline Mode
	@subsection Offline Mode
	@cindex context, offline mode
	@cindex offline mode

	@deftypefun void gpgme_set_offline (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{yes}})
	@since{1.6.0}

	The function @code{gpgme_set_offline} specifies if offline mode should
	be used. Offline mode is disabled if @var{yes} is zero, and enabled
	otherwise. By default, offline mode is disabled.

	The details of the offline mode depend on the used protocol and its
	backend engine. It may eventually be extended to be more stricter and
	for example completely disable the use of Dirmngr for any engine.

	For the CMS protocol the offline mode specifies whether Dirmngr shall
	be used to do additional validation that might require connecting
	external services (e.g. CRL / OCSP checks). Here the offline mode
	only affects the keylist mode @code{GPGME_KEYLIST_MODE_VALIDATE}.

	For the OpenPGP protocol offline mode entirely disables the use of the
	Dirmngr and will thus guarantee that no network connections are done
	as part of an operation on this context. It has only an effect with
	GnuPG versions 2.1.23 or later.

	For all other protocols the offline mode is currently ignored.

	@end deftypefun

	@deftypefun int gpgme_get_offline (@w{gpgme_ctx_t @var{ctx}})
	@since{1.6.0}

	The function @code{gpgme_get_offline} returns 1 if offline
	mode is enabled, and @code{0} if it is not, or if @var{ctx} is not a
	valid pointer.
	@end deftypefun


	@node Pinentry Mode
	@subsection Pinentry Mode
	@cindex context, pinentry mode
	@cindex pinentry mode

	@deftypefun gpgme_error_t gpgme_set_pinentry_mode (@w{gpgme_ctx_t @var{ctx}},
	@w{gpgme_pinentry_mode_t @var{mode}})

	@since{1.4.0}

	The function @code{gpgme_set_pinentry_mode} specifies the pinentry mode
	to be used.

	For GnuPG >= 2.1 this option is required to be set to
	@code{GPGME_PINENTRY_MODE_LOOPBACK} to enable the passphrase callback
	mechanism in GPGME through @code{gpgme_set_passphrase_cb}.
	@end deftypefun

	@deftypefun gpgme_pinentry_mode_t gpgme_get_pinentry_mode (@w{gpgme_ctx_t @var{ctx}})
	@since{1.4.0}

	The function @code{gpgme_get_pinenty_mode} returns the
	mode set for the context.
	@end deftypefun

	@deftp {Data type} {enum gpgme_pinentry_mode_t}
	@tindex gpgme_pinentry_mode_t
	@since{1.4.0}

	The @code{gpgme_minentry_mode_t} type specifies the set of possible pinentry
	modes that are supported by @acronym{GPGME} if GnuPG >= 2.1 is used.
	The following modes are supported:

	@table @code
	@item GPGME_PINENTRY_MODE_DEFAULT
	@since{1.4.0}

	Use the default of the agent, which is ask.

	@item GPGME_PINENTRY_MODE_ASK
	@since{1.4.0}

	Force the use of the Pinentry.

	@item GPGME_PINENTRY_MODE_CANCEL
	@since{1.4.0}

	Emulate use of Pinentry's cancel button.

	@item GPGME_PINENTRY_MODE_ERROR
	@since{1.4.0}

	Return a Pinentry error @code{No Pinentry}.

	@item GPGME_PINENTRY_MODE_LOOPBACK
	@since{1.4.0}

	Redirect Pinentry queries to the caller.
	This enables the use of @code{gpgme_set_passphrase_cb} because pinentry
	queries are redirected to gpgme.

	Note: For 2.1.0 - 2.1.12 this mode requires @code{allow-loopback-pinentry}
	to be enabled in the @file{gpg-agent.conf} or an agent started with that option.

	@end table
	@end deftp


	@node Included Certificates
	@subsection Included Certificates
	@cindex certificates, included

	@deftypefun void gpgme_set_include_certs (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{nr_of_certs}})
	The function @code{gpgme_set_include_certs} specifies how many
	certificates should be included in an S/MIME signed message. By
	default, only the sender's certificate is included. The possible
	values of @var{nr_of_certs} are:

	@table @code
	@item GPGME_INCLUDE_CERTS_DEFAULT
	@since{1.0.3}

	Fall back to the default of the crypto backend. This is the default
	for GPGME.
	@item -2
	Include all certificates except the root certificate.
	@item -1
	Include all certificates.
	@item 0
	Include no certificates.
	@item 1
	Include the sender's certificate only.
	@item n
	Include the first n certificates of the certificates path, starting
	from the sender's certificate. The number @code{n} must be positive.
	@end table

	Values of @var{nr_of_certs} smaller than -2 are undefined.

	This option is only relevant to the CMS crypto engine, and ignored by
	all other engines.
	@end deftypefun

	@deftypefun int gpgme_get_include_certs (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_get_include_certs} returns the number of
	certificates to include into an S/MIME signed message.
	@end deftypefun


	@node Key Listing Mode
	@subsection Key Listing Mode
	@cindex key listing mode
	@cindex key listing, mode of

	@deftypefun gpgme_error_t gpgme_set_keylist_mode (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_keylist_mode_t @var{mode}})
	The function @code{gpgme_set_keylist_mode} changes the default
	behaviour of the key listing functions. The value in @var{mode} is a
	bitwise-or combination of one or multiple of the following bit values:

	@table @code
	@item GPGME_KEYLIST_MODE_LOCAL
	The @code{GPGME_KEYLIST_MODE_LOCAL} symbol specifies that the local
	keyring should be searched for keys in the keylisting operation. This
	is the default.

	Using only this option results in a @code{--list-keys}.

	@item GPGME_KEYLIST_MODE_EXTERN
	The @code{GPGME_KEYLIST_MODE_EXTERN} symbol specifies that an external
	source should be searched for keys in the keylisting operation. The
	type of external source is dependent on the crypto engine used and
	whether it is combined with @code{GPGME_KEYLIST_MODE_LOCAL}. For
	example, it can be a remote keyserver or LDAP certificate server.

	Using only this option results in a @code{--search-keys} for
	@code{GPGME_PROTOCOL_OpenPGP} and something similar to
	@code{--list-external-keys} for @code{GPGME_PROTOCOL_CMS}.

	@item GPGME_KEYLIST_MODE_LOCATE
	This is a shortcut for the combination of
	@code{GPGME_KEYLIST_MODE_LOCAL} and @code{GPGME_KEYLIST_MODE_EXTERN}, which
	results in a @code{--locate-keys} for @code{GPGME_PROTOCOL_OpenPGP}.

	@item GPGME_KEYLIST_MODE_SIGS
	The @code{GPGME_KEYLIST_MODE_SIGS} symbol specifies that the key
	signatures should be included in the listed keys.

	@item GPGME_KEYLIST_MODE_SIG_NOTATIONS
	@since{1.1.1}

	The @code{GPGME_KEYLIST_MODE_SIG_NOTATIONS} symbol specifies that the
	signature notations on key signatures should be included in the listed
	keys. This only works if @code{GPGME_KEYLIST_MODE_SIGS} is also
	enabled.

	@item GPGME_KEYLIST_MODE_WITH_TOFU
	@since{1.7.0}

	The @code{GPGME_KEYLIST_MODE_WITH_TOFU} symbol specifies that
	information pertaining to the TOFU trust model should be included in
	the listed keys.

	@item GPGME_KEYLIST_MODE_WITH_KEYGRIP
	@since{1.14.0}

	The @code{GPGME_KEYLIST_MODE_WITH_KEYRIP} symbol specifies that the
	keygrip is always included in the listing. The default depends on the
	version of the backend and the used protocol.

	@item GPGME_KEYLIST_MODE_WITH_SECRET
	@since{1.5.1}

	The @code{GPGME_KEYLIST_MODE_WITH_SECRET} returns information about
	the presence of a corresponding secret key in a public key listing. A
	public key listing with this mode is slower than a standard listing
	but can be used instead of a second run to list the secret keys. This
	is only supported for GnuPG versions >= 2.1. Note that using this
	option also makes sure that the keygrip is available in the output.

	@item GPGME_KEYLIST_MODE_EPHEMERAL
	@since{1.2.0}

	The @code{GPGME_KEYLIST_MODE_EPHEMERAL} symbol specifies that keys
	flagged as ephemeral are included in the listing.

	@item GPGME_KEYLIST_MODE_VALIDATE
	@since{0.4.5}

	The @code{GPGME_KEYLIST_MODE_VALIDATE} symbol specifies that the
	backend should do key or certificate validation and not just get the
	validity information from an internal cache. This might be an
	expensive operation and is in general not useful. Currently only
	implemented for the S/MIME backend and ignored for other backends.

	@item GPGME_KEYLIST_MODE_FORCE_EXTERN
	@since{1.18.0}

	The @code{GPGME_KEYLIST_MODE_FORCE_EXTERN} symbol specifies that only
	external sources should be searched for keys in the keylisting
	operation. If used in combination with @code{GPGME_KEYLIST_MODE_LOCATE},
	the keylisting results in a @code{--locate-external-keys} for
	@code{GPGME_PROTOCOL_OpenPGP}. The combination with
	@code{GPGME_KEYLIST_MODE_LOCAL}, but without @code{GPGME_KEYLIST_MODE_EXTERN}
	is not allowed. Currently only implemented for the OpenPGP backend and
	ignored for other backends.

	@item GPGME_KEYLIST_MODE_LOCATE_EXTERNAL
	@since{1.18.0}

	This is a shortcut for the combination of
	@code{GPGME_KEYLIST_MODE_LOCATE} and @code{GPGME_KEYLIST_MODE_FORCE_EXTERN},
	which results in a @code{--locate-external-keys} for
	@code{GPGME_PROTOCOL_OpenPGP}.

	@end table

	At least one of @code{GPGME_KEYLIST_MODE_LOCAL} and
	@code{GPGME_KEYLIST_MODE_EXTERN} must be specified. For future binary
	compatibility, you should get the current mode with
	@code{gpgme_get_keylist_mode} and modify it by setting or clearing the
	appropriate bits, and then using that calculated value in the
	@code{gpgme_set_keylisting_mode} operation. This will leave all other
	bits in the mode value intact (in particular those that are not used
	in the current version of the library).

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	mode could be set correctly, and @code{GPG_ERR_INV_VALUE} if @var{ctx}
	is not a valid pointer or @var{mode} is not a valid mode.
	@end deftypefun


	@deftypefun gpgme_keylist_mode_t gpgme_get_keylist_mode (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_get_keylist_mode} returns the current key
	listing mode of the context @var{ctx}. This value can then be
	modified and used in a subsequent @code{gpgme_set_keylist_mode}
	operation to only affect the desired bits (and leave all others
	intact).

	The function returns 0 if @var{ctx} is not a valid pointer, and the
	current mode otherwise. Note that 0 is not a valid mode value.
	@end deftypefun


	@node Passphrase Callback
	@subsection Passphrase Callback
	@cindex callback, passphrase
	@cindex passphrase callback

	@deftp {Data type} {gpgme_error_t (gpgme_passphrase_cb_t)(void @var{hook}, const char @var{uid_hint}, const char @var{passphrase_info}, @w{int @var{prev_was_bad}}, @w{int @var{fd}})}
	@tindex gpgme_passphrase_cb_t
	The @code{gpgme_passphrase_cb_t} type is the type of functions usable as
	passphrase callback function.

	The argument @var{uid_hint} might contain a string that gives an
	indication for which user ID the passphrase is required. If this is
	not available, or not applicable (in the case of symmetric encryption,
	for example), @var{uid_hint} will be @code{NULL}.

	The argument @var{passphrase_info}, if not @code{NULL}, will give
	further information about the context in which the passphrase is
	required. This information is engine and operation specific.

	If this is the repeated attempt to get the passphrase, because
	previous attempts failed, then @var{prev_was_bad} is 1, otherwise it
	will be 0.

	The user must write the passphrase, followed by a newline character,
	to the file descriptor @var{fd}. The function @code{gpgme_io_writen}
	should be used for the write operation. Note that if the user returns
	0 to indicate success, the user must at least write a newline
	character before returning from the callback.

	If an error occurs, return the corresponding @code{gpgme_error_t}
	value. You can use the error code @code{GPG_ERR_CANCELED} to abort
	the operation. Otherwise, return @code{0}.

	Note: The passphrase_cb only works with GnuPG 1.x and 2.1.x and not
	with the 2.0.x series. See @code{gpgme_set_pinentry_mode} for more
	details on 2.1.x usage.
	@end deftp

	@deftypefun void gpgme_set_passphrase_cb (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_passphrase_cb_t @var{passfunc}}, @w{void *@var{hook_value}})
	The function @code{gpgme_set_passphrase_cb} sets the function that is
	used when a passphrase needs to be provided by the user to
	@var{passfunc}. The function @var{passfunc} needs to implemented by
	the user, and whenever it is called, it is called with its first
	argument being @var{hook_value}. By default, no passphrase callback
	function is set.

	Not all crypto engines require this callback to retrieve the
	passphrase. It is better if the engine retrieves the passphrase from
	a trusted agent (a daemon process), rather than having each user to
	implement their own passphrase query. Some engines do not even
	support an external passphrase callback at all, in this case the error
	code @code{GPG_ERR_NOT_SUPPORTED} is returned.

	For GnuPG >= 2.1 the pinentry mode has to be set to
	@code{GPGME_PINENTRY_MODE_LOOPBACK} to enable the passphrase callback.
	See @code{gpgme_set_pinentry_mode}.

	The user can disable the use of a passphrase callback function by
	calling @code{gpgme_set_passphrase_cb} with @var{passfunc} being
	@code{NULL}.
	@end deftypefun

	@deftypefun void gpgme_get_passphrase_cb (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_passphrase_cb_t @var{passfunc}}, @w{void *@var{hook_value}})
	The function @code{gpgme_get_passphrase_cb} returns the function that
	is used when a passphrase needs to be provided by the user in
	@var{*passfunc}, and the first argument for this function in
	@var{*hook_value}. If no passphrase callback is set, or @var{ctx} is
	not a valid pointer, @code{NULL} is returned in both variables.

	@var{passfunc} or @var{hook_value} can be @code{NULL}. In this case,
	the corresponding value will not be returned.
	@end deftypefun


	@node Progress Meter Callback
	@subsection Progress Meter Callback
	@cindex callback, progress meter
	@cindex progress meter callback

	@deftp {Data type} {void (gpgme_progress_cb_t)(void @var{hook}, const char *@var{what}, int @var{type}, int @var{current}, int @var{total})}
	@tindex gpgme_progress_cb_t
	The @code{gpgme_progress_cb_t} type is the type of functions usable as
	progress callback function.

	The arguments are specific to the crypto engine. More information
	about the progress information returned from the GnuPG engine can be
	found in the GnuPG source code in the file @file{doc/DETAILS} in the
	section PROGRESS.
	@end deftp

	@deftypefun void gpgme_set_progress_cb (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_progress_cb_t @var{progfunc}}, @w{void *@var{hook_value}})
	The function @code{gpgme_set_progress_cb} sets the function that is
	used when progress information about a cryptographic operation is
	available. The function @var{progfunc} needs to implemented by the
	user, and whenever it is called, it is called with its first argument
	being @var{hook_value}. By default, no progress callback function
	is set.

	Setting a callback function allows an interactive program to display
	progress information about a long operation to the user.

	The user can disable the use of a progress callback function by
	calling @code{gpgme_set_progress_cb} with @var{progfunc} being
	@code{NULL}.
	@end deftypefun

	@deftypefun void gpgme_get_progress_cb (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_progress_cb_t @var{progfunc}}, @w{void *@var{hook_value}})
	The function @code{gpgme_get_progress_cb} returns the function that is
	used to inform the user about the progress made in @var{*progfunc},
	and the first argument for this function in @var{*hook_value}. If no
	progress callback is set, or @var{ctx} is not a valid pointer,
	@code{NULL} is returned in both variables.

	@var{progfunc} or @var{hook_value} can be @code{NULL}. In this case,
	the corresponding value will not be returned.
	@end deftypefun


	@node Status Message Callback
	@subsection Status Message Callback
	@cindex callback, status message
	@cindex status message callback

	@deftp {Data type} {gpgme_error_t (gpgme_status_cb_t)(void @var{hook}, const char @var{keyword}, const char @var{args})}
	@tindex gpgme_status_cb_t
	The @code{gpgme_status_cb_t} type is the type of function usable as
	a status message callback function.

	The argument @var{keyword} is the name of the status message while the
	@var{args} argument contains any arguments for the status message.

	If an error occurs, return the corresponding @code{gpgme_error_t}
	value. Otherwise, return @code{0}.
	@end deftp

	@deftypefun void gpgme_set_status_cb (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_status_cb_t @var{statusfunc}}, @w{void *@var{hook_value}})
	@since{1.6.0}

	The function @code{gpgme_set_status_cb} sets the function that is used when a
	status message is received from gpg to @var{statusfunc}. The function
	@var{statusfunc} needs to be implemented by the user, and whenever it is
	called, it is called with its first argument being @var{hook_value}. By
	default, no status message callback function is set.

	The user can disable the use of a status message callback function by calling
	@code{gpgme_set_status_cb} with @var{statusfunc} being @code{NULL}.
	@end deftypefun

	@deftypefun void gpgme_get_status_cb (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_status_cb_t @var{statusfunc}}, @w{void *@var{hook_value}})
	@since{1.6.0}

	The function @code{gpgme_get_status_cb} returns the function that is used to
	process status messages from gpg in @var{*statusfunc}, and the first argument
	for this function in @var{*hook_value}. If no status message callback is set,
	or @var{ctx} is not a valid pointer, @code{NULL} is returned in both
	variables.
	@end deftypefun

	@node Context Flags
	@subsection Context Flags
	@cindex flags, of a context

	@deftypefun {gpgme_error_t} gpgme_set_ctx_flag @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const char *@var{name}}, @
	@w{const char *@var{value}})

	@since{1.7.0}

	Some minor properties of the context can be controlled with flags set
	by this function. The properties are identified by the following
	values for @var{name}:

	@table @code
	@item "redraw"
	This flag is normally not changed by the caller because GPGME sets and
	clears it automatically: The flag is cleared before an operation and
	set if an operation noticed that the engine has launched a Pinentry.
	A Curses based application may use this information to redraw the
	screen; for example:

	@example
	err = gpgme_op_keylist_start (ctx, "foo@@example.org", 0);
	while (!err)
	@{
	err = gpgme_op_keylist_next (ctx, &key);
	if (err)
	break;
	show_key (key);
	gpgme_key_release (key);
	@}
	if ((s = gpgme_get_ctx_flag (ctx, "redraw")) && *s)
	redraw_screen ();
	gpgme_release (ctx);
	@end example


	@item "full-status"
	Using a @var{value} of "1" the status callback set by
	gpgme_set_status_cb returns all status lines with the exception of
	PROGRESS lines. With the default of "0" the status callback is only
	called in certain situations.

	@item "raw-description"
	Setting the @var{value} to "1" returns human readable strings in a raw
	format. For example the non breaking space characters ("~") will not
	be removed from the @code{description} field of the
	@code{gpgme_tofu_info_t} object.

	@item "export-session-key"
	Using a @var{value} of "1" specifies that the context should try to
	export the symmetric session key when decrypting data. By default, or
	when using an empty string or "0" for @var{value}, session keys are
	not exported.

	@item "override-session-key"
	The string given in @var{value} is passed to the GnuPG engine to override
	the session key for decryption. The format of that session key is
	specific to GnuPG and can be retrieved during a decrypt operation when
	the context flag "export-session-key" is enabled. Please be aware that
	using this feature with GnuPG < 2.1.16 will leak the session key on
	many platforms via ps(1).

	@item "auto-key-retrieve"
	Setting the @var{value} to "1" asks the backend to automatically
	retrieve a key for signature verification if possible. Note that this
	option makes a "web bug" like behavior possible. Keyserver or Web Key
	Directory operators can see which keys you request, so by sending you
	a message signed by a brand new key (which you naturally will not have
	on your local keyring), the operator can tell both your IP address and
	the time when you verified the signature.

	@item "auto-key-import"
	Setting the @var{value} to "1" forces the GPG backend to automatically
	import a missing key for signature verification from the signature.

	@item "include-key-block"
	Setting the @var{value} to "1" forces the GPG backend to embed the
	signing key as well as an encryption subkey into the the signature.

	@item "request-origin"
	The string given in @var{value} is passed to the GnuPG engines to
	request restrictions based on the origin of the request. Valid values
	are documented in the GnuPG manual and the gpg man page under the
	option @option{--request-origin}. Requires at least GnuPG 2.2.6 to have an
	effect.

	@item "no-symkey-cache"
	For OpenPGP disable the passphrase cache used for symmetrical en- and
	decryption. This cache is based on the message specific salt value.
	Requires at least GnuPG 2.2.7 to have an effect.

	@item "ignore-mdc-error"
	This flag passes the option @option{--ignore-mdc-error} to gpg. This
	can be used to force decryption of a message which failed due to a
	missing integrity check. This flag must be used with great caution
	and only if it is a known non-corrupted old message and the decryption
	result of the former try had the decryption result flag
	@code{legacy_cipher_nomdc} set. For failsafe reasons this flag is
	reset after each operation.

	@item "auto-key-locate"
	The string given in @var{value} is passed to gpg. This can be used
	to change the behavior of a @code{GPGME_KEYLIST_MODE_LOCATE} keylisting.
	Valid values are documented in the GnuPG manual and the gpg man page under
	the option @option{--auto-key-locate}.
	Requires at least GnuPG 2.1.18.

	Note: Keys retrieved through @code{auto-key-locate} are automatically
	imported in the keyring.

	@item trust-model
	@since{1.11.2}

	Change the trust-model for all GnuPG engine operations. An empty
	string sets the trust-model back to the users default. If the
	trust-model is not supported by GnuPG the behavior is undefined
	and will likely cause all operations to fail. Example: "tofu+pgp".

	This options should be used carefully with a strict version
	requirement. In some versions of GnuPG setting the
	trust-model changes the default trust-model for future operations.
	A change in the trust-model also can have unintended side effects, like
	rebuilding the trust-db.

	@item "extended-edit"
	This flag passes the option @option{--expert} to gpg key edit. This
	can be used to get additional callbacks in @code{gpgme_op_edit}.

	@item "cert-expire"
	@since{1.15.2}
	The string given in @var{value} is passed to the GnuPG engine to set
	the expiration time to use for key signature expiration. Valid values
	are documented in the GnuPG manual and the gpg man page under
	the option @option{--default-cert-expire}.

	@item "key-origin"
	@since{1.16.1}
	The string given in @var{value} is passed to the GnuPG engine to set
	the origin of imported keys. Valid values are documented in the GnuPG
	manual and the gpg man page under the option @option{--key-origin}.

	@item "import-filter"
	@since{1.16.1}
	The string given in @var{value} is passed to the GnuPG engine to use as
	filter when importing keys. Valid values are documented in the GnuPG
	manual and the gpg man page under the option @option{--import-filter}.

	@end table

	This function returns @code{0} on success.
	@end deftypefun


	@deftypefun {const char *} gpgme_get_ctx_flag @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const char *@var{name}})

	@since{1.8.0}

	The value of flags settable by @code{gpgme_set_ctx_flag} can be
	retrieved by this function. If @var{name} is unknown the function
	returns @code{NULL}. For boolean flags an empty string is returned
	for False and the string "1" is returned for True; either atoi(3) or a
	test for an empty string can be used to get the boolean value.

	@end deftypefun


	@node Locale
	@subsection Locale
	@cindex locale, default
	@cindex locale, of a context

	A locale setting can be associated with a context. This locale is
	passed to the crypto engine, and used for applications like the PIN
	entry, which is displayed to the user when entering a passphrase is
	required.

	The default locale is used to initialize the locale setting of all
	contexts created afterwards.

	@deftypefun gpgme_error_t gpgme_set_locale (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{category}}, @w{const char *@var{value}})
	@since{0.4.3}

	The function @code{gpgme_set_locale} sets the locale of the context
	@var{ctx}, or the default locale if @var{ctx} is a null pointer.

	The locale settings that should be changed are specified by
	@var{category}. Supported categories are @code{LC_CTYPE},
	@code{LC_MESSAGES}, and @code{LC_ALL}, which is a wildcard you can use
	if you want to change all the categories at once.

	The value to be used for the locale setting is @var{value}, which will
	be copied to @acronym{GPGME}'s internal data structures. @var{value}
	can be a null pointer, which disables setting the locale, and will
	make PIN entry and other applications use their default setting, which
	is usually not what you want.

	Note that the settings are only used if the application runs on a text
	terminal, and that the settings should fit the configuration of the
	output terminal. Normally, it is sufficient to initialize the default
	value at startup.

	The function returns an error if not enough memory is available.
	@end deftypefun


	@node Additional Logs
	@subsection Additional Logs
	@cindex auditlog, of the engine
	@cindex auditlog

	Additional logs can be associated with a context. These logs are
	engine specific and can be be obtained with @code{gpgme_op_getauditlog}.

	@deftypefun gpgme_error_t gpgme_op_getauditlog @
	(@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{output}}, @
	@w{unsigned int @var{flags}})
	@since{1.1.1}

	The function @code{gpgme_op_getauditlog} is used to obtain additional
	logs as specified by @var{flags} into the @var{output} data. If

	The function returns the error code @code{GPG_ERR_NO_ERROR} if a
	log could be queried from the engine, and @code{GPG_ERR_NOT_IMPLEMENTED}
	if the log specified in @var{flags} is not available for this engine.
	If no log is available @code{GPG_ERR_NO_DATA} is returned.

	The value in @var{flags} is a bitwise-or combination of one or
	multiple of the following bit values:

	@table @code
	@item GPGME_AUDITLOG_DIAG
	@since{1.11.2}

	Obtain diagnostic output which would be written to @code{stderr} in
	interactive use of the engine. This can be used to provide additional
	diagnostic information in case of errors in other operations.

	Note: If log-file has been set in the configuration the log will
	be empty and @code{GPG_ERR_NO_DATA} will be returned.

	Implemented for: @code{GPGME_PROTOCOL_OpenPGP}

	@item GPGME_AUDITLOG_DEFAULT
	@since{1.11.2}

	This flag has the value 0 for compatibility reasons. Obtains additional
	information from the engine by issuing the @code{GETAUDITLOG} command.
	For @code{GPGME_PROTOCOL_CMS} this provides additional information about
	the X509 certificate chain.

	Implemented for: @code{GPGME_PROTOCOL_CMS}

	@item GPGME_AUDITLOG_HTML
	@since{1.1.1}

	Same as @code{GPGME_AUDITLOG_DEFAULT} but in HTML.

	Implemented for: @code{GPGME_PROTOCOL_CMS}
	@end table
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_getauditlog_start @
	(@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{output}}, @
	@w{unsigned int @var{flags}})
	@since{1.1.1}

	This is the asynchronous variant of @code{gpgme_op_getauditlog}.
	@end deftypefun

	@node Key Management
	@section Key Management
	@cindex key management

	Some of the cryptographic operations require that recipients or
	signers are specified. This is always done by specifying the
	respective keys that should be used for the operation. The following
	section describes how such keys can be selected and manipulated.


	@menu
	* Key objects:: Description of the key structures.
	* Listing Keys:: Browsing the list of available keys.
	* Information About Keys:: Requesting detailed information about keys.
	* Manipulating Keys:: Operations on keys.
	* Generating Keys:: Creating new key pairs.
	* Signing Keys:: Adding key signatures to public keys.
	* Exporting Keys:: Retrieving key data from the key ring.
	* Importing Keys:: Adding keys to the key ring.
	* Deleting Keys:: Removing keys from the key ring.
	* Changing Passphrases:: Change the passphrase of a key.
	* Changing TOFU Data:: Changing data pertaining to TOFU.
	* Advanced Key Editing:: Advanced key edit operation.
	@end menu

	@node Key objects
	@subsection Key objects

	The keys are represented in GPGME by structures which may only be read
	by the application but never be allocated or changed. They are valid
	as long as the key object itself is valid.

	@deftp {Data type} gpgme_key_t

	The @code{gpgme_key_t} type is a pointer to a key object. It has the
	following members:

	@table @code
	@item gpgme_keylist_mode_t keylist_mode
	@since{0.9.0}

	The keylist mode that was active when the key was retrieved.

	@item unsigned int revoked : 1
	This is true if the key is revoked.

	@item unsigned int expired : 1
	This is true if the key is expired.

	@item unsigned int disabled : 1
	This is true if the key is disabled.

	@item unsigned int invalid : 1
	This is true if the key is invalid. This might have several reasons,
	for a example for the S/MIME backend, it will be set during key
	listings if the key could not be validated due to missing
	certificates or unmatched policies.

	@item unsigned int can_encrypt : 1
	This is true if the key (ie one of its subkeys) can be used for
	encryption.

	@item unsigned int can_sign : 1
	This is true if the key (ie one of its subkeys) can be used to create
	data signatures.

	@item unsigned int can_certify : 1
	This is true if the key (ie one of its subkeys) can be used to create
	key certificates.

	@item unsigned int can_authenticate : 1
	@since{0.4.5}

	This is true if the key (ie one of its subkeys) can be used for
	authentication.

	@item unsigned int is_qualified : 1
	@since{1.1.0}

	This is true if the key can be used for qualified signatures according
	to local government regulations.

	@item unsigned int secret : 1
	This is true if the key is a secret key. Note, that this will always
	be true even if the corresponding subkey flag may be false
	(offline/stub keys). This is only set if a listing of secret keys has
	been requested or if @code{GPGME_KEYLIST_MODE_WITH_SECRET} is active.

	@item unsigned int origin : 5
	@since{1.8.0}

	Reserved for the origin of this key.

	@item gpgme_protocol_t protocol
	This is the protocol supported by this key.

	@item char *issuer_serial
	If @code{protocol} is @code{GPGME_PROTOCOL_CMS}, then this is the
	issuer serial.

	@item char *issuer_name
	If @code{protocol} is @code{GPGME_PROTOCOL_CMS}, then this is the
	issuer name.

	@item char *chain_id
	If @code{protocol} is @code{GPGME_PROTOCOL_CMS}, then this is the
	chain ID, which can be used to built the certificate chain.

	@item gpgme_validity_t owner_trust
	If @code{protocol} is @code{GPGME_PROTOCOL_OpenPGP}, then this is the
	owner trust.

	@item gpgme_subkey_t subkeys
	This is a linked list with the subkeys of the key. The first subkey
	in the list is the primary key and usually available.

	@item gpgme_user_id_t uids
	This is a linked list with the user IDs of the key. The first user ID
	in the list is the main (or primary) user ID.

	@item char *fpr
	@since{1.7.0}

	This field gives the fingerprint of the primary key. Note that
	this is a copy of the fingerprint of the first subkey. For an
	incomplete key (for example from a verification result) a subkey may
	be missing but this field may be set nevertheless.

	@item unsigned long last_update
	@since{1.8.0}

	Reserved for the time of the last update of this key.

	@end table
	@end deftp


	@deftp {Data type} gpgme_subkey_t
	@since{1.5.0}

	The @code{gpgme_subkey_t} type is a pointer to a subkey structure.
	Subkeys are one component of a @code{gpgme_key_t} object. In fact,
	subkeys are those parts that contains the real information about the
	individual cryptographic keys that belong to the same key object. One
	@code{gpgme_key_t} can contain several subkeys. The first subkey in
	the linked list is also called the primary key.

	The subkey structure has the following members:

	@table @code
	@item gpgme_subkey_t next
	This is a pointer to the next subkey structure in the linked list, or
	@code{NULL} if this is the last element.

	@item unsigned int revoked : 1
	This is true if the subkey is revoked.

	@item unsigned int expired : 1
	This is true if the subkey is expired.

	@item unsigned int disabled : 1
	This is true if the subkey is disabled.

	@item unsigned int invalid : 1
	This is true if the subkey is invalid.

	@item unsigned int can_encrypt : 1
	This is true if the subkey can be used for encryption.

	@item unsigned int can_sign : 1
	This is true if the subkey can be used to create data signatures.

	@item unsigned int can_certify : 1
	This is true if the subkey can be used to create key certificates.

	@item unsigned int can_authenticate : 1
	@since{0.4.5}

	This is true if the subkey can be used for authentication.

	@item unsigned int is_qualified : 1
	@since{1.1.0}

	This is true if the subkey can be used for qualified signatures
	according to local government regulations.

	@item unsigned int is_de_vs : 1
	@since{1.8.0}

	This is true if the subkey complies with the rules for classified
	information in Germany at the restricted level (VS-NfD). This are
	currently RSA keys of at least 2048 bits or ECDH/ECDSA keys using a
	Brainpool curve.

	@item unsigned int secret : 1
	This is true if the subkey is a secret key. Note that it will be
	false if the key is actually a stub key; i.e. a secret key operation
	is currently not possible (offline-key). This is only set if a
	listing of secret keys has been requested or if
	@code{GPGME_KEYLIST_MODE_WITH_SECRET} is active.

	@item gpgme_pubkey_algo_t pubkey_algo
	This is the public key algorithm supported by this subkey.

	@item unsigned int length
	This is the length of the subkey (in bits).

	@item char *keyid
	This is the key ID of the subkey in hexadecimal digits.

	@item char *fpr
	This is the fingerprint of the subkey in hexadecimal digits, if
	available.

	@item char *keygrip
	@since{1.7.0}

	The keygrip of the subkey in hex digit form or @code{NULL} if not
	available.

	@item long int timestamp
	This is the creation timestamp of the subkey. This is -1 if the
	timestamp is invalid, and 0 if it is not available.

	@item long int expires
	This is the expiration timestamp of the subkey, or 0 if the subkey
	does not expire.

	@item unsigned int is_cardkey : 1
	@since{1.2.0}

	True if the secret key is stored on a smart card.

	@item char *card_number
	@since{1.2.0}

	The serial number of a smart card holding this key or @code{NULL}.

	@item char *curve
	For ECC algorithms the name of the curve.

	@end table
	@end deftp

	@deftp {Data type} gpgme_user_id_t

	A user ID is a component of a @code{gpgme_key_t} object. One key can
	have many user IDs. The first one in the list is the main (or
	primary) user ID.

	The user ID structure has the following members.

	@table @code
	@item gpgme_user_id_t next
	This is a pointer to the next user ID structure in the linked list, or
	@code{NULL} if this is the last element.

	@item unsigned int revoked : 1
	This is true if the user ID is revoked.

	@item unsigned int invalid : 1
	This is true if the user ID is invalid.

	@item gpgme_validity_t validity
	This specifies the validity of the user ID.

	@item char *uid
	This is the user ID string.

	@item char *name
	This is the name component of @code{uid}, if available.

	@item char *comment
	This is the comment component of @code{uid}, if available.

	@item char *email
	This is the email component of @code{uid}, if available.

	@item char *address;
	The mail address (addr-spec from RFC-5322) of the user ID string.
	This is general the same as the @code{email} part of this structure
	but might be slightly different. If no mail address is available
	@code{NULL} is stored.

	@item gpgme_tofu_info_t tofu
	@since{1.7.0}

	If not @code{NULL} information from the TOFU database pertaining to
	this user id.

	@item gpgme_key_sig_t signatures
	This is a linked list with the signatures on this user ID.

	@item unsigned int origin : 5
	@since{1.8.0}

	Reserved for the origin of this user ID.

	@item unsigned long last_update
	@since{1.8.0}

	Reserved for the time of the last update of this user ID.

	@item char *uidhash;
	A string used by gpg to identify a user ID. This string can be used
	at certain prompts of @code{gpgme_op_edit} to select a user ID. Users
	must be prepared to see a @code{NULL} value here. The format of the
	value is not specified and may depend on the GPGME or GnuPG version.

	@end table
	@end deftp


	@deftp {Data type} gpgme_tofu_info_t

	@since{1.7.0}

	The @code{gpgme_tofu_info_t} type is a pointer to a tofu info
	structure. Tofu info structures are one component of a
	@code{gpgme_user_id_t} object, and provide information from the TOFU
	database pertaining to the user ID.

	The tofu info structure has the following members:

	@table @code
	@item gpgme_tofu_info_t next
	This is a pointer to the next tofu info structure in the linked
	list, or @code{NULL} if this is the last element.

	@item unsigned int validity : 3
	This is the TOFU validity. It can have the following values:

	@table @code
	@item 0
	The value @code{0} indicates a conflict.

	@item 1
	The value @code{1} indicates a key without history.

	@item 2
	The value @code{2} indicates a key with too little history.

	@item 3
	The value @code{3} indicates a key with enough history for basic trust.

	@item 4
	The value @code{4} indicates a key with a lot of history.

	@end table

	@item unsigned int policy : 4
	This is the TOFU policy, see @code{gpgme_tofu_policy_t}.

	@item unsigned short signcount
	This is the number of signatures seen for this binding (or
	@code{USHRT_MAX} if there are more than that).

	@item unsigned short encrcount
	This is the number of encryptions done with this binding (or
	@code{USHRT_MAX} if there are more than that).

	@item unsigned long signfirst
	Number of seconds since Epoch when the first signature was seen with
	this binding.

	@item unsigned long signlast
	Number of seconds since Epoch when the last signature was seen with
	this binding.

	@item unsigned long encrfirst
	Number of seconds since Epoch when the first encryption was done with
	this binding.

	@item unsigned long encrlast
	Number of seconds since Epoch when the last encryption was done with
	this binding.

	@item char *description
	A human-readable string summarizing the TOFU data (or NULL).

	@end table
	@end deftp


	@deftp {Data type} gpgme_key_sig_t

	The @code{gpgme_key_sig_t} type is a pointer to a key signature structure.
	Key signatures are one component of a @code{gpgme_key_t} object, and
	validate user IDs on the key in the OpenPGP protocol.

	The signatures on a key are only available if the key was retrieved
	via a listing operation with the @code{GPGME_KEYLIST_MODE_SIGS} mode
	enabled, because it can be expensive to retrieve all signatures of a
	key.

	The signature notations on a key signature are only available if the
	key was retrieved via a listing operation with the
	@code{GPGME_KEYLIST_MODE_SIG_NOTATIONS} mode enabled, because it can
	be expensive to retrieve all signature notations.

	The key signature structure has the following members:

	@table @code
	@item gpgme_key_sig_t next
	This is a pointer to the next key signature structure in the linked
	list, or @code{NULL} if this is the last element.

	@item unsigned int revoked : 1
	This is true if the key signature is a revocation signature.

	@item unsigned int expired : 1
	This is true if the key signature is expired.

	@item unsigned int invalid : 1
	This is true if the key signature is invalid.

	@item unsigned int exportable : 1
	This is true if the key signature is exportable.

	@item unsigned int trust_depth : 8
	This is the depth of a trust signature, or 0 if the key signature is not
	a trust signature.

	@item unsigned int trust_value : 8
	This is the trust amount of a trust signature.

	@item gpgme_pubkey_algo_t pubkey_algo
	This is the public key algorithm used to create the signature.

	@item char *keyid
	This is the key ID of the key (in hexadecimal digits) used to create
	the signature.

	@item long int timestamp
	This is the creation timestamp of the key signature. This is -1 if
	the timestamp is invalid, and 0 if it is not available.

	@item long int expires
	This is the expiration timestamp of the key signature, or 0 if the key
	signature does not expire.

	@item char *trust_scope
	This is a regular expression that limits the scope of a trust signature.
	Users must be prepared to see a @code{NULL} value here.

	@item gpgme_error_t status
	This is the status of the signature and has the same meaning as the
	member of the same name in a @code{gpgme_signature_t} object.

	@item unsigned int sig_class
	This specifies the signature class of the key signature. The meaning
	is specific to the crypto engine.

	@item char *uid
	This is the main user ID of the key used to create the signature.

	@item char *name
	This is the name component of @code{uid}, if available.

	@item char *comment
	This is the comment component of @code{uid}, if available.

	@item char *email
	This is the email component of @code{uid}, if available.

	@item gpgme_sig_notation_t notations
	This is a linked list with the notation data and policy URLs.
	@end table
	@end deftp



	@node Listing Keys
	@subsection Listing Keys
	@cindex listing keys
	@cindex key listing
	@cindex key listing, start
	@cindex key ring, list
	@cindex key ring, search

	@deftypefun gpgme_error_t gpgme_op_keylist_start (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{pattern}}, @w{int @var{secret_only}})

	The function @code{gpgme_op_keylist_start} initiates a key listing
	operation inside the context @var{ctx}. It sets everything up so that
	subsequent invocations of @code{gpgme_op_keylist_next} return the keys
	in the list.

	If @var{pattern} is @code{NULL}, all available keys are returned.
	Otherwise, @var{pattern} contains an engine specific expression that
	is used to limit the list to all keys matching the pattern. Note that
	the total length of the pattern is restricted to an engine-specific
	maximum (a couple of hundred characters are usually accepted). The
	pattern should be used to restrict the search to a certain common name
	or user, not to list many specific keys at once by listing their
	fingerprints or key IDs.

	If @var{secret_only} is not @code{0}, the list is restricted to secret
	keys only.

	The context will be busy until either all keys are received (and
	@code{gpgme_op_keylist_next} returns @code{GPG_ERR_EOF}), or
	@code{gpgme_op_keylist_end} is called to finish the operation.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and passes through any errors that
	are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_keylist_ext_start (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{pattern}[]}, @w{int @var{secret_only}}, @w{int @var{reserved}})

	The function @code{gpgme_op_keylist_ext_start} initiates an extended
	key listing operation inside the context @var{ctx}. It sets
	everything up so that subsequent invocations of
	@code{gpgme_op_keylist_next} return the keys in the list.

	If @var{pattern} or @var{*pattern} is @code{NULL}, all available keys
	are returned. Otherwise, @var{pattern} is a @code{NULL} terminated
	array of strings that are used to limit the list to all keys matching
	at least one of the patterns verbatim. Note that the total length of
	all patterns is restricted to an engine-specific maximum (the exact
	limit also depends on the number of patterns and amount of quoting
	required, but a couple of hundred characters are usually accepted).
	Patterns should be used to restrict the search to a certain common
	name or user, not to list many specific keys at once by listing their
	fingerprints or key IDs.

	If @var{secret_only} is not @code{0}, the list is restricted to secret
	keys only.

	The value of @var{reserved} must be @code{0}.

	The context will be busy until either all keys are received (and
	@code{gpgme_op_keylist_next} returns @code{GPG_ERR_EOF}), or
	@code{gpgme_op_keylist_end} is called to finish the operation.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and passes through any errors that
	are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_keylist_from_data_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_data_t @var{data}}, @
	@w{int @var{reserved}})

	@since{1.8.0}

	The function @code{gpgme_op_keylist_from_data_start} initiates a key
	listing operation inside the context @var{ctx}. In contrast to the
	other key listing operation the keys are read from the supplied
	@var{data} and not from the local key database. The keys are also not
	imported into the local key database. The function sets everything up
	so that subsequent invocations of @code{gpgme_op_keylist_next} return
	the keys from @var{data}.

	The value of @var{reserved} must be @code{0}.

	This function requires at least GnuPG version 2.1.14 and currently
	works only with OpenPGP keys.

	The context will be busy until either all keys are received (and
	@code{gpgme_op_keylist_next} returns @code{GPG_ERR_EOF}), or
	@code{gpgme_op_keylist_end} is called to finish the operation.
	While the context is busy @var{data} may not be released.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and passes through any errors that
	are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_keylist_next (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t *@var{r_key}})

	The function @code{gpgme_op_keylist_next} returns the next key in the
	list created by a previous @code{gpgme_op_keylist_start} operation in
	the context @var{ctx}. The key will have one reference for the user.
	@xref{Manipulating Keys}.

	This is the only way to get at @code{gpgme_key_t} objects in
	@acronym{GPGME}.

	If the last key in the list has already been returned,
	@code{gpgme_op_keylist_next} returns @code{GPG_ERR_EOF}.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{r_key} is not a valid pointer, and
	@code{GPG_ERR_ENOMEM} if there is not enough memory for the operation.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_keylist_end (@w{gpgme_ctx_t @var{ctx}})

	The function @code{gpgme_op_keylist_end} ends a pending key list
	operation in the context @var{ctx}.

	After the operation completed successfully, the result of the key
	listing operation can be retrieved with
	@code{gpgme_op_keylist_result}.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and @code{GPG_ERR_ENOMEM} if at some
	time during the operation there was not enough memory available.
	@end deftypefun

	The following example illustrates how all keys containing a certain
	string (@code{g10code}) can be listed with their key ID and the name
	and email address of the main user ID:

	@example
	gpgme_ctx_t ctx;
	gpgme_key_t key;
	gpgme_error_t err = gpgme_new (&ctx);

	if (!err)
	@{
	err = gpgme_op_keylist_start (ctx, "g10code", 0);
	while (!err)
	@{
	err = gpgme_op_keylist_next (ctx, &key);
	if (err)
	break;
	printf ("%s:", key->subkeys->keyid);
	if (key->uids && key->uids->name)
	printf (" %s", key->uids->name);
	if (key->uids && key->uids->email)
	printf (" <%s>", key->uids->email);
	putchar ('\n');
	gpgme_key_release (key);
	@}
	gpgme_release (ctx);
	@}
	if (gpg_err_code (err) != GPG_ERR_EOF)
	@{
	fprintf (stderr, "can not list keys: %s\n", gpgme_strerror (err));
	exit (1);
	@}
	@end example

	@deftp {Data type} {gpgme_keylist_result_t}
	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_keylist_*} operation. After successfully ending a key
	listing operation, you can retrieve the pointer to the result with
	@code{gpgme_op_keylist_result}. The structure contains the following
	member:

	@table @code
	@item unsigned int truncated : 1
	This is true if the crypto backend had to truncate the result, and
	less than the desired keys could be listed.
	@end table
	@end deftp

	@deftypefun gpgme_keylist_result_t gpgme_op_keylist_result (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_op_keylist_result} returns a
	@code{gpgme_keylist_result_t} pointer to a structure holding the
	result of a @code{gpgme_op_keylist_*} operation. The pointer is only
	valid if the last operation on the context was a key listing
	operation, and if this operation finished successfully. The returned
	pointer is only valid until the next operation is started on the
	context.
	@end deftypefun

	In a simple program, for which a blocking operation is acceptable, the
	following function can be used to retrieve a single key.

	@deftypefun gpgme_error_t gpgme_get_key (@w{gpgme_ctx_t @var{ctx}}, @w{const char @var{fpr}}, @w{gpgme_key_t @var{r_key}}, @w{int @var{secret}})
	The function @code{gpgme_get_key} gets the key with the fingerprint
	(or key ID) @var{fpr} from the crypto backend and return it in
	@var{r_key}. If @var{secret} is true, get the secret key. The
	currently active keylist mode is used to retrieve the key. The key
	will have one reference for the user.

	If the key is not found in the keyring, @code{gpgme_get_key} returns
	the error code @code{GPG_ERR_EOF} and *@var{r_key} will be set to
	@code{NULL}.

	The function returns the error code @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{r_key} is not a valid pointer or @var{fpr} is not a
	fingerprint or key ID, @code{GPG_ERR_AMBIGUOUS_NAME} if the key ID was
	not a unique specifier for a key, and @code{GPG_ERR_ENOMEM} if at some
	time during the operation there was not enough memory available.
	@end deftypefun


	@node Information About Keys
	@subsection Information About Keys
	@cindex key, information about
	@cindex key, attributes
	@cindex attributes, of a key

	Please see the beginning of this section for more information about
	@code{gpgme_key_t} objects.

	@deftp {Data type} gpgme_validity_t
	The @code{gpgme_validity_t} type is used to specify the validity of a user ID
	in a key. The following validities are defined:

	@table @code
	@item GPGME_VALIDITY_UNKNOWN
	The user ID is of unknown validity. The string representation of this
	validity is ``?''.

	@item GPGME_VALIDITY_UNDEFINED
	The validity of the user ID is undefined. The string representation of this
	validity is ``q''.

	@item GPGME_VALIDITY_NEVER
	The user ID is never valid. The string representation of this
	validity is ``n''.

	@item GPGME_VALIDITY_MARGINAL
	The user ID is marginally valid. The string representation of this
	validity is ``m''.

	@item GPGME_VALIDITY_FULL
	The user ID is fully valid. The string representation of this
	validity is ``f''.

	@item GPGME_VALIDITY_ULTIMATE
	The user ID is ultimately valid. The string representation of this
	validity is ``u''.
	@end table
	@end deftp




	@node Manipulating Keys
	@subsection Manipulating Keys
	@cindex key, manipulation

	@deftypefun void gpgme_key_ref (@w{gpgme_key_t @var{key}})
	The function @code{gpgme_key_ref} acquires an additional reference for
	the key @var{key}.
	@end deftypefun

	@deftypefun void gpgme_key_unref (@w{gpgme_key_t @var{key}})
	The function @code{gpgme_key_unref} releases a reference for the key
	@var{key}. If this was the last reference, the key will be destroyed
	and all resources associated to it will be released.
	@end deftypefun

	@c
	@c gpgme_op_setexpire
	@c
	@deftypefun gpgme_error_t gpgme_op_setexpire @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{unsigned long @var{expires}}, @
	@w{const char *@var{subfprs}}, @
	@w{unsigned int @var{reserved}});

	@since{1.14.1}

	The function @code{gpgme_op_setexpire} sets the expiration time of
	the key @var{key} or of the specified subkeys.
	This function requires at least version 2.1.22 of GnuPG.

	@var{key} specifies the key to operate on.

	@var{expires} specifies the expiration time in seconds from now.
	To be similar to other usages where expiration times are provided
	in unsigned long this is similar to the key creation date
	and so it is in seconds from NOW.

	The common case is to use 0 to not set an expiration time.
	Note that this parameter takes an unsigned long value and not
	a @code{time_t} to avoid problems on systems which use a signed
	32 bit @code{time_t}. Note further that the OpenPGP protocol
	uses 32 bit values for timestamps and thus can
	only encode dates up to the year 2106.

	@var{subfprs} selects the subkey(s) for which the expiration time
	should be set. If @var{subfprs} is set to @code{NULL}, then the
	expiration time of the primary key is set. If @var{subfprs} is
	an asterisk (@code{*}), then the expiration times of all non-revoked
	and not yet expired subkeys are set. To select more than one subkey
	put all subkey fingerprints into one string separated by linefeeds
	characters (@code{\n}).

	@var{reserved} is reserved for later use and must be @code{0}.

	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_setexpire_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{unsigned long @var{expires}}, @
	@w{const char *@var{subfprs}}, @
	@w{unsigned int @var{flags}});

	@since{1.14.1}

	The function @code{gpgme_op_setexpire_start} initiates a
	@code{gpgme_op_setexpire} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun


	@node Generating Keys
	@subsection Generating Keys
	@cindex key, creation
	@cindex key ring, add

	GPGME provides a set of functions to create public key pairs. Most of
	these functions require the use of GnuPG 2.1 and later; for older
	GnuPG versions the @code{gpgme_op_genkey} function can be used.
	Existing code which wants to update to the new functions or new code
	which shall supports older GnuPG versions may try the new functions
	first and provide a fallback to the old function if the error code
	@code{GPG_ERR_NOT_SUPPORTED} is received.

	@c
	@c gpgme_op_createkey
	@c
	@deftypefun gpgme_error_t gpgme_op_createkey @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const char *@var{userid}}, @
	@w{const char *@var{algo}}, @
	@w{unsigned long @var{reserved}}, @
	@w{unsigned long @var{expires}}, @
	@w{gpgme_key_t @var{extrakey}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_createkey} generates a new key for the
	procotol active in the context @var{ctx}. As of now this function
	does only work for OpenPGP and requires at least version 2.1.13 of
	GnuPG.

	@var{userid} is commonly the mail address associated with the key.
	GPGME does not require a specific syntax but if more than a mail
	address is given, RFC-822 style format is suggested. The value is
	expected to be in UTF-8 encoding (i.e. no IDN encoding for mail
	addresses). This is a required parameter.

	@var{algo} specifies the algorithm for the new key (actually a keypair
	of public and private key). For a list of supported algorithms, see
	the GnuPG manual. If @var{algo} is @code{NULL} or the string
	"default", the key is generated using the default algorithm of the
	engine. If the string "future-default" is used the engine may use an
	algorithm which is planned to be the default in a future release of
	the engine; however existing implementation of the protocol may not be
	able to already handle such future algorithms. For the OpenPGP
	protocol, the specification of a default algorithm, without requesting
	a non-default usage via @var{flags}, triggers the creation of a
	primary key plus a secondary key (subkey).

	@var{reserved} must be set to zero.

	@var{expires} specifies the expiration time in seconds. If you supply
	0, a reasonable expiration time is chosen. Use the flag
	@code{GPGME_CREATE_NOEXPIRE} to create keys that do not expire. Note
	that this parameter takes an unsigned long value and not a
	@code{time_t} to avoid problems on systems which use a signed 32 bit
	@code{time_t}. Note further that the OpenPGP protocol uses 32 bit
	values for timestamps and thus can only encode dates up to the year
	2106.

	@var{extrakey} is currently not used and must be set to @code{NULL}.
	A future version of GPGME may use this parameter to create X.509 keys.

	@var{flags} can be set to the bit-wise OR of the following flags:

	@table @code
	@item GPGME_CREATE_SIGN
	@itemx GPGME_CREATE_ENCR
	@itemx GPGME_CREATE_CERT
	@itemx GPGME_CREATE_AUTH
	@since{1.7.0}

	Do not create the key with the default capabilities (key usage) of the
	requested algorithm but use those explicitly given by these flags:
	``signing'', ``encryption'', ``certification'', or ``authentication''.
	The allowed combinations depend on the algorithm.

	If any of these flags are set and a default algorithm has been
	selected only one key is created in the case of the OpenPGP
	protocol.

	@item GPGME_CREATE_NOPASSWD
	@since{1.7.0}

	Request generation of the key without password protection.

	@item GPGME_CREATE_SELFSIGNED
	@since{1.7.0}

	For an X.509 key do not create a CSR but a self-signed certificate.
	This has not yet been implemented.

	@item GPGME_CREATE_NOSTORE
	@since{1.7.0}

	Do not store the created key in the local key database.
	This has not yet been implemented.

	@item GPGME_CREATE_WANTPUB
	@itemx GPGME_CREATE_WANTSEC
	@since{1.7.0}

	Return the public or secret key as part of the result structure.
	This has not yet been implemented.

	@item GPGME_CREATE_FORCE
	@since{1.7.0}

	The engine does not allow the creation of a key with a user ID
	already existing in the local key database. This flag can be used to
	override this check.

	@item GPGME_CREATE_NOEXPIRE
	@since{1.9.0}

	Request generation of keys that do not expire.

	@end table

	After the operation completed successfully, information about the
	created key can be retrieved with @code{gpgme_op_genkey_result}.

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_createkey_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const char *@var{userid}}, @
	@w{const char *@var{algo}}, @
	@w{unsigned long @var{reserved}}, @
	@w{unsigned long @var{expires}}, @
	@w{gpgme_key_t @var{extrakey}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_createkey_start} initiates a
	@code{gpgme_op_createkey} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun

	@c
	@c gpgme_op_createsubkey
	@c
	@deftypefun gpgme_error_t gpgme_op_createsubkey @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{algo}}, @
	@w{unsigned long @var{reserved}}, @
	@w{unsigned long @var{expires}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_createsubkey} creates and adds a new
	subkey to the primary OpenPGP key given by @var{KEY}. The only
	allowed protocol in @var{ctx} is @code{GPGME_PROTOCOL_OPENPGP}.
	Subkeys (aka secondary keys) are a concept in the OpenPGP protocol to
	bind several keys to a primary key. As of now this function requires
	at least version 2.1.13 of GnuPG.

	@var{key} specifies the key to operate on.

	@var{algo} specifies the algorithm for the new subkey. For a list of
	supported algorithms, see the GnuPG manual. If @var{algo} is
	@code{NULL} or the string "default", the subkey is generated using the
	default algorithm for an encryption subkey of the engine. If the
	string "future-default" is used the engine may use an encryption
	algorithm which is planned to be the default in a future release of
	the engine; however existing implementation of the protocol may not be
	able to already handle such future algorithms.

	@var{reserved} must be set to zero.

	@var{expires} specifies the expiration time in seconds. If you supply
	0, a reasonable expiration time is chosen. Use the flag
	@code{GPGME_CREATE_NOEXPIRE} to create keys that do not expire. Note
	that this parameter takes an unsigned long value and not a
	@code{time_t} to avoid problems on systems which use a signed 32 bit
	@code{time_t}. Note further that the OpenPGP protocol uses 32 bit
	values for timestamps and thus can only encode dates up to the year
	2106.

	@var{flags} takes the same values as described above for
	@code{gpgme_op_createkey}.

	After the operation completed successfully, information about the
	created key can be retrieved with @code{gpgme_op_genkey_result}.

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.


	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_createsubkey_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{algo}}, @
	@w{unsigned long @var{reserved}}, @
	@w{unsigned long @var{expires}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_createsubkey_start} initiates a
	@code{gpgme_op_createsubkey} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun


	@c
	@c gpgme_op_adduid
	@c
	@deftypefun gpgme_error_t gpgme_op_adduid @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_adduid} adds a new user ID to the OpenPGP
	key given by @var{KEY}. Adding additional user IDs after key creation
	is a feature of the OpenPGP protocol and thus the protocol for the
	context @var{ctx} must be set to OpenPGP. As of now this function
	requires at least version 2.1.13 of GnuPG.

	@var{key} specifies the key to operate on.

	@var{userid} is the user ID to add to the key. A user ID is commonly
	the mail address to be associated with the key. GPGME does not
	require a specific syntax but if more than a mail address is given,
	RFC-822 style format is suggested. The value is expected to be in
	UTF-8 encoding (i.e. no IDN encoding for mail addresses). This is a
	required parameter.

	@var{flags} are currently not used and must be set to zero.

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_adduid_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_adduid_start} initiates a
	@code{gpgme_op_adduid} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun


	@c
	@c gpgme_op_revuid
	@c
	@deftypefun gpgme_error_t gpgme_op_revuid @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_revuid} revokes a user ID from the OpenPGP
	key given by @var{KEY}. Revoking user IDs after key creation is a
	feature of the OpenPGP protocol and thus the protocol for the context
	@var{ctx} must be set to OpenPGP. As of now this function requires at
	least version 2.1.13 of GnuPG.

	@var{key} specifies the key to operate on.

	@var{userid} is the user ID to be revoked from the key. The user ID
	must be given verbatim because the engine does an exact and case
	sensitive match. Thus the @code{uid} field from the user ID object
	(@code{gpgme_user_id_t}) is to be used. This is a required parameter.

	@var{flags} are currently not used and must be set to zero.

	Note that the engine won't allow to revoke the last valid user ID. To
	change a user ID is better to first add the new user ID, then revoke
	the old one, and finally publish the key.

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_revuid_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_revuid_start} initiates a
	@code{gpgme_op_revuid} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun


	@c
	@c gpgme_op_set_uid_flag
	@c
	@deftypefun gpgme_error_t gpgme_op_set_ui_flag @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{cons char * @var{name}}, @
	@w{cons char * @var{value}});

	@since{1.8.0}

	The function @code{gpgme_op_set_uid_flag} is used to set flags on a
	user ID from the OpenPGP key given by @var{KEY}. Setting flags on
	user IDs after key creation is a feature of the OpenPGP protocol and
	thus the protocol for the context @var{ctx} must be set to OpenPGP.

	@var{key} specifies the key to operate on. This parameters is required.

	@var{userid} is the user ID of the key to be manipulated. This user ID
	must be given verbatim because the engine does an exact and case
	sensitive match. Thus the @code{uid} field from the user ID object
	(@code{gpgme_user_id_t}) is to be used. This is a required parameter.

	@var{name} names the flag which is to be changed. The only currently
	supported flag is:

	@table @code
	@item primary
	This sets the primary key flag on the given user ID. All other
	primary key flag on other user IDs are removed. @var{value} must be
	given as NULL. For technical reasons this functions bumps the
	creation timestamp of all affected self-signatures up by one second.
	At least GnuPG version 2.1.20 is required.

	@end table

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_set_uid_flag_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{cons char * @var{name}}, @
	@w{cons char * @var{value}});

	@since{1.8.0}

	The function @code{gpgme_op_set_uid_flag_start} initiates a
	@code{gpgme_op_set_uid_flag} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun

	@c
	@c gpgme_op_genkey
	@c
	@deftypefun gpgme_error_t gpgme_op_genkey @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const char *@var{parms}}, @
	@w{gpgme_data_t @var{public}}, @
	@w{gpgme_data_t @var{secret}})

	The function @code{gpgme_op_genkey} generates a new key pair in the
	context @var{ctx}. The meaning of @var{public} and @var{secret}
	depends on the crypto backend.

	GPG does not support @var{public} and @var{secret}, they should be
	@code{NULL}. GnuPG will generate a key pair and add it to the
	standard key ring. The fingerprint of the generated key is available
	with @code{gpgme_op_genkey_result}.

	GpgSM requires @var{public} to be a writable data object. GpgSM will
	generate a secret key (which will be stored by @command{gpg-agent},
	and return a certificate request in @var{public}, which then needs to
	be signed by the certification authority and imported before it can be
	used. GpgSM does not make the fingerprint available.

	The argument @var{parms} specifies parameters for the key in an string
	that looks something like XML. The details about the format of
	@var{parms} are specific to the crypto engine used by @var{ctx}. The
	first line of the parameters must be @code{<GnupgKeyParams
	format="internal">} and the last line must be
	@code{</GnupgKeyParams>}. Every line in between the first and last
	lines is treated as a Header: Value pair. In particular, no XML
	escaping is necessary if you need to include the characters @code{<},
	@code{>}, or @code{&}.

	Here is an example for GnuPG as the crypto engine (all parameters of
	OpenPGP key generation are documented in the GPG manual):

	@example
	<GnupgKeyParms format="internal">
	Key-Type: default
	Subkey-Type: default
	Name-Real: Joe Tester
	Name-Comment: with stupid passphrase
	Name-Email: joe@@foo.bar
	Expire-Date: 0
	Passphrase: abc
	</GnupgKeyParms>
	@end example

	Here is an example for GpgSM as the crypto engine (all parameters of
	OpenPGP key generation are documented in the GPGSM manual):

	@example
	<GnupgKeyParms format="internal">
	Key-Type: RSA
	Key-Length: 1024
	Name-DN: C=de,O=g10 code,OU=Testlab,CN=Joe 2 Tester
	Name-Email: joe@@foo.bar
	</GnupgKeyParms>
	@end example

	Strings should be given in UTF-8 encoding. The only format supported
	for now is ``internal''. The content of the @code{GnupgKeyParms}
	container is passed verbatim to the crypto backend. Control
	statements are not allowed.

	After the operation completed successfully, the result can be
	retrieved with @code{gpgme_op_genkey_result}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{parms} is not a well-formed string (e.g. does not have the
	expected tag-like headers and footers), @code{GPG_ERR_NOT_SUPPORTED}
	if @var{public} or @var{secret} is not valid, and
	@code{GPG_ERR_GENERAL} if no key was created by the backend.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_genkey_start (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{parms}}, @w{gpgme_data_t @var{public}}, @w{gpgme_data_t @var{secret}})

	The function @code{gpgme_op_genkey_start} initiates a
	@code{gpgme_op_genkey} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{parms} is not a valid XML string, and
	@code{GPG_ERR_NOT_SUPPORTED} if @var{public} or @var{secret} is not
	@code{NULL}.
	@end deftypefun


	@c
	@c gpgme_op_genkey_result
	@c
	@deftp {Data type} {gpgme_genkey_result_t}

	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_genkey} operation. After successfully generating a
	key, you can retrieve the pointer to the result with
	@code{gpgme_op_genkey_result}. The structure contains the following
	members:

	@table @code
	@item unsigned int primary : 1
	This flag is set to 1 if a primary key was created and to 0
	if not.

	@item unsigned int sub : 1
	This flag is set to 1 if a subkey was created and to 0 if not.

	@item unsigned int uid : 1
	This flag is set to 1 if a user ID was created and to 0 if not.

	@item char *fpr
	This is the fingerprint of the key that was created. If both a
	primary and a subkey were generated, the fingerprint of the primary
	key will be returned. If the crypto engine does not provide the
	fingerprint, @code{fpr} will be a null pointer.

	@item gpgme_data_t pubkey
	@since{1.7.0}

	This will eventually be used to return the public key. It is
	currently not used.

	@item gpgme_data_t seckey
	@since{1.7.0}

	This will eventually be used to return the secret key. It is
	currently not used.

	@end table
	@end deftp

	@deftypefun gpgme_genkey_result_t gpgme_op_genkey_result (@w{gpgme_ctx_t @var{ctx}})

	The function @code{gpgme_op_genkey_result} returns a
	@code{gpgme_genkey_result_t} pointer to a structure holding the result of
	a @code{gpgme_op_genkey} operation. The pointer is only valid if the
	last operation on the context was a @code{gpgme_op_genkey} or
	@code{gpgme_op_genkey_start} operation, and if this operation finished
	successfully. The returned pointer is only valid until the next
	operation is started on the context.

	@end deftypefun


	@c
	@c SIGNING KEYS
	@c
	@node Signing Keys
	@subsection Signing Keys
	@cindex key, signing

	Key signatures are a unique concept of the OpenPGP protocol. They can
	be used to certify the validity of a key and are used to create the
	Web-of-Trust (WoT). Instead of using the @code{gpgme_op_interact}
	function along with a finite state machine, GPGME provides a
	convenient function to create key signatures when using modern GnuPG
	versions.


	@c
	@c gpgme_op_keysign
	@c
	@deftypefun gpgme_error_t gpgme_op_keysign @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned long @var{expires}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_keysign} adds a new key signature to the
	public key @var{KEY}. This function requires at least version 2.1.12 of
	GnuPG.

	@var{CTX} is the usual context which describes the protocol to use
	(which must be OpenPGP) and has also the list of signer keys to be
	used for the signature. The common case is to use the default key for
	signing other keys. If another key or more than one key shall be used
	for a key signature, @code{gpgme_signers_add} can be used.
	@xref{Selecting Signers}.

	@var{key} specifies the key to operate on.

	@var{userid} selects the user ID or user IDs to be signed. If
	@var{userid} is set to @code{NULL} all valid user IDs are signed. The
	user ID must be given verbatim because the engine does an exact and
	case sensitive match. Thus the @code{uid} field from the user ID
	object (@code{gpgme_user_id_t}) is to be used. To select more than
	one user ID put them all into one string separated by linefeeds
	characters (@code{\n}) and set the flag @code{GPGME_KEYSIGN_LFSEP}.

	@var{expires} specifies the expiration time of the new signature in
	seconds. The common case is to use 0 to not set an expiration date.
	However, if the configuration of the engine defines a default
	expiration for key signatures, that is still used unless the flag
	@code{GPGME_KEYSIGN_NOEXPIRE} is used. Note that this parameter takes
	an unsigned long value and not a @code{time_t} to avoid problems on
	systems which use a signed 32 bit @code{time_t}. Note further that
	the OpenPGP protocol uses 32 bit values for timestamps and thus can
	only encode dates up to the year 2106.

	@var{flags} can be set to the bit-wise OR of the following flags:

	@table @code
	@item GPGME_KEYSIGN_LOCAL
	@since{1.7.0}

	Instead of creating an exportable key signature, create a key
	signature which is is marked as non-exportable.

	@item GPGME_KEYSIGN_LFSEP
	@since{1.7.0}

	Although linefeeds are uncommon in user IDs this flag is required to
	explicitly declare that @var{userid} may contain several linefeed
	separated user IDs.

	@item GPGME_KEYSIGN_NOEXPIRE
	Force the creation of a key signature without an expiration date. This
	overrides @var{expire} and any local configuration of the engine.

	@item GPGME_KEYSIGN_FORCE
	Force the creation of a new signature even if one already exists.
	This flag has an effect only if the gpg version is at least 2.2.28 but
	won't return an error with older versions.

	@end table

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_keysign_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned long @var{expires}}, @
	@w{unsigned int @var{flags}});

	@since{1.7.0}

	The function @code{gpgme_op_keysign_start} initiates a
	@code{gpgme_op_keysign} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun


	@c
	@c gpgme_op_revsig
	@c
	@deftypefun gpgme_error_t gpgme_op_revsig @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{gpgme_key_t @var{signing_key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned int @var{flags}});

	@since{1.14.1}

	The function @code{gpgme_op_revsig} revokes key signatures of the
	public key @var{key} made with the key @var{signing_key}. This
	function requires at least version 2.2.24 of GnuPG.

	@var{key} specifies the key to operate on.

	@var{signing_key} specifies the key whose signatures shall be revoked.

	@var{userid} selects the user ID or user IDs whose signatures shall
	be revoked. If @var{userid} is set to @code{NULL} the signatures
	on all user IDs are revoked. The user ID must be given verbatim
	because the engine does an exact and case sensitive match. Thus the
	@code{uid} field from the user ID object (@code{gpgme_user_id_t}) is to
	be used. To select more than one user ID put them all into one string
	separated by linefeeds characters (@code{\n}) and set the flag
	@code{GPGME_REVSIG_LFSEP}.

	@var{flags} can be set to the bit-wise OR of the following flags:

	@table @code
	@item GPGME_REVSIG_LFSEP
	@since{1.14.1}

	Although linefeeds are uncommon in user IDs this flag is required to
	explicitly declare that @var{userid} may contain several linefeed
	separated user IDs.

	@end table

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_revsig_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{gpgme_key_t @var{signing_key}}, @
	@w{const char *@var{userid}}, @
	@w{unsigned int @var{flags}});

	@since{1.14.1}

	The function @code{gpgme_op_revsig_start} initiates a
	@code{gpgme_op_revsig} operation; see there for details. It must
	be completed by calling @code{gpgme_wait} on the context.
	@xref{Waiting For Completion}.

	@end deftypefun


	@c
	@c EXPORTING KEYS
	@c
	@node Exporting Keys
	@subsection Exporting Keys
	@cindex key, export
	@cindex key ring, export from

	Exporting keys means the same as running @command{gpg} with the command
	@option{--export}. However, a mode flag can be used to change the way
	the export works. The available mode flags are described below, they
	may be or-ed together.

	@table @code

	@item GPGME_EXPORT_MODE_EXTERN
	If this bit is set, the output is send directly to the default
	keyserver. This is currently only allowed for OpenPGP keys. It is good
	practise to not send more than a few dozens key to a keyserver at one
	time. Using this flag requires that the @var{keydata} argument of the
	export function is set to @code{NULL}.

	@item GPGME_EXPORT_MODE_MINIMAL
	@since{1.3.1}

	If this bit is set, the smallest possible key is exported. For OpenPGP
	keys it removes all signatures except for the latest self-signatures.
	For X.509 keys it has no effect.

	@item GPGME_EXPORT_MODE_SSH
	@since{1.4.0}

	If this bit is set, the latest authentication key of the requested
	OpenPGP key is exported in the OpenSSH public key format. This
	accepts just a single key; to force the export of a specific subkey
	a fingerprint pattern with an appended exclamation mark may be used.

	@item GPGME_EXPORT_MODE_SECRET
	@since{1.6.0}

	Instead of exporting the public key, the secret key is exported. This
	may not be combined with @code{GPGME_EXPORT_MODE_EXTERN}. For X.509
	the export format is PKCS#8.

	@item GPGME_EXPORT_MODE_SECRET_SUBKEY
	@since{1.17.0}

	If this bit is set, then a secret subkey is exported. The subkey to
	export must be specified with fingerprint pattern with an appended
	exclamation mark. This is currently only allowed for OpenPGP keys.
	This flag may not be combined with @code{GPGME_EXPORT_MODE_EXTERN}.
	This flag is not supported by the export functions that take an array
	of keys.

	@item GPGME_EXPORT_MODE_RAW
	@since{1.6.0}

	If this flag is used with @code{GPGME_EXPORT_MODE_SECRET} for an X.509
	key the export format will be changed to PKCS#1. This flag may not be
	used with OpenPGP.

	@item GPGME_EXPORT_MODE_PKCS12
	@since{1.6.0}

	If this flag is used with @code{GPGME_EXPORT_MODE_SECRET} for an X.509
	key the export format will be changed to PKCS#12 which also includes
	the certificate. This flag may not be used with OpenPGP.

	@end table



	@deftypefun gpgme_error_t gpgme_op_export (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{pattern}}, @w{gpgme_export_mode_t @var{mode}}, @w{gpgme_data_t @var{keydata}})
	The function @code{gpgme_op_export} extracts public keys and returns
	them in the data buffer @var{keydata}. The output format of the key
	data returned is determined by the @acronym{ASCII} armor attribute set
	for the context @var{ctx}, or, if that is not set, by the encoding
	specified for @var{keydata}.

	If @var{pattern} is @code{NULL}, all available keys are returned.
	Otherwise, @var{pattern} contains an engine specific expression that
	is used to limit the list to all keys matching the pattern.

	@var{mode} is usually 0; other values are described above.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{keydata} is not a valid empty data buffer, and passes through any
	errors that are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_export_start (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{pattern}}, @w{gpgme_export_mode_t @var{mode}}, @w{gpgme_data_t @var{keydata}})
	The function @code{gpgme_op_export_start} initiates a
	@code{gpgme_op_export} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, and @code{GPG_ERR_INV_VALUE}
	if @var{keydata} is not a valid empty data buffer.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_export_ext (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{pattern}[]}, @w{gpgme_export_mode_t @var{mode}}, @w{gpgme_data_t @var{keydata}})
	The function @code{gpgme_op_export} extracts public keys and returns
	them in the data buffer @var{keydata}. The output format of the key
	data returned is determined by the @acronym{ASCII} armor attribute set
	for the context @var{ctx}, or, if that is not set, by the encoding
	specified for @var{keydata}.

	If @var{pattern} or @var{*pattern} is @code{NULL}, all available keys
	are returned. Otherwise, @var{pattern} is a @code{NULL} terminated
	array of strings that are used to limit the list to all keys matching
	at least one of the patterns verbatim.

	@var{mode} is usually 0; other values are described above.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{keydata} is not a valid empty data buffer, and passes through any
	errors that are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_export_ext_start (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{pattern}[]}, @w{gpgme_export_mode_t @var{mode}}, @w{gpgme_data_t @var{keydata}})
	The function @code{gpgme_op_export_ext_start} initiates a
	@code{gpgme_op_export_ext} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, and @code{GPG_ERR_INV_VALUE}
	if @var{keydata} is not a valid empty data buffer.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_export_keys (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t keys[]}, @w{gpgme_export_mode_t @var{mode}}, @w{gpgme_data_t @var{keydata}})
	@since{1.2.0}

	The function @code{gpgme_op_export_keys} extracts public keys and returns
	them in the data buffer @var{keydata}. The output format of the key
	data returned is determined by the @acronym{ASCII} armor attribute set
	for the context @var{ctx}, or, if that is not set, by the encoding
	specified for @var{keydata}.

	The keys to export are taken form the @code{NULL} terminated array
	@var{keys}. Only keys of the currently selected protocol of
	@var{ctx} which do have a fingerprint set are considered for export.
	Other keys specified by the @var{keys} are ignored. In particular
	OpenPGP keys retrieved via an external key listing are not included.

	@var{mode} is usually 0; other values are described above.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{keydata} is not a valid empty data buffer, @code{GPG_ERR_NO_DATA}
	if no useful keys are in @var{keys} and passes through any errors that
	are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_export_keys_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{keys}[]}, @w{gpgme_export_mode_t @var{mode}}, @w{gpgme_data_t @var{keydata}})
	@since{1.2.0}

	The function @code{gpgme_op_export_keys_start} initiates a
	@code{gpgme_op_export_ext} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, and @code{GPG_ERR_INV_VALUE}
	if @var{keydata} is not a valid empty data buffer, @code{GPG_ERR_NO_DATA}
	if no useful keys are in @var{keys} and passes through any errors that
	are reported by the crypto engine support routines.
	@end deftypefun


	@node Importing Keys
	@subsection Importing Keys
	@cindex key, import
	@cindex key ring, import to

	Importing keys means the same as running @command{gpg} with the command
	@option{--import}.


	@deftypefun gpgme_error_t gpgme_op_import (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{keydata}})
	The function @code{gpgme_op_import} adds the keys in the data buffer
	@var{keydata} to the key ring of the crypto engine used by @var{ctx}.
	The format of @var{keydata} can be @acronym{ASCII} armored, for example,
	but the details are specific to the crypto engine.

	After the operation completed successfully, the result can be
	retrieved with @code{gpgme_op_import_result}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	import was completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{keydata} is not a valid pointer,
	and @code{GPG_ERR_NO_DATA} if @var{keydata} is an empty data buffer.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_import_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{keydata}})
	The function @code{gpgme_op_import_start} initiates a
	@code{gpgme_op_import} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	import could be started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{keydata} is not a valid pointer, and
	@code{GPG_ERR_NO_DATA} if @var{keydata} is an empty data buffer.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_import_keys (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t *@var{keys}})
	@since{1.2.0}

	The function @code{gpgme_op_import_keys} adds the keys described by
	the @code{NULL} terminated array @var{keys} to the key ring of the
	crypto engine used by @var{ctx}. It is used to actually import and
	make keys permanent which have been retrieved from an external source
	(i.e. using @code{GPGME_KEYLIST_MODE_EXTERN}) earlier. The external
	keylisting must have been made with the same context configuration (in
	particular the same home directory). @footnote{Thus it is a
	replacement for the usual workaround of exporting and then importing a
	key to make an X.509 key permanent.} Note that for OpenPGP this may
	require another access to the keyserver over the network.

	Only keys of the currently selected protocol of @var{ctx} are
	considered for import. Other keys specified by the @var{keys} are
	ignored. As of now all considered keys must have been retrieved using
	the same method, i.e. the used key listing mode must be identical.

	After the operation completed successfully, the result can be
	retrieved with @code{gpgme_op_import_result}.

	To move keys from one home directory to another, export and import the
	keydata using @code{gpgme_op_export} and @code{gpgme_op_import}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	import was completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, @code{GPG_ERR_CONFLICT} if the key
	listing mode does not match, and @code{GPG_ERR_NO_DATA} if no keys were
	considered for import.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_import_keys_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t *@var{keys}})
	@since{1.2.0}

	The function @code{gpgme_op_import_keys_start} initiates a
	@code{gpgme_op_import_keys} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	import was started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, @code{GPG_ERR_CONFLICT} if the key
	listing mode does not match, and @code{GPG_ERR_NO_DATA} if no keys were
	considered for import.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_receive_keys (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{keyids}[]})
	@since{1.17.0}

	The function @code{gpgme_op_receive_keys} adds the keys described by
	the @code{NULL} terminated array @var{keyids} to the key ring of the
	crypto engine used by @var{ctx}. It is used to retrieve and import keys
	from an external source. This function currently works only for OpenPGP.

	After the operation completed successfully, the result can be
	retrieved with @code{gpgme_op_import_result}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	import was completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and @code{GPG_ERR_NO_DATA} if no keys
	were considered for import.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_receive_keys_start (@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{keyids}[]})
	@since{1.17.0}

	The function @code{gpgme_op_receive_keys_start} initiates a
	@code{gpgme_op_receive_keys} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	import was started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} is not a valid pointer, and @code{GPG_ERR_NO_DATA} if no keys
	were considered for import.
	@end deftypefun

	@deftp {Data type} {gpgme_import_status_t}
	This is a pointer to a structure used to store a part of the result of
	a @code{gpgme_op_import} operation. For each considered key one
	status is added that contains information about the result of the
	import. The structure contains the following members:

	@table @code
	@item gpgme_import_status_t next
	This is a pointer to the next status structure in the linked list, or
	@code{NULL} if this is the last element.

	@item char *fpr
	This is the fingerprint of the key that was considered, or @code{NULL}
	if the fingerprint of the key is not known, e.g. because the key to
	import was encrypted and decryption failed.

	@item gpgme_error_t result
	If the import was not successful, this is the error value that caused
	the import to fail. Otherwise the error code is
	@code{GPG_ERR_NO_ERROR}.

	@item unsigned int status
	This is a bit-wise OR of the following flags that give more
	information about what part of the key was imported. If the key was
	already known, this might be 0.

	@table @code
	@item GPGME_IMPORT_NEW
	The key was new.

	@item GPGME_IMPORT_UID
	The key contained new user IDs.

	@item GPGME_IMPORT_SIG
	The key contained new signatures.

	@item GPGME_IMPORT_SUBKEY
	The key contained new sub keys.

	@item GPGME_IMPORT_SECRET
	The key contained a secret key.
	@end table
	@end table
	@end deftp

	@deftp {Data type} {gpgme_import_result_t}
	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_import} operation. After a successful import
	operation, you can retrieve the pointer to the result with
	@code{gpgme_op_import_result}. The structure contains the following
	members:

	@table @code
	@item int considered
	The total number of considered keys.

	@item int no_user_id
	The number of keys without user ID.

	@item int imported
	The total number of imported keys.

	@item int imported_rsa
	The number of imported RSA keys.

	@item int unchanged
	The number of unchanged keys.

	@item int new_user_ids
	The number of new user IDs.

	@item int new_sub_keys
	The number of new sub keys.

	@item int new_signatures
	The number of new signatures.

	@item int new_revocations
	The number of new revocations.

	@item int secret_read
	The total number of secret keys read.

	@item int secret_imported
	The number of imported secret keys.

	@item int secret_unchanged
	The number of unchanged secret keys.

	@item int not_imported
	The number of keys not imported.

	@item gpgme_import_status_t imports
	A list of gpgme_import_status_t objects which contain more information
	about the keys for which an import was attempted.

	@item int skipped_v3_keys
	For security reasons modern versions of GnuPG do not anymore support
	v3 keys (created with PGP 2.x) and ignores them on import. This
	counter provides the number of such skipped v3 keys.

	@end table
	@end deftp

	@deftypefun gpgme_import_result_t gpgme_op_import_result (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_op_import_result} returns a
	@code{gpgme_import_result_t} pointer to a structure holding the result
	of a @code{gpgme_op_import} operation. The pointer is only valid if
	the last operation on the context was a @code{gpgme_op_import} or
	@code{gpgme_op_import_start} operation, and if this operation finished
	successfully. The returned pointer is only valid until the next
	operation is started on the context.
	@end deftypefun

	@node Deleting Keys
	@subsection Deleting Keys
	@cindex key, delete
	@cindex key ring, delete from

	@deftypefun gpgme_error_t gpgme_op_delete_ext (@w{gpgme_ctx_t @var{ctx}}, @w{const gpgme_key_t @var{key}}, @w{unsigned int @var{flags}})
	@since{1.9.1}

	The function @code{gpgme_op_delete_ext} deletes the key @var{key} from
	the key ring of the crypto engine used by @var{ctx}.

	@var{flags} can be set to the bit-wise OR of the following flags:

	@table @code
	@item GPGME_DELETE_ALLOW_SECRET
	@since{1.9.1}

	If not set, only public keys are deleted. If set, secret keys are
	deleted as well, if that is supported.

	@item GPGME_DELETE_FORCE
	@since{1.9.1}

	If set, the user is not asked to confirm the deletion.
	@end table

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the key
	was deleted successfully, @code{GPG_ERR_INV_VALUE} if @var{ctx} or
	@var{key} is not a valid pointer, @code{GPG_ERR_NO_PUBKEY} if
	@var{key} could not be found in the keyring,
	@code{GPG_ERR_AMBIGUOUS_NAME} if the key was not specified
	unambiguously, and @code{GPG_ERR_CONFLICT} if the secret key for
	@var{key} is available, but @var{allow_secret} is zero.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_delete_ext_start (@w{gpgme_ctx_t @var{ctx}}, @w{const gpgme_key_t @var{key}}, @w{unsigned int @var{flags}})
	@since{1.9.1}

	The function @code{gpgme_op_delete_ext_start} initiates a
	@code{gpgme_op_delete} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation was started successfully, and @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{key} is not a valid pointer.
	@end deftypefun

	The following functions allow only to use one particular flag.

	@deftypefun gpgme_error_t gpgme_op_delete (@w{gpgme_ctx_t @var{ctx}}, @w{const gpgme_key_t @var{key}}, @w{int @var{allow_secret}})
	Similar to @code{gpgme_op_delete_ext}, but only the flag
	@code{GPGME_DELETE_ALLOW_SECRET} can be provided.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_delete_start (@w{gpgme_ctx_t @var{ctx}}, @w{const gpgme_key_t @var{key}}, @w{int @var{allow_secret}})
	Similar to @code{gpgme_op_delete_ext_start}, but only the flag
	@code{GPGME_DELETE_ALLOW_SECRET} can be provided.
	@end deftypefun


	@node Changing Passphrases
	@subsection Changing Passphrases
	@cindex passphrase, change

	@deftypefun gpgme_error_t gpgme_op_passwd @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const gpgme_key_t @var{key}}, @
	@w{unsigned int @var{flags}})

	@since{1.3.0}

	The function @code{gpgme_op_passwd} changes the passphrase of the
	private key associated with @var{key}. The only allowed value for
	@var{flags} is @code{0}. The backend engine will usually popup a window
	to ask for the old and the new passphrase. Thus this function is not
	useful in a server application (where passphrases are not required
	anyway).

	Note that old @code{gpg} engines (before version 2.0.15) do not support
	this command and will silently ignore it.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_passwd_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const gpgme_key_t @var{key}}, @
	@w{unsigned int @var{flags}})

	@since{1.3.0}

	The function @code{gpgme_op_passwd_start} initiates a
	@code{gpgme_op_passwd} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns @code{0} if the operation was started successfully,
	and an error code if one of the arguments is not valid or the oepration
	could not be started.
	@end deftypefun


	@c
	@c CHANGING TOFU DATA
	@c
	@node Changing TOFU Data
	@subsection Changing TOFU Data
	@cindex validity, TOFU

	The OpenPGP engine features a Trust-On-First-Use (TOFU) key validation
	model. For resolving conflicts it is necessary to declare the policy
	for a key. See the GnuPG manual for details on the TOFU
	implementation.

	@deftp {Data type} {enum gpgme_tofu_policy_t}
	@since{1.7.0}

	@tindex gpgme_tofu_policy_t
	The @code{gpgme_tofu_policy_t} type specifies the set of possible
	policy values that are supported by @acronym{GPGME}:

	@table @code
	@item GPGME_TOFU_POLICY_AUTO
	Set the policy to ``auto''.
	@item GPGME_TOFU_POLICY_GOOD
	Set the policy to ``good''.
	@item GPGME_TOFU_POLICY_BAD
	Set the policy to ``bad''.
	@item GPGME_TOFU_POLICY_ASK
	Set the policy to ``ask''.
	@item GPGME_TOFU_POLICY_UNKNOWN
	Set the policy to ``unknown''.
	@end table

	@end deftp

	To change the policy for a key the following functions can be used:

	@deftypefun gpgme_error_t gpgme_op_tofu_policy @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const gpgme_key_t @var{key}}, @
	@w{gpgme_tofu_policy_t @var{policy}})

	@since{1.7.0}

	The function @code{gpgme_op_tofu_policy} changes the TOFU policy of
	@var{key}. The valid values for @var{policy} are listed above. As of
	now this function does only work for OpenPGP and requires at least
	version 2.1.10 of GnuPG.

	The function returns zero on success, @code{GPG_ERR_NOT_SUPPORTED} if
	the engine does not support the command, or a bunch of other error
	codes.

	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_tofu_policy_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const gpgme_key_t @var{key}}, @
	@w{gpgme_tofu_policy_t @var{policy}})

	@since{1.7.0}

	The function @code{gpgme_op_tofu_policy_start} initiates a
	@code{gpgme_op_tofu_policy} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns @code{0} if the operation was started successfully,
	and an error code if one of the arguments is not valid or the oepration
	could not be started.

	@end deftypefun


	@node Advanced Key Editing
	@subsection Advanced Key Editing
	@cindex key, edit

	@deftp {Data type} {gpgme_error_t (*gpgme_interact_cb_t) @
	(@w{void *@var{handle}}, @
	@w{const char *@var{status}}, @
	@w{const char *@var{args}}, @
	@w{int @var{fd}})}

	@since{1.7.0}

	@tindex gpgme_interact_cb_t
	The @code{gpgme_interact_cb_t} type is the type of functions which
	@acronym{GPGME} calls if it a key interact operation is on-going. The
	status keyword @var{status} and the argument line @var{args} are
	passed through by @acronym{GPGME} from the crypto engine. An empty
	string represents EOF. The file descriptor @var{fd} is -1 for normal
	status messages. If @var{status} indicates a command rather than a
	status message, the response to the command should be written to
	@var{fd}. The @var{handle} is provided by the user at start of
	operation.

	The function should return @code{GPG_ERR_FALSE} if it did not handle
	the status code, @code{0} for success, or any other error value.
	@end deftp

	@deftypefun gpgme_error_t gpgme_op_interact (@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{unsigned int @var{flags}}, @
	@w{gpgme_interact_cb_t @var{fnc}}, @
	@w{void *@var{handle}}, @
	@w{gpgme_data_t @var{out}})

	@since{1.7.0}

	The function @code{gpgme_op_interact} processes the key @var{KEY}
	interactively, using the interact callback function @var{FNC} with the
	handle @var{HANDLE}. The callback is invoked for every status and
	command request from the crypto engine. The output of the crypto
	engine is written to the data object @var{out}.

	Note that the protocol between the callback function and the crypto
	engine is specific to the crypto engine and no further support in
	implementing this protocol correctly is provided by @acronym{GPGME}.

	@var{flags} modifies the behaviour of the function; the only defined
	bit value is:

	@table @code
	@item GPGME_INTERACT_CARD
	@since{1.7.0}

	This is used for smartcard based keys and uses gpg’s
	@code{--card-edit} command.

	@end table

	The function returns @code{0} if the edit operation completes
	successfully, @code{GPG_ERR_INV_VALUE} if @var{ctx} or @var{key} is
	not a valid pointer, and any error returned by the crypto engine or
	the edit callback handler.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_interact_start (@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{key}}, @
	@w{unsigned int @var{flags}}, @
	@w{gpgme_interact_cb_t @var{fnc}}, @
	@w{void *@var{handle}}, @
	@w{gpgme_data_t @var{out}})

	@since{1.7.0}

	The function @code{gpgme_op_interact_start} initiates a
	@code{gpgme_op_interact} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns @code{0} if the operation was started
	successfully, and @code{GPG_ERR_INV_VALUE} if @var{ctx} or @var{key}
	is not a valid pointer.
	@end deftypefun


	@node Crypto Operations
	@section Crypto Operations
	@cindex cryptographic operation

	Sometimes, the result of a crypto operation returns a list of invalid
	keys encountered in processing the request. The following structure
	is used to hold information about such a key.

	@deftp {Data type} {gpgme_invalid_key_t}
	This is a pointer to a structure used to store a part of the result of
	a crypto operation which takes user IDs as one input parameter. The
	structure contains the following members:

	@table @code
	@item gpgme_invalid_key_t next
	This is a pointer to the next invalid key structure in the linked
	list, or @code{NULL} if this is the last element.

	@item char *fpr
	The fingerprint or key ID of the invalid key encountered.

	@item gpgme_error_t reason
	An error code describing the reason why the key was found invalid.
	@end table
	@end deftp


	@menu
	* Decrypt:: Decrypting a ciphertext.
	* Verify:: Verifying a signature.
	* Decrypt and Verify:: Decrypting a signed ciphertext.
	* Sign:: Creating a signature.
	* Encrypt:: Encrypting a plaintext.
	@end menu


	@node Decrypt
	@subsection Decrypt
	@cindex decryption
	@cindex cryptographic operation, decryption

	@deftypefun gpgme_error_t gpgme_op_decrypt (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{cipher}}, @w{gpgme_data_t @var{plain}})
	The function @code{gpgme_op_decrypt} decrypts the ciphertext in the
	data object @var{cipher} and stores it into the data object
	@var{plain}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	ciphertext could be decrypted successfully, @code{GPG_ERR_INV_VALUE}
	if @var{ctx}, @var{cipher} or @var{plain} is not a valid pointer,
	@code{GPG_ERR_NO_DATA} if @var{cipher} does not contain any data to
	decrypt, @code{GPG_ERR_DECRYPT_FAILED} if @var{cipher} is not a valid
	cipher text, @code{GPG_ERR_BAD_PASSPHRASE} if the passphrase for the
	secret key could not be retrieved, and passes through some errors that
	are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_decrypt_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{cipher}}, @w{gpgme_data_t @var{plain}})
	The function @code{gpgme_op_decrypt_start} initiates a
	@code{gpgme_op_decrypt} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, and @code{GPG_ERR_INV_VALUE}
	if @var{cipher} or @var{plain} is not a valid pointer.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_decrypt_ext ( @
	@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_decrypt_flags_t @var{flags}}, @
	@w{gpgme_data_t @var{cipher}}, @
	@w{gpgme_data_t @var{plain}})

	@since{1.8.0}

	The function @code{gpgme_op_decrypt_ext} is the same as
	@code{gpgme_op_decrypt} but has an additional argument
	@var{flags}. If @var{flags} is 0 both function behave identically.

	The value in @var{flags} is a bitwise-or combination of one or
	multiple of the following bit values:

	@table @code
	@item GPGME_DECRYPT_VERIFY
	@since{1.8.0}

	The @code{GPGME_DECRYPT_VERIFY} symbol specifies that this function
	shall exactly act as @code{gpgme_op_decrypt_verify}.

	@item GPGME_DECRYPT_UNWRAP
	@since{1.8.0}

	The @code{GPGME_DECRYPT_UNWRAP} symbol specifies that the output shall
	be an OpenPGP message with only the encryption layer removed. This
	requires GnuPG 2.1.12 and works only for OpenPGP. This is the
	counterpart to @code{GPGME_ENCRYPT_WRAP}.

	@end table

	The function returns the error codes as described for
	@code{gpgme_op_decrypt}.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_decrypt_ext_start ( @
	@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_decrypt_flags_t @var{flags}}, @
	@w{gpgme_data_t @var{cipher}}, @
	@w{gpgme_data_t @var{plain}})

	@since{1.8.0}

	The function @code{gpgme_op_decrypt_ext_start} initiates a
	@code{gpgme_op_decrypt_ext} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, and @code{GPG_ERR_INV_VALUE}
	if @var{cipher} or @var{plain} is not a valid pointer.
	@end deftypefun


	@deftp {Data type} {gpgme_recipient_t}
	@since{1.1.0}

	This is a pointer to a structure used to store information about the
	recipient of an encrypted text which is decrypted in a
	@code{gpgme_op_decrypt} operation. This information (except for the
	status field) is even available before the operation finished
	successfully, for example in a passphrase callback. The structure
	contains the following members:

	@table @code
	@item gpgme_recipient_t next
	This is a pointer to the next recipient structure in the linked list,
	or @code{NULL} if this is the last element.

	@item gpgme_pubkey_algo_t
	The public key algorithm used in the encryption.

	@item char *keyid
	This is the key ID of the key (in hexadecimal digits) used as
	recipient.

	@item gpgme_error_t status
	This is an error number with the error code GPG_ERR_NO_SECKEY if the
	secret key for this recipient is not available, and 0 otherwise.
	@end table
	@end deftp

	@deftp {Data type} {gpgme_decrypt_result_t}
	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_decrypt} operation. After successfully decrypting
	data, you can retrieve the pointer to the result with
	@code{gpgme_op_decrypt_result}. As with all result structures, it
	this structure shall be considered read-only and an application must
	not allocate such a strucure on its own. The structure contains the
	following members:

	@table @code
	@item char *unsupported_algorithm
	If an unsupported algorithm was encountered, this string describes the
	algorithm that is not supported.

	@item unsigned int wrong_key_usage : 1
	@since{0.9.0}
	This is true if the key was not used according to its policy.

	@item unsigned int legacy_cipher_nomdc : 1
	@since{1.11.2}
	The message was made by a legacy algorithm without any integrity
	protection. This might be an old but legitimate message.

	@item unsigned int is_mime : 1;
	@since{1.11.0}
	The message claims that the content is a MIME object.

	@item unsigned int is_de_vs : 1;
	@since{1.10.0}
	The message was encrypted in a VS-NfD compliant way. This is a
	specification in Germany for a restricted communication level.

	@item gpgme_recipient_t recipients
	@since{1.1.0}

	This is a linked list of recipients to which this message was encrypted.

	@item char *file_name
	This is the filename of the original plaintext message file if it is
	known, otherwise this is a null pointer.

	@item char *session_key
	@since{1.8.0}

	A textual representation (nul-terminated string) of the session key
	used in symmetric encryption of the message, if the context has been
	set to export session keys (see @code{gpgme_set_ctx_flag,
	"export-session-key"}), and a session key was available for the most
	recent decryption operation. Otherwise, this is a null pointer.

	You must not try to access this member of the struct unless
	@code{gpgme_set_ctx_flag (ctx, "export-session-key")} returns success
	or @code{gpgme_get_ctx_flag (ctx, "export-session-key")} returns true
	(non-empty string).

	@item char *symkey_algo
	@since{1.11.0}

	A string with the symmetric encryption algorithm and mode using the
	format "<algo>.<mode>". Note that the deprecated non-MDC encryption mode of
	OpenPGP is given as "PGPCFB".

	@end table
	@end deftp

	@deftypefun gpgme_decrypt_result_t gpgme_op_decrypt_result (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_op_decrypt_result} returns a
	@code{gpgme_decrypt_result_t} pointer to a structure holding the
	result of a @code{gpgme_op_decrypt} operation. The pointer is only
	valid if the last operation on the context was a
	@code{gpgme_op_decrypt} or @code{gpgme_op_decrypt_start} operation.
	If the operation failed this might be a @code{NULL} pointer. The
	returned pointer is only valid until the next operation is started on
	the context.
	@end deftypefun


	@node Verify
	@subsection Verify
	@cindex verification
	@cindex signature, verification
	@cindex cryptographic operation, verification
	@cindex cryptographic operation, signature check
	@cindex signature notation data
	@cindex notation data

	@deftypefun gpgme_error_t gpgme_op_verify (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{sig}}, @w{gpgme_data_t @var{signed_text}}, @w{gpgme_data_t @var{plain}})
	The function @code{gpgme_op_verify} verifies that the signature in the
	data object @var{sig} is a valid signature. If @var{sig} is a
	detached signature, then the signed text should be provided in
	@var{signed_text} and @var{plain} should be a null pointer.
	Otherwise, if @var{sig} is a normal (or cleartext) signature,
	@var{signed_text} should be a null pointer and @var{plain} should be a
	writable data object that will contain the plaintext after successful
	verification.

	The results of the individual signature verifications can be retrieved
	with @code{gpgme_op_verify_result}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be completed successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx}, @var{sig} or @var{plain} is not a valid pointer,
	@code{GPG_ERR_NO_DATA} if @var{sig} does not contain any data to
	verify, and passes through any errors that are reported by the crypto
	engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_verify_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{sig}}, @w{gpgme_data_t @var{signed_text}}, @w{gpgme_data_t @var{plain}})
	The function @code{gpgme_op_verify_start} initiates a
	@code{gpgme_op_verify} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx}, @var{sig} or @var{plain} is not a valid pointer, and
	@code{GPG_ERR_NO_DATA} if @var{sig} or @var{plain} does not contain
	any data to verify.
	@end deftypefun

	@deftp {Data type} {gpgme_sig_notation_t}
	This is a pointer to a structure used to store a part of the result of
	a @code{gpgme_op_verify} operation. The structure contains the
	following members:

	@table @code
	@item gpgme_sig_notation_t next
	This is a pointer to the next new signature notation structure in the
	linked list, or @code{NULL} if this is the last element.

	@item char *name
	The name of the notation field. If this is @code{NULL}, then the
	member @code{value} will contain a policy URL.

	@item int name_len
	The length of the @code{name} field. For strings the length is
	counted without the trailing binary zero.

	@item char *value
	The value of the notation field. If @code{name} is @code{NULL}, then
	this is a policy URL.

	@item int value_len
	The length of the @code{value} field. For strings the length is
	counted without the trailing binary zero.

	@item gpgme_sig_notation_flags_t flags
	The accumulated flags field. This field contains the flags associated
	with the notation data in an accumulated form which can be used as an
	argument to the function @code{gpgme_sig_notation_add}. The value
	@code{flags} is a bitwise-or combination of one or multiple of the
	following bit values:

	@table @code
	@item GPGME_SIG_NOTATION_HUMAN_READABLE
	@since{1.1.0}

	The @code{GPGME_SIG_NOTATION_HUMAN_READABLE} symbol specifies that the
	notation data is in human readable form

	@item GPGME_SIG_NOTATION_CRITICAL
	@since{1.1.0}

	The @code{GPGME_SIG_NOTATION_CRITICAL} symbol specifies that the
	notation data is critical.

	@end table

	@item unsigned int human_readable : 1
	This is true if the @code{GPGME_SIG_NOTATION_HUMAN_READABLE} flag is
	set and false otherwise. This flag is only valid for notation data,
	not for policy URLs.

	@item unsigned int critical : 1
	This is true if the @code{GPGME_SIG_NOTATION_CRITICAL} flag is set and
	false otherwise. This flag is valid for notation data and policy URLs.

	@end table
	@end deftp

	@deftp {Data type} {gpgme_signature_t}
	This is a pointer to a structure used to store a part of the result of
	a @code{gpgme_op_verify} operation. The structure contains the
	following members:

	@table @code
	@item gpgme_signature_t next
	This is a pointer to the next new signature structure in the linked
	list, or @code{NULL} if this is the last element.

	@item gpgme_sigsum_t summary
	This is a bit vector giving a summary of the signature status. It
	provides an easy interface to a defined semantic of the signature
	status. Checking just one bit is sufficient to see whether a
	signature is valid without any restrictions. This means that
	you can check for GPGME_SIGSUM_VALID like this:

	@example
	if ((sig.summary & GPGME_SIGSUM_VALID))
	@{
	..do stuff if valid..
	@}
	else
	@{
	..do stuff if not fully valid..
	@}
	@end example

	The defined bits are:
	@table @code
	@item GPGME_SIGSUM_VALID
	The signature is fully valid.

	@item GPGME_SIGSUM_GREEN
	The signature is good but one might want to display some extra
	information. Check the other bits.

	@item GPGME_SIGSUM_RED
	The signature is bad. It might be useful to check other bits and
	display more information, i.e. a revoked certificate might not render a
	signature invalid when the message was received prior to the cause for
	the revocation.

	@item GPGME_SIGSUM_KEY_REVOKED
	The key or at least one certificate has been revoked.

	@item GPGME_SIGSUM_KEY_EXPIRED
	The key or one of the certificates has expired. It is probably a good
	idea to display the date of the expiration.

	@item GPGME_SIGSUM_SIG_EXPIRED
	The signature has expired.

	@item GPGME_SIGSUM_KEY_MISSING
	Can't verify due to a missing key or certificate.

	@item GPGME_SIGSUM_CRL_MISSING
	The CRL (or an equivalent mechanism) is not available.

	@item GPGME_SIGSUM_CRL_TOO_OLD
	Available CRL is too old.

	@item GPGME_SIGSUM_BAD_POLICY
	A policy requirement was not met.

	@item GPGME_SIGSUM_SYS_ERROR
	A system error occurred.

	@item GPGME_SIGSUM_TOFU_CONFLICT
	A TOFU conflict was detected.
	@end table

	@item char *fpr
	This is the fingerprint or key ID of the signature.

	@item gpgme_error_t status
	This is the status of the signature. In particular, the following
	status codes are of interest:

	@table @code
	@item GPG_ERR_NO_ERROR
	This status indicates that the signature could be verified or that
	there is no signature. For the combined result this status
	means that all signatures could be verified.

	Note: This does not mean that a valid signature could be found. Check
	the @code{summary} field for that.

	For example a @code{gpgme_op_decrypt_verify} returns a verification
	result with GPG_ERR_NO_ERROR for encrypted but unsigned data.

	@item GPG_ERR_SIG_EXPIRED
	This status indicates that the signature is valid but expired. For
	the combined result this status means that all signatures are valid
	and expired.

	@item GPG_ERR_KEY_EXPIRED
	This status indicates that the signature is valid but the key used to
	verify the signature has expired. For the combined result this status
	means that all signatures are valid and all keys are expired.

	@item GPG_ERR_CERT_REVOKED
	This status indicates that the signature is valid but the key used
	to verify the signature has been revoked. For the combined result
	this status means that all signatures are valid and all keys are
	revoked.

	@item GPG_ERR_BAD_SIGNATURE
	This status indicates that the signature is invalid. For the combined
	result this status means that all signatures are invalid.

	@item GPG_ERR_NO_PUBKEY
	This status indicates that the signature could not be verified due to
	a missing key. For the combined result this status means that all
	signatures could not be checked due to missing keys.

	@item GPG_ERR_GENERAL
	This status indicates that there was some other error which prevented
	the signature verification.
	@end table

	@item gpgme_sig_notation_t notations
	This is a linked list with the notation data and policy URLs.

	@item unsigned long timestamp
	The creation timestamp of this signature.

	@item unsigned long exp_timestamp
	The expiration timestamp of this signature, or 0 if the signature does
	not expire.

	@item unsigned int wrong_key_usage : 1
	This is true if the key was not used according to its policy.

	@item unsigned int pka_trust : 2
	This is set to the trust information gained by means of the PKA system.
	Values are:
	@table @code
	@item 0
	No PKA information available or verification not possible.
	@item 1
	PKA verification failed.
	@item 2
	PKA verification succeeded.
	@item 3
	Reserved for future use.
	@end table
	Depending on the configuration of the engine, this metric may also be
	reflected by the validity of the signature.

	@item unsigned int chain_model : 1
	@since{1.1.6}

	This is true if the validity of the signature has been checked using the
	chain model. In the chain model the time the signature has been created
	must be within the validity period of the certificate and the time the
	certificate itself has been created must be within the validity period
	of the issuing certificate. In contrast the default validation model
	checks the validity of signature as well at the entire certificate chain
	at the current time.


	@item gpgme_validity_t validity
	The validity of the signature.

	@item gpgme_error_t validity_reason
	If a signature is not valid, this provides a reason why.

	@item gpgme_pubkey_algo_t
	The public key algorithm used to create this signature.

	@item gpgme_hash_algo_t
	The hash algorithm used to create this signature.

	@item char *pka_address
	The mailbox from the PKA information or @code{NULL}.

	@item gpgme_key_t key
	@since{1.7.0}

	An object describing the key used to create the signature. This key
	object may be incomplete in that it only conveys information
	availabale directly with a signature. It may also be @code{NULL} if
	such information is not readily available.

	@end table
	@end deftp

	@deftp {Data type} {gpgme_verify_result_t}
	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_verify} operation. After verifying a signature, you
	can retrieve the pointer to the result with
	@code{gpgme_op_verify_result}. If the operation failed this might be
	a @code{NULL} pointer. The structure contains the following member:

	@table @code
	@item gpgme_signature_t signatures
	A linked list with information about all signatures for which a
	verification was attempted.

	@item char *file_name
	This is the filename of the original plaintext message file if it is
	known, otherwise this is a null pointer. Warning: The filename is
	not covered by the signature.

	@item unsigned int is_mime : 1;
	@since{1.11.0}

	The message claims that the content is a MIME object. Warning: This
	flag is not covered by the signature.

	@end table
	@end deftp

	@deftypefun gpgme_verify_result_t gpgme_op_verify_result (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_op_verify_result} returns a
	@code{gpgme_verify_result_t} pointer to a structure holding the result
	of a @code{gpgme_op_verify} operation. The pointer is only valid if
	the last operation on the context was a @code{gpgme_op_verify},
	@code{gpgme_op_verify_start}, @code{gpgme_op_decrypt_verify} or
	@code{gpgme_op_decrypt_verify_start} operation, and if this operation
	finished successfully (for @code{gpgme_op_decrypt_verify} and
	@code{gpgme_op_decrypt_verify_start}, the error code
	@code{GPG_ERR_NO_DATA} counts as successful in this context). The
	returned pointer is only valid until the next operation is started on
	the context.
	@end deftypefun


	@node Decrypt and Verify
	@subsection Decrypt and Verify
	@cindex decryption and verification
	@cindex verification and decryption
	@cindex signature check
	@cindex cryptographic operation, decryption and verification

	@deftypefun gpgme_error_t gpgme_op_decrypt_verify (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{cipher}}, @w{gpgme_data_t @var{plain}})
	The function @code{gpgme_op_decrypt_verify} decrypts the ciphertext in
	the data object @var{cipher} and stores it into the data object
	@var{plain}. If @var{cipher} contains signatures, they will be
	verified.

	After the operation completed, @code{gpgme_op_decrypt_result} and
	@code{gpgme_op_verify_result} can be used to retrieve more information
	about the signatures.

	If the error code @code{GPG_ERR_NO_DATA} is returned, @var{cipher}
	does not contain any data to decrypt. However, it might still be
	signed. The information about detected signatures is available with
	@code{gpgme_op_verify_result} in this case.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	ciphertext could be decrypted successfully, @code{GPG_ERR_INV_VALUE}
	if @var{ctx}, @var{cipher} or @var{plain} is not a valid pointer,
	@code{GPG_ERR_NO_DATA} if @var{cipher} does not contain any data to
	decrypt, @code{GPG_ERR_DECRYPT_FAILED} if @var{cipher} is not a valid
	cipher text, @code{GPG_ERR_BAD_PASSPHRASE} if the passphrase for the
	secret key could not be retrieved, and passes through any errors that
	are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_decrypt_verify_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{cipher}}, @w{gpgme_data_t @var{plain}})
	The function @code{gpgme_op_decrypt_verify_start} initiates a
	@code{gpgme_op_decrypt_verify} operation. It can be completed by
	calling @code{gpgme_wait} on the context. @xref{Waiting For
	Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx}, @var{cipher}, @var{plain} or @var{r_stat} is not a valid
	pointer, and @code{GPG_ERR_NO_DATA} if @var{cipher} does not contain
	any data to decrypt.
	@end deftypefun

	When processing mails it is sometimes useful to extract the actual
	mail address (the ``addr-spec'') from a string. GPGME provides this
	helper function which uses the same semantics as the internal
	functions in GPGME and GnuPG:

	@deftypefun @w{char } gpgme_addrspec_from_uid (@w{const char @var{uid}})

	@since{1.7.1}

	Return the mail address (called ``addr-spec'' in RFC-5322) from the
	string @var{uid} which is assumed to be a user id (called ``address''
	in RFC-5322). All plain ASCII characters (i.e. those with bit 7
	cleared) in the result are converted to lowercase. Caller must free
	the result using @code{gpgme_free}. Returns @code{NULL} if no valid
	address was found (in which case @code{ERRNO} is set to @code{EINVAL})
	or for other errors.

	@end deftypefun


	@node Sign
	@subsection Sign
	@cindex signature, creation
	@cindex sign
	@cindex cryptographic operation, signing

	A signature can contain signatures by one or more keys. The set of
	keys used to create a signatures is contained in a context, and is
	applied to all following signing operations in this context (until the
	set is changed).

	@menu
	* Selecting Signers:: How to choose the keys to sign with.
	* Creating a Signature:: How to create a signature.
	* Signature Notation Data:: How to add notation data to a signature.
	@end menu


	@node Selecting Signers
	@subsubsection Selecting Signers
	@cindex signature, selecting signers
	@cindex signers, selecting

	The key or the keys used to create a signature are stored in the
	context. The following functions can be used to manipulate this list.
	If no signer has been set into the context a default key is used for
	signing.

	@deftypefun void gpgme_signers_clear (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_signers_clear} releases a reference for each
	key on the signers list and removes the list of signers from the
	context @var{ctx}.

	Every context starts with an empty list.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_signers_add (@w{gpgme_ctx_t @var{ctx}}, @w{const gpgme_key_t @var{key}})
	The function @code{gpgme_signers_add} adds the key @var{key} to the
	list of signers in the context @var{ctx}.

	Calling this function acquires an additional reference for the key.
	@end deftypefun

	@deftypefun @w{unsigned int} gpgme_signers_count (@w{const gpgme_ctx_t @var{ctx}})
	@since{1.4.3}

	The function @code{gpgme_signers_count} returns the number of signer keys in
	the context @var{ctx}.
	@end deftypefun

	@deftypefun gpgme_key_t gpgme_signers_enum (@w{const gpgme_ctx_t @var{ctx}}, @w{int @var{seq}})
	The function @code{gpgme_signers_enum} returns the @var{seq}th key in
	the list of signers in the context @var{ctx}. An additional reference
	is acquired for the user.

	If @var{seq} is out of range, @code{NULL} is returned.
	@end deftypefun


	@node Creating a Signature
	@subsubsection Creating a Signature

	@deftp {Data type} {enum gpgme_sig_mode_t}
	@tindex gpgme_sig_mode_t
	The @code{gpgme_sig_mode_t} type is used to specify the desired type of a
	signature. The following modes are available:

	@table @code
	@item GPGME_SIG_MODE_NORMAL
	A normal signature is made, the output includes the plaintext and the
	signature.

	@item GPGME_SIG_MODE_DETACH
	A detached signature is made.

	@item GPGME_SIG_MODE_CLEAR
	A clear text signature is made. The @acronym{ASCII} armor and text
	mode settings of the context are ignored.
	@end table
	@end deftp

	@deftypefun gpgme_error_t gpgme_op_sign (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{sig}}, @w{gpgme_sig_mode_t @var{mode}})
	The function @code{gpgme_op_sign} creates a signature for the text in
	the data object @var{plain} and returns it in the data object
	@var{sig}. The type of the signature created is determined by the
	@acronym{ASCII} armor (or, if that is not set, by the encoding
	specified for @var{sig}), the text mode attributes set for the context
	@var{ctx} and the requested signature mode @var{mode}.

	After the operation completed successfully, the result can be
	retrieved with @code{gpgme_op_sign_result}.

	If an S/MIME signed message is created using the CMS crypto engine,
	the number of certificates to include in the message can be specified
	with @code{gpgme_set_include_certs}. @xref{Included Certificates}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	signature could be created successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx}, @var{plain} or @var{sig} is not a valid pointer,
	@code{GPG_ERR_NO_DATA} if the signature could not be created,
	@code{GPG_ERR_BAD_PASSPHRASE} if the passphrase for the secret key
	could not be retrieved, @code{GPG_ERR_UNUSABLE_SECKEY} if there are
	invalid signers, and passes through any errors that are reported by the
	crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_sign_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{sig}}, @w{gpgme_sig_mode_t @var{mode}})
	The function @code{gpgme_op_sign_start} initiates a
	@code{gpgme_op_sign} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the operation could be
	started successfully, and @code{GPG_ERR_INV_VALUE} if @var{ctx},
	@var{plain} or @var{sig} is not a valid pointer.
	@end deftypefun

	@deftp {Data type} {gpgme_new_signature_t}
	This is a pointer to a structure used to store a part of the result of
	a @code{gpgme_op_sign} operation. The structure contains the
	following members:

	@table @code
	@item gpgme_new_signature_t next
	This is a pointer to the next new signature structure in the linked
	list, or @code{NULL} if this is the last element.

	@item gpgme_sig_mode_t type
	The type of this signature.

	@item gpgme_pubkey_algo_t pubkey_algo
	The public key algorithm used to create this signature.

	@item gpgme_hash_algo_t hash_algo
	The hash algorithm used to create this signature.

	@item unsigned int sig_class
	-The signature class of this signature.
	+The signature class of this signature. Note that only the values 0,
	+1, and 2 are well-defined.

	@item long int timestamp
	The creation timestamp of this signature.

	@item char *fpr
	The fingerprint of the key which was used to create this signature.
	@end table
	@end deftp

	@deftp {Data type} {gpgme_sign_result_t}
	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_sign} operation. After successfully generating a
	signature, you can retrieve the pointer to the result with
	@code{gpgme_op_sign_result}. The structure contains the following
	members:

	@table @code
	@item gpgme_invalid_key_t invalid_signers
	A linked list with information about all invalid keys for which a
	signature could not be created.

	@item gpgme_new_signature_t signatures
	A linked list with information about all signatures created.
	@end table
	@end deftp

	@deftypefun gpgme_sign_result_t gpgme_op_sign_result (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_op_sign_result} returns a
	@code{gpgme_sign_result_t} pointer to a structure holding the result
	of a @code{gpgme_op_sign} operation. The pointer is only valid if the
	last operation on the context was a @code{gpgme_op_sign},
	@code{gpgme_op_sign_start}, @code{gpgme_op_encrypt_sign} or
	@code{gpgme_op_encrypt_sign_start} operation. If that operation
	failed, the function might return a @code{NULL} pointer. The returned
	pointer is only valid until the next operation is started on the
	context.
	@end deftypefun


	@node Signature Notation Data
	@subsubsection Signature Notation Data
	@cindex notation data
	@cindex signature notation data
	@cindex policy URL

	Using the following functions, you can attach arbitrary notation data
	to a signature. This information is then available to the user when
	the signature is verified.

	@deftypefun void gpgme_sig_notation_clear (@w{gpgme_ctx_t @var{ctx}})
	@since{1.1.0}

	The function @code{gpgme_sig_notation_clear} removes the notation data
	from the context @var{ctx}. Subsequent signing operations from this
	context will not include any notation data.

	Every context starts with an empty notation data list.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_sig_notation_add (@w{gpgme_ctx_t @var{ctx}}, @w{const char @var{name}}, @w{const char @var{value}}, @w{gpgme_sig_notation_flags_t @var{flags}})
	@since{1.1.0}

	The function @code{gpgme_sig_notation_add} adds the notation data with
	the name @var{name} and the value @var{value} to the context
	@var{ctx}.

	Subsequent signing operations will include this notation data, as well
	as any other notation data that was added since the creation of the
	context or the last @code{gpgme_sig_notation_clear} operation.

	The arguments @var{name} and @var{value} must be @code{NUL}-terminated
	strings in human-readable form. The flag
	@code{GPGME_SIG_NOTATION_HUMAN_READABLE} is implied
	(non-human-readable notation data is currently not supported). The
	strings must be in UTF-8 encoding.

	If @var{name} is @code{NULL}, then @var{value} should be a policy URL.

	The function @code{gpgme_sig_notation_add} returns the error code
	@code{GPG_ERR_NO_ERROR} if the notation data could be added
	successfully, @code{GPG_ERR_INV_VALUE} if @var{ctx} is not a valid
	pointer, or if @var{name}, @var{value} and @var{flags} are an invalid
	combination. The function also passes through any errors that are
	reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_sig_notation_t gpgme_sig_notation_get (@w{const gpgme_ctx_t @var{ctx}})
	@since{1.1.0}

	The function @code{gpgme_sig_notation_get} returns the linked list of
	notation data structures that are contained in the context @var{ctx}.

	If @var{ctx} is not a valid pointer, or there is no notation data
	added for this context, @code{NULL} is returned.
	@end deftypefun


	@node Encrypt
	@subsection Encrypt
	@cindex encryption
	@cindex cryptographic operation, encryption

	One plaintext can be encrypted for several recipients at the same
	time. The list of recipients is created independently of any context,
	and then passed to the encryption operation.

	@menu
	* Encrypting a Plaintext:: How to encrypt a plaintext.
	@end menu


	@node Encrypting a Plaintext
	@subsubsection Encrypting a Plaintext

	@deftypefun gpgme_error_t gpgme_op_encrypt (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{recp}[]}, @w{gpgme_encrypt_flags_t @var{flags}}, @w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})
	The function @code{gpgme_op_encrypt} encrypts the plaintext in the
	data object @var{plain} for the recipients @var{recp} and stores the
	ciphertext in the data object @var{cipher}. The type of the
	ciphertext created is determined by the @acronym{ASCII} armor (or, if
	that is not set, by the encoding specified for @var{cipher}) and the
	text mode attributes set for the context @var{ctx}.

	@var{recp} must be a @code{NULL}-terminated array of keys. The user
	must keep references for all keys during the whole duration of the
	call (but see @code{gpgme_op_encrypt_start} for the requirements with
	the asynchronous variant).

	The value in @var{flags} is a bitwise-or combination of one or
	multiple of the following bit values:

	@table @code
	@item GPGME_ENCRYPT_ALWAYS_TRUST
	The @code{GPGME_ENCRYPT_ALWAYS_TRUST} symbol specifies that all the
	recipients in @var{recp} should be trusted, even if the keys do not
	have a high enough validity in the keyring. This flag should be used
	with care; in general it is not a good idea to use any untrusted keys.

	@item GPGME_ENCRYPT_NO_ENCRYPT_TO
	@since{1.2.0}

	The @code{GPGME_ENCRYPT_NO_ENCRYPT_TO} symbol specifies that no
	default or hidden default recipients as configured in the crypto
	backend should be included. This can be useful for managing different
	user profiles.

	@item GPGME_ENCRYPT_NO_COMPRESS
	@since{1.5.0}

	The @code{GPGME_ENCRYPT_NO_COMPRESS} symbol specifies that the
	plaintext shall not be compressed before it is encrypted. This is
	in some cases useful if the length of the encrypted message
	may reveal information about the plaintext.

	@item GPGME_ENCRYPT_PREPARE
	@itemx GPGME_ENCRYPT_EXPECT_SIGN
	The @code{GPGME_ENCRYPT_PREPARE} symbol is used with the UI Server
	protocol to prepare an encryption (i.e. sending the
	@code{PREP_ENCRYPT} command). With the
	@code{GPGME_ENCRYPT_EXPECT_SIGN} symbol the UI Server is advised to
	also expect a sign command.

	@item GPGME_ENCRYPT_SYMMETRIC
	@since{1.7.0}

	The @code{GPGME_ENCRYPT_SYMMETRIC} symbol specifies that the
	output should be additionally encrypted symmetrically even
	if recipients are provided. This feature is only supported
	for the OpenPGP crypto engine.

	@item GPGME_ENCRYPT_THROW_KEYIDS
	@since{1.8.0}

	The @code{GPGME_ENCRYPT_THROW_KEYIDS} symbols requests that the
	identifiers for the decrption keys are not included in the ciphertext.
	On the receiving side, the use of this flag may slow down the
	decryption process because all available secret keys must be tried.
	This flag is only honored for OpenPGP encryption.

	@item GPGME_ENCRYPT_WRAP
	@since{1.8.0}

	The @code{GPGME_ENCRYPT_WRAP} symbol specifies that the input is an
	OpenPGP message and not a plain data. This is the counterpart to
	@code{GPGME_DECRYPT_UNWRAP}.

	@item GPGME_ENCRYPT_WANT_ADDRESS
	@since{1.11.0}

	The @code{GPGME_ENCRYPT_WANT_ADDRESS} symbol requests that all
	supplied keys or key specifications include a syntactically valid mail
	address. If this is not the case the operation is not even tried and
	the error code @code{GPG_ERR_INV_USER_ID} is returned. Only the
	address part of the key specification is conveyed to the backend. As
	of now the key must be specified using the @var{recpstring} argument
	of the extended encrypt functions. This feature is currently only
	supported for the OpenPGP crypto engine.

	@end table

	If @code{GPG_ERR_UNUSABLE_PUBKEY} is returned, some recipients in
	@var{recp} are invalid, but not all. In this case the plaintext might
	be encrypted for all valid recipients and returned in @var{cipher} (if
	this happens depends on the crypto engine). More information about
	the invalid recipients is available with
	@code{gpgme_op_encrypt_result}.

	If @var{recp} is @code{NULL}, symmetric rather than public key
	encryption is performed. Symmetrically encrypted cipher text can be
	deciphered with @code{gpgme_op_decrypt}. Note that in this case the
	crypto backend needs to retrieve a passphrase from the user.
	Symmetric encryption is currently only supported for the OpenPGP
	crypto backend.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	ciphertext could be created successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx}, @var{recp}, @var{plain} or @var{cipher} is not a valid
	pointer, @code{GPG_ERR_UNUSABLE_PUBKEY} if @var{recp} contains some
	invalid recipients, @code{GPG_ERR_BAD_PASSPHRASE} if the passphrase
	for the symmetric key could not be retrieved, and passes through any
	errors that are reported by the crypto engine support routines.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_encrypt_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{recp}[]}, @w{gpgme_encrypt_flags_t @var{flags}}, @w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})
	The function @code{gpgme_op_encrypt_start} initiates a
	@code{gpgme_op_encrypt} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	References to the keys only need to be held for the duration of this
	call. The user can release its references to the keys after this
	function returns, even if the operation is not yet finished.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx}, @var{rset}, @var{plain} or @var{cipher} is not a valid
	pointer, and @code{GPG_ERR_UNUSABLE_PUBKEY} if @var{rset} does not
	contain any valid recipients.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_encrypt_ext @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{recp}[]}, @
	@w{const char *@var{recpstring}}, @
	@w{gpgme_encrypt_flags_t @var{flags}}, @
	@w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})

	@since{1.11.0}

	This is an extended version of @code{gpgme_op_encrypt} with
	@var{recpstring} as additional parameter. If @var{recp} is NULL and
	@var{recpstring} is not NULL, the latter is expected to be a linefeed
	delimited string with the set of key specifications. In contrast to
	@var{recp} the keys are given directly as strings and there is no need
	to first create key objects. Leading and trailing white space is
	remove from each line in @var{recpstring}. The keys are then passed
	verbatim to the backend engine.

	For the OpenPGP backend several special keywords are supported to
	modify the operation. These keywords are given instead of a key
	specification. The currently supported keywords are:

	@table @code
	@item --hidden
	@itemx --no-hidden
	These keywords toggle between normal and hidden recipients for all
	following key specifications. When a hidden recipient is requested
	the gpg option @option{-R} (or @option{-F} in file mode) is used
	instead of @option{-r} (@option{-f} in file mode).

	@item --file
	@itemx --no-file
	These keywords toggle between regular and file mode for all following
	key specification. In file mode the option @option{-f} or @option{-F}
	is passed to gpg. At least GnuPG version 2.1.14 is required to handle
	these options. The @code{GPGME_ENCRYPT_WANT_ADDRESS} flag is ignored
	in file mode.

	@item --
	This keyword disables all keyword detection up to the end of the
	string. All keywords are treated as verbatim arguments.

	@end table

	To create a @var{recpstring} it is often useful to employ a strconcat
	style function. For example this function creates a string to encrypt
	to two keys:

	@example
	char *
	xbuild_recpstring (const char key1, const char key2)
	@{
	char *result = gpgrt_strconcat ("--\n", key1, "\n", key2, NULL);
	if (!result)
	@{ perror ("strconcat failed"); exit (2); @}
	return result;
	@}
	@end example

	Note the use of the double dash here; unless you want to specify a
	keyword, it is a good idea to avoid any possible trouble with key
	specifications starting with a double dash. The used strconcat
	function is available in Libgpg-error 1.28 and later; Libgpg-error
	(aka Gpgrt) is a dependency of GPGME. The number of arguments to
	@code{gpgrt_strconcat} is limited to 47 but that should always be
	sufficient. In case a larger and non-fixed number of keys are to be
	supplied the following code can be used:

	@example
	char *
	xbuild_long_recpstring (void)
	@{
	gpgrt_stream_t memfp;
	const char *s;
	void *result;

	memfp = gpgrt_fopenmem (0, "w+b");
	if (!memfp)
	@{ perror ("fopenmem failed"); exit (2); @}
	gpgrt_fputs ("--", memfp);
	while ((s = get_next_keyspec ()))
	@{
	gpgrt_fputc ('\n', memfp);
	gpgrt_fputs (s, memfp);
	@}
	gpgrt_fputc (0, memfp);
	if (gpgrt_ferror (memfp))
	@{ perror ("writing to memstream failed"); exit (2); @}
	if (gpgrt_fclose_snatch (memfp, &result, NULL))
	@{ perror ("fclose_snatch failed"); exit (2); @}
	return result;
	@}
	@end example

	In this example @code{get_next_keyspec} is expected to return the next
	key to be added to the string. Please take care: Encrypting to a
	large number of recipients is often questionable due to security
	reasons and also for the technicality that all keys are currently
	passed on the command line to @command{gpg} which has as a platform
	specific length limitation.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_encrypt_ext_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{recp}[]}, @
	@w{const char *@var{recpstring}}, @
	@w{gpgme_encrypt_flags_t @var{flags}}, @
	@w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})

	@since{1.11.0}

	This is an extended version of @code{gpgme_op_encrypt_start} with
	@var{recpstring} as additional parameter. If @var{recp} is NULL and
	@var{recpstring} is not NULL, the latter is expected to be a linefeed
	delimited string with the set of key specifications. In contrast to
	@var{recp} the keys are given directly as strings and there is no need
	to first create key objects. The keys are passed verbatim to the
	backend engine.

	@end deftypefun

	@deftp {Data type} {gpgme_encrypt_result_t}
	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_encrypt} operation. After successfully encrypting
	data, you can retrieve the pointer to the result with
	@code{gpgme_op_encrypt_result}. The structure contains the following
	members:

	@table @code
	@item gpgme_invalid_key_t invalid_recipients
	A linked list with information about all invalid keys for which
	the data could not be encrypted.
	@end table
	@end deftp

	@deftypefun gpgme_encrypt_result_t gpgme_op_encrypt_result (@w{gpgme_ctx_t @var{ctx}})
	The function @code{gpgme_op_encrypt_result} returns a
	@code{gpgme_encrypt_result_t} pointer to a structure holding the
	result of a @code{gpgme_op_encrypt} operation. The pointer is only
	valid if the last operation on the context was a
	@code{gpgme_op_encrypt}, @code{gpgme_op_encrypt_start},
	@code{gpgme_op_sign} or @code{gpgme_op_sign_start} operation. If this
	operation failed, this might be a @code{NULL} pointer. The returned
	pointer is only valid until the next operation is started on the
	context.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_encrypt_sign (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{recp}[]}, @w{gpgme_encrypt_flags_t @var{flags}}, @w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})
	The function @code{gpgme_op_encrypt_sign} does a combined encrypt and
	sign operation. It is used like @code{gpgme_op_encrypt}, but the
	ciphertext also contains signatures for the signers listed in
	@var{ctx}.

	The combined encrypt and sign operation is currently only available
	for the OpenPGP crypto engine.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_encrypt_sign_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{recp}[]}, @w{gpgme_encrypt_flags_t @var{flags}}, @w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})
	The function @code{gpgme_op_encrypt_sign_start} initiates a
	@code{gpgme_op_encrypt_sign} operation. It can be completed by
	calling @code{gpgme_wait} on the context. @xref{Waiting For
	Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation could be started successfully, and @code{GPG_ERR_INV_VALUE}
	if @var{ctx}, @var{rset}, @var{plain} or @var{cipher} is not a valid
	pointer.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_encrypt_sign_ext @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{recp}[]}, @
	@w{const char *@var{recpstring}}, @
	@w{gpgme_encrypt_flags_t @var{flags}}, @
	@w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})

	@since{1.11.0}

	This is an extended version of @code{gpgme_op_encrypt_sign} with
	@var{recpstring} as additional parameter. If @var{recp} is NULL and
	@var{recpstring} is not NULL, the latter is expected to be a linefeed
	delimited string with the set of key specifications. In contrast to
	@var{recp} the keys are given directly as strings and there is no need
	to first create the key objects. The keys are passed verbatim to the
	backend engine.

	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_encrypt_sign_ext_start @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{gpgme_key_t @var{recp}[]}, @
	@w{const char *@var{recpstring}}, @
	@w{gpgme_encrypt_flags_t @var{flags}}, @
	@w{gpgme_data_t @var{plain}}, @w{gpgme_data_t @var{cipher}})

	@since{1.11.0}

	This is an extended version of @code{gpgme_op_encrypt_sign_start} with
	@var{recpstring} as additional parameter. If @var{recp} is NULL and
	@var{recpstring} is not NULL, the latter is expected to be a linefeed
	delimited string with the set of key specifications. In contrast to
	@var{recp} the keys are given directly as strings and there is no need
	to first create the key objects. The keys are passed verbatim to the
	backend engine.

	@end deftypefun


	@node Miscellaneous
	@section Miscellaneous operations

	Here are some support functions which are sometimes useful.

	@menu
	* Running other Programs:: Running other Programs
	* Using the Assuan protocol:: Using the Assuan protocol
	* Checking for updates:: How to check for software updates
	@end menu


	@node Running other Programs
	@subsection Running other Programs

	GPGME features an internal subsystem to run the actual backend
	engines. Along with data abstraction object this subsystem can be
	used to run arbitrary simple programs which even need not be related
	to cryptographic features. It may for example be used to run tools
	which are part of the GnuPG system but are not directly accessible
	with the GPGME API.


	@deftypefun gpgme_error_t gpgme_op_spawn @
	(@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{file}}, @
	@w{const char *@var{argv}[]}, @w{gpgme_data_t @var{datain}}, @
	@w{gpgme_data_t @var{dataout}}, @w{gpgme_data_t @var{dataerr}}, @
	@w{unsigned int @var{flags}})

	@since{1.5.0}

	The function @code{gpgme_op_spawn} runs the program @var{file} with
	the arguments taken from the NULL terminated array @var{argv}. If no
	arguments are required @var{argv} may be given as @code{NULL}. In the
	latter case or if @code{argv[0]} is the empty string, GPGME uses the
	basename of @var{file} for @code{argv[0]}. The file descriptors
	@code{stdin}, @code{stdout}, and @code{stderr} are connected to the
	data objects @var{datain}, @var{dataout}, and @var{dataerr}. If NULL
	is passed for one of these data objects the corresponding file
	descriptor is connected to @file{/dev/null}.

	The value in @var{flags} is a bitwise-or combination of one or
	multiple of the following bit values:

	@table @code
	@item GPGME_SPAWN_DETACHED
	@since{1.5.0}

	Under Windows this flag inhibits the allocation of a new console for
	the program. This is useful for a GUI application which needs to call
	a command line helper tool.

	@item GPGME_SPAWN_ALLOW_SET_FG
	@since{1.5.0}

	Under Windows this flag allows the called program to put itself into
	the foreground.
	@end table
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_spawn_start @
	(@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{file}}, @
	@w{const char *@var{argv}[]}, @w{gpgme_data_t @var{datain}}, @
	@w{gpgme_data_t @var{dataout}}, @w{gpgme_data_t @var{dataerr}}, @
	@w{unsigned int @var{flags}})

	@since{1.5.0}

	This is the asynchronous variant of @code{gpgme_op_spawn}.
	@end deftypefun


	@node Using the Assuan protocol
	@subsection Using the Assuan protocol

	The Assuan protocol can be used to talk to arbitrary Assuan servers.
	By default it is connected to the GnuPG agent, but it may be connected
	to arbitrary servers by using @code{gpgme_ctx_set_engine_info},
	passing the location of the servers socket as @var{file_name}
	argument, and an empty string as @var{home_dir} argument.

	The Assuan protocol functions use three kinds of callbacks to transfer
	data:

	@deftp {Data type} {gpgme_error_t (*gpgme_assuan_data_cb_t) @
	(@w{void @var{opaque}}, @w{const void @var{data}}, @
	@w{size_t @var{datalen}})}

	@since{1.2.0}

	This callback receives any data sent by the server. @var{opaque} is
	the pointer passed to @code{gpgme_op_assuan_transact_start},
	@var{data} of length @var{datalen} refers to the data sent.
	@end deftp

	@deftp {Data type} {gpgme_error_t (*gpgme_assuan_inquire_cb_t) @
	(@w{void @var{opaque}}, @w{const char @var{name}}, @
	@w{const char @var{args}}, @w{gpgme_data_t @var{r_data}})}

	@since{1.2.0}

	This callback is used to provide additional data to the Assuan server.
	@var{opaque} is the pointer passed to
	@code{gpgme_op_assuan_transact_start}, @var{name} and @var{args}
	specify what kind of data the server requested, and @var{r_data} is
	used to return the actual data.

	Note: Returning data is currently not implemented in @acronym{GPGME}.
	@end deftp

	@deftp {Data type} {gpgme_error_t (*gpgme_assuan_status_cb_t) @
	(@w{void @var{opaque}}, @w{const char @var{status}}, @
	@w{const char *@var{args}})}

	@since{1.2.0}

	This callback receives any status lines sent by the server.
	@var{opaque} is the pointer passed to
	@code{gpgme_op_assuan_transact_start}, @var{status} and @var{args}
	denote the status update sent.
	@end deftp

	@deftypefun gpgme_error_t gpgme_op_assuan_transact_start @
	(@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{command}}, @
	@w{gpgme_assuan_data_cb_t @var{data_cb}}, @
	@w{void * @var{data_cb_value}}, @
	@w{gpgme_assuan_inquire_cb_t @var{inquire_cb}}, @
	@w{void * @var{inquire_cb_value}}, @
	@w{gpgme_assuan_status_cb_t @var{status_cb}}, @
	@w{void * @var{status_cb_value}})

	@since{1.2.0}

	Send the Assuan @var{command} and return results via the callbacks.
	Any callback may be @code{NULL}. The result of the operation may be
	retrieved using @code{gpgme_wait_ext}.

	Asynchronous variant.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_assuan_transact_ext @
	(@w{gpgme_ctx_t @var{ctx}}, @w{const char *@var{command}}, @
	@w{gpgme_assuan_data_cb_t @var{data_cb}}, @
	@w{void * @var{data_cb_value}}, @
	@w{gpgme_assuan_inquire_cb_t @var{inquire_cb}}, @
	@w{void * @var{inquire_cb_value}}, @
	@w{gpgme_assuan_status_cb_t @var{status_cb}}, @
	@w{void * @var{status_cb_value}}, @
	@w{gpgme_error_t *@var{op_err}})

	Send the Assuan @var{command} and return results via the callbacks.
	The result of the operation is returned in @var{op_err}.

	Synchronous variant.
	@end deftypefun


	@node Checking for updates
	@subsection How to check for software updates

	The GnuPG Project operates a server to query the current versions of
	software packages related to GnuPG. GPGME can be used to
	access this online database and check whether a new version of a
	software package is available.

	@deftp {Data type} {gpgme_query_swdb_result_t}
	@since{1.8.0}

	This is a pointer to a structure used to store the result of a
	@code{gpgme_op_query_swdb} operation. After success full call to that
	function, you can retrieve the pointer to the result with
	@code{gpgme_op_query_swdb_result}. The structure contains the
	following member:

	@table @code
	@item name
	This is the name of the package.

	@item iversion
	The currently installed version or an empty string. This value is
	either a copy of the argument given to @code{gpgme_op_query_swdb} or
	the version of the installed software as figured out by GPGME or GnuPG.

	@item created
	This gives the date the file with the list of version numbers has
	originally be created by the GnuPG project.

	@item retrieved
	This gives the date the file was downloaded.

	@item warning
	If this flag is set either an error has occurred or some of the
	information in this structure are not properly set. For example if
	the version number of the installed software could not be figured out,
	the @code{update} flag may not reflect a required update status.

	@item update
	If this flag is set an update of the software is available.

	@item urgent
	If this flag is set an available update is important.

	@item noinfo
	If this flag is set, no valid information could be retrieved.

	@item unknown
	If this flag is set the given @code{name} is not known.

	@item tooold
	If this flag is set the available information is not fresh enough.

	@item error
	If this flag is set some other error has occurred.

	@item version
	The version string of the latest released version.

	@item reldate
	The release date of the latest released version.

	@end table
	@end deftp

	@deftypefun gpgme_error_t gpgme_op_query_swdb @
	(@w{gpgme_ctx_t @var{ctx}}, @
	@w{const char *@var{name}}, @
	@w{const char *@var{iversion}}, @
	@w{gpgme_data_t @var{reserved}})

	@since{1.8.0}

	Query the software version database for software package @var{name}
	and check against the installed version given by @var{iversion}. If
	@var{iversion} is given as @code{NULL} a check is only done if GPGME
	can figure out the version by itself (for example when using
	"gpgme" or "gnupg"). If @code{NULL} is used for @var{name} the
	current gpgme version is checked. @var{reserved} must be set to 0.

	@end deftypefun

	@deftypefun gpgme_query_swdb_result_t gpgme_op_query_swdb_result @
	(@w{gpgme_ctx_t @var{ctx}})

	@since{1.8.0}

	The function @code{gpgme_op_query_swdb_result} returns a
	@code{gpgme_query_swdb_result_t} pointer to a structure holding the
	result of a @code{gpgme_op_query_swdb} operation. The pointer is only
	valid if the last operation on the context was a successful call to
	@code{gpgme_op_query_swdb}. If that call failed, the result might
	be a @code{NULL} pointer. The returned pointer is only valid until
	the next operation is started on the context @var{ctx}.
	@end deftypefun

	@noindent
	Here is an example on how to check whether GnuPG is current:

	@example
	#include <gpgme.h>

	int
	main (void)
	@{
	gpg_error_t err;
	gpgme_ctx_t ctx;
	gpgme_query_swdb_result_t result;

	gpgme_check_version (NULL);
	err = gpgme_new (&ctx);
	if (err)
	fprintf (stderr, "error creating context: %s\n", gpg_strerror (err));
	else
	@{
	gpgme_set_protocol (ctx, GPGME_PROTOCOL_GPGCONF);

	err = gpgme_op_query_swdb (ctx, "gnupg", NULL, 0);
	if (err)
	fprintf (stderr, "error querying swdb: %s\n", gpg_strerror (err));
	else
	@{
	result = gpgme_op_query_swdb_result (ctx);
	if (!result)
	fprintf (stderr, "error querying swdb\n");
	if (!result->warning && !result->update)
	printf ("GnuPG version %s is current\n",
	result->iversion);
	else if (!result->warning && result->update)
	printf ("GnuPG version %s can be updated to %s\n",
	result->iversion, result->version);
	else
	fprintf (stderr, "error finding the update status\n");
	@}
	gpgme_release (ctx);
	@}
	return 0;
	@}
	@end example


	@node Run Control
	@section Run Control
	@cindex run control
	@cindex cryptographic operation, running

	@acronym{GPGME} supports running operations synchronously and
	asynchronously. You can use asynchronous operation to set up a
	context up to initiating the desired operation, but delay performing
	it to a later point.

	Furthermore, you can use an external event loop to control exactly
	when @acronym{GPGME} runs. This ensures that @acronym{GPGME} only
	runs when necessary and also prevents it from blocking for a long
	time.

	@menu
	* Waiting For Completion:: Waiting until an operation is completed.
	* Using External Event Loops:: Advanced control over what happens when.
	* Cancellation:: How to end pending operations prematurely.
	@end menu


	@node Waiting For Completion
	@subsection Waiting For Completion
	@cindex cryptographic operation, wait for
	@cindex wait for completion

	@deftypefun gpgme_ctx_t gpgme_wait (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_error_t *@var{status}}, @w{int @var{hang}})
	The function @code{gpgme_wait} continues the pending operation within
	the context @var{ctx}. In particular, it ensures the data exchange
	between @acronym{GPGME} and the crypto backend and watches over the
	run time status of the backend process.

	If @var{hang} is true, the function does not return until the
	operation is completed or cancelled. Otherwise the function will not
	block for a long time.

	The error status of the finished operation is returned in @var{status}
	if @code{gpgme_wait} does not return @code{NULL}.

	The @var{ctx} argument can be @code{NULL}. In that case,
	@code{gpgme_wait} waits for any context to complete its operation.

	@code{gpgme_wait} can be used only in conjunction with any context
	that has a pending operation initiated with one of the
	@code{gpgme_op_*_start} functions except @code{gpgme_op_keylist_start}
	and @code{gpgme_op_trustlist_start} (for which you should use the
	corresponding @code{gpgme_op_*_next} functions). If @var{ctx} is
	@code{NULL}, all of such contexts are waited upon and possibly
	returned. Synchronous operations running in parallel, as well as key
	and trust item list operations, do not affect @code{gpgme_wait}.

	In a multi-threaded environment, only one thread should ever call
	@code{gpgme_wait} at any time, regardless of whether @var{ctx} is specified
	or not. This means that all calls to this function should be fully
	synchronized by locking primitives. It is safe to start asynchronous
	operations while a thread is running in @code{gpgme_wait}.

	The function returns the @var{ctx} of the context which has finished
	the operation. If @var{hang} is false, and the timeout expires,
	@code{NULL} is returned and @code{*status} will be set to 0. If an
	error occurs, @code{NULL} is returned and the error is returned in
	@code{*status}.
	@end deftypefun


	@node Using External Event Loops
	@subsection Using External Event Loops
	@cindex event loop, external

	@acronym{GPGME} hides the complexity of the communication between the
	library and the crypto engine. The price of this convenience is that
	the calling thread can block arbitrary long waiting for the data
	returned by the crypto engine. In single-threaded programs, in
	particular if they are interactive, this is an unwanted side-effect.
	OTOH, if @code{gpgme_wait} is used without the @var{hang} option being
	enabled, it might be called unnecessarily often, wasting CPU time that
	could be used otherwise.

	The I/O callback interface described in this section lets the user
	take control over what happens when. @acronym{GPGME} will provide the
	user with the file descriptors that should be monitored, and the
	callback functions that should be invoked when a file descriptor is
	ready for reading or writing. It is then the user's responsibility to
	decide when to check the file descriptors and when to invoke the
	callback functions. Usually this is done in an event loop, that also
	checks for events in other parts of the program. If the callback
	functions are only called when the file descriptors are ready,
	@acronym{GPGME} will never block. This gives the user more control
	over the program flow, and allows to perform other tasks when
	@acronym{GPGME} would block otherwise.

	By using this advanced mechanism, @acronym{GPGME} can be integrated
	smoothly into GUI toolkits like GTK+ even for single-threaded
	programs.

	@menu
	* I/O Callback Interface:: How I/O callbacks are registered.
	* Registering I/O Callbacks:: How to use I/O callbacks for a context.
	* I/O Callback Example:: An example how to use I/O callbacks.
	* I/O Callback Example GTK+:: How to use @acronym{GPGME} with GTK+.
	* I/O Callback Example GDK:: How to use @acronym{GPGME} with GDK.
	* I/O Callback Example Qt:: How to use @acronym{GPGME} with Qt.
	@end menu


	@node I/O Callback Interface
	@subsubsection I/O Callback Interface

	@deftp {Data type} {gpgme_error_t (gpgme_io_cb_t) (@w{void @var{data}}, @w{int @var{fd}})}
	@tindex gpgme_io_cb_t
	The @code{gpgme_io_cb_t} type is the type of functions which
	@acronym{GPGME} wants to register as I/O callback handlers using the
	@code{gpgme_register_io_cb_t} functions provided by the user.

	@var{data} and @var{fd} are provided by @acronym{GPGME} when the I/O
	callback handler is registered, and should be passed through to the
	handler when it is invoked by the user because it noticed activity on
	the file descriptor @var{fd}.

	The callback handler always returns @code{0}, but you should consider
	the return value to be reserved for later use.
	@end deftp

	@deftp {Data type} {gpgme_error_t (gpgme_register_io_cb_t) (@w{void @var{data}}, @w{int @var{fd}}, @w{int @var{dir}}, @w{gpgme_io_cb_t @var{fnc}}, @w{void @var{fnc_data}}, @w{void *@var{tag}})}
	@tindex gpgme_register_io_cb_t
	The @code{gpgme_register_io_cb_t} type is the type of functions which can
	be called by @acronym{GPGME} to register an I/O callback function
	@var{fnc} for the file descriptor @var{fd} with the user.
	@var{fnc_data} should be passed as the first argument to @var{fnc}
	when the handler is invoked (the second argument should be @var{fd}).
	If @var{dir} is 0, @var{fnc} should be called by the user when
	@var{fd} is ready for writing. If @var{dir} is 1, @var{fnc} should be
	called when @var{fd} is ready for reading.

	@var{data} was provided by the user when registering the
	@code{gpgme_register_io_cb_t} function with @acronym{GPGME} and will always
	be passed as the first argument when registering a callback function.
	For example, the user can use this to determine the event loop to
	which the file descriptor should be added.

	@acronym{GPGME} will call this function when a crypto operation is
	initiated in a context for which the user has registered I/O callback
	handler functions with @code{gpgme_set_io_cbs}. It can also call this
	function when it is in an I/O callback handler for a file descriptor
	associated to this context.

	The user should return a unique handle in @var{tag} identifying this
	I/O callback registration, which will be passed to the
	@code{gpgme_register_io_cb_t} function without interpretation when the file
	descriptor should not be monitored anymore.
	@end deftp

	@deftp {Data type} {void (gpgme_remove_io_cb_t) (@w{void @var{tag}})}
	The @code{gpgme_remove_io_cb_t} type is the type of functions which can be
	called by @acronym{GPGME} to remove an I/O callback handler that was
	registered before. @var{tag} is the handle that was returned by the
	@code{gpgme_register_io_cb_t} for this I/O callback.

	@acronym{GPGME} can call this function when a crypto operation is in
	an I/O callback. It will also call this function when the context is
	destroyed while an operation is pending.
	@end deftp

	@deftp {Data type} {enum gpgme_event_io_t}
	@tindex gpgme_event_io_t
	The @code{gpgme_event_io_t} type specifies the type of an event that is
	reported to the user by @acronym{GPGME} as a consequence of an I/O
	operation. The following events are defined:

	@table @code
	@item GPGME_EVENT_START
	The operation is fully initialized now, and you can start to run the
	registered I/O callback handlers now. Note that registered I/O
	callback handlers must not be run before this event is signalled.
	@var{type_data} is @code{NULL} and reserved for later use.

	@item GPGME_EVENT_DONE
	The operation is finished, the last I/O callback for this operation
	was removed. The accompanying @var{type_data} points to a
	@code{struct gpgme_io_event_done_data} variable that contains the
	status of the operation that finished. This event is signalled after
	the last I/O callback has been removed.

	@item GPGME_EVENT_NEXT_KEY
	In a @code{gpgme_op_keylist_start} operation, the next key was
	received from the crypto engine. The accompanying @var{type_data} is
	a @code{gpgme_key_t} variable that contains the key with one reference
	for the user.

	@end table
	@end deftp

	@deftp {Data type} {void (gpgme_event_io_cb_t) (@w{void @var{data}}, @w{gpgme_event_io_t @var{type}}, @w{void *@var{type_data}})}
	The @code{gpgme_event_io_cb_t} type is the type of functions which can be
	called by @acronym{GPGME} to signal an event for an operation running
	in a context which has I/O callback functions registered by the user.

	@var{data} was provided by the user when registering the
	@code{gpgme_event_io_cb_t} function with @acronym{GPGME} and will always be
	passed as the first argument when registering a callback function.
	For example, the user can use this to determine the context in which
	this event has occurred.

	@var{type} will specify the type of event that has occurred.
	@var{type_data} specifies the event further, as described in the above
	list of possible @code{gpgme_event_io_t} types.

	@acronym{GPGME} can call this function in an I/O callback handler.
	@end deftp


	@node Registering I/O Callbacks
	@subsubsection Registering I/O Callbacks

	@deftp {Data type} {struct gpgme_io_cbs}
	@tindex gpgme_event_io_t
	This structure is used to store the I/O callback interface functions
	described in the previous section. It has the following members:

	@table @code
	@item gpgme_register_io_cb_t add
	This is the function called by @acronym{GPGME} to register an I/O
	callback handler. It must be specified.

	@item void *add_priv
	This is passed as the first argument to the @code{add} function when
	it is called by @acronym{GPGME}. For example, it can be used to
	determine the event loop to which the file descriptor should be added.

	@item gpgme_remove_io_cb_t remove
	This is the function called by @acronym{GPGME} to remove an I/O
	callback handler. It must be specified.

	@item gpgme_event_io_cb_t event
	This is the function called by @acronym{GPGME} to signal an event for
	an operation. It must be specified, because at least the start event
	must be processed.

	@item void *event_priv
	This is passed as the first argument to the @code{event} function when
	it is called by @acronym{GPGME}. For example, it can be used to
	determine the context in which the event has occurred.
	@end table
	@end deftp

	@deftypefun void gpgme_set_io_cbs (@w{gpgme_ctx_t @var{ctx}}, @w{struct gpgme_io_cbs *@var{io_cbs}})
	The function @code{gpgme_set_io_cbs} enables the I/O callback
	interface for the context @var{ctx}. The I/O callback functions are
	specified by @var{io_cbs}.

	If @var{io_cbs}->@code{add} is @code{NULL}, the I/O callback interface
	is disabled for the context, and normal operation is restored.
	@end deftypefun

	@deftypefun void gpgme_get_io_cbs (@w{gpgme_ctx_t @var{ctx}}, @w{struct gpgme_io_cbs *@var{io_cbs}})
	The function @code{gpgme_get_io_cbs} returns the I/O callback
	functions set with @code{gpgme_set_io_cbs} in @var{io_cbs}.
	@end deftypefun


	@node I/O Callback Example
	@subsubsection I/O Callback Example

	To actually use an external event loop, you have to implement the I/O
	callback functions that are used by @acronym{GPGME} to register and
	unregister file descriptors. Furthermore, you have to actually
	monitor these file descriptors for activity and call the appropriate
	I/O callbacks.

	The following example illustrates how to do that. The example uses
	locking to show in which way the callbacks and the event loop can
	run concurrently. For the event loop, we use a fixed array. For a
	real-world implementation, you should use a dynamically sized
	structure because the number of file descriptors needed for a crypto
	operation in @acronym{GPGME} is not predictable.

	@example
	#include <assert.h>
	#include <errno.h>
	#include <stdlib.h>
	#include <pthread.h>
	#include <sys/types.h>
	#include <gpgme.h>

	/* The following structure holds the result of a crypto operation. */
	struct op_result
	@{
	int done;
	gpgme_error_t err;
	@};

	/* The following structure holds the data associated with one I/O
	callback. */
	struct one_fd
	@{
	int fd;
	int dir;
	gpgme_io_cb_t fnc;
	void *fnc_data;
	void *loop;
	@};

	struct event_loop
	@{
	pthread_mutex_t lock;
	#define MAX_FDS 32
	/* Unused slots are marked with FD being -1. */
	struct one_fd fds[MAX_FDS];
	@};
	@end example

	The following functions implement the I/O callback interface.

	@example
	gpgme_error_t
	add_io_cb (void data, int fd, int dir, gpgme_io_cb_t fnc, void fnc_data,
	void **r_tag)
	@{
	struct event_loop *loop = data;
	struct one_fd *fds = loop->fds;
	int i;

	pthread_mutex_lock (&loop->lock);
	for (i = 0; i < MAX_FDS; i++)
	@{
	if (fds[i].fd == -1)
	@{
	fds[i].fd = fd;
	fds[i].dir = dir;
	fds[i].fnc = fnc;
	fds[i].fnc_data = fnc_data;
	fds[i].loop = loop;
	break;
	@}
	@}
	pthread_mutex_unlock (&loop->lock);
	if (i == MAX_FDS)
	return gpg_error (GPG_ERR_GENERAL);
	*r_tag = &fds[i];
	return 0;
	@}

	void
	remove_io_cb (void *tag)
	@{
	struct one_fd *fd = tag;
	struct event_loop *loop = fd->loop;

	pthread_mutex_lock (&loop->lock);
	fd->fd = -1;
	pthread_mutex_unlock (&loop->lock);
	@}

	void
	event_io_cb (void data, gpgme_event_io_t type, void type_data)
	@{
	struct op_result *result = data;

	/* We don't support list operations here. */
	if (type == GPGME_EVENT_DONE)
	@{
	result->done = 1;
	result->err = *type_data;
	@}
	@}
	@end example

	The final missing piece is the event loop, which will be presented
	next. We only support waiting for the success of a single operation.

	@example
	int
	do_select (struct event_loop *loop)
	@{
	fd_set rfds;
	fd_set wfds;
	int i, n;
	int any = 0;
	struct timeval tv;
	struct one_fd *fdlist = loop->fds;

	pthread_mutex_lock (&loop->lock);
	FD_ZERO (&rfds);
	FD_ZERO (&wfds);
	for (i = 0; i < MAX_FDS; i++)
	if (fdlist[i].fd != -1)
	FD_SET (fdlist[i].fd, fdlist[i].dir ? &rfds : &wfds);
	pthread_mutex_unlock (&loop->lock);

	tv.tv_sec = 0;
	tv.tv_usec = 1000;

	do
	@{
	n = select (FD_SETSIZE, &rfds, &wfds, NULL, &tv);
	@}
	while (n < 0 && errno == EINTR);

	if (n < 0)
	return n; /* Error or timeout. */

	pthread_mutex_lock (&loop->lock);
	for (i = 0; i < MAX_FDS && n; i++)
	@{
	if (fdlist[i].fd != -1)
	@{
	if (FD_ISSET (fdlist[i].fd, fdlist[i].dir ? &rfds : &wfds))
	@{
	assert (n);
	n--;
	any = 1;
	/* The I/O callback handler can register/remove callbacks,
	so we have to unlock the file descriptor list. */
	pthread_mutex_unlock (&loop->lock);
	(*fdlist[i].fnc) (fdlist[i].fnc_data, fdlist[i].fd);
	pthread_mutex_lock (&loop->lock);
	@}
	@}
	@}
	pthread_mutex_unlock (&loop->lock);
	return any;
	@}

	void
	wait_for_op (struct event_loop loop, struct op_result result)
	@{
	int ret;

	do
	@{
	ret = do_select (loop);
	@}
	while (ret >= 0 && !result->done);
	@}
	@end example

	The main function shows how to put it all together.

	@example
	int
	main (int argc, char *argv[])
	@{
	struct event_loop loop;
	struct op_result result;
	gpgme_ctx_t ctx;
	gpgme_error_t err;
	gpgme_data_t sig, text;
	int i;
	pthread_mutexattr_t attr;
	struct gpgme_io_cbs io_cbs =
	@{
	add_io_cb,
	&loop,
	remove_io_cb,
	event_io_cb,
	&result
	@};

	init_gpgme ();

	/* Initialize the loop structure. */

	/* The mutex must be recursive, since remove_io_cb (which acquires a
	lock) can be called while holding a lock acquired in do_select. */
	pthread_mutexattr_init (&attr);
	pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_RECURSIVE);
	pthread_mutex_init (&loop.lock, &attr);
	pthread_mutexattr_destroy (&attr);

	for (i = 0; i < MAX_FDS; i++)
	loop.fds[i].fd = -1;

	/* Initialize the result structure. */
	result.done = 0;

	err = gpgme_data_new_from_file (&sig, "signature", 1);
	if (!err)
	err = gpgme_data_new_from_file (&text, "text", 1);
	if (!err)
	err = gpgme_new (&ctx);
	if (!err)
	@{
	gpgme_set_io_cbs (ctx, &io_cbs);
	err = gpgme_op_verify_start (ctx, sig, text, NULL);
	@}
	if (err)
	@{
	fprintf (stderr, "gpgme error: %s: %s\n",
	gpgme_strsource (err), gpgme_strerror (err));
	exit (1);
	@}

	wait_for_op (&loop, &result);
	if (!result.done)
	@{
	fprintf (stderr, "select error\n");
	exit (1);
	@}
	if (!result.err)
	@{
	fprintf (stderr, "verification failed: %s: %s\n",
	gpgme_strsource (result.err), gpgme_strerror (result.err));
	exit (1);
	@}
	/* Evaluate verify result. */
	@dots{}
	return 0;
	@}
	@end example


	@node I/O Callback Example GTK+
	@subsubsection I/O Callback Example GTK+
	@cindex GTK+, using @acronym{GPGME} with

	The I/O callback interface can be used to integrate @acronym{GPGME}
	with the GTK+ event loop. The following code snippets shows how this
	can be done using the appropriate register and remove I/O callback
	functions. In this example, the private data of the register I/O
	callback function is unused. The event notifications is missing
	because it does not require any GTK+ specific setup.

	@example
	#include <gtk/gtk.h>

	struct my_gpgme_io_cb
	@{
	gpgme_io_cb_t fnc;
	void *fnc_data;
	guint input_handler_id
	@};

	void
	my_gpgme_io_cb (gpointer data, gint source, GdkInputCondition condition)
	@{
	struct my_gpgme_io_cb *iocb = data;
	(*(iocb->fnc)) (iocb->data, source);
	@}

	void
	my_gpgme_remove_io_cb (void *data)
	@{
	struct my_gpgme_io_cb *iocb = data;
	gtk_input_remove (data->input_handler_id);
	@}

	void
	my_gpgme_register_io_callback (void *data, int fd, int dir, gpgme_io_cb_t fnc,
	void fnc_data, void *tag)
	@{
	struct my_gpgme_io_cb *iocb = g_malloc (sizeof (struct my_gpgme_io_cb));
	iocb->fnc = fnc;
	iocb->data = fnc_data;
	iocb->input_handler_id = gtk_input_add_full (fd, dir
	? GDK_INPUT_READ
	: GDK_INPUT_WRITE,
	my_gpgme_io_callback,
	0, iocb, NULL);
	*tag = iocb;
	return 0;
	@}
	@end example


	@node I/O Callback Example GDK
	@subsubsection I/O Callback Example GDK
	@cindex GDK, using @acronym{GPGME} with

	The I/O callback interface can also be used to integrate
	@acronym{GPGME} with the GDK event loop. The following code snippets
	shows how this can be done using the appropriate register and remove
	I/O callback functions. In this example, the private data of the
	register I/O callback function is unused. The event notifications is
	missing because it does not require any GDK specific setup.

	It is very similar to the GTK+ example in the previous section.

	@example
	#include <gdk/gdk.h>

	struct my_gpgme_io_cb
	@{
	gpgme_io_cb_t fnc;
	void *fnc_data;
	gint tag;
	@};

	void
	my_gpgme_io_cb (gpointer data, gint source, GdkInputCondition condition)
	@{
	struct my_gpgme_io_cb *iocb = data;
	(*(iocb->fnc)) (iocb->data, source);
	@}

	void
	my_gpgme_remove_io_cb (void *data)
	@{
	struct my_gpgme_io_cb *iocb = data;
	gdk_input_remove (data->tag);
	@}

	void
	my_gpgme_register_io_callback (void *data, int fd, int dir, gpgme_io_cb_t fnc,
	void fnc_data, void *tag)
	@{
	struct my_gpgme_io_cb *iocb = g_malloc (sizeof (struct my_gpgme_io_cb));
	iocb->fnc = fnc;
	iocb->data = fnc_data;
	iocb->tag = gtk_input_add_full (fd, dir ? GDK_INPUT_READ : GDK_INPUT_WRITE,
	my_gpgme_io_callback, iocb, NULL);
	*tag = iocb;
	return 0;
	@}
	@end example


	@node I/O Callback Example Qt
	@subsubsection I/O Callback Example Qt
	@cindex Qt, using @acronym{GPGME} with

	The I/O callback interface can also be used to integrate
	@acronym{GPGME} with the Qt event loop. The following code snippets
	show how this can be done using the appropriate register and remove
	I/O callback functions. In this example, the private data of the
	register I/O callback function is unused. The event notifications is
	missing because it does not require any Qt specific setup.

	@example
	#include <qsocketnotifier.h>
	#include <qapplication.h>

	struct IOCB @{
	IOCB( GpgmeIOCb f, void * d, QSocketNotifier * n )
	: func( f ), data( d ), notifier( n ) @{@}
	GpgmeIOCb func;
	void * data;
	QSocketNotifier * notifier;
	@}

	class MyApp : public QApplication @{

	// ...

	static void registerGpgmeIOCallback( void * data, int fd, int dir,
	GpgmeIOCb func, void * func_data,
	void ** tag ) @{
	QSocketNotifier * n =
	new QSocketNotifier( fd, dir ? QSocketNotifier::Read
	: QSocketNotifier::Write );
	connect( n, SIGNAL(activated(int)),
	qApp, SLOT(slotGpgmeIOCallback(int)) );
	qApp->mIOCBs.push_back( IOCB( func, func_data, n ) );
	tag = (void)n;
	@}

	static void removeGpgmeIOCallback( void * tag ) @{
	if ( !tag ) return;
	QSocketNotifier * n = static_cast<QSocketNotifier*>( tag );
	for ( QValueList<IOCB>::iterator it = qApp->mIOCBs.begin() ;
	it != qApp->mIOCBs.end() ; ++it )
	if ( it->notifier == n ) @{
	delete it->notifier;
	qApp->mIOCBs.erase( it );
	return;
	@}
	@}

	public slots:
	void slotGpgmeIOCallback( int fd ) @{
	for ( QValueList<IOCB>::const_iterator it = mIOCBs.begin() ;
	it != mIOCBs.end() ; ++it )
	if ( it->notifier && it->notifier->socket() == fd )
	(*(it->func)) ( it->func_data, fd );
	@}

	// ...

	private:
	QValueList<IOCB> mIOCBs;
	// ...
	@};
	@end example


	@node Cancellation
	@subsection Cancellation
	@cindex cryptographic operation, aborting
	@cindex cryptographic operation, cancelling
	@cindex aborting operations
	@cindex cancelling operations

	Sometimes you do not want to wait for an operation to finish.
	@acronym{GPGME} provides two different functions to achieve that. The
	function @code{gpgme_cancel} takes effect immediately. When it
	returns, the operation is effectively canceled. However, it has some
	limitations and can not be used with synchronous operations. In
	contrast, the function @code{gpgme_cancel_async} can be used with any
	context and from any thread, but it is not guaranteed to take effect
	immediately. Instead, cancellation occurs at the next possible time
	(typically the next time I/O occurs in the target context).

	@deftypefun gpgme_ctx_t gpgme_cancel (@w{gpgme_ctx_t @var{ctx}})
	@since{0.4.5}

	The function @code{gpgme_cancel} attempts to cancel a pending
	operation in the context @var{ctx}. This only works if you use the
	global event loop or your own event loop.

	If you use the global event loop, you must not call @code{gpgme_wait}
	during cancellation. After successful
	cancellation, you can call @code{gpgme_wait} (optionally waiting on
	@var{ctx}), and the context @var{ctx} will appear as if it had
	finished with the error code @code{GPG_ERR_CANCEL}.

	If you use an external event loop, you must ensure that no I/O
	callbacks are invoked for this context (for example by halting the
	event loop). On successful cancellation, all registered I/O callbacks
	for this context will be unregistered, and a @code{GPGME_EVENT_DONE}
	event with the error code @code{GPG_ERR_CANCEL} will be signalled.

	The function returns an error code if the cancellation failed (in this
	case the state of @var{ctx} is not modified).
	@end deftypefun


	@deftypefun gpgme_ctx_t gpgme_cancel_async (@w{gpgme_ctx_t @var{ctx}})
	@since{1.1.7}

	The function @code{gpgme_cancel_async} attempts to cancel a pending
	operation in the context @var{ctx}. This can be called by any thread
	at any time after starting an operation on the context, but will not
	take effect immediately. The actual cancellation happens at the next
	time GPGME processes I/O in that context.

	The function returns an error code if the cancellation failed (in this
	case the state of @var{ctx} is not modified).
	@end deftypefun

	@c **********************************************************
	@c ***************** Appendices ***********************
	@c **********************************************************

	@include uiserver.texi

	@node Debugging
	@appendix How to solve problems
	@cindex debug
	@cindex GPGME_DEBUG

	Everyone knows that software often does not do what it should do and thus
	there is a need to track down problems. This is in particular true
	for applications using a complex library like @acronym{GPGME} and of
	course also for the library itself. Here we give a few hints on how
	to solve such problems.

	First of all you should make sure that the keys you want to use are
	installed in the GnuPG engine and are usable. Thus the first test is
	to run the desired operation using @command{gpg} or @command{gpgsm} on
	the command line. If you can't figure out why things don't work, you
	may use @acronym{GPGME}'s built in trace feature. This feature is
	either enabled using the environment variable @code{GPGME_DEBUG} or,
	if this is not possible, by calling the function
	@code{gpgme_set_global_flag}. The value is the trace level and
	an optional file name. If no file name is given the trace output is
	printed to @code{stderr}.

	@noindent
	For example
	@smallexample
	GPGME_DEBUG=9:/home/user/mygpgme.log
	@end smallexample
	@noindent
	(Note that under Windows you use a semicolon in place of the colon to
	separate the fields.)

	A trace level of 9 is pretty verbose and thus you may want to start
	off with a lower level. The exact definition of the trace levels and
	the output format may change with any release; you need to check the
	source code for details. In any case the trace log should be helpful
	to understand what is going going on. Warning: The trace log may
	reveal sensitive details like passphrases or other data you use in
	your application. If you are asked to send a log file, make sure that
	you run your tests only with play data.


	@node Deprecated Functions
	@appendix Deprecated Functions
	@cindex deprecated

	For backward compatibility @acronym{GPGME} has a number of functions,
	data types and constants which are deprecated and should not be used
	anymore. We document here those which are really old to help
	understanding old code and to allow migration to their modern
	counterparts.

	@strong{Warning:} These interfaces will be removed in a future version
	of @acronym{GPGME}.

	@deftypefun void gpgme_key_release (@w{gpgme_key_t @var{key}})
	The function @code{gpgme_key_release} is equivalent to
	@code{gpgme_key_unref}.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_import_ext (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_data_t @var{keydata}}, @w{int *@var{nr}})
	@since{0.3.9}

	The function @code{gpgme_op_import_ext} is equivalent to:

	@example
	gpgme_error_t err = gpgme_op_import (ctx, keydata);
	if (!err)
	@{
	gpgme_import_result_t result = gpgme_op_import_result (ctx);
	*nr = result->considered;
	@}
	@end example
	@end deftypefun


	@deftp {Data type} {gpgme_error_t (*gpgme_edit_cb_t) @
	(@w{void *@var{handle}}, @
	@w{gpgme_status_code_t @var{status}}, @
	@w{const char *@var{args}}, @
	@w{int @var{fd}})}
	@tindex gpgme_edit_cb_t
	The @code{gpgme_edit_cb_t} type is the type of functions which
	@acronym{GPGME} calls if it a key edit operation is on-going. The
	status code @var{status} and the argument line @var{args} are passed
	through by @acronym{GPGME} from the crypto engine. The file
	descriptor @var{fd} is -1 for normal status messages. If @var{status}
	indicates a command rather than a status message, the response to the
	command should be written to @var{fd}. The @var{handle} is provided
	by the user at start of operation.

	The function should return @code{GPG_ERR_FALSE} if it did not handle
	the status code, @code{0} for success, or any other error value.
	@end deftp

	@deftypefun gpgme_error_t gpgme_op_edit (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{key}}, @w{gpgme_edit_cb_t @var{fnc}}, @w{void *@var{handle}}, @w{gpgme_data_t @var{out}})
	@since{0.3.9}

	Note: This function is deprecated, please use
	@code{gpgme_op_interact} instead.

	The function @code{gpgme_op_edit} processes the key @var{KEY}
	interactively, using the edit callback function @var{FNC} with the
	handle @var{HANDLE}. The callback is invoked for every status and
	command request from the crypto engine. The output of the crypto
	engine is written to the data object @var{out}.

	Note that the protocol between the callback function and the crypto
	engine is specific to the crypto engine and no further support in
	implementing this protocol correctly is provided by @acronym{GPGME}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	edit operation completes successfully, @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{key} is not a valid pointer, and any error returned
	by the crypto engine or the edit callback handler.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_edit_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{key}}, @w{gpgme_edit_cb_t @var{fnc}}, @w{void *@var{handle}}, @w{gpgme_data_t @var{out}})

	@since{0.3.9}

	Note: This function is deprecated, please use
	@code{gpgme_op_interact_start} instead.

	The function @code{gpgme_op_edit_start} initiates a
	@code{gpgme_op_edit} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation was started successfully, and @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{key} is not a valid pointer.
	@end deftypefun


	@deftypefun gpgme_error_t gpgme_op_card_edit (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{key}}, @w{gpgme_edit_cb_t @var{fnc}}, @w{void *@var{handle}}, @w{gpgme_data_t @var{out}})
	Note: This function is deprecated, please use @code{gpgme_op_interact}
	with the flag @code{GPGME_INTERACT_CARD} instead.

	The function @code{gpgme_op_card_edit} is analogous to
	@code{gpgme_op_edit}, but should be used to process the smart card corresponding to the key @var{key}.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_op_card_edit_start (@w{gpgme_ctx_t @var{ctx}}, @w{gpgme_key_t @var{key}}, @w{gpgme_edit_cb_t @var{fnc}}, @w{void *@var{handle}}, @w{gpgme_data_t @var{out}})
	Note: This function is deprecated, please use @code{gpgme_op_interact_start}
	with the flag @code{GPGME_INTERACT_CARD} instead.

	The function @code{gpgme_op_card_edit_start} initiates a
	@code{gpgme_op_card_edit} operation. It can be completed by calling
	@code{gpgme_wait} on the context. @xref{Waiting For Completion}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	operation was started successfully, and @code{GPG_ERR_INV_VALUE} if
	@var{ctx} or @var{key} is not a valid pointer.
	@end deftypefun



	@deftypefun gpgme_error_t gpgme_data_new_with_read_cb (@w{gpgme_data_t @var{dh}}, @w{int (@var{readfunc})} (@w{void @var{hook}}, @w{char @var{buffer}}, @w{size_t @var{count}}, @w{size_t @var{nread}}), @w{void @var{hook_value}})
	The function @code{gpgme_data_new_with_read_cb} creates a new
	@code{gpgme_data_t} object and uses the callback function @var{readfunc}
	to retrieve the data on demand. As the callback function can supply
	the data in any way it wants, this is the most flexible data type
	@acronym{GPGME} provides. However, it can not be used to write data.

	The callback function receives @var{hook_value} as its first argument
	whenever it is invoked. It should return up to @var{count} bytes in
	@var{buffer}, and return the number of bytes actually read in
	@var{nread}. It may return @code{0} in @var{nread} if no data is
	currently available. To indicate @code{EOF} the function should
	return with an error code of @code{-1} and set @var{nread} to
	@code{0}. The callback function may support to reset its internal
	read pointer if it is invoked with @var{buffer} and @var{nread} being
	@code{NULL} and @var{count} being @code{0}.

	The function returns the error code @code{GPG_ERR_NO_ERROR} if the
	data object was successfully created, @code{GPG_ERR_INV_VALUE} if
	@var{dh} or @var{readfunc} is not a valid pointer, and
	@code{GPG_ERR_ENOMEM} if not enough memory is available.
	@end deftypefun

	@deftypefun gpgme_error_t gpgme_data_rewind (@w{gpgme_data_t @var{dh}})
	The function @code{gpgme_data_rewind} is equivalent to:

	@example
	return (gpgme_data_seek (dh, 0, SEEK_SET) == -1)
	? gpgme_error_from_errno (errno) : 0;
	@end example
	@end deftypefun


	@deftp {Data type} gpgme_attr_t
	The @code{gpgme_attr_t} type is used to specify a key or trust item
	attribute. The following attributes are defined:

	@table @code
	@item GPGME_ATTR_KEYID
	This is the key ID of a sub key. It is representable as a string.

	@item GPGME_ATTR_FPR
	This is the fingerprint of a sub key. It is representable as a
	string.

	@item GPGME_ATTR_ALGO
	This is the crypto algorithm for which the sub key can be used. It
	is representable as a string and as a number. The numbers correspond
	to the @code{enum gcry_pk_algos} values in the gcrypt library.

	@item GPGME_ATTR_LEN
	This is the key length of a sub key. It is representable as a
	number.

	@item GPGME_ATTR_CREATED
	This is the timestamp at creation time of a sub key. It is
	representable as a number.

	@item GPGME_ATTR_EXPIRE
	This is the expiration time of a sub key. It is representable as a
	number.

	@item GPGME_ATTR_USERID
	This is a user ID. There can be more than one user IDs in a
	@var{gpgme_key_t} object. The first one (with index 0) is the primary
	user ID. The user ID is representable as a number.

	@item GPGME_ATTR_NAME
	This is the name belonging to a user ID. It is representable as a string.

	@item GPGME_ATTR_EMAIL
	This is the email address belonging to a user ID. It is representable
	as a string.

	@item GPGME_ATTR_COMMENT
	This is the comment belonging to a user ID. It is representable as a
	string.

	@item GPGME_ATTR_VALIDITY
	This is the validity belonging to a user ID. It is representable as a
	string and as a number. See below for a list of available validities.

	@item GPGME_ATTR_UID_REVOKED
	This specifies if a user ID is revoked. It is representable as a
	number, and is @code{1} if the user ID is revoked, and @code{0}
	otherwise.

	@item GPGME_ATTR_UID_INVALID
	This specifies if a user ID is invalid. It is representable as a
	number, and is @code{1} if the user ID is invalid, and @code{0}
	otherwise.

	@item GPGME_ATTR_TYPE
	This returns information about the type of key. For the string function
	this will eother be "PGP" or "X.509". The integer function returns 0
	for PGP and 1 for X.509.

	@item GPGME_ATTR_IS_SECRET
	This specifies if the key is a secret key. It is representable as a
	number, and is @code{1} if the key is revoked, and @code{0} otherwise.

	@item GPGME_ATTR_KEY_REVOKED
	This specifies if a sub key is revoked. It is representable as a
	number, and is @code{1} if the key is revoked, and @code{0} otherwise.

	@item GPGME_ATTR_KEY_INVALID
	This specifies if a sub key is invalid. It is representable as a
	number, and is @code{1} if the key is invalid, and @code{0} otherwise.

	@item GPGME_ATTR_KEY_EXPIRED
	This specifies if a sub key is expired. It is representable as a
	number, and is @code{1} if the key is expired, and @code{0} otherwise.

	@item GPGME_ATTR_KEY_DISABLED
	This specifies if a sub key is disabled. It is representable as a
	number, and is @code{1} if the key is disabled, and @code{0} otherwise.

	@item GPGME_ATTR_KEY_CAPS
	This is a description of the capabilities of a sub key. It is
	representable as a string. The string contains the letter ``e'' if
	the key can be used for encryption, ``s'' if the key can be used for
	signatures, and ``c'' if the key can be used for certifications.

	@item GPGME_ATTR_CAN_ENCRYPT
	This specifies if a sub key can be used for encryption. It is
	representable as a number, and is @code{1} if the sub key can be used
	for encryption, and @code{0} otherwise.

	@item GPGME_ATTR_CAN_SIGN
	This specifies if a sub key can be used to create data signatures. It
	is representable as a number, and is @code{1} if the sub key can be
	used for signatures, and @code{0} otherwise.

	@item GPGME_ATTR_CAN_CERTIFY
	This specifies if a sub key can be used to create key certificates.
	It is representable as a number, and is @code{1} if the sub key can be
	used for certifications, and @code{0} otherwise.

	@item GPGME_ATTR_SERIAL
	The X.509 issuer serial attribute of the key. It is representable as
	a string.

	@item GPGME_ATTR_ISSUE
	The X.509 issuer name attribute of the key. It is representable as a
	string.

	@item GPGME_ATTR_CHAINID
	The X.509 chain ID can be used to build the certification chain. It
	is representable as a string.
	@end table
	@end deftp

	@deftypefun {const char } gpgme_key_get_string_attr (@w{gpgme_key_t @var{key}}, @w{gpgme_attr_t @var{what}}, @w{const void @var{reserved}}, @w{int @var{idx}})
	The function @code{gpgme_key_get_string_attr} returns the value of the
	string-representable attribute @var{what} of key @var{key}. If the
	attribute is an attribute of a sub key or an user ID, @var{idx}
	specifies the sub key or user ID of which the attribute value is
	returned. The argument @var{reserved} is reserved for later use and
	should be @code{NULL}.

	The string returned is only valid as long as the key is valid.

	The function returns @code{0} if an attribute can't be returned as a
	string, @var{key} is not a valid pointer, @var{idx} out of range,
	or @var{reserved} not @code{NULL}.
	@end deftypefun

	@deftypefun {unsigned long} gpgme_key_get_ulong_attr (@w{gpgme_key_t @var{key}}, @w{gpgme_attr_t @var{what}}, @w{const void *@var{reserved}}, @w{int @var{idx}})
	The function @code{gpgme_key_get_ulong_attr} returns the value of the
	number-representable attribute @var{what} of key @var{key}. If the
	attribute is an attribute of a sub key or an user ID, @var{idx}
	specifies the sub key or user ID of which the attribute value is
	returned. The argument @var{reserved} is reserved for later use and
	should be @code{NULL}.

	The function returns @code{0} if the attribute can't be returned as a
	number, @var{key} is not a valid pointer, @var{idx} out of range, or
	@var{reserved} not @code{NULL}.
	@end deftypefun


	@c
	@c Key Signatures
	@c
	The signatures on a key are only available if the key was retrieved
	via a listing operation with the @code{GPGME_KEYLIST_MODE_SIGS} mode
	enabled, because it is expensive to retrieve all signatures of a key.

	So, before using the below interfaces to retrieve the signatures on a
	key, you have to make sure that the key was listed with signatures
	enabled. One convenient, but blocking, way to do this is to use the
	function @code{gpgme_get_key}.

	@deftp {Data type} gpgme_attr_t
	The @code{gpgme_attr_t} type is used to specify a key signature
	attribute. The following attributes are defined:

	@table @code
	@item GPGME_ATTR_KEYID
	This is the key ID of the key which was used for the signature. It is
	representable as a string.

	@item GPGME_ATTR_ALGO
	This is the crypto algorithm used to create the signature. It is
	representable as a string and as a number. The numbers correspond to
	the @code{enum gcry_pk_algos} values in the gcrypt library.

	@item GPGME_ATTR_CREATED
	This is the timestamp at creation time of the signature. It is
	representable as a number.

	@item GPGME_ATTR_EXPIRE
	This is the expiration time of the signature. It is representable as
	a number.

	@item GPGME_ATTR_USERID
	This is the user ID associated with the signing key. The user ID is
	representable as a number.

	@item GPGME_ATTR_NAME
	This is the name belonging to a user ID. It is representable as a string.

	@item GPGME_ATTR_EMAIL
	This is the email address belonging to a user ID. It is representable
	as a string.

	@item GPGME_ATTR_COMMENT
	This is the comment belonging to a user ID. It is representable as a
	string.

	@item GPGME_ATTR_KEY_REVOKED
	This specifies if a key signature is a revocation signature. It is
	representable as a number, and is @code{1} if the key is revoked, and
	@code{0} otherwise.

	@c @item GPGME_ATTR_KEY_EXPIRED
	@c This specifies if a key signature is expired. It is representable as
	@c a number, and is @code{1} if the key is revoked, and @code{0}
	@c otherwise.
	@c
	@item GPGME_ATTR_SIG_CLASS
	This specifies the signature class of a key signature. It is
	representable as a number. The meaning is specific to the crypto
	engine.

	@item GPGME_ATTR_SIG_CLASS
	This specifies the signature class of a key signature. It is
	representable as a number. The meaning is specific to the crypto
	engine.

	@item GPGME_ATTR_SIG_STATUS
	This is the same value as returned by @code{gpgme_get_sig_status}.
	@end table
	@end deftp

	@deftypefun {const char } gpgme_key_sig_get_string_attr (@w{gpgme_key_t @var{key}}, @w{int @var{uid_idx}}, @w{gpgme_attr_t @var{what}}, @w{const void @var{reserved}}, @w{int @var{idx}})
	The function @code{gpgme_key_sig_get_string_attr} returns the value of
	the string-representable attribute @var{what} of the signature
	@var{idx} on the user ID @var{uid_idx} in the key @var{key}. The
	argument @var{reserved} is reserved for later use and should be
	@code{NULL}.

	The string returned is only valid as long as the key is valid.

	The function returns @code{0} if an attribute can't be returned as a
	string, @var{key} is not a valid pointer, @var{uid_idx} or @var{idx}
	out of range, or @var{reserved} not @code{NULL}.
	@end deftypefun

	@deftypefun {unsigned long} gpgme_key_sig_get_ulong_attr (@w{gpgme_key_t @var{key}}, @w{int @var{uid_idx}}, @w{gpgme_attr_t @var{what}}, @w{const void *@var{reserved}}, @w{int @var{idx}})
	The function @code{gpgme_key_sig_get_ulong_attr} returns the value of
	the number-representable attribute @var{what} of the signature
	@var{idx} on the user ID @var{uid_idx} in the key @var{key}. The
	argument @var{reserved} is reserved for later use and should be
	@code{NULL}.

	The function returns @code{0} if an attribute can't be returned as a
	string, @var{key} is not a valid pointer, @var{uid_idx} or @var{idx}
	out of range, or @var{reserved} not @code{NULL}.
	@end deftypefun


	@deftp {Data type} {enum gpgme_sig_stat_t}
	@tindex gpgme_sig_stat_t
	The @code{gpgme_sig_stat_t} type holds the result of a signature check, or
	the combined result of all signatures. The following results are
	possible:

	@table @code
	@item GPGME_SIG_STAT_NONE
	This status should not occur in normal operation.

	@item GPGME_SIG_STAT_GOOD
	This status indicates that the signature is valid. For the combined
	result this status means that all signatures are valid.

	@item GPGME_SIG_STAT_GOOD_EXP
	This status indicates that the signature is valid but expired. For
	the combined result this status means that all signatures are valid
	and expired.

	@item GPGME_SIG_STAT_GOOD_EXPKEY
	This status indicates that the signature is valid but the key used to
	verify the signature has expired. For the combined result this status
	means that all signatures are valid and all keys are expired.

	@item GPGME_SIG_STAT_BAD
	This status indicates that the signature is invalid. For the combined
	result this status means that all signatures are invalid.

	@item GPGME_SIG_STAT_NOKEY
	This status indicates that the signature could not be verified due to
	a missing key. For the combined result this status means that all
	signatures could not be checked due to missing keys.

	@item GPGME_SIG_STAT_NOSIG
	This status indicates that the signature data provided was not a real
	signature.

	@item GPGME_SIG_STAT_ERROR
	This status indicates that there was some other error which prevented
	the signature verification.

	@item GPGME_SIG_STAT_DIFF
	For the combined result this status means that at least two signatures
	have a different status. You can get each key's status with
	@code{gpgme_get_sig_status}.
	@end table
	@end deftp

	@deftypefun {const char } gpgme_get_sig_status (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{idx}}, @w{gpgme_sig_stat_t @var{r_stat}}, @w{time_t *@var{r_created}})
	The function @code{gpgme_get_sig_status} is equivalent to:

	@example
	gpgme_verify_result_t result;
	gpgme_signature_t sig;

	result = gpgme_op_verify_result (ctx);
	sig = result->signatures;

	while (sig && idx)
	@{
	sig = sig->next;
	idx--;
	@}
	if (!sig \|\| idx)
	return NULL;

	if (r_stat)
	@{
	switch (gpg_err_code (sig->status))
	@{
	case GPG_ERR_NO_ERROR:
	*r_stat = GPGME_SIG_STAT_GOOD;
	break;

	case GPG_ERR_BAD_SIGNATURE:
	*r_stat = GPGME_SIG_STAT_BAD;
	break;

	case GPG_ERR_NO_PUBKEY:
	*r_stat = GPGME_SIG_STAT_NOKEY;
	break;

	case GPG_ERR_NO_DATA:
	*r_stat = GPGME_SIG_STAT_NOSIG;
	break;

	case GPG_ERR_SIG_EXPIRED:
	*r_stat = GPGME_SIG_STAT_GOOD_EXP;
	break;

	case GPG_ERR_KEY_EXPIRED:
	*r_stat = GPGME_SIG_STAT_GOOD_EXPKEY;
	break;

	default:
	*r_stat = GPGME_SIG_STAT_ERROR;
	break;
	@}
	@}
	if (r_created)
	*r_created = sig->timestamp;
	return sig->fpr;
	@end example
	@end deftypefun

	@deftypefun {const char *} gpgme_get_sig_string_attr (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{idx}}, @w{gpgme_attr_t @var{what}}, @w{int @var{whatidx}})
	The function @code{gpgme_get_sig_string_attr} is equivalent to:

	@example
	gpgme_verify_result_t result;
	gpgme_signature_t sig;

	result = gpgme_op_verify_result (ctx);
	sig = result->signatures;

	while (sig && idx)
	@{
	sig = sig->next;
	idx--;
	@}
	if (!sig \|\| idx)
	return NULL;

	switch (what)
	@{
	case GPGME_ATTR_FPR:
	return sig->fpr;

	case GPGME_ATTR_ERRTOK:
	if (whatidx == 1)
	return sig->wrong_key_usage ? "Wrong_Key_Usage" : "";
	else
	return "";
	default:
	break;
	@}

	return NULL;
	@end example
	@end deftypefun

	@deftypefun {const char *} gpgme_get_sig_ulong_attr (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{idx}}, @w{gpgme_attr_t @var{what}}, @w{int @var{whatidx}})
	The function @code{gpgme_get_sig_ulong_attr} is equivalent to:

	@example
	gpgme_verify_result_t result;
	gpgme_signature_t sig;

	result = gpgme_op_verify_result (ctx);
	sig = result->signatures;

	while (sig && idx)
	@{
	sig = sig->next;
	idx--;
	@}
	if (!sig \|\| idx)
	return 0;

	switch (what)
	@{
	case GPGME_ATTR_CREATED:
	return sig->timestamp;

	case GPGME_ATTR_EXPIRE:
	return sig->exp_timestamp;

	case GPGME_ATTR_VALIDITY:
	return (unsigned long) sig->validity;

	case GPGME_ATTR_SIG_STATUS:
	switch (sig->status)
	@{
	case GPG_ERR_NO_ERROR:
	return GPGME_SIG_STAT_GOOD;

	case GPG_ERR_BAD_SIGNATURE:
	return GPGME_SIG_STAT_BAD;

	case GPG_ERR_NO_PUBKEY:
	return GPGME_SIG_STAT_NOKEY;

	case GPG_ERR_NO_DATA:
	return GPGME_SIG_STAT_NOSIG;

	case GPG_ERR_SIG_EXPIRED:
	return GPGME_SIG_STAT_GOOD_EXP;

	case GPG_ERR_KEY_EXPIRED:
	return GPGME_SIG_STAT_GOOD_EXPKEY;

	default:
	return GPGME_SIG_STAT_ERROR;
	@}

	case GPGME_ATTR_SIG_SUMMARY:
	return sig->summary;

	default:
	break;
	@}
	return 0;
	@end example
	@end deftypefun

	@deftypefun {const char } gpgme_get_sig_key (@w{gpgme_ctx_t @var{ctx}}, @w{int @var{idx}}, @w{gpgme_key_t @var{r_key}})
	The function @code{gpgme_get_sig_key} is equivalent to:

	@example
	gpgme_verify_result_t result;
	gpgme_signature_t sig;

	result = gpgme_op_verify_result (ctx);
	sig = result->signatures;

	while (sig && idx)
	@{
	sig = sig->next;
	idx--;
	@}
	if (!sig \|\| idx)
	return gpg_error (GPG_ERR_EOF);

	return gpgme_get_key (ctx, sig->fpr, r_key, 0);
	@end example
	@end deftypefun





	@include lesser.texi

	@include gpl.texi

	@node Concept Index
	@unnumbered Concept Index

	@printindex cp

	@node Function and Data Index
	@unnumbered Function and Data Index

	@printindex fn


	@bye
	diff --git a/src/sign.c b/src/sign.c
	index 31081aea..31db9bde 100644
	--- a/src/sign.c
	+++ b/src/sign.c
	@@ -1,500 +1,509 @@
	/* sign.c - Signing function.
	* Copyright (C) 2000 Werner Koch (dd9jn)
	* Copyright (C) 2001, 2002, 2003, 2004, 2007 g10 Code GmbH
	*
	* This file is part of GPGME.
	*
	* GPGME is free software; you can redistribute it and/or modify it
	* under the terms of the GNU Lesser General Public License as
	* published by the Free Software Foundation; either version 2.1 of
	* the License, or (at your option) any later version.
	*
	* GPGME is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public
	* License along with this program; if not, see <https://gnu.org/licenses/>.
	* SPDX-License-Identifier: LGPL-2.1-or-later
	*/

	#if HAVE_CONFIG_H
	#include <config.h>
	#endif
	#include <stdlib.h>
	#include <string.h>
	#include <errno.h>

	/* Suppress warning for accessing deprecated member "class". */
	#define _GPGME_IN_GPGME 1
	#include "gpgme.h"
	#include "context.h"
	#include "ops.h"
	#include "util.h"
	#include "debug.h"


	typedef struct
	{
	struct _gpgme_op_sign_result result;

	/* The error code from a FAILURE status line or 0. */
	gpg_error_t failure_code;

	/* The fingerprint from the last KEY_CONSIDERED status line. */
	char *kc_fpr;

	/* The flags from the last KEY_CONSIDERED status line. */
	unsigned int kc_flags;

	/* A pointer to the next pointer of the last invalid signer in
	the list. This makes appending new invalid signers painless
	while preserving the order. */
	gpgme_invalid_key_t *last_signer_p;

	/* Likewise for signature information. */
	gpgme_new_signature_t *last_sig_p;

	/* Flags used while processing the status lines. */
	unsigned int ignore_inv_recp:1;
	unsigned int inv_sgnr_seen:1;
	unsigned int sig_created_seen:1;
	} *op_data_t;


	static void
	release_signatures (gpgme_new_signature_t sig)
	{
	while (sig)
	{
	gpgme_new_signature_t next = sig->next;
	free (sig->fpr);
	free (sig);
	sig = next;
	}
	}


	static void
	release_op_data (void *hook)
	{
	op_data_t opd = (op_data_t) hook;
	gpgme_invalid_key_t invalid_signer = opd->result.invalid_signers;

	while (invalid_signer)
	{
	gpgme_invalid_key_t next = invalid_signer->next;
	if (invalid_signer->fpr)
	free (invalid_signer->fpr);
	free (invalid_signer);
	invalid_signer = next;
	}

	release_signatures (opd->result.signatures);
	free (opd->kc_fpr);
	}


	gpgme_sign_result_t
	gpgme_op_sign_result (gpgme_ctx_t ctx)
	{
	void *hook;
	op_data_t opd;
	gpgme_error_t err;
	gpgme_invalid_key_t inv_key, key;
	gpgme_new_signature_t sig;
	unsigned int inv_signers = 0;
	unsigned int signatures = 0;

	TRACE_BEG (DEBUG_CTX, "gpgme_op_sign_result", ctx, "");

	err = _gpgme_op_data_lookup (ctx, OPDATA_SIGN, &hook, -1, NULL);
	opd = hook;
	if (err \|\| !opd)
	{
	TRACE_SUC ("result=(null)");
	return NULL;
	}

	for (inv_key = opd->result.invalid_signers; inv_key; inv_key = inv_key->next)
	inv_signers++;
	for (sig = opd->result.signatures; sig; sig = sig->next)
	signatures++;

	if (gpgme_signers_count (ctx)
	&& signatures + inv_signers != gpgme_signers_count (ctx))
	{
	/* In this case at least one signatures was not created perhaps
	due to a bad passphrase etc. Thus the entire message is
	broken and should not be used. We add the already created
	signatures to the invalid signers list and thus this case can
	be detected. */
	TRACE_LOG ("result: invalid signers: %u, signatures: %u, count: %u",
	inv_signers, signatures, gpgme_signers_count (ctx));

	for (sig = opd->result.signatures; sig; sig = sig->next)
	{
	key = calloc (1, sizeof *key);
	if (!key)
	{
	TRACE_SUC ("out of core; result=(null)");
	return NULL;
	}
	if (sig->fpr)
	{
	key->fpr = strdup (sig->fpr);
	if (!key->fpr)
	{
	free (key);
	TRACE_SUC ("out of core; result=(null)");
	return NULL;
	}
	}
	key->reason = GPG_ERR_GENERAL;

	inv_key = opd->result.invalid_signers;
	if (inv_key)
	{
	for (; inv_key->next; inv_key = inv_key->next)
	;
	inv_key->next = key;
	}
	else
	opd->result.invalid_signers = key;
	}

	release_signatures (opd->result.signatures);
	opd->result.signatures = NULL;
	}

	if (_gpgme_debug_trace())
	{
	TRACE_LOG ("result: invalid signers: %i, signatures: %i",
	inv_signers, signatures);
	for (inv_key=opd->result.invalid_signers; inv_key; inv_key=inv_key->next)
	{
	TRACE_LOG ("result: invalid signer: fpr=%s, reason=%s <%s>",
	inv_key->fpr, gpgme_strerror (inv_key->reason),
	gpgme_strsource (inv_key->reason));
	}
	for (sig = opd->result.signatures; sig; sig = sig->next)
	{
	TRACE_LOG ("result: signature: type=%i, pubkey_algo=%i, "
	"hash_algo=%i, timestamp=%li, fpr=%s, sig_class=%i",
	sig->type, sig->pubkey_algo, sig->hash_algo,
	sig->timestamp, sig->fpr, sig->sig_class);
	}
	}

	TRACE_SUC ("result=%p", &opd->result);
	return &opd->result;
	}



	static gpgme_error_t
	parse_sig_created (char args, gpgme_new_signature_t sigp,
	gpgme_protocol_t protocol)
	{
	gpgme_new_signature_t sig;
	char *tail;

	sig = malloc (sizeof (*sig));
	if (!sig)
	return gpg_error_from_syserror ();

	sig->next = NULL;
	switch (*args)
	{
	case 'S':
	sig->type = GPGME_SIG_MODE_NORMAL;
	break;

	case 'D':
	sig->type = GPGME_SIG_MODE_DETACH;
	break;

	case 'C':
	sig->type = GPGME_SIG_MODE_CLEAR;
	break;

	default:
	/* The backend engine is not behaving. */
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}

	args++;
	if (*args != ' ')
	{
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}

	gpg_err_set_errno (0);
	sig->pubkey_algo = _gpgme_map_pk_algo (strtol (args, &tail, 0), protocol);
	if (errno \|\| args == tail \|\| *tail != ' ')
	{
	/* The crypto backend does not behave. */
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}
	args = tail;

	sig->hash_algo = strtol (args, &tail, 0);
	if (errno \|\| args == tail \|\| *tail != ' ')
	{
	/* The crypto backend does not behave. */
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}
	args = tail;

	+ /* strtol has been used wrongly here. We can't change this anymore
	+ * but we now take care of the 0x1f class which would otherwise let
	+ * us run into an error. */
	sig->sig_class = strtol (args, &tail, 0);
	+ if (!errno && args != tail && sig->sig_class == 1
	+ && (tail == 'F' \|\| tail == 'f'))
	+ {
	+ tail++;
	+ sig->sig_class = 131; /* Arbitrary unused value in rfc4880. */
	+ }
	sig->class = sig->sig_class;
	sig->_obsolete_class = sig->sig_class;
	if (errno \|\| args == tail \|\| *tail != ' ')
	{
	/* The crypto backend does not behave. */
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}
	args = tail;

	sig->timestamp = _gpgme_parse_timestamp (args, &tail);
	if (sig->timestamp == -1 \|\| args == tail \|\| *tail != ' ')
	{
	/* The crypto backend does not behave. */
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}
	args = tail;
	while (*args == ' ')
	args++;

	if (!*args)
	{
	/* The crypto backend does not behave. */
	free (sig);
	return trace_gpg_error (GPG_ERR_INV_ENGINE);
	}

	tail = strchr (args, ' ');
	if (tail)
	*tail = '\0';

	sig->fpr = strdup (args);
	if (!sig->fpr)
	{
	free (sig);
	return gpg_error_from_syserror ();
	}
	*sigp = sig;
	return 0;
	}


	gpgme_error_t
	_gpgme_sign_status_handler (void priv, gpgme_status_code_t code, char args)
	{
	gpgme_ctx_t ctx = (gpgme_ctx_t) priv;
	gpgme_error_t err;
	void *hook;
	op_data_t opd;

	err = _gpgme_passphrase_status_handler (priv, code, args);
	if (err)
	return err;

	err = _gpgme_op_data_lookup (ctx, OPDATA_SIGN, &hook, -1, NULL);
	opd = hook;
	if (err)
	return err;

	switch (code)
	{
	case GPGME_STATUS_SIG_CREATED:
	opd->sig_created_seen = 1;
	err = parse_sig_created (args, opd->last_sig_p, ctx->protocol);
	if (err)
	return err;

	opd->last_sig_p = &(*opd->last_sig_p)->next;
	break;

	case GPGME_STATUS_KEY_CONSIDERED:
	/* This is emitted during gpg's key lookup to give information
	* about the lookup results. We store the last one so it can be
	* used in connection with INV_RECP. */
	free (opd->kc_fpr);
	opd->kc_fpr = NULL;
	err = _gpgme_parse_key_considered (args, &opd->kc_fpr, &opd->kc_flags);
	if (err)
	return err;
	break;

	case GPGME_STATUS_INV_RECP:
	if (opd->inv_sgnr_seen && opd->ignore_inv_recp)
	break;
	/* FALLTHROUGH */
	case GPGME_STATUS_INV_SGNR:
	if (code == GPGME_STATUS_INV_SGNR)
	opd->inv_sgnr_seen = 1;
	free (opd->kc_fpr);
	opd->kc_fpr = NULL;
	err = _gpgme_parse_inv_recp (args, 1, opd->kc_fpr, opd->kc_flags,
	opd->last_signer_p);
	if (err)
	return err;

	opd->last_signer_p = &(*opd->last_signer_p)->next;
	free (opd->kc_fpr);
	opd->kc_fpr = NULL;
	break;

	case GPGME_STATUS_FAILURE:
	opd->failure_code = _gpgme_parse_failure (args);
	break;

	case GPGME_STATUS_EOF:
	/* The UI server does not send information about the created
	signature. This is irrelevant for this protocol and thus we
	should not check for that. */
	if (opd->result.invalid_signers)
	err = gpg_error (GPG_ERR_UNUSABLE_SECKEY);
	else if (!opd->sig_created_seen
	&& ctx->protocol != GPGME_PROTOCOL_UISERVER)
	err = opd->failure_code? opd->failure_code:gpg_error (GPG_ERR_GENERAL);
	break;

	case GPGME_STATUS_INQUIRE_MAXLEN:
	if (ctx->status_cb && !ctx->full_status)
	err = ctx->status_cb (ctx->status_cb_value, "INQUIRE_MAXLEN", args);
	break;

	default:
	break;
	}
	return err;
	}


	static gpgme_error_t
	sign_status_handler (void priv, gpgme_status_code_t code, char args)
	{
	gpgme_error_t err;

	err = _gpgme_progress_status_handler (priv, code, args);
	if (!err)
	err = _gpgme_sign_status_handler (priv, code, args);
	return err;
	}


	static gpgme_error_t
	sign_init_result (gpgme_ctx_t ctx, int ignore_inv_recp)
	{
	gpgme_error_t err;
	void *hook;
	op_data_t opd;

	err = _gpgme_op_data_lookup (ctx, OPDATA_SIGN, &hook,
	sizeof (*opd), release_op_data);
	opd = hook;
	if (err)
	return err;
	opd->failure_code = 0;
	opd->last_signer_p = &opd->result.invalid_signers;
	opd->last_sig_p = &opd->result.signatures;
	opd->ignore_inv_recp = !!ignore_inv_recp;
	opd->inv_sgnr_seen = 0;
	opd->sig_created_seen = 0;
	return 0;
	}

	gpgme_error_t
	_gpgme_op_sign_init_result (gpgme_ctx_t ctx)
	{
	return sign_init_result (ctx, 0);
	}


	static gpgme_error_t
	sign_start (gpgme_ctx_t ctx, int synchronous, gpgme_data_t plain,
	gpgme_data_t sig, gpgme_sig_mode_t mode)
	{
	gpgme_error_t err;

	err = _gpgme_op_reset (ctx, synchronous);
	if (err)
	return err;

	/* If we are using the CMS protocol, we ignore the INV_RECP status
	code if a newer GPGSM is in use. GPGMS does not support combined
	sign+encrypt and thus this can't harm. */
	err = sign_init_result (ctx, (ctx->protocol == GPGME_PROTOCOL_CMS));
	if (err)
	return err;

	if (mode != GPGME_SIG_MODE_NORMAL && mode != GPGME_SIG_MODE_DETACH
	&& mode != GPGME_SIG_MODE_CLEAR)
	return gpg_error (GPG_ERR_INV_VALUE);

	if (!plain)
	return gpg_error (GPG_ERR_NO_DATA);
	if (!sig)
	return gpg_error (GPG_ERR_INV_VALUE);

	if (ctx->passphrase_cb)
	{
	err = _gpgme_engine_set_command_handler
	(ctx->engine, _gpgme_passphrase_command_handler, ctx);
	if (err)
	return err;
	}

	_gpgme_engine_set_status_handler (ctx->engine, sign_status_handler,
	ctx);

	return _gpgme_engine_op_sign (ctx->engine, plain, sig, mode, ctx->use_armor,
	ctx->use_textmode, ctx->include_certs,
	ctx /* FIXME */);
	}


	/* Sign the plaintext PLAIN and store the signature in SIG. */
	gpgme_error_t
	gpgme_op_sign_start (gpgme_ctx_t ctx, gpgme_data_t plain, gpgme_data_t sig,
	gpgme_sig_mode_t mode)
	{
	gpg_error_t err;
	TRACE_BEG (DEBUG_CTX, "gpgme_op_sign_start", ctx,
	"plain=%p, sig=%p, mode=%i", plain, sig, mode);

	if (!ctx)
	return TRACE_ERR (gpg_error (GPG_ERR_INV_VALUE));

	err = sign_start (ctx, 0, plain, sig, mode);
	return TRACE_ERR (err);
	}


	/* Sign the plaintext PLAIN and store the signature in SIG. */
	gpgme_error_t
	gpgme_op_sign (gpgme_ctx_t ctx, gpgme_data_t plain, gpgme_data_t sig,
	gpgme_sig_mode_t mode)
	{
	gpgme_error_t err;

	TRACE_BEG (DEBUG_CTX, "gpgme_op_sign", ctx,
	"plain=%p, sig=%p, mode=%i", plain, sig, mode);

	if (!ctx)
	return TRACE_ERR (gpg_error (GPG_ERR_INV_VALUE));

	err = sign_start (ctx, 1, plain, sig, mode);
	if (!err)
	err = _gpgme_wait_one (ctx);
	return TRACE_ERR (err);
	}

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