/* sig-check.c - Check a signature * Copyright (C) 1998, 1999, 2000, 2001, 2002 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 #include #include #include #include #include "util.h" #include "packet.h" #include "memory.h" #include "mpi.h" #include "keydb.h" #include "cipher.h" #include "main.h" #include "status.h" #include "i18n.h" #include "options.h" struct cmp_help_context_s { PKT_signature *sig; MD_HANDLE md; }; static int do_check( PKT_public_key *pk, PKT_signature *sig, MD_HANDLE digest, int *r_expired ); /**************** * Check the signature which is contained in SIG. * The MD_HANDLE should be currently open, so that this function * is able to append some data, before finalizing the digest. */ int signature_check( PKT_signature *sig, MD_HANDLE digest ) { u32 dummy; int dum2; return signature_check2( sig, digest, &dummy, &dum2 ); } int signature_check2( PKT_signature *sig, MD_HANDLE digest, u32 *r_expiredate, int *r_expired ) { PKT_public_key *pk = m_alloc_clear( sizeof *pk ); int rc=0; *r_expiredate = 0; /* Sanity check that the md has a context for the hash that the sig is expecting. This can happen if a onepass sig header does not match the actual sig, and also if the clearsign "Hash:" header is missing or does not match the actual sig. */ if(!md_algo_present(digest,sig->digest_algo)) { log_info(_("WARNING: signature digest conflict in message\n")); rc=G10ERR_BAD_SIGN; } else if( get_pubkey( pk, sig->keyid ) ) rc = G10ERR_NO_PUBKEY; else if(!pk->is_valid && (pk->main_keyid[0]!=pk->keyid[0] || pk->main_keyid[1]!=pk->keyid[1])) rc=G10ERR_BAD_PUBKEY; /* you cannot have a good sig from an invalid subkey */ 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 batch processing applications might * like this feature here */ MD_HANDLE md; u32 a = sig->timestamp; int i, nsig = pubkey_get_nsig( sig->pubkey_algo ); byte *p, *buffer; md = md_open( DIGEST_ALGO_RMD160, 0); md_putc( digest, sig->pubkey_algo ); md_putc( digest, sig->digest_algo ); md_putc( digest, (a >> 24) & 0xff ); md_putc( digest, (a >> 16) & 0xff ); md_putc( digest, (a >> 8) & 0xff ); md_putc( digest, a & 0xff ); for(i=0; i < nsig; i++ ) { unsigned n = mpi_get_nbits( sig->data[i]); md_putc( md, n>>8); md_putc( md, n ); p = mpi_get_buffer( sig->data[i], &n, NULL ); md_write( md, p, n ); m_free(p); } md_final( md ); p = make_radix64_string( md_read( md, 0 ), 20 ); buffer = m_alloc( strlen(p) + 60 ); sprintf( buffer, "%s %s %lu", p, strtimestamp( sig->timestamp ), (ulong)sig->timestamp ); write_status_text( STATUS_SIG_ID, buffer ); m_free(buffer); m_free(p); 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; MD_HANDLE 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 G10ERR_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 G10ERR_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 G10ERR_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 G10ERR_BAD_PUBKEY; } dp = md_read( digest, sig->digest_algo ); for(i=mdlen-1; i >= 0; i--, dp++ ) { if( mpi_getbyte( result, i ) != *dp ) return G10ERR_BAD_SIGN; } return 0; #else return -1; #endif } static int do_check_messages( PKT_public_key *pk, PKT_signature *sig, int *r_expired ) { u32 cur_time; *r_expired = 0; if( pk->version == 4 && pk->pubkey_algo == PUBKEY_ALGO_ELGAMAL_E ) { log_info(_("this is a PGP generated " "ElGamal key which is NOT secure for signatures!\n")); return G10ERR_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 G10ERR_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 G10ERR_TIME_CONFLICT; } if( pk->expiredate && pk->expiredate < cur_time ) { char buf[11]; if (opt.verbose) { u32 tmp_kid[2]; keyid_from_pk( pk, tmp_kid ); log_info(_("NOTE: signature key %08lX expired %s\n"), (ulong)tmp_kid[1], asctimestamp( pk->expiredate ) ); } /* SIGEXPIRED is deprecated. Use KEYEXPIRED. */ sprintf(buf,"%lu",(ulong)pk->expiredate); write_status_text(STATUS_KEYEXPIRED,buf); write_status(STATUS_SIGEXPIRED); *r_expired = 1; } return 0; } static int do_check( PKT_public_key *pk, PKT_signature *sig, MD_HANDLE digest, int *r_expired ) { MPI result = NULL; int rc=0; struct cmp_help_context_s ctx; if( (rc=do_check_messages(pk,sig,r_expired)) ) return rc; if( (rc=check_digest_algo(sig->digest_algo)) ) return rc; if( (rc=check_pubkey_algo(sig->pubkey_algo)) ) return rc; /* make sure the digest algo is enabled (in case of a detached signature)*/ md_enable( digest, sig->digest_algo ); /* complete the digest */ if( sig->version >= 4 ) md_putc( digest, sig->version ); md_putc( digest, sig->sig_class ); if( sig->version < 4 ) { u32 a = sig->timestamp; md_putc( digest, (a >> 24) & 0xff ); md_putc( digest, (a >> 16) & 0xff ); md_putc( digest, (a >> 8) & 0xff ); md_putc( digest, a & 0xff ); } else { byte buf[6]; size_t n; md_putc( digest, sig->pubkey_algo ); md_putc( digest, sig->digest_algo ); if( sig->hashed ) { n = sig->hashed->len; md_putc (digest, (n >> 8) ); md_putc (digest, n ); md_write (digest, sig->hashed->data, n); n += 6; } else { /* Two octets for the (empty) length of the hashed section. */ md_putc (digest, 0); md_putc (digest, 0); 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; md_write( digest, buf, 6 ); } md_final( digest ); result = encode_md_value( pk->pubkey_algo, digest, sig->digest_algo, mpi_get_nbits(pk->pkey[0]), 0 ); if (!result) return G10ERR_GENERAL; ctx.sig = sig; ctx.md = digest; rc = pubkey_verify( pk->pubkey_algo, result, sig->data, pk->pkey, cmp_help, &ctx ); mpi_free( result ); if( (opt.emulate_bugs & EMUBUG_MDENCODE) && rc == G10ERR_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, mpi_get_nbits(pk->pkey[0]), (sig->version < 5) ); if (!result) rc = G10ERR_GENERAL; else { ctx.sig = sig; ctx.md = digest; rc = pubkey_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 = G10ERR_BAD_SIGN; } return rc; } static void hash_uid_node( KBNODE unode, MD_HANDLE md, PKT_signature *sig ) { PKT_user_id *uid = unode->pkt->pkt.user_id; assert( unode->pkt->pkttype == PKT_USER_ID ); if( uid->attrib_data ) { if( sig->version >=4 ) { byte buf[5]; buf[0] = 0xd1; /* packet of type 17 */ buf[1] = uid->attrib_len >> 24; /* always use 4 length bytes */ buf[2] = uid->attrib_len >> 16; buf[3] = uid->attrib_len >> 8; buf[4] = uid->attrib_len; md_write( md, buf, 5 ); } md_write( md, uid->attrib_data, uid->attrib_len ); } 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; md_write( md, buf, 5 ); } md_write( md, uid->name, uid->len ); } } static void cache_sig_result ( PKT_signature *sig, int result ) { if ( !result ) { sig->flags.checked = 1; sig->flags.valid = 1; } else if ( result == G10ERR_BAD_SIGN ) { sig->flags.checked = 1; sig->flags.valid = 0; } else { sig->flags.checked = 0; sig->flags.valid = 0; } } /**************** * 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 ) { MD_HANDLE 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; /* check whether we have cached the result of a previous signature check.*/ if ( !opt.no_sig_cache ) { if (sig->flags.checked) { /*cached status available*/ if( is_selfsig ) { u32 keyid[2]; keyid_from_pk( pk, keyid ); if( keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1] ) *is_selfsig = 1; } if((rc=do_check_messages(pk,sig,r_expired))) return rc; return sig->flags.valid? 0 : G10ERR_BAD_SIGN; } } if( (rc=check_digest_algo(algo)) ) return rc; if( sig->sig_class == 0x20 ) { /* key revocation */ md = md_open( algo, 0 ); hash_public_key( md, pk ); rc = do_check( pk, sig, md, r_expired ); cache_sig_result ( sig, rc ); md_close(md); } else if( sig->sig_class == 0x28 ) { /* subkey revocation */ KBNODE snode = find_prev_kbnode( root, node, PKT_PUBLIC_SUBKEY ); if( snode ) { md = md_open( algo, 0 ); hash_public_key( md, pk ); hash_public_key( md, snode->pkt->pkt.public_key ); rc = do_check( pk, sig, md, r_expired ); cache_sig_result ( sig, rc ); md_close(md); } else { if (!opt.quiet) log_info ("key %08lX: no subkey for subkey revocation packet\n", (ulong)keyid_from_pk (pk, NULL)); rc = G10ERR_SIG_CLASS; } } else if( sig->sig_class == 0x18 ) { /* key binding */ 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; } md = md_open( algo, 0 ); hash_public_key( md, pk ); hash_public_key( md, snode->pkt->pkt.public_key ); rc = do_check( pk, sig, md, r_expired ); cache_sig_result ( sig, rc ); md_close(md); } else { if (!opt.quiet) log_info ("key %08lX: no subkey for subkey binding packet\n", (ulong)keyid_from_pk (pk, NULL)); rc = G10ERR_SIG_CLASS; } } else if( sig->sig_class == 0x1f ) { /* direct key signature */ md = md_open( algo, 0 ); hash_public_key( md, pk ); rc = do_check( pk, sig, md, r_expired ); cache_sig_result ( sig, rc ); md_close(md); } else { /* all other classes */ 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; }