mirror of
git://git.gnupg.org/gnupg.git
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265 lines
6.9 KiB
C
265 lines
6.9 KiB
C
/* sig-check.c - Check a signature
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* Copyright (c) 1997 by Werner Koch (dd9jn)
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*
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* This file is part of G10.
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*
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* G10 is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* G10 is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <assert.h>
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#include "util.h"
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#include "packet.h"
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#include "memory.h"
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#include "mpi.h"
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#include "keydb.h"
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#include "cipher.h"
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#include "main.h"
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/****************
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* Check the signature which is contained in the rsa_integer.
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* The md5handle should be currently open, so that this function
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* is able to append some data, before getting the digest.
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*/
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int
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signature_check( PKT_signature *sig, MD_HANDLE *digest )
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{
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PKT_public_cert *pkc = m_alloc_clear( sizeof *pkc );
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MPI result = NULL;
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int rc=0, i, j, c, old_enc;
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byte *dp;
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if( get_pubkey( pkc, sig->keyid ) ) {
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rc = G10ERR_NO_PUBKEY;
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goto leave;
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}
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if( pkc->pubkey_algo == PUBKEY_ALGO_ELGAMAL ) {
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ELG_public_key pkey;
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if( (rc=md_okay(sig->d.elg.digest_algo)) )
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goto leave;
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/* complete the digest */
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md_putchar( digest, sig->sig_class );
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{ u32 a = sig->timestamp;
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md_putchar( digest, (a >> 24) & 0xff );
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md_putchar( digest, (a >> 16) & 0xff );
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md_putchar( digest, (a >> 8) & 0xff );
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md_putchar( digest, a & 0xff );
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}
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result = encode_md_value( digest, mpi_get_nbits(pkc->d.elg.p));
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pkey.p = pkc->d.elg.p;
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pkey.g = pkc->d.elg.g;
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pkey.y = pkc->d.elg.y;
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if( !elg_verify( sig->d.elg.a, sig->d.elg.b, result, &pkey ) )
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rc = G10ERR_BAD_SIGN;
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}
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#ifdef HAVE_RSA_CIPHER
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else if( pkc->pubkey_algo == PUBKEY_ALGO_RSA ) {
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RSA_public_key pkey;
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result = mpi_alloc(40);
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pkey.n = pkc->d.rsa.rsa_n;
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pkey.e = pkc->d.rsa.rsa_e;
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rsa_public( result, sig->d.rsa.rsa_integer, &pkey );
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old_enc = 0;
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for(i=j=0; (c=mpi_getbyte(result, i)) != -1; i++ ) {
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if( !j ) {
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if( !i && c != 1 )
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break;
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else if( i && c == 0xff )
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; /* skip the padding */
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else if( i && !c )
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j++;
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else
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break;
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}
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else if( ++j == 18 && c != 1 )
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break;
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else if( j == 19 && c == 0 ) {
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old_enc++;
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break;
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}
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}
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if( old_enc ) {
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log_error("old encoding scheme is not supported\n");
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rc = G10ERR_GENERAL;
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goto leave;
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}
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if( sig->d.rsa.digest_algo == DIGEST_ALGO_RMD160 ) {
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static byte asn[15] = /* stored reverse */
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{ 0x14, 0x04, 0x00, 0x05, 0x01, 0x02, 0x03, 0x24, 0x2b,
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0x05, 0x06, 0x09, 0x30, 0x21, 0x30 };
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for(i=20,j=0; (c=mpi_getbyte(result, i)) != -1 && j < 15; i++, j++ )
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if( asn[j] != c )
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break;
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if( j != 15 || mpi_getbyte(result, i) ) { /* ASN is wrong */
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rc = G10ERR_BAD_PUBKEY;
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goto leave;
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}
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for(i++; (c=mpi_getbyte(result, i)) != -1; i++ )
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if( c != 0xff )
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break;
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i++;
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if( c != DIGEST_ALGO_RMD160 || mpi_getbyte(result, i) ) {
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/* Padding or leading bytes in signature is wrong */
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rc = G10ERR_BAD_PUBKEY;
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goto leave;
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}
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if( mpi_getbyte(result, 19) != sig->d.rsa.digest_start[0]
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|| mpi_getbyte(result, 18) != sig->d.rsa.digest_start[1] ) {
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/* Wrong key used to check the signature */
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rc = G10ERR_BAD_PUBKEY;
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goto leave;
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}
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/* complete the digest */
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md_putchar( digest, sig->sig_class );
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{ u32 a = sig->timestamp;
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md_putchar( digest, (a >> 24) & 0xff );
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md_putchar( digest, (a >> 16) & 0xff );
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md_putchar( digest, (a >> 8) & 0xff );
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md_putchar( digest, a & 0xff );
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}
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dp = md_final( digest );
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for(i=19; i >= 0; i--, dp++ )
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if( mpi_getbyte( result, i ) != *dp ) {
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rc = G10ERR_BAD_SIGN;
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goto leave;
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}
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}
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else if( sig->d.rsa.digest_algo == DIGEST_ALGO_MD5 ) {
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static byte asn[18] = /* stored reverse */
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{ 0x10, 0x04, 0x00, 0x05, 0x05, 0x02, 0x0d, 0xf7, 0x86,
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0x48, 0x86, 0x2a, 0x08, 0x06, 0x0c, 0x30, 0x20, 0x30 };
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for(i=16,j=0; j < 18 && (c=mpi_getbyte(result, i)) != -1; i++, j++ )
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if( asn[j] != c )
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break;
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if( j != 18 || mpi_getbyte(result, i) ) { /* ASN is wrong */
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rc = G10ERR_BAD_PUBKEY;
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goto leave;
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}
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for(i++; (c=mpi_getbyte(result, i)) != -1; i++ )
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if( c != 0xff )
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break;
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i++;
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if( c != DIGEST_ALGO_MD5 || mpi_getbyte(result, i) ) {
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/* Padding or leading bytes in signature is wrong */
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rc = G10ERR_BAD_PUBKEY;
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goto leave;
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}
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if( mpi_getbyte(result, 15) != sig->d.rsa.digest_start[0]
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|| mpi_getbyte(result, 14) != sig->d.rsa.digest_start[1] ) {
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/* Wrong key used to check the signature */
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rc = G10ERR_BAD_PUBKEY;
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goto leave;
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}
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/* complete the digest */
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md_putchar( digest, sig->sig_class );
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{ u32 a = sig->timestamp;
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md_putchar( digest, (a >> 24) & 0xff );
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md_putchar( digest, (a >> 16) & 0xff );
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md_putchar( digest, (a >> 8) & 0xff );
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md_putchar( digest, a & 0xff );
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}
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dp = md_final( digest );
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for(i=15; i >= 0; i--, dp++ )
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if( mpi_getbyte( result, i ) != *dp ) {
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rc = G10ERR_BAD_SIGN;
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goto leave;
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}
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}
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else {
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rc = G10ERR_DIGEST_ALGO;
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goto leave;
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}
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}
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#endif/*HAVE_RSA_CIPHER*/
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else {
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/*log_debug("signature_check: unsupported pubkey algo %d\n",
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pkc->pubkey_algo );*/
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rc = G10ERR_PUBKEY_ALGO;
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goto leave;
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}
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leave:
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if( pkc )
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free_public_cert( pkc );
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mpi_free( result );
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return rc;
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}
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/****************
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* check the signature pointed to by NODE. This is a key signatures
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*/
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int
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check_key_signature( KBNODE root, KBNODE node )
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{
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KBNODE unode;
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MD_HANDLE *md;
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PKT_public_cert *pkc;
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PKT_signature *sig;
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int algo;
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int rc;
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assert( node->pkt->pkttype == PKT_SIGNATURE );
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assert( (node->pkt->pkt.signature->sig_class&~3) == 0x10 );
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assert( root->pkt->pkttype == PKT_PUBLIC_CERT );
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pkc = root->pkt->pkt.public_cert;
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sig = node->pkt->pkt.signature;
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if( sig->pubkey_algo == PUBKEY_ALGO_ELGAMAL )
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algo = sig->d.elg.digest_algo;
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else if(sig->pubkey_algo == PUBKEY_ALGO_RSA )
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algo = sig->d.rsa.digest_algo;
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else
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return G10ERR_PUBKEY_ALGO;
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if( (rc=md_okay(algo)) )
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return rc;
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unode = find_kbparent( root, node );
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if( unode && unode->pkt->pkttype == PKT_USER_ID ) {
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PKT_user_id *uid = unode->pkt->pkt.user_id;
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md = md_open( algo, 0 );
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hash_public_cert( md, pkc );
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md_write( md, uid->name, uid->len );
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rc = signature_check( sig, md );
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md_close(md);
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}
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else {
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log_error("no user id for key signature packet\n");
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rc = G10ERR_SIG_CLASS;
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}
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return rc;
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}
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