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sig-check.c
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/* sig-check.c - Check a signature
* Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it 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.
*
* GnuPG 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.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <gcrypt.h>
#include "util.h"
#include "packet.h"
#include "keydb.h"
#include "main.h"
#include "status.h"
#include "i18n.h"
#include "options.h"
struct cmp_help_context_s {
PKT_signature *sig;
GCRY_MD_HD md;
};
static int do_signature_check( PKT_signature *sig, GCRY_MD_HD digest,
u32 *r_expiredate, int *r_expired );
static int do_check( PKT_public_key *pk, PKT_signature *sig,
GCRY_MD_HD digest, int *r_expired );
/****************
* Emulate our old PK interface here - sometime in the future we might
* change the internal design to directly fit to libgcrypt.
*/
static int
pk_verify( int algo, MPI hash, MPI *data, MPI *pkey,
int (*cmp)(void *, MPI), void *opaque )
{
GCRY_SEXP s_sig, s_hash, s_pkey;
int rc;
/* forget about cmp and opaque - we never used it */
/* make a sexp from pkey */
if( algo == GCRY_PK_DSA ) {
rc = gcry_sexp_build ( &s_pkey, NULL,
"(public-key(dsa(p%m)(q%m)(g%m)(y%m)))",
pkey[0], pkey[1], pkey[2], pkey[3] );
}
else if( algo == GCRY_PK_ELG || algo == GCRY_PK_ELG_E ) {
rc = gcry_sexp_build ( &s_pkey, NULL,
"(public-key(elg(p%m)(g%m)(y%m)))",
pkey[0], pkey[1], pkey[2] );
}
else if( algo == GCRY_PK_RSA ) {
rc = gcry_sexp_build ( &s_pkey, NULL,
"(public-key(rsa(n%m)(e%m)))",
pkey[0], pkey[1] );
}
else
return GPGERR_PUBKEY_ALGO;
if ( rc )
BUG ();
/* put hash into a S-Exp s_hash */
if ( gcry_sexp_build( &s_hash, NULL, "%m", hash ) )
BUG ();
/* put data into a S-Exp s_sig */
if( algo == GCRY_PK_DSA ) {
rc = gcry_sexp_build ( &s_sig, NULL,
"(sig-val(dsa(r%m)(s%m)))", data[0], data[1] );
}
else if( algo == GCRY_PK_ELG || algo == GCRY_PK_ELG_E ) {
rc = gcry_sexp_build ( &s_sig, NULL,
"(sig-val(elg(r%m)(s%m)))", data[0], data[1] );
}
else if( algo == GCRY_PK_RSA ) {
rc = gcry_sexp_build ( &s_sig, NULL,
"(sig-val(rsa(s%m)))", data[0] );
}
else
BUG();
if ( rc )
BUG ();
rc = gcry_pk_verify( s_sig, s_hash, s_pkey );
gcry_sexp_release( s_sig );
gcry_sexp_release( s_hash );
gcry_sexp_release( s_pkey );
return rc;
}
/****************
* Check the signature which is contained in SIG.
* The GCRY_MD_HD should be currently open, so that this function
* is able to append some data, before finalizing the digest.
*/
int
signature_check( PKT_signature *sig, GCRY_MD_HD digest )
{
u32 dummy;
int dum2;
return do_signature_check( sig, digest, &dummy, &dum2 );
}
static int
do_signature_check( PKT_signature *sig, GCRY_MD_HD digest,
u32 *r_expiredate, int *r_expired )
{
PKT_public_key *pk = gcry_xcalloc( 1, sizeof *pk );
int rc=0;
*r_expiredate = 0;
if( get_pubkey( pk, sig->keyid ) )
rc = GPGERR_NO_PUBKEY;
else {
*r_expiredate = pk->expiredate;
rc = do_check( pk, sig, digest, r_expired );
}
free_public_key( pk );
if( !rc && sig->sig_class < 2 && is_status_enabled() ) {
/* This signature id works best with DLP algorithms because
* they use a random parameter for every signature. Instead of
* this sig-id we could have also used the hash of the document
* and the timestamp, but the drawback of this is, that it is
* not possible to sign more than one identical document within
* one second. Some remote bacth processing applications might
* like this feature here */
GCRY_MD_HD md;
u32 a = sig->timestamp;
int i, nsig = pubkey_get_nsig( sig->pubkey_algo );
byte *p, *buffer;
if( !(md = gcry_md_open( GCRY_MD_RMD160, 0)) )
BUG();
gcry_md_putc( digest, sig->pubkey_algo );
gcry_md_putc( digest, sig->digest_algo );
gcry_md_putc( digest, (a >> 24) & 0xff );
gcry_md_putc( digest, (a >> 16) & 0xff );
gcry_md_putc( digest, (a >> 8) & 0xff );
gcry_md_putc( digest, a & 0xff );
for(i=0; i < nsig; i++ ) {
size_t n = gcry_mpi_get_nbits( sig->data[i]);
gcry_md_putc( md, n>>8);
gcry_md_putc( md, n );
if( gcry_mpi_aprint( GCRYMPI_FMT_USG, &p, &n, sig->data[i] ) )
BUG();
gcry_md_write( md, p, n );
gcry_free(p);
}
gcry_md_final( md );
p = make_radix64_string( gcry_md_read( md, 0 ), 20 );
buffer = gcry_xmalloc( strlen(p) + 60 );
sprintf( buffer, "%s %s %lu",
p, strtimestamp( sig->timestamp ), (ulong)sig->timestamp );
write_status_text( STATUS_SIG_ID, buffer );
gcry_free(buffer);
gcry_free(p);
gcry_md_close(md);
}
return rc;
}
/****************
* This function gets called by pubkey_verify() if the algorithm needs it.
*/
static int
cmp_help( void *opaque, MPI result )
{
#if 0 /* we do not use this anymore */
int rc=0, i, j, c, old_enc;
byte *dp;
const byte *asn;
size_t mdlen, asnlen;
struct cmp_help_context_s *ctx = opaque;
PKT_signature *sig = ctx->sig;
GCRY_MD_HD digest = ctx->md;
old_enc = 0;
for(i=j=0; (c=mpi_getbyte(result, i)) != -1; i++ ) {
if( !j ) {
if( !i && c != 1 )
break;
else if( i && c == 0xff )
; /* skip the padding */
else if( i && !c )
j++;
else
break;
}
else if( ++j == 18 && c != 1 )
break;
else if( j == 19 && c == 0 ) {
old_enc++;
break;
}
}
if( old_enc ) {
log_error("old encoding scheme is not supported\n");
return GPGERR_GENERAL;
}
if( (rc=check_digest_algo(sig->digest_algo)) )
return rc; /* unsupported algo */
asn = md_asn_oid( sig->digest_algo, &asnlen, &mdlen );
for(i=mdlen,j=asnlen-1; (c=mpi_getbyte(result, i)) != -1 && j >= 0;
i++, j-- )
if( asn[j] != c )
break;
if( j != -1 || mpi_getbyte(result, i) )
return GPGERR_BAD_PUBKEY; /* ASN is wrong */
for(i++; (c=mpi_getbyte(result, i)) != -1; i++ )
if( c != 0xff )
break;
i++;
if( c != sig->digest_algo || mpi_getbyte(result, i) ) {
/* Padding or leading bytes in signature is wrong */
return GPGERR_BAD_PUBKEY;
}
if( mpi_getbyte(result, mdlen-1) != sig->digest_start[0]
|| mpi_getbyte(result, mdlen-2) != sig->digest_start[1] ) {
/* Wrong key used to check the signature */
return GPGERR_BAD_PUBKEY;
}
dp = md_read( digest, sig->digest_algo );
for(i=mdlen-1; i >= 0; i--, dp++ ) {
if( mpi_getbyte( result, i ) != *dp )
return GPGERR_BAD_SIGN;
}
return 0;
#else
return -1;
#endif
}
static int
do_check( PKT_public_key *pk, PKT_signature *sig, GCRY_MD_HD digest,
int *r_expired )
{
MPI result = NULL;
int rc=0;
struct cmp_help_context_s ctx;
u32 cur_time;
*r_expired = 0;
if( pk->version == 4 && pk->pubkey_algo == GCRY_PK_ELG_E ) {
log_info(_("this is a PGP generated "
"ElGamal key which is NOT secure for signatures!\n"));
return GPGERR_PUBKEY_ALGO;
}
if( pk->timestamp > sig->timestamp ) {
ulong d = pk->timestamp - sig->timestamp;
log_info( d==1
? _("public key is %lu second newer than the signature\n")
: _("public key is %lu seconds newer than the signature\n"),
d );
if( !opt.ignore_time_conflict )
return GPGERR_TIME_CONFLICT; /* pubkey newer than signature */
}
cur_time = make_timestamp();
if( pk->timestamp > cur_time ) {
ulong d = pk->timestamp - cur_time;
log_info( d==1 ? _("key has been created %lu second "
"in future (time warp or clock problem)\n")
: _("key has been created %lu seconds "
"in future (time warp or clock problem)\n"), d );
if( !opt.ignore_time_conflict )
return GPGERR_TIME_CONFLICT;
}
if( pk->expiredate && pk->expiredate < cur_time ) {
log_info(_("NOTE: signature key expired %s\n"),
asctimestamp( pk->expiredate ) );
write_status(STATUS_SIGEXPIRED);
*r_expired = 1;
}
if( (rc=openpgp_md_test_algo(sig->digest_algo)) )
return rc;
if( (rc=openpgp_pk_test_algo(sig->pubkey_algo, 0)) )
return rc;
/* make sure the digest algo is enabled (in case of a detached signature)*/
gcry_md_enable( digest, sig->digest_algo );
/* complete the digest */
if( sig->version >= 4 )
gcry_md_putc( digest, sig->version );
gcry_md_putc( digest, sig->sig_class );
if( sig->version < 4 ) {
u32 a = sig->timestamp;
gcry_md_putc( digest, (a >> 24) & 0xff );
gcry_md_putc( digest, (a >> 16) & 0xff );
gcry_md_putc( digest, (a >> 8) & 0xff );
gcry_md_putc( digest, a & 0xff );
}
else {
byte buf[6];
size_t n;
gcry_md_putc( digest, sig->pubkey_algo );
gcry_md_putc( digest, sig->digest_algo );
if( sig->hashed_data ) {
n = (sig->hashed_data[0] << 8) | sig->hashed_data[1];
gcry_md_write( digest, sig->hashed_data, n+2 );
n += 6;
}
else
n = 6;
/* add some magic */
buf[0] = sig->version;
buf[1] = 0xff;
buf[2] = n >> 24;
buf[3] = n >> 16;
buf[4] = n >> 8;
buf[5] = n;
gcry_md_write( digest, buf, 6 );
}
gcry_md_final( digest );
result = encode_md_value( pk->pubkey_algo, digest, sig->digest_algo,
gcry_mpi_get_nbits(pk->pkey[0]), 0);
ctx.sig = sig;
ctx.md = digest;
rc = pk_verify( pk->pubkey_algo, result, sig->data, pk->pkey,
cmp_help, &ctx );
mpi_release( result );
if( (opt.emulate_bugs & EMUBUG_MDENCODE)
&& rc == GPGERR_BAD_SIGN && is_ELGAMAL(pk->pubkey_algo) ) {
/* In this case we try again because old GnuPG versions didn't encode
* the hash right. There is no problem with DSA however */
result = encode_md_value( pk->pubkey_algo, digest, sig->digest_algo,
gcry_mpi_get_nbits(pk->pkey[0]), (sig->version < 5) );
ctx.sig = sig;
ctx.md = digest;
rc = pk_verify( pk->pubkey_algo, result, sig->data, pk->pkey,
cmp_help, &ctx );
}
if( !rc && sig->flags.unknown_critical ) {
log_info(_("assuming bad signature due to an unknown critical bit\n"));
rc = GPGERR_BAD_SIGN;
}
sig->flags.checked = 1;
sig->flags.valid = !rc;
return rc;
}
static void
hash_uid_node( KBNODE unode, GCRY_MD_HD md, PKT_signature *sig )
{
PKT_user_id *uid = unode->pkt->pkt.user_id;
assert( unode->pkt->pkttype == PKT_USER_ID );
if( uid->photo ) {
if( sig->version >=4 ) {
byte buf[5];
buf[0] = 0xd1; /* packet of type 17 */
buf[1] = uid->photolen >> 24; /* always use 4 length bytes */
buf[2] = uid->photolen >> 16;
buf[3] = uid->photolen >> 8;
buf[4] = uid->photolen;
gcry_md_write( md, buf, 5 );
}
gcry_md_write( md, uid->photo, uid->photolen );
}
else {
if( sig->version >=4 ) {
byte buf[5];
buf[0] = 0xb4; /* indicates a userid packet */
buf[1] = uid->len >> 24; /* always use 4 length bytes */
buf[2] = uid->len >> 16;
buf[3] = uid->len >> 8;
buf[4] = uid->len;
gcry_md_write( md, buf, 5 );
}
gcry_md_write( md, uid->name, uid->len );
}
}
/****************
* check the signature pointed to by NODE. This is a key signature.
* If the function detects a self-signature, it uses the PK from
* ROOT and does not read any public key.
*/
int
check_key_signature( KBNODE root, KBNODE node, int *is_selfsig )
{
u32 dummy;
int dum2;
return check_key_signature2(root, node, is_selfsig, &dummy, &dum2 );
}
int
check_key_signature2( KBNODE root, KBNODE node, int *is_selfsig,
u32 *r_expiredate, int *r_expired )
{
GCRY_MD_HD md;
PKT_public_key *pk;
PKT_signature *sig;
int algo;
int rc;
if( is_selfsig )
*is_selfsig = 0;
*r_expiredate = 0;
*r_expired = 0;
assert( node->pkt->pkttype == PKT_SIGNATURE );
assert( root->pkt->pkttype == PKT_PUBLIC_KEY );
pk = root->pkt->pkt.public_key;
sig = node->pkt->pkt.signature;
algo = sig->digest_algo;
#if 0
if( sig->flags.checked ) {
log_debug("check_key_signature: already checked: %s\n",
sig->flags.valid? "good":"bad" );
if ( sig->flags.valid )
return 0; /* shortcut already checked signatures */
/* FIXME: We should also do this with bad signatures but here we
* have to distinguish between several reasons; e.g. for a missing
* public key. the key may now be available.
* For now we simply don't shortcut bad signatures
*/
}
#endif
if( (rc=openpgp_md_test_algo(algo)) )
return rc;
if( sig->sig_class == 0x20 ) {
if( !(md = gcry_md_open( algo, 0 )) )
BUG();
hash_public_key( md, pk );
rc = do_check( pk, sig, md, r_expired );
gcry_md_close(md);
}
else if( sig->sig_class == 0x28 ) { /* subkey revocation */
KBNODE snode = find_prev_kbnode( root, node, PKT_PUBLIC_SUBKEY );
if( snode ) {
if( !(md = gcry_md_open( algo, 0 )) )
BUG();
hash_public_key( md, pk );
hash_public_key( md, snode->pkt->pkt.public_key );
rc = do_check( pk, sig, md, r_expired );
gcry_md_close(md);
}
else {
log_error("no subkey for subkey revocation packet\n");
rc = GPGERR_SIG_CLASS;
}
}
else if( sig->sig_class == 0x18 ) {
KBNODE snode = find_prev_kbnode( root, node, PKT_PUBLIC_SUBKEY );
if( snode ) {
if( is_selfsig ) { /* does this make sense????? */
u32 keyid[2]; /* it should always be a selfsig */
keyid_from_pk( pk, keyid );
if( keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1] )
*is_selfsig = 1;
}
if( !(md = gcry_md_open( algo, 0 )) )
BUG();
hash_public_key( md, pk );
hash_public_key( md, snode->pkt->pkt.public_key );
rc = do_check( pk, sig, md, r_expired );
gcry_md_close(md);
}
else {
log_error("no subkey for key signature packet\n");
rc = GPGERR_SIG_CLASS;
}
}
else {
KBNODE unode = find_prev_kbnode( root, node, PKT_USER_ID );
if( unode ) {
u32 keyid[2];
keyid_from_pk( pk, keyid );
if( !(md = gcry_md_open( algo, 0 )) )
BUG();
hash_public_key( md, pk );
hash_uid_node( unode, md, sig );
if( keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1] ) {
if( is_selfsig )
*is_selfsig = 1;
rc = do_check( pk, sig, md, r_expired );
}
else {
rc = do_signature_check( sig, md, r_expiredate, r_expired );
}
gcry_md_close(md);
}
else {
log_error("no user ID for key signature packet\n");
rc = GPGERR_SIG_CLASS;
}
}
return rc;
}

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