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 v4trailer[6];
  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         keyheader[0] = 0x99;
  67         keyheader[1] = key->publickey->length >> 8;
  68         keyheader[2] = key->publickey->length & 0xFF;
  69         hashdata[0] = keyheader;
  70         hashlen[0] = 3;
  71         hashdata[1] = key->publickey->data;
  72         hashlen[1] = key->publickey->length;
  73         chunks = 2;
  74
  75         switch (sig->data[0]) {
  76         case 2:
  77         case 3:
  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                 hashtype = sig->data[3];
 103
 104                 /* Check to see if this is an X509 based signature */
 105                 if (sig->data[2] == 0 || sig->data[2] == 100) {
 106                         size_t len;
 107
 108                         keyid = 0;
 109                         res = parse_subpackets(&sig->data[4],
 110                                                 sig->length - 4, &len,
 111                                                 &keyid, NULL);
 112                         if (res != ONAK_E_OK) {
 113                                 /* If it parses badly, reject it */
 114                                 return 0;
 115                         }
 116                         if (keyid == 0 &&
 117                                         /* No unhashed data */
 118                                         sig->data[4 + len] == 0 &&
 119                                         sig->data[5 + len] == 0 &&
 120                                         /* Dummy 0 checksum */
 121                                         sig->data[6 + len] == 0 &&
 122                                         sig->data[7 + len] == 0 &&
 123                                         /* Dummy MPI of 1 */
 124                                         sig->data[8 + len] == 0 &&
 125                                         sig->data[9 + len] == 1 &&
 126                                         sig->data[10 + len] == 1) {
 127                                 get_keyid(key, &keyid);
 128                                 logthing(LOGTHING_DEBUG,
 129                                         "Skipping X509 signature on 0x%016"
 130                                         PRIX64,
 131                                         keyid);
 132                                 return -1;
 133                         }
 134                 }
 135
 136                 if (packet != NULL) {
 137                         if (packet->tag == OPENPGP_PACKET_PUBLICSUBKEY) {
 138                                 packetheader[0] = 0x99;
 139                                 packetheader[1] = packet->length >> 8;
 140                                 packetheader[2] = packet->length & 0xFF;
 141                                 hashdata[chunks] = packetheader;
 142                                 hashlen[chunks] = 3;
 143                                 chunks++;
 144                         } else if (packet->tag == OPENPGP_PACKET_UID ||
 145                                         packet->tag == OPENPGP_PACKET_UAT) {
 146                                 packetheader[0] = (packet->tag ==
 147                                         OPENPGP_PACKET_UID) ?  0xB4 : 0xD1;
 148                                 packetheader[1] = packet->length >> 24;
 149                                 packetheader[2] = (packet->length >> 16) & 0xFF;
 150                                 packetheader[3] = (packet->length >> 8) & 0xFF;
 151                                 packetheader[4] = packet->length & 0xFF;
 152                                 hashdata[chunks] = packetheader;
 153                                 hashlen[chunks] = 5;
 154                                 chunks++;
 155                         }
 156                         hashdata[chunks] = packet->data;
 157                         hashlen[chunks] = packet->length;
 158                         chunks++;
 159                 }
 160
 161                 hashdata[chunks] = sig->data;
 162                 hashlen[chunks] = siglen = (sig->data[4] << 8) +
 163                         sig->data[5] + 6;;
 164                 if (siglen > sig->length) {
 165                         /* Signature data exceed packet length, bogus */
 166                         return 0;
 167                 }
 168                 chunks++;
 169
 170                 v4trailer[0] = 4;
 171                 v4trailer[1] = 0xFF;
 172                 v4trailer[2] = siglen >> 24;
 173                 v4trailer[3] = (siglen >> 16) & 0xFF;
 174                 v4trailer[4] = (siglen >> 8) & 0xFF;
 175                 v4trailer[5] = siglen & 0xFF;
 176                 hashdata[chunks] = v4trailer;
 177                 hashlen[chunks] = 6;
 178                 chunks++;
 179
 180                 unhashedlen = (sig->data[siglen] << 8) +
 181                         sig->data[siglen + 1];
 182                 sighash = &sig->data[siglen + unhashedlen + 2];
 183                 break;
 184         default:
 185                 get_keyid(key, &keyid);
 186                 logthing(LOGTHING_ERROR,
 187                         "Unknown signature version %d on 0x%016" PRIX64,
 188                         sig->data[0], keyid);
 189                 return -1;
 190         }
 191
 192         switch (hashtype) {
 193         case OPENPGP_HASH_MD5:
 194                 md5_init(&md5_context);
 195                 for (i = 0; i < chunks; i++) {
 196                         md5_update(&md5_context, hashlen[i], hashdata[i]);
 197                 }
 198                 md5_digest(&md5_context, 16, hash);
 199                 break;
 200         case OPENPGP_HASH_SHA1:
 201                 sha1_init(&sha1_context);
 202                 for (i = 0; i < chunks; i++) {
 203                         sha1_update(&sha1_context, hashlen[i], hashdata[i]);
 204                 }
 205                 sha1_digest(&sha1_context, 20, hash);
 206                 break;
 207         case OPENPGP_HASH_SHA1X:
 208                 sha1x_init(&sha1x_context);
 209                 for (i = 0; i < chunks; i++) {
 210                         sha1x_update(&sha1x_context, hashlen[i], hashdata[i]);
 211                 }
 212                 sha1x_digest(&sha1x_context, 20, hash);
 213                 break;
 214 #ifdef HAVE_NETTLE
 215         case OPENPGP_HASH_RIPEMD160:
 216                 ripemd160_init(&ripemd160_context);
 217                 for (i = 0; i < chunks; i++) {
 218                         ripemd160_update(&ripemd160_context, hashlen[i],
 219                                 hashdata[i]);
 220                 }
 221                 ripemd160_digest(&ripemd160_context, RIPEMD160_DIGEST_SIZE,
 222                         hash);
 223                 break;
 224         case OPENPGP_HASH_SHA224:
 225                 sha224_init(&sha224_context);
 226                 for (i = 0; i < chunks; i++) {
 227                         sha224_update(&sha224_context, hashlen[i],
 228                                 hashdata[i]);
 229                 }
 230                 sha224_digest(&sha224_context, SHA224_DIGEST_SIZE, hash);
 231                 break;
 232         case OPENPGP_HASH_SHA256:
 233                 sha256_init(&sha256_context);
 234                 for (i = 0; i < chunks; i++) {
 235                         sha256_update(&sha256_context, hashlen[i],
 236                                 hashdata[i]);
 237                 }
 238                 sha256_digest(&sha256_context, SHA256_DIGEST_SIZE, hash);
 239                 break;
 240         case OPENPGP_HASH_SHA384:
 241                 sha384_init(&sha384_context);
 242                 for (i = 0; i < chunks; i++) {
 243                         sha384_update(&sha384_context, hashlen[i],
 244                                 hashdata[i]);
 245                 }
 246                 sha384_digest(&sha384_context, SHA384_DIGEST_SIZE, hash);
 247                 break;
 248         case OPENPGP_HASH_SHA512:
 249                 sha512_init(&sha512_context);
 250                 for (i = 0; i < chunks; i++) {
 251                         sha512_update(&sha512_context, hashlen[i],
 252                                 hashdata[i]);
 253                 }
 254                 sha512_digest(&sha512_context, SHA512_DIGEST_SIZE, hash);
 255                 break;
 256 #endif
 257         default:
 258                 get_keyid(key, &keyid);
 259                 logthing(LOGTHING_ERROR,
 260                         "Unsupported signature hash type %d on 0x%016" PRIX64,
 261                         hashtype,
 262                         keyid);
 263                 return -1;
 264         }
 265
 266         logthing(LOGTHING_DEBUG, "Hash type: %d, %d chunks, "
 267                 "calculated: %02X%02X / actual: %02X%02X",
 268                 hashtype, chunks,
 269                 hash[0], hash[1], sighash[0], sighash[1]);
 270
 271         return (hash[0] == sighash[0] && hash[1] == sighash[1]);
 272 }