sigcheck.c

   1 /*
   2  * sigcheck.c - routines to check OpenPGP signatures
   3  *
   4  * Copyright 2012 Jonathan McDowell <noodles@earth.li>
   5  *
   6  * This program is free software: you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License as published by the Free
   8  * Software Foundation; version 2 of the License.
   9  *
  10  * This program is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
  13  * more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along with
  16  * this program; if not, write to the Free Software Foundation, Inc., 51
  17  * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  */
  19
  20 #include <stdint.h>
  21
  22 #include "config.h"
  23 #include "keystructs.h"
  24 #include "log.h"
  25 #include "openpgp.h"
  26 #include "sigcheck.h"
  27
  28 #ifdef HAVE_NETTLE
  29 #include <nettle/md5.h>
  30 #include <nettle/sha.h>
  31 #else
  32 #include "md5.h"
  33 #include "sha1.h"
  34 #endif
  35
  36 int check_packet_sighash(struct openpgp_publickey *key,
  37                         struct openpgp_packet *packet,
  38                         struct openpgp_packet *sig)
  39 {
  40         uint8_t hashtype;
  41         uint8_t *sighash;
  42         size_t siglen, unhashedlen;
  43         struct sha1_ctx sha1_context;
  44         struct md5_ctx md5_context;
  45 #ifdef NETTLE_WITH_SHA224
  46         struct sha224_ctx sha224_context;
  47 #endif
  48 #ifdef NETTLE_WITH_SHA256
  49         struct sha256_ctx sha256_context;
  50 #endif
  51 #ifdef NETTLE_WITH_SHA384
  52         struct sha384_ctx sha384_context;
  53 #endif
  54 #ifdef NETTLE_WITH_SHA512
  55         struct sha512_ctx sha512_context;
  56 #endif
  57         uint8_t keyheader[3];
  58         uint8_t packetheader[5];
  59         uint8_t v4trailer[6];
  60         uint8_t hash[20];
  61         uint8_t *hashdata[8];
  62         size_t hashlen[8];
  63         int chunks, i;
  64
  65         keyheader[0] = 0x99;
  66         keyheader[1] = key->publickey->length >> 8;
  67         keyheader[2] = key->publickey->length & 0xFF;
  68         hashdata[0] = keyheader;
  69         hashlen[0] = 3;
  70         hashdata[1] = key->publickey->data;
  71         hashlen[1] = key->publickey->length;
  72         chunks = 2;
  73
  74         switch (sig->data[0]) {
  75         case 2:
  76         case 3:
  77                 hashtype = sig->data[16];
  78
  79                 if (packet != NULL) {
  80                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
  81                                 packetheader[0] = 0x99;
  82                                 packetheader[1] = packet->length >> 8;
  83                                 packetheader[2] = packet->length & 0xFF;
  84                                 hashdata[chunks] = packetheader;
  85                                 hashlen[chunks] = 3;
  86                                 chunks++;
  87                         }
  88
  89                         // TODO: Things other than UIDS/subkeys?
  90                         hashdata[chunks] = packet->data;
  91                         hashlen[chunks] = packet->length;
  92                         chunks++;
  93                 }
  94
  95                 hashdata[chunks] = &sig->data[2];
  96                 hashlen[chunks] = 5;
  97                 chunks++;
  98                 sighash = &sig->data[17];
  99                 break;
 100         case 4:
 101                 hashtype = sig->data[3];
 102
 103                 if (packet != NULL) {
 104                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
 105                                 packetheader[0] = 0x99;
 106                                 packetheader[1] = packet->length >> 8;
 107                                 packetheader[2] = packet->length & 0xFF;
 108                                 hashdata[chunks] = packetheader;
 109                                 hashlen[chunks] = 3;
 110                                 chunks++;
 111                         } else if (packet->tag == OPENPGP_PACKET_UID ||
 112                                         packet->tag == OPENPGP_PACKET_UAT) {
 113                                 packetheader[0] = (packet->tag ==
 114                                         OPENPGP_PACKET_UID) ?  0xB4 : 0xD1;
 115                                 packetheader[1] = packet->length >> 24;
 116                                 packetheader[2] = (packet->length >> 16) & 0xFF;
 117                                 packetheader[3] = (packet->length >> 8) & 0xFF;
 118                                 packetheader[4] = packet->length & 0xFF;
 119                                 hashdata[chunks] = packetheader;
 120                                 hashlen[chunks] = 5;
 121                                 chunks++;
 122                         }
 123                         hashdata[chunks] = packet->data;
 124                         hashlen[chunks] = packet->length;
 125                         chunks++;
 126                 }
 127
 128                 hashdata[chunks] = sig->data;
 129                 hashlen[chunks] = siglen = (sig->data[4] << 8) +
 130                         sig->data[5] + 6;;
 131                 chunks++;
 132
 133                 v4trailer[0] = 4;
 134                 v4trailer[1] = 0xFF;
 135                 v4trailer[2] = siglen >> 24;
 136                 v4trailer[3] = (siglen >> 16) & 0xFF;
 137                 v4trailer[4] = (siglen >> 8) & 0xFF;
 138                 v4trailer[5] = siglen & 0xFF;
 139                 hashdata[chunks] = v4trailer;
 140                 hashlen[chunks] = 6;
 141                 chunks++;
 142
 143                 unhashedlen = (sig->data[siglen] << 8) +
 144                         sig->data[siglen + 1];
 145                 sighash = &sig->data[siglen + unhashedlen + 2];
 146                 break;
 147         default:
 148                 logthing(LOGTHING_ERROR, "Unknown signature version %d",
 149                                 sig->data[0]);
 150                 return -1;
 151         }
 152
 153         switch (hashtype) {
 154         case OPENPGP_HASH_MD5:
 155                 md5_init(&md5_context);
 156                 for (i = 0; i < chunks; i++) {
 157                         md5_update(&md5_context, hashlen[i], hashdata[i]);
 158                 }
 159                 md5_digest(&md5_context, 16, hash);
 160                 break;
 161         case OPENPGP_HASH_SHA1:
 162                 sha1_init(&sha1_context);
 163                 for (i = 0; i < chunks; i++) {
 164                         sha1_update(&sha1_context, hashlen[i], hashdata[i]);
 165                 }
 166                 sha1_digest(&sha1_context, 20, hash);
 167                 break;
 168         case OPENPGP_HASH_SHA224:
 169 #ifdef NETTLE_WITH_SHA224
 170                 sha224_init(&sha224_context);
 171                 for (i = 0; i < chunks; i++) {
 172                         sha224_update(&sha224_context, hashlen[i],
 173                                 hashdata[i]);
 174                 }
 175                 sha224_digest(&sha224_context, SHA224_DIGEST_SIZE, hash);
 176 #else
 177                 logthing(LOGTHING_INFO, "SHA224 support not available.");
 178 #endif
 179                 break;
 180         case OPENPGP_HASH_SHA256:
 181 #ifdef NETTLE_WITH_SHA256
 182                 sha256_init(&sha256_context);
 183                 for (i = 0; i < chunks; i++) {
 184                         sha256_update(&sha256_context, hashlen[i],
 185                                 hashdata[i]);
 186                 }
 187                 sha256_digest(&sha256_context, SHA256_DIGEST_SIZE, hash);
 188 #else
 189                 logthing(LOGTHING_INFO, "SHA256 support not available.");
 190 #endif
 191                 break;
 192         case OPENPGP_HASH_SHA384:
 193 #ifdef NETTLE_WITH_SHA384
 194                 sha384_init(&sha384_context);
 195                 for (i = 0; i < chunks; i++) {
 196                         sha384_update(&sha384_context, hashlen[i],
 197                                 hashdata[i]);
 198                 }
 199                 sha384_digest(&sha384_context, SHA384_DIGEST_SIZE, hash);
 200 #else
 201                 logthing(LOGTHING_INFO, "SHA384 support not available.");
 202 #endif
 203                 break;
 204         case OPENPGP_HASH_SHA512:
 205 #ifdef NETTLE_WITH_SHA512
 206                 sha512_init(&sha512_context);
 207                 for (i = 0; i < chunks; i++) {
 208                         sha512_update(&sha512_context, hashlen[i],
 209                                 hashdata[i]);
 210                 }
 211                 sha512_digest(&sha512_context, SHA512_DIGEST_SIZE, hash);
 212 #else
 213                 logthing(LOGTHING_INFO, "SHA512 support not available.");
 214 #endif
 215                 break;
 216         default:
 217                 logthing(LOGTHING_ERROR, "Unsupported signature hash type %d",
 218                                 hashtype);
 219                 return -1;
 220         }
 221
 222         logthing(LOGTHING_DEBUG, "Hash type: %d, %d chunks, "
 223                 "calculated: %02X%02X / actual: %02X%02X\n",
 224                 hashtype, chunks,
 225                 hash[0], hash[1], sighash[0], sighash[1]);
 226
 227         return (hash[0] == sighash[0] && hash[1] == sighash[1]);
 228 }