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git://git.gnupg.org/gnupg.git
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aedeefcc5f
digest algorithm is used with DSA. Changed all callers to cope with a NULL return. Problem noted by Imad R. Faiad.
517 lines
14 KiB
C
517 lines
14 KiB
C
/* sig-check.c - Check a signature
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* Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG 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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* GnuPG 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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#include "status.h"
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#include "i18n.h"
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#include "options.h"
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struct cmp_help_context_s {
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PKT_signature *sig;
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MD_HANDLE md;
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};
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static int do_check( PKT_public_key *pk, PKT_signature *sig,
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MD_HANDLE digest, int *r_expired );
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/****************
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* Check the signature which is contained in SIG.
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* The MD_HANDLE should be currently open, so that this function
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* is able to append some data, before finalizing 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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u32 dummy;
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int dum2;
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return signature_check2( sig, digest, &dummy, &dum2 );
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}
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int
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signature_check2( PKT_signature *sig, MD_HANDLE digest,
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u32 *r_expiredate, int *r_expired )
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{
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PKT_public_key *pk = m_alloc_clear( sizeof *pk );
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int rc=0;
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*r_expiredate = 0;
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if( get_pubkey( pk, sig->keyid ) )
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rc = G10ERR_NO_PUBKEY;
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else {
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*r_expiredate = pk->expiredate;
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rc = do_check( pk, sig, digest, r_expired );
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}
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free_public_key( pk );
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if( !rc && sig->sig_class < 2 && is_status_enabled() ) {
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/* This signature id works best with DLP algorithms because
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* they use a random parameter for every signature. Instead of
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* this sig-id we could have also used the hash of the document
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* and the timestamp, but the drawback of this is, that it is
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* not possible to sign more than one identical document within
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* one second. Some remote batch processing applications might
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* like this feature here */
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MD_HANDLE md;
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u32 a = sig->timestamp;
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int i, nsig = pubkey_get_nsig( sig->pubkey_algo );
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byte *p, *buffer;
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md = md_open( DIGEST_ALGO_RMD160, 0);
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md_putc( digest, sig->pubkey_algo );
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md_putc( digest, sig->digest_algo );
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md_putc( digest, (a >> 24) & 0xff );
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md_putc( digest, (a >> 16) & 0xff );
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md_putc( digest, (a >> 8) & 0xff );
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md_putc( digest, a & 0xff );
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for(i=0; i < nsig; i++ ) {
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unsigned n = mpi_get_nbits( sig->data[i]);
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md_putc( md, n>>8);
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md_putc( md, n );
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p = mpi_get_buffer( sig->data[i], &n, NULL );
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md_write( md, p, n );
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m_free(p);
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}
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md_final( md );
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p = make_radix64_string( md_read( md, 0 ), 20 );
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buffer = m_alloc( strlen(p) + 60 );
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sprintf( buffer, "%s %s %lu",
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p, strtimestamp( sig->timestamp ), (ulong)sig->timestamp );
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write_status_text( STATUS_SIG_ID, buffer );
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m_free(buffer);
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m_free(p);
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md_close(md);
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}
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return rc;
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}
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/****************
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* This function gets called by pubkey_verify() if the algorithm needs it.
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*/
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static int
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cmp_help( void *opaque, MPI result )
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{
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#if 0 /* we do not use this anymore */
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int rc=0, i, j, c, old_enc;
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byte *dp;
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const byte *asn;
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size_t mdlen, asnlen;
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struct cmp_help_context_s *ctx = opaque;
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PKT_signature *sig = ctx->sig;
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MD_HANDLE digest = ctx->md;
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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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return G10ERR_GENERAL;
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}
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if( (rc=check_digest_algo(sig->digest_algo)) )
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return rc; /* unsupported algo */
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asn = md_asn_oid( sig->digest_algo, &asnlen, &mdlen );
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for(i=mdlen,j=asnlen-1; (c=mpi_getbyte(result, i)) != -1 && j >= 0;
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i++, j-- )
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if( asn[j] != c )
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break;
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if( j != -1 || mpi_getbyte(result, i) )
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return G10ERR_BAD_PUBKEY; /* ASN is wrong */
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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 != sig->digest_algo || mpi_getbyte(result, i) ) {
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/* Padding or leading bytes in signature is wrong */
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return G10ERR_BAD_PUBKEY;
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}
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if( mpi_getbyte(result, mdlen-1) != sig->digest_start[0]
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|| mpi_getbyte(result, mdlen-2) != sig->digest_start[1] ) {
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/* Wrong key used to check the signature */
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return G10ERR_BAD_PUBKEY;
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}
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dp = md_read( digest, sig->digest_algo );
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for(i=mdlen-1; i >= 0; i--, dp++ ) {
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if( mpi_getbyte( result, i ) != *dp )
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return G10ERR_BAD_SIGN;
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}
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return 0;
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#else
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return -1;
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#endif
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}
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static int
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do_check( PKT_public_key *pk, PKT_signature *sig, MD_HANDLE digest,
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int *r_expired )
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{
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MPI result = NULL;
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int rc=0;
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struct cmp_help_context_s ctx;
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u32 cur_time;
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*r_expired = 0;
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if( pk->version == 4 && pk->pubkey_algo == PUBKEY_ALGO_ELGAMAL_E ) {
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log_info(_("this is a PGP generated "
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"ElGamal key which is NOT secure for signatures!\n"));
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return G10ERR_PUBKEY_ALGO;
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}
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if( pk->timestamp > sig->timestamp ) {
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ulong d = pk->timestamp - sig->timestamp;
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log_info( d==1
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? _("public key is %lu second newer than the signature\n")
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: _("public key is %lu seconds newer than the signature\n"),
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d );
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if( !opt.ignore_time_conflict )
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return G10ERR_TIME_CONFLICT; /* pubkey newer than signature */
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}
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cur_time = make_timestamp();
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if( pk->timestamp > cur_time ) {
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ulong d = pk->timestamp - cur_time;
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log_info( d==1 ? _("key has been created %lu second "
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"in future (time warp or clock problem)\n")
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: _("key has been created %lu seconds "
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"in future (time warp or clock problem)\n"), d );
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if( !opt.ignore_time_conflict )
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return G10ERR_TIME_CONFLICT;
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}
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if( pk->expiredate && pk->expiredate < cur_time ) {
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char buf[11];
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if (opt.verbose) {
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u32 tmp_kid[2];
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keyid_from_pk( pk, tmp_kid );
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log_info(_("NOTE: signature key %08lX expired %s\n"),
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(ulong)tmp_kid[1], asctimestamp( pk->expiredate ) );
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}
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/* SIGEXPIRED is deprecated. Use KEYEXPIRED. */
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sprintf(buf,"%lu",(ulong)pk->expiredate);
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write_status_text(STATUS_KEYEXPIRED,buf);
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write_status(STATUS_SIGEXPIRED);
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*r_expired = 1;
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}
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if( (rc=check_digest_algo(sig->digest_algo)) )
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return rc;
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if( (rc=check_pubkey_algo(sig->pubkey_algo)) )
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return rc;
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/* make sure the digest algo is enabled (in case of a detached signature)*/
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md_enable( digest, sig->digest_algo );
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/* complete the digest */
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if( sig->version >= 4 )
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md_putc( digest, sig->version );
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md_putc( digest, sig->sig_class );
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if( sig->version < 4 ) {
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u32 a = sig->timestamp;
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md_putc( digest, (a >> 24) & 0xff );
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md_putc( digest, (a >> 16) & 0xff );
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md_putc( digest, (a >> 8) & 0xff );
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md_putc( digest, a & 0xff );
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}
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else {
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byte buf[6];
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size_t n;
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md_putc( digest, sig->pubkey_algo );
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md_putc( digest, sig->digest_algo );
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if( sig->hashed ) {
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n = sig->hashed->len;
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md_putc (digest, (n >> 8) );
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md_putc (digest, n );
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md_write (digest, sig->hashed->data, n);
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n += 6;
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}
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else
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n = 6;
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/* add some magic */
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buf[0] = sig->version;
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buf[1] = 0xff;
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buf[2] = n >> 24;
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buf[3] = n >> 16;
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buf[4] = n >> 8;
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buf[5] = n;
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md_write( digest, buf, 6 );
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}
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md_final( digest );
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result = encode_md_value( pk->pubkey_algo, digest, sig->digest_algo,
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mpi_get_nbits(pk->pkey[0]), 0 );
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if (!result)
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return G10ERR_GENERAL;
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ctx.sig = sig;
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ctx.md = digest;
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rc = pubkey_verify( pk->pubkey_algo, result, sig->data, pk->pkey,
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cmp_help, &ctx );
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mpi_free( result );
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if( (opt.emulate_bugs & EMUBUG_MDENCODE)
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&& rc == G10ERR_BAD_SIGN && is_ELGAMAL(pk->pubkey_algo) ) {
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/* In this case we try again because old GnuPG versions didn't encode
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* the hash right. There is no problem with DSA however */
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result = encode_md_value( pk->pubkey_algo, digest, sig->digest_algo,
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mpi_get_nbits(pk->pkey[0]), (sig->version < 5) );
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if (!result)
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rc = G10ERR_GENERAL;
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else {
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ctx.sig = sig;
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ctx.md = digest;
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rc = pubkey_verify( pk->pubkey_algo, result, sig->data, pk->pkey,
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cmp_help, &ctx );
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}
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}
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if( !rc && sig->flags.unknown_critical ) {
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log_info(_("assuming bad signature due to an unknown critical bit\n"));
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rc = G10ERR_BAD_SIGN;
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}
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return rc;
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}
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static void
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hash_uid_node( KBNODE unode, MD_HANDLE md, PKT_signature *sig )
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{
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PKT_user_id *uid = unode->pkt->pkt.user_id;
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assert( unode->pkt->pkttype == PKT_USER_ID );
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if( uid->attrib_data ) {
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if( sig->version >=4 ) {
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byte buf[5];
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buf[0] = 0xd1; /* packet of type 17 */
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buf[1] = uid->attrib_len >> 24; /* always use 4 length bytes */
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buf[2] = uid->attrib_len >> 16;
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buf[3] = uid->attrib_len >> 8;
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buf[4] = uid->attrib_len;
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md_write( md, buf, 5 );
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}
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md_write( md, uid->attrib_data, uid->attrib_len );
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}
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else {
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if( sig->version >=4 ) {
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byte buf[5];
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buf[0] = 0xb4; /* indicates a userid packet */
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buf[1] = uid->len >> 24; /* always use 4 length bytes */
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buf[2] = uid->len >> 16;
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buf[3] = uid->len >> 8;
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buf[4] = uid->len;
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md_write( md, buf, 5 );
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}
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md_write( md, uid->name, uid->len );
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}
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}
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static void
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cache_sig_result ( PKT_signature *sig, int result )
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{
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if ( !result ) {
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sig->flags.checked = 1;
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sig->flags.valid = 1;
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}
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else if ( result == G10ERR_BAD_SIGN ) {
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sig->flags.checked = 1;
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sig->flags.valid = 0;
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}
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else {
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sig->flags.checked = 0;
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sig->flags.valid = 0;
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}
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}
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/****************
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* check the signature pointed to by NODE. This is a key signature.
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* If the function detects a self-signature, it uses the PK from
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* ROOT and does not read any public key.
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*/
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int
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check_key_signature( KBNODE root, KBNODE node, int *is_selfsig )
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{
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u32 dummy;
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int dum2;
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return check_key_signature2(root, node, is_selfsig, &dummy, &dum2 );
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}
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int
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check_key_signature2( KBNODE root, KBNODE node, int *is_selfsig,
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u32 *r_expiredate, int *r_expired )
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{
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MD_HANDLE md;
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PKT_public_key *pk;
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PKT_signature *sig;
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int algo;
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int rc;
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if( is_selfsig )
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*is_selfsig = 0;
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*r_expiredate = 0;
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*r_expired = 0;
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assert( node->pkt->pkttype == PKT_SIGNATURE );
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assert( root->pkt->pkttype == PKT_PUBLIC_KEY );
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pk = root->pkt->pkt.public_key;
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sig = node->pkt->pkt.signature;
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algo = sig->digest_algo;
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/* check whether we have cached the result of a previous signature check.*/
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if ( !opt.no_sig_cache ) {
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if (sig->flags.checked) { /*cached status available*/
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if( is_selfsig ) {
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u32 keyid[2];
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keyid_from_pk( pk, keyid );
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if( keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1] )
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*is_selfsig = 1;
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}
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return sig->flags.valid? 0 : G10ERR_BAD_SIGN;
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}
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}
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if( (rc=check_digest_algo(algo)) )
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return rc;
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if( sig->sig_class == 0x20 ) { /* key revocation */
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md = md_open( algo, 0 );
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hash_public_key( md, pk );
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rc = do_check( pk, sig, md, r_expired );
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cache_sig_result ( sig, rc );
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md_close(md);
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}
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else if( sig->sig_class == 0x28 ) { /* subkey revocation */
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KBNODE snode = find_prev_kbnode( root, node, PKT_PUBLIC_SUBKEY );
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if( snode ) {
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md = md_open( algo, 0 );
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hash_public_key( md, pk );
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hash_public_key( md, snode->pkt->pkt.public_key );
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rc = do_check( pk, sig, md, r_expired );
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cache_sig_result ( sig, rc );
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md_close(md);
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}
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else {
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if (!opt.quiet)
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log_info ("key %08lX: no subkey for subkey revocation packet\n",
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(ulong)keyid_from_pk (pk, NULL));
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rc = G10ERR_SIG_CLASS;
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}
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}
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else if( sig->sig_class == 0x18 ) { /* key binding */
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KBNODE snode = find_prev_kbnode( root, node, PKT_PUBLIC_SUBKEY );
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if( snode ) {
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if( is_selfsig ) { /* does this make sense????? */
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u32 keyid[2]; /* it should always be a selfsig */
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keyid_from_pk( pk, keyid );
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if( keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1] )
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*is_selfsig = 1;
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}
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md = md_open( algo, 0 );
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hash_public_key( md, pk );
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hash_public_key( md, snode->pkt->pkt.public_key );
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rc = do_check( pk, sig, md, r_expired );
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cache_sig_result ( sig, rc );
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md_close(md);
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}
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else {
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if (!opt.quiet)
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log_info ("key %08lX: no subkey for subkey binding packet\n",
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(ulong)keyid_from_pk (pk, NULL));
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rc = G10ERR_SIG_CLASS;
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}
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}
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else if( sig->sig_class == 0x1f ) { /* direct key signature */
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md = md_open( algo, 0 );
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hash_public_key( md, pk );
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rc = do_check( pk, sig, md, r_expired );
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cache_sig_result ( sig, rc );
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md_close(md);
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}
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else { /* all other classes */
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KBNODE unode = find_prev_kbnode( root, node, PKT_USER_ID );
|
|
|
|
if( unode ) {
|
|
u32 keyid[2];
|
|
|
|
keyid_from_pk( pk, keyid );
|
|
md = md_open( algo, 0 );
|
|
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 = signature_check2( sig, md, r_expiredate, r_expired );
|
|
}
|
|
cache_sig_result ( sig, rc );
|
|
md_close(md);
|
|
}
|
|
else {
|
|
if (!opt.quiet)
|
|
log_info ("key %08lX: no user ID for key signature packet "
|
|
"of class %02x\n",
|
|
(ulong)keyid_from_pk (pk, NULL), sig->sig_class );
|
|
rc = G10ERR_SIG_CLASS;
|
|
}
|
|
}
|
|
|
|
return rc;
|
|
}
|
|
|
|
|