/* 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 #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" static int do_check( PKT_public_cert *pkc, PKT_signature *sig, MD_HANDLE digest ); /**************** * 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 ); int rc=0; if( get_pubkey( pkc, sig->keyid ) ) rc = G10ERR_NO_PUBKEY; else rc = do_check( pkc, sig, digest ); free_public_cert( pkc ); return rc; } static int do_check( PKT_public_cert *pkc, PKT_signature *sig, MD_HANDLE digest ) { MPI result = NULL; int rc=0; if( pkc->pubkey_algo == PUBKEY_ALGO_ELGAMAL ) { ELG_public_key pkey; if( (rc=check_digest_algo(sig->d.elg.digest_algo)) ) goto leave; /* complete the digest */ md_putc( digest, sig->sig_class ); { 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 ); } md_final( digest ); 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 ) { int i, j, c, old_enc; byte *dp; RSA_public_key pkey; const byte *asn; size_t mdlen, asnlen; 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( (rc=check_digest_algo(sig->d.rsa.digest_algo)) ) goto leave; /* unsupported algo */ asn = md_asn_oid( sig->d.rsa.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) ) { /* 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 != sig->d.rsa.digest_algo || mpi_getbyte(result, i) ) { /* Padding or leading bytes in signature is wrong */ rc = G10ERR_BAD_PUBKEY; goto leave; } if( mpi_getbyte(result, mdlen-1) != sig->d.rsa.digest_start[0] || mpi_getbyte(result, mdlen-2) != sig->d.rsa.digest_start[1] ) { /* Wrong key used to check the signature */ rc = G10ERR_BAD_PUBKEY; goto leave; } /* complete the digest */ md_putc( digest, sig->sig_class ); { 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 ); } md_final( digest ); dp = md_read( digest, sig->d.rsa.digest_algo ); for(i=mdlen-1; i >= 0; i--, dp++ ) { if( mpi_getbyte( result, i ) != *dp ) { rc = G10ERR_BAD_SIGN; 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: mpi_free( result ); return rc; } /**************** * check the signature pointed to by NODE. This is a key signatures. * If the function detects a elf signature, it uses the PKC from * NODE and does not read the any public key. */ int check_key_signature( KBNODE root, KBNODE node, int *is_selfsig ) { KBNODE unode; MD_HANDLE md; PKT_public_cert *pkc; PKT_signature *sig; int algo; int rc; if( is_selfsig ) *is_selfsig = 0; assert( node->pkt->pkttype == PKT_SIGNATURE ); assert( root->pkt->pkttype == PKT_PUBLIC_CERT ); pkc = root->pkt->pkt.public_cert; sig = node->pkt->pkt.signature; if( sig->pubkey_algo == PUBKEY_ALGO_ELGAMAL ) algo = sig->d.elg.digest_algo; else if(sig->pubkey_algo == PUBKEY_ALGO_RSA ) algo = sig->d.rsa.digest_algo; else return G10ERR_PUBKEY_ALGO; if( (rc=check_digest_algo(algo)) ) return rc; if( sig->sig_class == 0x20 ) { md = md_open( algo, 0 ); hash_public_cert( md, pkc ); rc = do_check( pkc, sig, md ); md_close(md); } else { unode = find_prev_kbnode( root, node, PKT_USER_ID ); if( unode ) { PKT_user_id *uid = unode->pkt->pkt.user_id; u32 keyid[2]; keyid_from_pkc( pkc, keyid ); md = md_open( algo, 0 ); hash_public_cert( md, pkc ); md_write( md, uid->name, uid->len ); if( keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1] ) { if( is_selfsig ) *is_selfsig = 1; rc = do_check( pkc, sig, md ); } else rc = signature_check( sig, md ); md_close(md); } else { log_error("no user id for key signature packet\n"); rc = G10ERR_SIG_CLASS; } } return rc; }