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/* sig-check.c - Check a signature
* Copyright (c) 1997 by Werner Koch (dd9jn)
*
* This file is part of G10.
*
* G10 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.
*
* G10 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 "util.h"
#include "packet.h"
#include "memory.h"
#include "mpi.h"
#include "keydb.h"
#include "cipher.h"
#include "main.h"
/****************
* Check the signature which is contained in the rsa_integer.
* The md5handle should be currently open, so that this function
* is able to append some data, before getting the digest.
*/
int
signature_check( PKT_signature *sig, MD_HANDLE *digest )
{
PKT_public_cert *pkc = m_alloc_clear( sizeof *pkc );
MPI result = NULL;
int rc=0, i, j, c, old_enc;
byte *dp;
if( get_pubkey( pkc, sig->keyid ) ) {
rc = G10ERR_NO_PUBKEY;
goto leave;
}
if( pkc->pubkey_algo == PUBKEY_ALGO_ELGAMAL ) {
ELG_public_key pkey;
if( (rc=md_okay(sig->d.elg.digest_algo)) )
goto leave;
/* complete the digest */
md_putchar( digest, sig->sig_class );
{ u32 a = sig->timestamp;
md_putchar( digest, (a >> 24) & 0xff );
md_putchar( digest, (a >> 16) & 0xff );
md_putchar( digest, (a >> 8) & 0xff );
md_putchar( digest, a & 0xff );
}
result = encode_md_value( digest, mpi_get_nbits(pkc->d.elg.p));
pkey.p = pkc->d.elg.p;
pkey.g = pkc->d.elg.g;
pkey.y = pkc->d.elg.y;
if( !elg_verify( sig->d.elg.a, sig->d.elg.b, result, &pkey ) )
rc = G10ERR_BAD_SIGN;
}
#ifdef HAVE_RSA_CIPHER
else if( pkc->pubkey_algo == PUBKEY_ALGO_RSA ) {
RSA_public_key pkey;
result = mpi_alloc(40);
pkey.n = pkc->d.rsa.rsa_n;
pkey.e = pkc->d.rsa.rsa_e;
rsa_public( result, sig->d.rsa.rsa_integer, &pkey );
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");
rc = G10ERR_GENERAL;
goto leave;
}
if( sig->d.rsa.digest_algo == DIGEST_ALGO_RMD160 ) {
static byte asn[18] = /* stored reverse FIXME: need other values*/
{ 0x10, 0x04, 0x00, 0x05, 0x05, 0x02, 0x0d, 0xf7, 0x86,
0x48, 0x86, 0x2a, 0x08, 0x06, 0x0c, 0x30, 0x20, 0x30 };
for(i=20,j=0; (c=mpi_getbyte(result, i)) != -1 && j < 18; i++, j++ )
if( asn[j] != c )
break;
if( j != 18 || mpi_getbyte(result, i) ) { /* ASN is wrong */
rc = G10ERR_BAD_PUBKEY;
goto leave;
}
for(i++; (c=mpi_getbyte(result, i)) != -1; i++ )
if( c != 0xff )
break;
i++;
if( c != DIGEST_ALGO_RMD160 || mpi_getbyte(result, i) ) {
/* Padding or leading bytes in signature is wrong */
rc = G10ERR_BAD_PUBKEY;
goto leave;
}
if( mpi_getbyte(result, 19) != sig->d.rsa.digest_start[0]
|| mpi_getbyte(result, 18) != sig->d.rsa.digest_start[1] ) {
/* Wrong key used to check the signature */
rc = G10ERR_BAD_PUBKEY;
goto leave;
}
/* complete the digest */
md_putchar( digest, sig->sig_class );
{ u32 a = sig->timestamp;
md_putchar( digest, (a >> 24) & 0xff );
md_putchar( digest, (a >> 16) & 0xff );
md_putchar( digest, (a >> 8) & 0xff );
md_putchar( digest, a & 0xff );
}
dp = md_final( digest );
for(i=19; i >= 0; i--, dp++ )
if( mpi_getbyte( result, i ) != *dp ) {
rc = G10ERR_BAD_SIGN;
goto leave;
}
}
else if( sig->d.rsa.digest_algo == DIGEST_ALGO_MD5 ) {
static byte asn[18] = /* stored reverse */
{ 0x10, 0x04, 0x00, 0x05, 0x05, 0x02, 0x0d, 0xf7, 0x86,
0x48, 0x86, 0x2a, 0x08, 0x06, 0x0c, 0x30, 0x20, 0x30 };
for(i=16,j=0; j < 18 && (c=mpi_getbyte(result, i)) != -1; i++, j++ )
if( asn[j] != c )
break;
if( j != 18 || mpi_getbyte(result, i) ) { /* ASN is wrong */
rc = G10ERR_BAD_PUBKEY;
goto leave;
}
for(i++; (c=mpi_getbyte(result, i)) != -1; i++ )
if( c != 0xff )
break;
i++;
if( c != DIGEST_ALGO_MD5 || mpi_getbyte(result, i) ) {
/* Padding or leading bytes in signature is wrong */
rc = G10ERR_BAD_PUBKEY;
goto leave;
}
if( mpi_getbyte(result, 15) != sig->d.rsa.digest_start[0]
|| mpi_getbyte(result, 14) != sig->d.rsa.digest_start[1] ) {
/* Wrong key used to check the signature */
rc = G10ERR_BAD_PUBKEY;
goto leave;
}
/* complete the digest */
md_putchar( digest, sig->sig_class );
{ u32 a = sig->timestamp;
md_putchar( digest, (a >> 24) & 0xff );
md_putchar( digest, (a >> 16) & 0xff );
md_putchar( digest, (a >> 8) & 0xff );
md_putchar( digest, a & 0xff );
}
dp = md_final( digest );
for(i=15; i >= 0; i--, dp++ )
if( mpi_getbyte( result, i ) != *dp ) {
rc = G10ERR_BAD_SIGN;
goto leave;
}
}
else {
rc = G10ERR_DIGEST_ALGO;
goto leave;
}
}
#endif/*HAVE_RSA_CIPHER*/
else {
log_debug("signature_check: unsupported pubkey algo %d\n",
pkc->pubkey_algo );
rc = G10ERR_PUBKEY_ALGO;
goto leave;
}
leave:
if( pkc )
free_public_cert( pkc );
mpi_free( result );
return rc;
}
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