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	\input texinfo @c --texinfo--
	@c %**start of header
	@setfilename pinentry.info

	@include version.texi

	@macro copyrightnotice
	Copyright @copyright{} 2002, 2005, 2015 g10 Code GmbH
	@end macro
	@macro permissionnotice
	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 2 of the License, or (at your
	option) any later version. The text of the license can be found in the
	section entitled ``Copying''.
	@end macro

	@macro pinentry
	@sc{pinentry}
	@end macro

	@settitle Using the PIN-Entry

	@c Create a separate index for command line options.
	@defcodeindex op
	@c Merge the standard indexes into a single one.
	@syncodeindex fn cp
	@syncodeindex vr cp
	@syncodeindex ky cp
	@syncodeindex pg cp
	@syncodeindex tp cp

	@c printing stuff taken from gcc.
	@macro gnupgtabopt{body}
	@code{\body\}
	@end macro
	@macro gnupgoptlist{body}
	@smallexample
	\body\
	@end smallexample
	@end macro
	@c Makeinfo handles the above macro OK, TeX needs manual line breaks;
	@c they get lost at some point in handling the macro. But if @macro is
	@c used here rather than @alias, it produces double line breaks.
	@iftex
	@alias gol = *
	@end iftex
	@ifnottex
	@macro gol
	@end macro
	@end ifnottex


	@c %**end of header

	@ifnottex
	@dircategory GNU Utilities
	@direntry
	* pinentry: (pinentry). Securely ask for a passphrase or PIN.
	@end direntry
	This file documents the use and the internals of the @pinentry{}.

	This is edition @value{EDITION}, last updated @value{UPDATED}, of
	@cite{The `PINEntry' Manual}, for version @value{VERSION}.
	@sp 1
	Published by g10 Code GmbH@*
	Hüttenstr. 61@*
	40699 Erkrath, Germany
	@sp 1
	@copyrightnotice{}
	@sp 1
	@permissionnotice{}
	@end ifnottex

	@setchapternewpage odd

	@titlepage
	@title Using the PIN-Entry
	@subtitle Version @value{VERSION}
	@subtitle @value{UPDATED}
	@author Werner Koch @code{(wk@@gnupg.org)}

	@page
	@vskip 0pt plus 1filll
	@copyrightnotice{}
	@sp 2
	@permissionnotice{}
	@end titlepage
	@summarycontents
	@contents
	@page


	@node Top
	@top Introduction
	@cindex introduction

	This manual documents how to use the @pinentry{} and its protocol.

	The @pinentry{} is a small GUI application used to enter PINs or
	passphrases. It is usually invoked by @sc{gpg-agent}
	(@pxref{Invoking GPG-AGENT, ,Invoking the gpg-agent, gnupg,
	The `GNU Privacy Guard' Manual}, for details).

	@pinentry{} comes in several flavors to fit the look and feel of the
	used GUI toolkit: A @sc{GTK+} based one named @code{pinentry-gtk}; a
	@sc{Qt} based one named @code{pinentry-qt}; and, two non-graphical
	ones @code{pinentry-curses}, which uses curses, and
	@code{pinentry-tty}, which doesn't require anything more than a simple
	terminal. Not all of them are necessarily available on your
	installation. If curses is supported on your system, the GUI-based
	flavors fall back to curses when the @code{DISPLAY} variable is not
	set.


	@menu
	* Using pinentry:: How to use the beast.
	* Front ends:: Description and comparison of the front ends

	Developer information

	* Protocol:: The Assuan protocol description.
	* Implementation Details:: For those extending or writing a new pinentry.

	Miscellaneous

	* Copying:: GNU General Public License says
	how you can copy and share PIN-Entry
	as well as this manual.

	Indices

	* Option Index:: Index to command line options.
	* Index:: Index of concepts and symbol names.
	@end menu

	@node Using pinentry
	@chapter How to use the @pinentry{}

	@c man begin DESCRIPTION

	You may run @pinentry{} directly from the command line and pass the
	commands according to the Assuan protocol via stdin/stdout.


	@c man end

	@c man begin OPTIONS

	Here is a list of options supported by all flavors of pinentry:

	@table @gnupgtabopt
	@item --version
	@opindex version
	Print the program version and licensing information.

	@item --help
	@opindex help
	Print a usage message summarizing the most useful command line options.

	@item --debug
	@itemx -d
	@opindex debug
	@opindex d
	Turn on some debugging. Mostly useful for the maintainers. Note that
	this may reveal sensitive information like the entered passphrase.

	@c @item --enhanced
	@c @itemx -e
	@c @opindex enhanced
	@c @opindex e
	@c Ask for timeouts and insurance, too. Note that this is currently not
	@c fully supported.

	@item --no-global-grab
	@itemx -g
	@opindex no-global-grab
	@opindex g
	Grab the keyboard only when the window is focused. Use this option if
	you are debugging software using the @pinentry{}; otherwise you may
	not be able to to access your X session anymore (unless you have other
	means to connect to the machine to kill the @pinentry{}).

	@item --parent-wid @var{n}
	@opindex parent-wid
	Use window ID @var{n} as the parent window for positioning the window.
	Note, that this is not fully supported by all flavors of @pinentry{}.

	@item --timeout @var{seconds}
	@opindex timeout
	Give up waiting for input from the user after the specified number of
	seconds and return an error. The error returned is the same as if the
	Cancel button was selected. To disable the timeout and wait
	indefinitely, set this to 0, which is the default.

	@item --display @var{string}
	@itemx --ttyname @var{string}
	@itemx --ttytype @var{string}
	@itemx --lc-ctype @var{string}
	@itemx --lc-messages @var{string}
	@opindex display
	@opindex ttyname
	@opindex ttytype
	@opindex lc-ctype
	@opindex lc-messa
	These options are used to pass localization information to
	@pinentry{}. They are required because @pinentry{} is usually called
	by some background process which does not have any information about
	the locale and terminal to use. It is also possible to pass these
	options using Assuan protocol options.
	@end table

	@node Front ends
	@chapter Front Ends

	There are several different flavors of @pinentry{}. Concretely, there
	are Gtk+2, Qt@tie{}4, Gnome@tie{}3, Emacs, curses and tty variants.
	These different implementations provide higher levels of integration
	with a specific environment. For instance, the Gnome@tie{}3
	@pinentry{} uses Gnome@tie{}3 widgets to display the prompts. For
	Gnome@tie{}3 users, this higher level of integration provides a more
	consistent aesthetic. However, this comes at a cost. Because this
	@pinentry{} uses so many components, there is a larger chance of a
	failure. In particular, there is a larger chance that the passphrase
	is saved in memory and that memory is exposed to an attacker (consider
	the OpenSSL Heartbeat vulnerability).

	To understand how many components touch the passphrase, consider again
	the Gnome@tie{}3 implementation. When a user presses a button on the
	keyboard, the key is passed from the kernel to the X@tie{}server to
	the toolkit (Gtk+) and to the actual text entry widget. Along the
	way, the key is saved in memory and processed. In fact, the key
	presses are probably read using standard C library functions, which
	buffer the input. None of this code is careful to make sure the
	contents of the memory are not leaked by keeping the data in unpagable
	memory and wiping it when the buffer is freed. However, even if they
	did, there is still the problem that when a computer hibernates, the
	system writes unpagable memory to disk anyway. Further, many
	installations are virtualized (e.g., running on Xen) and have little
	control over their actual environment.

	The curses variant uses a significant smaller software stack and the
	tty variant uses an even smaller one. However, if they are run in an
	X@tie{}terminal, then a similar number of components are handling the
	passphrase as in the Gnome@tie{}3 case! Thus, to be most secure, you
	need to direct GPG@tie{}Agent to use a fixed virtual console. Since
	you need to remain logged in for GPG@tie{}Agent to use that console,
	you should run there and have @code{screen} or @code{tmux} lock the
	tty.

	The Emacs pinentry implementation interacts with a running Emacs
	session and directs the Emacs instance to display the passphrase
	prompt. Since this doesn't work very well if there is no Emacs
	running, the generic @pinentry{} backend checks if a
	@pinentry{}-enabled Emacs should be used. Specifically, it looks to
	see if the @code{INSIDE_EMACS} variable is set and then attempts to
	establish a connection to the specified address. If this is the case,
	then instead of, e.g., @code{pinentry-gtk2} displaying a Gtk+2
	pinentry, it interacts with the Emacs session. This functionality can
	be explicitly disabled by passing @code{--disable-inside-emacs} to
	@code{configure} when building @pinentry{}.

	Having Emacs get the passphrase is convenient, however, it is a
	significant security risk. Emacs is a huge program, which doesn't
	provide any process isolation to speak of. As such, having it handle
	the passphrase adds a huge chunk of code to the user's trusted computing
	base. Because of this concern, Emacs doesn't enable this by default,
	unless the @code{allow-emacs-pinentry} option is explicitly set in his
	or her @code{.gnupg/gpg-agent.conf} file.

	Similar to the inside-emacs check, the @pinentry{} frontends check
	whether the @code{DISPLAY} variable is set and a working X server is
	available. If this is not the case, then they fallback to the curses
	front end. This can also be disabled by passing
	@code{--disable-fallback-curses} to @code{configure} at build time.

	@c
	@c Assuan Protocol
	@c
	@node Protocol
	@chapter @pinentry{}'s Assuan Protocol

	The @pinentry{} should never service more than one connection at once.
	It is reasonable to exec the @pinentry{} prior to a request.

	The @pinentry{} does not need to stay in memory because the
	@sc{gpg-agent} has the ability to cache passphrases. The usual way to
	run the @pinentry{} is by setting up a pipe (not a socket) and then
	fork/exec the @pinentry{}. The communication is then done by means of
	the protocol described here until the client is satisfied with the
	result.

	Although it is called a @pinentry{}, it allows entering reasonably
	long strings (strings that are up to 2048 characters long are
	supported by every pinentry). The client using the @pinentry{} has to
	check for correctness.

	Note that all strings are expected to be encoded as UTF-8; @pinentry{}
	takes care of converting it to the locally used codeset. To include
	linefeeds or other special characters, you may percent-escape them
	(e.g., a line feed is encoded as @code{%0A}, the percent sign itself
	is encoded as @code{%25}, etc.).

	The following is a list of supported commands:

	@table @gnupgtabopt

	@item Set the timeout before returning an error
	@example
	C: SETTIMEOUT 30
	S: OK
	@end example

	@item Set the descriptive text to display
	@example
	C: SETDESC Enter PIN for Richard Nixon <nobody@@trickydicky.gov>
	S: OK
	@end example

	@item Set the prompt to show
	When asking for a PIN, set the text just before the widget for
	passphrase entry.
	@example
	C: SETPROMPT PIN:
	S: OK
	@end example

	You should use an underscore in the text only if you know that a
	modern version of pinentry is used. Modern versions underline the
	next character after the underscore and use the first such underlined
	character as a keyboard accelerator. Use a double underscore to
	escape an underscore.

	@item Set the window title
	This command may be used to change the default window title. When
	using this feature you should take care that the window is still
	identifiable as the pinentry.
	@example
	C: SETTITLE Tape Recorder Room
	S: OK
	@end example

	@item Set the button texts
	There are three texts which should be used to override the English
	defaults:

	To set the text for the button signaling confirmation (in UTF-8).
	See SETPROMPT on how to use an keyboard accelerator.
	@example
	C: SETOK Yes
	S: OK
	@end example


	To set the text for the button signaling cancellation or disagreement
	(in UTF-8). See SETPROMPT on how to use an keyboard accelerator.
	@example
	C: SETCANCEL No
	S: OK
	@end example


	In case three buttons are required, use the following command to set
	the text (UTF-8) for the non-affirmative response button. The
	affirmative button text is still set using SETOK and the CANCEL button
	text with SETCANCEL. See SETPROMPT on how to use an keyboard
	accelerator.
	@example
	C: SETNOTOK Do not do this
	S: OK
	@end example



	@item Set the Error text
	This is used by the client to display an error message. In contrast
	to the other commands, the error message is automatically reset with
	a GETPIN or CONFIRM, and is only displayed when asking for a PIN.
	@example
	C: SETERROR Invalid PIN entered - please try again
	S: OK
	@end example

	@item Enable a passphrase quality indicator
	Adds a quality indicator to the GETPIN window. This indicator is
	updated as the passphrase is typed. The clients needs to implement an
	inquiry named "QUALITY" which gets passed the current passphrase
	(percent-plus escaped) and should send back a string with a single
	numerical value between -100 and 100. Negative values will be
	displayed in red.
	@example
	C: SETQUALITYBAR
	S: OK
	@end example

	If a custom label for the quality bar is required, just add that label
	as an argument as a percent-escaped string. You will need this
	feature to translate the label because @pinentry{} has no internal
	gettext except for stock strings from the toolkit library.

	If you want to show a tooltip for the quality bar, you may use
	@example
	C: SETQUALITYBAR_TT string
	S: OK
	@end example

	@noindent
	With STRING being a percent escaped string shown as the tooltip.


	@item Ask for a PIN
	The meat of this tool is to ask for a passphrase of PIN, it is done with
	this command:
	@example
	C: GETPIN
	S: D no more tapes
	S: OK
	@end example
	Note that the passphrase is transmitted in clear using standard data
	responses. Expect it to be in UTF-8.

	@item Ask for confirmation
	To ask for a confirmation (yes or no), you can use this command:
	@example
	C: CONFIRM
	S: OK
	@end example
	The client should use SETDESC to set an appropriate text before
	issuing this command, and may use SETPROMPT to set the button texts.
	The value returned is either OK for YES or the error code
	@code{ASSUAN_Not_Confirmed}.

	@item Show a message
	To show a message, you can use this command:
	@example
	C: MESSAGE
	S: OK
	@end example
	alternatively you may add an option to confirm:
	@example
	C: CONFIRM --one-button
	S: OK
	@end example
	The client should use SETDESC to set an appropriate text before issuing
	this command, and may use SETOK to set the text for the dismiss button.
	The value returned is OK or an error message.

	@item Set the output device
	When using X, the @pinentry{} program must be invoked with an
	appropriate @code{DISPLAY} environment variable or the
	@code{--display} option.

	When using a text terminal:
	@example
	C: OPTION ttyname=/dev/tty3
	S: OK
	C: OPTION ttytype=vt100
	S: OK
	C: OPTION lc-ctype=de_DE.UTF-8
	S: OK
	@end example
	The client should use the @code{ttyname} option to set the output TTY
	file name, the @code{ttytype} option to the @code{TERM} variable
	appropriate for this tty and @code{lc-ctype} to the locale which
	defines the character set to use for this terminal.

	@item Set the default strings
	To avoid having translations in Pinentry proper, the caller may set
	certain translated strings which are used by @pinentry{} as default
	strings.

	@example
	C: OPTION default-ok=_Korrekt
	S: OK
	C: OPTION default-cancel=Abbruch
	S: OK
	C: OPTION default-prompt=PIN eingeben:
	S: OK
	@end example
	The strings are subject to accelerator marking, see SETPROMPT for
	details.

	@item Passphrase caching

	Some environments, such as GNOME, cache passwords and passphrases.
	The @pinentry{} should only use an external cache if the
	@code{allow-external-password-cache} option was set and a stable key
	identifier (using SETKEYINFO) was provided. In this case, if the
	passphrase was read from the cache, the @pinentry{} should send the
	@code{PASSWORD_FROM_CACHE} status message before returning the
	passphrase. This indicates to GPG Agent that it should not increment
	the passphrase retry counter.

	@example
	C: OPTION allow-external-password-cache
	S: OK
	C: SETKEYINFO key-grip
	S: OK
	C: getpin
	S: S PASSWORD_FROM_CACHE
	S: D 1234
	C: OK
	@end example

	Note: if @code{allow-external-password-cache} is not specified, an
	external password cache must not be used: this can lead to subtle
	bugs. In particular, if this option is not specified, then GPG Agent
	does not recognize the @code{PASSWORD_FROM_CACHE} status message and
	will count trying a cached password against the password retry count.
	If the password retry count is 1, then the user will never have the
	opportunity to correct the cached password.

	Note: it is strongly recommended that a pinentry supporting this
	feature provide the user an option to enable it manually. That is,
	saving a passphrase in an external password manager should be opt-in.

	The key identifier provided SETKEYINFO must be considered opaque and
	may change in the future. It currently has the form
	@code{X/HEXSTRING} where @code{X} is either @code{n}, @code{s}, or
	@code{u}. In the former two cases, the HEXSTRING corresponds to the
	key grip. The key grip is not the OpenPGP Key ID, but it can be
	mapped to the key using the following:

	@example
	# gpg2 --with-keygrip --list-secret-keys
	@end example

	@noindent
	and searching the output for the key grip. The same command-line
	options can also be used with gpgsm.

	@end table

	@node Implementation Details
	@chapter Implementation Details

	The pinentry source code can be divided into three categories. There
	is a backend module, which lives in @code{pinentry/}, there are
	utility functions, e.g., in @code{secmem/}, and there are various
	frontends.

	All of the low-level logic lives in the backend. This frees the
	frontends from having to implement, e.g., the Assuan protocol. When
	the backend receives an option, it updates the state in a
	@code{pinentry_t} struct. The frontend is called when the client
	either calls @code{GETPIN}, @code{CONFIRM} or @code{MESSAGE}. In
	these cases, the backend invokes the @code{pinentry_cmd_handler},
	which is passed the @code{pinentry_t} struct.

	When the callback is invoked, the frontend should create a window
	based on the state in the @code{pinentry_t} struct. For instance, the
	title to use for the dialog's window (if any) is stored in the
	@code{title} field. If the is @code{NULL}, the frontend should choose
	a reasonable default value. (Default is not always provided, because
	different tool kits and environments have different reasonable
	defaults.)

	The widget needs to support a number of different interactions with
	the user. Each of them is described below.

	@table @gnupgtabopt
	@item Passphrase Confirmation

	When creating a new key, the passphrase should be entered twice. The
	client (typically GPG Agent) indicates this to the @pinentry{} by
	invoking @code{SETREPEAT}. In this case, the backend sets the
	@code{repeat_passphrase} field to a copy of the passed string. The
	value of this field should be used to label a second text input.

	It is the frontend's responsibility to check that the passwords match.
	If they don't match, the frontend should display an error message and
	continue to prompt the user.

	If the passwords do match, then, when the user presses the okay
	button, the @code{repeat_okay} field should be set to @code{1} (this
	causes the backend to emit the @code{S PIN_REPEATED} status message).

	@item Message Box

	Sometimes GPG Agent needs to display a message. In this case, the
	@code{pin} variable is @code{NULL}.

	At the Assuan level, this mode is selected by using either the
	@code{MESSAGE} or the @code{CONFIRM} command instead of the
	@code{GETPIN} command. The @code{MESSAGE} command never shows the
	cancel or an other button. The same holds for @code{CONFIRM} if it
	was passed the ``--one-button'' argument. If @code{CONFIRM} was not
	passed this argument, the dialog for @code{CONFIRM} should show both
	the @code{ok} and the @code{cancel} buttons and optionally the
	@code{notok} button. The frontend can determine whether the dialog is
	a one-button dialog by inspecting the @code{one_button} variable.

	@item Passphrase Entry

	If neither of the above cases holds, then GPG Agent is simply
	requesting the passphrase. In this case, the @code{ok} and
	@code{cancel} buttons should be displayed.

	@end table

	The layout of the three variants is quite similar. Here are the
	relevant elements that describe the layout:

	@table @gnupgtabopt
	@item @code{title}
	The window's title.

	@item @code{description}
	The reason for the dialog. When requesting a passphrase, this
	describes the key. When showing a message box, this is the message to
	show.

	@item @code{error}
	If GPG Agent determines that the passphrase was incorrect, it will
	call @code{GETPIN} again (up to a configurable number of times) to
	again prompt the user. In this case, this variable contains a
	description of the error message. This text should typically be
	highlighted in someway.

	@item @code{prompt}, @code{default-prompt}
	The string to associate with the passphrase entry box.

	There is a subtle difference between @code{prompt} and
	@code{default-prompt}. @code{default-prompt} means that a stylized
	prompt (e.g., an icon suggesting a prompt) may be used. @code{prompt}
	means that the entry's meaning is not consistent with such a style
	and, as such, no icon should be used.

	If both variables are set, the @code{prompt} variant takes precedence.

	@item @code{repeat_passphrase}
	The string to associate with the second passphrase entry box. The
	second passphrase entry box should only be shown if this is not
	@code{NULL}.

	@item @code{ok}, @code{default-ok}
	The string to show in the @code{ok} button.

	If there are any @code{_} characters, the following character should
	be used as an accelerator. (A double underscore means a plain
	underscore should be shown.) If the frontend does not support
	accelerators, then the underscores should be removed manually.

	There is a subtle difference between @code{ok} and @code{default-ok}.
	@code{default-ok} means that a stylized OK button should be used. For
	instance, it could include a check mark. @code{ok} means that the
	button's meaning is not consistent with such an icon and, as such, no
	icon should be used. Thus, if the @code{ok} button should have the
	text ``No password required'' then @code{ok} should be used because a
	check mark icon doesn't make sense.

	If this variable is @code{NULL}, the frontend should choose a
	reasonable default.

	If both variables are set, the @code{ok} variant takes precedence.

	@item @code{cancel}, @code{default-cancel}
	Like the @code{ok} and @code{default-ok} buttons except these strings
	are used for the cancel button.

	This button should not be shown if @code{one_button} is set.

	@code{default-notok}
	Like the @code{default-ok} button except this string is used for the
	other button.

	This button should only be displayed when showing a message box. If
	these variables are @code{NULL} or @code{one_button} is set, this
	button should not be displayed.

	@item @code{quality_bar}
	If this is set, a widget should be used to show the password's
	quality. The value of this field is a label for the widget.

	Note: to update the password quality, whenever the password changes,
	call the @code{pinentry_inq_quality} function and then update the
	password quality widget correspondingly.

	@item @code{quality_bar_tt}
	A tooltip for the quality bar.

	@item @code{default_pwmngr}
	If @code{may_cache_password} and @code{keyinfo} are set and the user
	consents, then the @pinentry{} may cache the password with an external
	manager. Note: getting the user's consent is essential, because
	password managers often provide a different level of security. If the
	above condition is true and @code{tried_password_cache} is false, then
	a check box with the specified string should be displayed. The check
	box must default to off.

	@item @code{default-cf-visi}
	The string to show with a question if you want to confirm that
	the user wants to change the visibility of the password.

	@item @code{default-tt-visi}
	Tooltip for an action that would reveal the entered password.

	@item @code{default-tt-hide}
	Tooltip for an action that would hide the password revealed
	by the action labeld with @code{default-tt-visi}

	@end table

	When the handler is done, it should store the passphrase in
	@code{pin}, if appropriate. This variable is allocated in secure
	memory. Use @code{pinentry_setbufferlen} to size the buffer.

	The actual return code is dependent on whether the dialog is in
	message mode or in passphrase mode.

	If the dialog is in message mode and the user pressed ok, return 1.
	Otherwise, return 0. If an error occurred, indicate this by setting it
	in @code{specific_err} or setting @code{locale_err} to @code{1} (for
	locale specific errors). If the dialog was canceled, then the handler
	should set the @code{canceled} variable to @code{1}. If the not ok
	button was pressed, don't do anything else.

	If the dialog is in passphrase mode return @code{1} if the user
	entered a password and pressed ok. If an error occurred, return
	@code{-1} and set @code{specific_err} or @code{locale_err}, as above.
	If the user canceled the dialog box, return @code{-1}.

	If the window was closed, then the handler should set the
	@code{close_button} variable and otherwise act as if the cancel button
	was pressed.



	@c ---------------------------------------------------------------------
	@c Legal Blurbs
	@c ---------------------------------------------------------------------

	@include gpl.texi

	@c ---------------------------------------------------------------------
	@c Indexes
	@c ---------------------------------------------------------------------

	@node Option Index
	@unnumbered Option Index

	@printindex op

	@node Index
	@unnumbered Index

	@printindex cp

	@c ---------------------------------------------------------------------
	@c Epilogue
	@c ---------------------------------------------------------------------

	@bye

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