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/ripemd160.h>
  31 #include <nettle/sha.h>
  32 #else
  33 #include "md5.h"
  34 #include "sha1.h"
  35 #endif
  36
  37 int check_packet_sighash(struct openpgp_publickey *key,
  38                         struct openpgp_packet *packet,
  39                         struct openpgp_packet *sig)
  40 {
  41         uint8_t hashtype;
  42         uint8_t *sighash;
  43         size_t siglen, unhashedlen;
  44         struct sha1_ctx sha1_context;
  45         struct md5_ctx md5_context;
  46 #ifdef NETTLE_WITH_RIPEMD160
  47         struct ripemd160_ctx ripemd160_context;
  48 #endif
  49 #ifdef NETTLE_WITH_SHA224
  50         struct sha224_ctx sha224_context;
  51 #endif
  52 #ifdef NETTLE_WITH_SHA256
  53         struct sha256_ctx sha256_context;
  54 #endif
  55 #ifdef NETTLE_WITH_SHA384
  56         struct sha384_ctx sha384_context;
  57 #endif
  58 #ifdef NETTLE_WITH_SHA512
  59         struct sha512_ctx sha512_context;
  60 #endif
  61         uint8_t keyheader[3];
  62         uint8_t packetheader[5];
  63         uint8_t v4trailer[6];
  64         uint8_t hash[64];
  65         uint8_t *hashdata[8];
  66         size_t hashlen[8];
  67         int chunks, i;
  68
  69         keyheader[0] = 0x99;
  70         keyheader[1] = key->publickey->length >> 8;
  71         keyheader[2] = key->publickey->length & 0xFF;
  72         hashdata[0] = keyheader;
  73         hashlen[0] = 3;
  74         hashdata[1] = key->publickey->data;
  75         hashlen[1] = key->publickey->length;
  76         chunks = 2;
  77
  78         switch (sig->data[0]) {
  79         case 2:
  80         case 3:
  81                 hashtype = sig->data[16];
  82
  83                 if (packet != NULL) {
  84                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
  85                                 packetheader[0] = 0x99;
  86                                 packetheader[1] = packet->length >> 8;
  87                                 packetheader[2] = packet->length & 0xFF;
  88                                 hashdata[chunks] = packetheader;
  89                                 hashlen[chunks] = 3;
  90                                 chunks++;
  91                         }
  92
  93                         // TODO: Things other than UIDS/subkeys?
  94                         hashdata[chunks] = packet->data;
  95                         hashlen[chunks] = packet->length;
  96                         chunks++;
  97                 }
  98
  99                 hashdata[chunks] = &sig->data[2];
 100                 hashlen[chunks] = 5;
 101                 chunks++;
 102                 sighash = &sig->data[17];
 103                 break;
 104         case 4:
 105                 hashtype = sig->data[3];
 106
 107                 if (packet != NULL) {
 108                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
 109                                 packetheader[0] = 0x99;
 110                                 packetheader[1] = packet->length >> 8;
 111                                 packetheader[2] = packet->length & 0xFF;
 112                                 hashdata[chunks] = packetheader;
 113                                 hashlen[chunks] = 3;
 114                                 chunks++;
 115                         } else if (packet->tag == OPENPGP_PACKET_UID ||
 116                                         packet->tag == OPENPGP_PACKET_UAT) {
 117                                 packetheader[0] = (packet->tag ==
 118                                         OPENPGP_PACKET_UID) ?  0xB4 : 0xD1;
 119                                 packetheader[1] = packet->length >> 24;
 120                                 packetheader[2] = (packet->length >> 16) & 0xFF;
 121                                 packetheader[3] = (packet->length >> 8) & 0xFF;
 122                                 packetheader[4] = packet->length & 0xFF;
 123                                 hashdata[chunks] = packetheader;
 124                                 hashlen[chunks] = 5;
 125                                 chunks++;
 126                         }
 127                         hashdata[chunks] = packet->data;
 128                         hashlen[chunks] = packet->length;
 129                         chunks++;
 130                 }
 131
 132                 hashdata[chunks] = sig->data;
 133                 hashlen[chunks] = siglen = (sig->data[4] << 8) +
 134                         sig->data[5] + 6;;
 135                 chunks++;
 136
 137                 v4trailer[0] = 4;
 138                 v4trailer[1] = 0xFF;
 139                 v4trailer[2] = siglen >> 24;
 140                 v4trailer[3] = (siglen >> 16) & 0xFF;
 141                 v4trailer[4] = (siglen >> 8) & 0xFF;
 142                 v4trailer[5] = siglen & 0xFF;
 143                 hashdata[chunks] = v4trailer;
 144                 hashlen[chunks] = 6;
 145                 chunks++;
 146
 147                 unhashedlen = (sig->data[siglen] << 8) +
 148                         sig->data[siglen + 1];
 149                 sighash = &sig->data[siglen + unhashedlen + 2];
 150                 break;
 151         default:
 152                 logthing(LOGTHING_ERROR, "Unknown signature version %d",
 153                                 sig->data[0]);
 154                 return -1;
 155         }
 156
 157         switch (hashtype) {
 158         case OPENPGP_HASH_MD5:
 159                 md5_init(&md5_context);
 160                 for (i = 0; i < chunks; i++) {
 161                         md5_update(&md5_context, hashlen[i], hashdata[i]);
 162                 }
 163                 md5_digest(&md5_context, 16, hash);
 164                 break;
 165         case OPENPGP_HASH_SHA1:
 166                 sha1_init(&sha1_context);
 167                 for (i = 0; i < chunks; i++) {
 168                         sha1_update(&sha1_context, hashlen[i], hashdata[i]);
 169                 }
 170                 sha1_digest(&sha1_context, 20, hash);
 171                 break;
 172         case OPENPGP_HASH_RIPEMD160:
 173 #ifdef NETTLE_WITH_RIPEMD160
 174                 ripemd160_init(&ripemd160_context);
 175                 for (i = 0; i < chunks; i++) {
 176                         ripemd160_update(&ripemd160_context, hashlen[i],
 177                                 hashdata[i]);
 178                 }
 179                 ripemd160_digest(&ripemd160_context, RIPEMD160_DIGEST_SIZE,
 180                         hash);
 181 #else
 182                 logthing(LOGTHING_INFO, "RIPEMD160 support not available.");
 183                 return -1;
 184 #endif
 185         case OPENPGP_HASH_SHA224:
 186 #ifdef NETTLE_WITH_SHA224
 187                 sha224_init(&sha224_context);
 188                 for (i = 0; i < chunks; i++) {
 189                         sha224_update(&sha224_context, hashlen[i],
 190                                 hashdata[i]);
 191                 }
 192                 sha224_digest(&sha224_context, SHA224_DIGEST_SIZE, hash);
 193                 break;
 194 #else
 195                 logthing(LOGTHING_INFO, "SHA224 support not available.");
 196                 return -1;
 197 #endif
 198         case OPENPGP_HASH_SHA256:
 199 #ifdef NETTLE_WITH_SHA256
 200                 sha256_init(&sha256_context);
 201                 for (i = 0; i < chunks; i++) {
 202                         sha256_update(&sha256_context, hashlen[i],
 203                                 hashdata[i]);
 204                 }
 205                 sha256_digest(&sha256_context, SHA256_DIGEST_SIZE, hash);
 206                 break;
 207 #else
 208                 logthing(LOGTHING_INFO, "SHA256 support not available.");
 209                 return -1;
 210 #endif
 211         case OPENPGP_HASH_SHA384:
 212 #ifdef NETTLE_WITH_SHA384
 213                 sha384_init(&sha384_context);
 214                 for (i = 0; i < chunks; i++) {
 215                         sha384_update(&sha384_context, hashlen[i],
 216                                 hashdata[i]);
 217                 }
 218                 sha384_digest(&sha384_context, SHA384_DIGEST_SIZE, hash);
 219                 break;
 220 #else
 221                 logthing(LOGTHING_INFO, "SHA384 support not available.");
 222                 return -1;
 223 #endif
 224         case OPENPGP_HASH_SHA512:
 225 #ifdef NETTLE_WITH_SHA512
 226                 sha512_init(&sha512_context);
 227                 for (i = 0; i < chunks; i++) {
 228                         sha512_update(&sha512_context, hashlen[i],
 229                                 hashdata[i]);
 230                 }
 231                 sha512_digest(&sha512_context, SHA512_DIGEST_SIZE, hash);
 232                 break;
 233 #else
 234                 logthing(LOGTHING_INFO, "SHA512 support not available.");
 235                 return -1;
 236 #endif
 237         default:
 238                 logthing(LOGTHING_ERROR, "Unsupported signature hash type %d",
 239                                 hashtype);
 240                 return -1;
 241         }
 242
 243         logthing(LOGTHING_DEBUG, "Hash type: %d, %d chunks, "
 244                 "calculated: %02X%02X / actual: %02X%02X\n",
 245                 hashtype, chunks,
 246                 hash[0], hash[1], sighash[0], sighash[1]);
 247
 248         return (hash[0] == sighash[0] && hash[1] == sighash[1]);
 249 }