1 /* 2 * Copyright (c) 2000 Niels Provos. All rights reserved. 3 * Copyright (c) 2001 Markus Friedl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 #include "includes.h" 27 RCSID("$OpenBSD: kexgex.c,v 1.5 2001/04/05 10:42:50 markus Exp $"); 28 29 #include <openssl/bn.h> 30 31 #include "xmalloc.h" 32 #include "buffer.h" 33 #include "bufaux.h" 34 #include "key.h" 35 #include "kex.h" 36 #include "log.h" 37 #include "packet.h" 38 #include "dh.h" 39 #include "ssh2.h" 40 #include "compat.h" 41 42 u_char * 43 kexgex_hash( 44 char *client_version_string, 45 char *server_version_string, 46 char *ckexinit, int ckexinitlen, 47 char *skexinit, int skexinitlen, 48 char *serverhostkeyblob, int sbloblen, 49 int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen, 50 BIGNUM *client_dh_pub, 51 BIGNUM *server_dh_pub, 52 BIGNUM *shared_secret) 53 { 54 Buffer b; 55 static u_char digest[EVP_MAX_MD_SIZE]; 56 EVP_MD *evp_md = EVP_sha1(); 57 EVP_MD_CTX md; 58 59 buffer_init(&b); 60 buffer_put_string(&b, client_version_string, strlen(client_version_string)); 61 buffer_put_string(&b, server_version_string, strlen(server_version_string)); 62 63 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 64 buffer_put_int(&b, ckexinitlen+1); 65 buffer_put_char(&b, SSH2_MSG_KEXINIT); 66 buffer_append(&b, ckexinit, ckexinitlen); 67 buffer_put_int(&b, skexinitlen+1); 68 buffer_put_char(&b, SSH2_MSG_KEXINIT); 69 buffer_append(&b, skexinit, skexinitlen); 70 71 buffer_put_string(&b, serverhostkeyblob, sbloblen); 72 if (min == -1 || max == -1) 73 buffer_put_int(&b, wantbits); 74 else { 75 buffer_put_int(&b, min); 76 buffer_put_int(&b, wantbits); 77 buffer_put_int(&b, max); 78 } 79 buffer_put_bignum2(&b, prime); 80 buffer_put_bignum2(&b, gen); 81 buffer_put_bignum2(&b, client_dh_pub); 82 buffer_put_bignum2(&b, server_dh_pub); 83 buffer_put_bignum2(&b, shared_secret); 84 85 #ifdef DEBUG_KEXDH 86 buffer_dump(&b); 87 #endif 88 EVP_DigestInit(&md, evp_md); 89 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 90 EVP_DigestFinal(&md, digest, NULL); 91 92 buffer_free(&b); 93 94 #ifdef DEBUG_KEXDH 95 dump_digest("hash", digest, evp_md->md_size); 96 #endif 97 return digest; 98 } 99 100 /* client */ 101 102 void 103 kexgex_client(Kex *kex) 104 { 105 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 106 BIGNUM *p = NULL, *g = NULL; 107 Key *server_host_key; 108 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 109 u_int klen, kout, slen, sbloblen; 110 int dlen, plen, min, max, nbits; 111 DH *dh; 112 113 nbits = dh_estimate(kex->we_need * 8); 114 115 if (datafellows & SSH_OLD_DHGEX) { 116 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent"); 117 118 /* Old GEX request */ 119 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); 120 packet_put_int(nbits); 121 min = DH_GRP_MIN; 122 max = DH_GRP_MAX; 123 } else { 124 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent"); 125 126 /* New GEX request */ 127 min = DH_GRP_MIN; 128 max = DH_GRP_MAX; 129 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); 130 packet_put_int(min); 131 packet_put_int(nbits); 132 packet_put_int(max); 133 } 134 #ifdef DEBUG_KEXDH 135 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 136 min, nbits, max); 137 #endif 138 packet_send(); 139 140 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 141 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP); 142 143 if ((p = BN_new()) == NULL) 144 fatal("BN_new"); 145 packet_get_bignum2(p, &dlen); 146 if ((g = BN_new()) == NULL) 147 fatal("BN_new"); 148 packet_get_bignum2(g, &dlen); 149 packet_done(); 150 151 if (BN_num_bits(p) < min || BN_num_bits(p) > max) 152 fatal("DH_GEX group out of range: %d !< %d !< %d", 153 min, BN_num_bits(p), max); 154 155 dh = dh_new_group(g, p); 156 dh_gen_key(dh, kex->we_need * 8); 157 158 #ifdef DEBUG_KEXDH 159 DHparams_print_fp(stderr, dh); 160 fprintf(stderr, "pub= "); 161 BN_print_fp(stderr, dh->pub_key); 162 fprintf(stderr, "\n"); 163 #endif 164 165 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 166 /* generate and send 'e', client DH public key */ 167 packet_start(SSH2_MSG_KEX_DH_GEX_INIT); 168 packet_put_bignum2(dh->pub_key); 169 packet_send(); 170 171 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 172 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_REPLY); 173 174 /* key, cert */ 175 server_host_key_blob = packet_get_string(&sbloblen); 176 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 177 if (server_host_key == NULL) 178 fatal("cannot decode server_host_key_blob"); 179 180 if (kex->check_host_key == NULL) 181 fatal("cannot check server_host_key"); 182 kex->check_host_key(server_host_key); 183 184 /* DH paramter f, server public DH key */ 185 dh_server_pub = BN_new(); 186 if (dh_server_pub == NULL) 187 fatal("dh_server_pub == NULL"); 188 packet_get_bignum2(dh_server_pub, &dlen); 189 190 #ifdef DEBUG_KEXDH 191 fprintf(stderr, "dh_server_pub= "); 192 BN_print_fp(stderr, dh_server_pub); 193 fprintf(stderr, "\n"); 194 debug("bits %d", BN_num_bits(dh_server_pub)); 195 #endif 196 197 /* signed H */ 198 signature = packet_get_string(&slen); 199 packet_done(); 200 201 if (!dh_pub_is_valid(dh, dh_server_pub)) 202 packet_disconnect("bad server public DH value"); 203 204 klen = DH_size(dh); 205 kbuf = xmalloc(klen); 206 kout = DH_compute_key(kbuf, dh_server_pub, dh); 207 #ifdef DEBUG_KEXDH 208 dump_digest("shared secret", kbuf, kout); 209 #endif 210 shared_secret = BN_new(); 211 BN_bin2bn(kbuf, kout, shared_secret); 212 memset(kbuf, 0, klen); 213 xfree(kbuf); 214 215 if (datafellows & SSH_OLD_DHGEX) 216 min = max = -1; 217 218 /* calc and verify H */ 219 hash = kexgex_hash( 220 kex->client_version_string, 221 kex->server_version_string, 222 buffer_ptr(&kex->my), buffer_len(&kex->my), 223 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 224 server_host_key_blob, sbloblen, 225 min, nbits, max, 226 dh->p, dh->g, 227 dh->pub_key, 228 dh_server_pub, 229 shared_secret 230 ); 231 /* have keys, free DH */ 232 DH_free(dh); 233 xfree(server_host_key_blob); 234 BN_free(dh_server_pub); 235 236 if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1) 237 fatal("key_verify failed for server_host_key"); 238 key_free(server_host_key); 239 xfree(signature); 240 241 /* save session id */ 242 if (kex->session_id == NULL) { 243 kex->session_id_len = 20; 244 kex->session_id = xmalloc(kex->session_id_len); 245 memcpy(kex->session_id, hash, kex->session_id_len); 246 } 247 kex_derive_keys(kex, hash, shared_secret); 248 BN_clear_free(shared_secret); 249 250 kex_finish(kex); 251 } 252 253 /* server */ 254 255 void 256 kexgex_server(Kex *kex) 257 { 258 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 259 Key *server_host_key; 260 DH *dh = dh; 261 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 262 u_int sbloblen, klen, kout; 263 int min = -1, max = -1, nbits = -1, type, plen, dlen, slen; 264 265 if (kex->load_host_key == NULL) 266 fatal("Cannot load hostkey"); 267 server_host_key = kex->load_host_key(kex->hostkey_type); 268 if (server_host_key == NULL) 269 fatal("Unsupported hostkey type %d", kex->hostkey_type); 270 271 type = packet_read(&plen); 272 switch(type){ 273 case SSH2_MSG_KEX_DH_GEX_REQUEST: 274 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 275 min = packet_get_int(); 276 nbits = packet_get_int(); 277 max = packet_get_int(); 278 min = MAX(DH_GRP_MIN, min); 279 max = MIN(DH_GRP_MAX, max); 280 break; 281 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 282 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 283 nbits = packet_get_int(); 284 min = DH_GRP_MIN; 285 max = DH_GRP_MAX; 286 /* unused for old GEX */ 287 break; 288 default: 289 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 290 } 291 packet_done(); 292 293 if (max < min || nbits < min || max < nbits) 294 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 295 min, nbits, max); 296 297 dh = choose_dh(min, nbits, max); 298 if (dh == NULL) 299 packet_disconnect("Protocol error: no matching DH grp found"); 300 301 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 302 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 303 packet_put_bignum2(dh->p); 304 packet_put_bignum2(dh->g); 305 packet_send(); 306 307 /* flush */ 308 packet_write_wait(); 309 310 /* Compute our exchange value in parallel with the client */ 311 dh_gen_key(dh, kex->we_need * 8); 312 313 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 314 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT); 315 316 /* key, cert */ 317 dh_client_pub = BN_new(); 318 if (dh_client_pub == NULL) 319 fatal("dh_client_pub == NULL"); 320 packet_get_bignum2(dh_client_pub, &dlen); 321 322 #ifdef DEBUG_KEXDH 323 fprintf(stderr, "dh_client_pub= "); 324 BN_print_fp(stderr, dh_client_pub); 325 fprintf(stderr, "\n"); 326 debug("bits %d", BN_num_bits(dh_client_pub)); 327 #endif 328 329 #ifdef DEBUG_KEXDH 330 DHparams_print_fp(stderr, dh); 331 fprintf(stderr, "pub= "); 332 BN_print_fp(stderr, dh->pub_key); 333 fprintf(stderr, "\n"); 334 #endif 335 if (!dh_pub_is_valid(dh, dh_client_pub)) 336 packet_disconnect("bad client public DH value"); 337 338 klen = DH_size(dh); 339 kbuf = xmalloc(klen); 340 kout = DH_compute_key(kbuf, dh_client_pub, dh); 341 #ifdef DEBUG_KEXDH 342 dump_digest("shared secret", kbuf, kout); 343 #endif 344 shared_secret = BN_new(); 345 BN_bin2bn(kbuf, kout, shared_secret); 346 memset(kbuf, 0, klen); 347 xfree(kbuf); 348 349 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 350 351 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 352 min = max = -1; 353 354 /* calc H */ /* XXX depends on 'kex' */ 355 hash = kexgex_hash( 356 kex->client_version_string, 357 kex->server_version_string, 358 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 359 buffer_ptr(&kex->my), buffer_len(&kex->my), 360 (char *)server_host_key_blob, sbloblen, 361 min, nbits, max, 362 dh->p, dh->g, 363 dh_client_pub, 364 dh->pub_key, 365 shared_secret 366 ); 367 BN_free(dh_client_pub); 368 369 /* save session id := H */ 370 /* XXX hashlen depends on KEX */ 371 if (kex->session_id == NULL) { 372 kex->session_id_len = 20; 373 kex->session_id = xmalloc(kex->session_id_len); 374 memcpy(kex->session_id, hash, kex->session_id_len); 375 } 376 377 /* sign H */ 378 /* XXX hashlen depends on KEX */ 379 key_sign(server_host_key, &signature, &slen, hash, 20); 380 381 /* destroy_sensitive_data(); */ 382 383 /* send server hostkey, DH pubkey 'f' and singed H */ 384 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 385 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 386 packet_put_string((char *)server_host_key_blob, sbloblen); 387 packet_put_bignum2(dh->pub_key); /* f */ 388 packet_put_string((char *)signature, slen); 389 packet_send(); 390 xfree(signature); 391 xfree(server_host_key_blob); 392 /* have keys, free DH */ 393 DH_free(dh); 394 395 kex_derive_keys(kex, hash, shared_secret); 396 BN_clear_free(shared_secret); 397 398 kex_finish(kex); 399 } 400 401 void 402 kexgex(Kex *kex) 403 { 404 if (kex->server) 405 kexgex_server(kex); 406 else 407 kexgex_client(kex); 408 } 409