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, see <https://www.gnu.org/licenses/>.
  17  */
  18
  19 #include <stdint.h>
  20
  21 #include "build-config.h"
  22 #include "decodekey.h"
  23 #include "keyid.h"
  24 #include "keystructs.h"
  25 #include "log.h"
  26 #include "openpgp.h"
  27 #include "sigcheck.h"
  28
  29 #ifdef HAVE_NETTLE
  30 #include <nettle/md5.h>
  31 #include <nettle/ripemd160.h>
  32 #include <nettle/sha.h>
  33 #else
  34 #include "md5.h"
  35 #include "sha1.h"
  36 #endif
  37 #include "sha1x.h"
  38
  39 int check_packet_sighash(struct openpgp_publickey *key,
  40                         struct openpgp_packet *packet,
  41                         struct openpgp_packet *sig)
  42 {
  43         uint8_t hashtype;
  44         uint8_t *sighash;
  45         size_t siglen, unhashedlen;
  46         struct sha1_ctx sha1_context;
  47         struct sha1x_ctx sha1x_context;
  48         struct md5_ctx md5_context;
  49 #ifdef HAVE_NETTLE
  50         struct ripemd160_ctx ripemd160_context;
  51         struct sha224_ctx sha224_context;
  52         struct sha256_ctx sha256_context;
  53         struct sha384_ctx sha384_context;
  54         struct sha512_ctx sha512_context;
  55 #endif
  56         uint8_t keyheader[3];
  57         uint8_t packetheader[5];
  58         uint8_t trailer[10];
  59         uint8_t hash[64];
  60         uint8_t *hashdata[8];
  61         size_t hashlen[8];
  62         int chunks, i;
  63         uint64_t keyid;
  64         onak_status_t res;
  65
  66         switch (sig->data[0]) {
  67         case 2:
  68         case 3:
  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                 hashtype = sig->data[16];
  79
  80                 if (packet != NULL) {
  81                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
  82                                 packetheader[0] = 0x99;
  83                                 packetheader[1] = packet->length >> 8;
  84                                 packetheader[2] = packet->length & 0xFF;
  85                                 hashdata[chunks] = packetheader;
  86                                 hashlen[chunks] = 3;
  87                                 chunks++;
  88                         }
  89
  90                         // TODO: Things other than UIDS/subkeys?
  91                         hashdata[chunks] = packet->data;
  92                         hashlen[chunks] = packet->length;
  93                         chunks++;
  94                 }
  95
  96                 hashdata[chunks] = &sig->data[2];
  97                 hashlen[chunks] = 5;
  98                 chunks++;
  99                 sighash = &sig->data[17];
 100                 break;
 101         case 4:
 102                 keyheader[0] = 0x99;
 103                 keyheader[1] = key->publickey->length >> 8;
 104                 keyheader[2] = key->publickey->length & 0xFF;
 105                 hashdata[0] = keyheader;
 106                 hashlen[0] = 3;
 107                 hashdata[1] = key->publickey->data;
 108                 hashlen[1] = key->publickey->length;
 109                 chunks = 2;
 110
 111                 hashtype = sig->data[3];
 112
 113                 /* Check to see if this is an X509 based signature */
 114                 if (sig->data[2] == 0 || sig->data[2] == 100) {
 115                         size_t len;
 116
 117                         keyid = 0;
 118                         res = parse_subpackets(&sig->data[4],
 119                                                 sig->length - 4, &len,
 120                                                 &keyid, NULL);
 121                         if (res != ONAK_E_OK) {
 122                                 /* If it parses badly, reject it */
 123                                 return 0;
 124                         }
 125                         if (keyid == 0 &&
 126                                         /* No unhashed data */
 127                                         sig->data[4 + len] == 0 &&
 128                                         sig->data[5 + len] == 0 &&
 129                                         /* Dummy 0 checksum */
 130                                         sig->data[6 + len] == 0 &&
 131                                         sig->data[7 + len] == 0 &&
 132                                         /* Dummy MPI of 1 */
 133                                         sig->data[8 + len] == 0 &&
 134                                         sig->data[9 + len] == 1 &&
 135                                         sig->data[10 + len] == 1) {
 136                                 get_keyid(key, &keyid);
 137                                 logthing(LOGTHING_DEBUG,
 138                                         "Skipping X509 signature on 0x%016"
 139                                         PRIX64,
 140                                         keyid);
 141                                 return -1;
 142                         }
 143                 }
 144
 145                 if (packet != NULL) {
 146                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
 147                                 packetheader[0] = 0x99;
 148                                 packetheader[1] = packet->length >> 8;
 149                                 packetheader[2] = packet->length & 0xFF;
 150                                 hashdata[chunks] = packetheader;
 151                                 hashlen[chunks] = 3;
 152                                 chunks++;
 153                         } else if (packet->tag == OPENPGP_PACKET_UID ||
 154                                         packet->tag == OPENPGP_PACKET_UAT) {
 155                                 packetheader[0] = (packet->tag ==
 156                                         OPENPGP_PACKET_UID) ?  0xB4 : 0xD1;
 157                                 packetheader[1] = packet->length >> 24;
 158                                 packetheader[2] = (packet->length >> 16) & 0xFF;
 159                                 packetheader[3] = (packet->length >> 8) & 0xFF;
 160                                 packetheader[4] = packet->length & 0xFF;
 161                                 hashdata[chunks] = packetheader;
 162                                 hashlen[chunks] = 5;
 163                                 chunks++;
 164                         }
 165                         hashdata[chunks] = packet->data;
 166                         hashlen[chunks] = packet->length;
 167                         chunks++;
 168                 }
 169
 170                 hashdata[chunks] = sig->data;
 171                 hashlen[chunks] = siglen = (sig->data[4] << 8) +
 172                         sig->data[5] + 6;;
 173                 if (siglen > sig->length) {
 174                         /* Signature data exceed packet length, bogus */
 175                         return 0;
 176                 }
 177                 chunks++;
 178
 179                 trailer[0] = 4;
 180                 trailer[1] = 0xFF;
 181                 trailer[2] = siglen >> 24;
 182                 trailer[3] = (siglen >> 16) & 0xFF;
 183                 trailer[4] = (siglen >> 8) & 0xFF;
 184                 trailer[5] = siglen & 0xFF;
 185                 hashdata[chunks] = trailer;
 186                 hashlen[chunks] = 6;
 187                 chunks++;
 188
 189                 unhashedlen = (sig->data[siglen] << 8) +
 190                         sig->data[siglen + 1];
 191                 sighash = &sig->data[siglen + unhashedlen + 2];
 192                 break;
 193         case 5:
 194                 keyheader[0] = 0x9A;
 195                 keyheader[1] = 0;
 196                 keyheader[2] = 0;
 197                 keyheader[3] = key->publickey->length >> 8;
 198                 keyheader[4] = key->publickey->length & 0xFF;
 199                 hashdata[0] = keyheader;
 200                 hashlen[0] = 5;
 201                 hashdata[1] = key->publickey->data;
 202                 hashlen[1] = key->publickey->length;
 203                 chunks = 2;
 204
 205                 hashtype = sig->data[3];
 206
 207                 if (packet != NULL) {
 208                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
 209                                 packetheader[0] = 0x9A;
 210                                 packetheader[1] = 0;
 211                                 packetheader[2] = 0;
 212                                 packetheader[3] = packet->length >> 8;
 213                                 packetheader[4] = packet->length & 0xFF;
 214                                 hashdata[chunks] = packetheader;
 215                                 hashlen[chunks] = 5;
 216                                 chunks++;
 217                         } else if (packet->tag == OPENPGP_PACKET_UID ||
 218                                         packet->tag == OPENPGP_PACKET_UAT) {
 219                                 packetheader[0] = (packet->tag ==
 220                                         OPENPGP_PACKET_UID) ?  0xB4 : 0xD1;
 221                                 packetheader[1] = packet->length >> 24;
 222                                 packetheader[2] = (packet->length >> 16) & 0xFF;
 223                                 packetheader[3] = (packet->length >> 8) & 0xFF;
 224                                 packetheader[4] = packet->length & 0xFF;
 225                                 hashdata[chunks] = packetheader;
 226                                 hashlen[chunks] = 5;
 227                                 chunks++;
 228                         }
 229                         hashdata[chunks] = packet->data;
 230                         hashlen[chunks] = packet->length;
 231                         chunks++;
 232                 }
 233
 234                 hashdata[chunks] = sig->data;
 235                 hashlen[chunks] = siglen = (sig->data[4] << 8) +
 236                         sig->data[5] + 6;;
 237                 if (siglen > sig->length) {
 238                         /* Signature data exceed packet length, bogus */
 239                         return 0;
 240                 }
 241                 chunks++;
 242
 243                 trailer[0] = 5;
 244                 trailer[1] = 0xFF;
 245                 trailer[2] = 0;
 246                 trailer[3] = 0;
 247                 trailer[4] = 0;
 248                 trailer[5] = 0;
 249                 trailer[6] = siglen >> 24;
 250                 trailer[7] = (siglen >> 16) & 0xFF;
 251                 trailer[8] = (siglen >> 8) & 0xFF;
 252                 trailer[9] = siglen & 0xFF;
 253                 hashdata[chunks] = trailer;
 254                 hashlen[chunks] = 10;
 255                 chunks++;
 256
 257                 unhashedlen = (sig->data[siglen] << 8) +
 258                         sig->data[siglen + 1];
 259                 sighash = &sig->data[siglen + unhashedlen + 2];
 260                 break;
 261         default:
 262                 get_keyid(key, &keyid);
 263                 logthing(LOGTHING_ERROR,
 264                         "Unknown signature version %d on 0x%016" PRIX64,
 265                         sig->data[0], keyid);
 266                 return -1;
 267         }
 268
 269         switch (hashtype) {
 270         case OPENPGP_HASH_MD5:
 271                 md5_init(&md5_context);
 272                 for (i = 0; i < chunks; i++) {
 273                         md5_update(&md5_context, hashlen[i], hashdata[i]);
 274                 }
 275                 md5_digest(&md5_context, 16, hash);
 276                 break;
 277         case OPENPGP_HASH_SHA1:
 278                 sha1_init(&sha1_context);
 279                 for (i = 0; i < chunks; i++) {
 280                         sha1_update(&sha1_context, hashlen[i], hashdata[i]);
 281                 }
 282                 sha1_digest(&sha1_context, 20, hash);
 283                 break;
 284         case OPENPGP_HASH_SHA1X:
 285                 sha1x_init(&sha1x_context);
 286                 for (i = 0; i < chunks; i++) {
 287                         sha1x_update(&sha1x_context, hashlen[i], hashdata[i]);
 288                 }
 289                 sha1x_digest(&sha1x_context, 20, hash);
 290                 break;
 291 #ifdef HAVE_NETTLE
 292         case OPENPGP_HASH_RIPEMD160:
 293                 ripemd160_init(&ripemd160_context);
 294                 for (i = 0; i < chunks; i++) {
 295                         ripemd160_update(&ripemd160_context, hashlen[i],
 296                                 hashdata[i]);
 297                 }
 298                 ripemd160_digest(&ripemd160_context, RIPEMD160_DIGEST_SIZE,
 299                         hash);
 300                 break;
 301         case OPENPGP_HASH_SHA224:
 302                 sha224_init(&sha224_context);
 303                 for (i = 0; i < chunks; i++) {
 304                         sha224_update(&sha224_context, hashlen[i],
 305                                 hashdata[i]);
 306                 }
 307                 sha224_digest(&sha224_context, SHA224_DIGEST_SIZE, hash);
 308                 break;
 309         case OPENPGP_HASH_SHA256:
 310                 sha256_init(&sha256_context);
 311                 for (i = 0; i < chunks; i++) {
 312                         sha256_update(&sha256_context, hashlen[i],
 313                                 hashdata[i]);
 314                 }
 315                 sha256_digest(&sha256_context, SHA256_DIGEST_SIZE, hash);
 316                 break;
 317         case OPENPGP_HASH_SHA384:
 318                 sha384_init(&sha384_context);
 319                 for (i = 0; i < chunks; i++) {
 320                         sha384_update(&sha384_context, hashlen[i],
 321                                 hashdata[i]);
 322                 }
 323                 sha384_digest(&sha384_context, SHA384_DIGEST_SIZE, hash);
 324                 break;
 325         case OPENPGP_HASH_SHA512:
 326                 sha512_init(&sha512_context);
 327                 for (i = 0; i < chunks; i++) {
 328                         sha512_update(&sha512_context, hashlen[i],
 329                                 hashdata[i]);
 330                 }
 331                 sha512_digest(&sha512_context, SHA512_DIGEST_SIZE, hash);
 332                 break;
 333 #endif
 334         default:
 335                 get_keyid(key, &keyid);
 336                 logthing(LOGTHING_ERROR,
 337                         "Unsupported signature hash type %d on 0x%016" PRIX64,
 338                         hashtype,
 339                         keyid);
 340                 return -1;
 341         }
 342
 343         logthing(LOGTHING_DEBUG, "Hash type: %d, %d chunks, "
 344                 "calculated: %02X%02X / actual: %02X%02X",
 345                 hashtype, chunks,
 346                 hash[0], hash[1], sighash[0], sighash[1]);
 347
 348         return (hash[0] == sighash[0] && hash[1] == sighash[1]);
 349 }