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 1.20 2002/02/28 15:46:33 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 static 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 u_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 const EVP_MD *evp_md = EVP_sha1(); 57 EVP_MD_CTX md; 58 59 buffer_init(&b); 60 buffer_put_cstring(&b, client_version_string); 61 buffer_put_cstring(&b, 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_size(evp_md)); 96 #endif 97 return digest; 98 } 99 100 /* client */ 101 102 static 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 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(SSH2_MSG_KEX_DH_GEX_GROUP); 142 143 if ((p = BN_new()) == NULL) 144 fatal("BN_new"); 145 packet_get_bignum2(p); 146 if ((g = BN_new()) == NULL) 147 fatal("BN_new"); 148 packet_get_bignum2(g); 149 packet_check_eom(); 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(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 if (server_host_key->type != kex->hostkey_type) 180 fatal("type mismatch for decoded server_host_key_blob"); 181 if (kex->verify_host_key == NULL) 182 fatal("cannot verify server_host_key"); 183 if (kex->verify_host_key(server_host_key) == -1) 184 fatal("server_host_key verification failed"); 185 186 /* DH paramter f, server public DH key */ 187 if ((dh_server_pub = BN_new()) == NULL) 188 fatal("dh_server_pub == NULL"); 189 packet_get_bignum2(dh_server_pub); 190 191 #ifdef DEBUG_KEXDH 192 fprintf(stderr, "dh_server_pub= "); 193 BN_print_fp(stderr, dh_server_pub); 194 fprintf(stderr, "\n"); 195 debug("bits %d", BN_num_bits(dh_server_pub)); 196 #endif 197 198 /* signed H */ 199 signature = packet_get_string(&slen); 200 packet_check_eom(); 201 202 if (!dh_pub_is_valid(dh, dh_server_pub)) 203 packet_disconnect("bad server public DH value"); 204 205 klen = DH_size(dh); 206 kbuf = xmalloc(klen); 207 kout = DH_compute_key(kbuf, dh_server_pub, dh); 208 #ifdef DEBUG_KEXDH 209 dump_digest("shared secret", kbuf, kout); 210 #endif 211 if ((shared_secret = BN_new()) == NULL) 212 fatal("kexgex_client: BN_new failed"); 213 BN_bin2bn(kbuf, kout, shared_secret); 214 memset(kbuf, 0, klen); 215 xfree(kbuf); 216 217 if (datafellows & SSH_OLD_DHGEX) 218 min = max = -1; 219 220 /* calc and verify H */ 221 hash = kexgex_hash( 222 kex->client_version_string, 223 kex->server_version_string, 224 buffer_ptr(&kex->my), buffer_len(&kex->my), 225 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 226 server_host_key_blob, sbloblen, 227 min, nbits, max, 228 dh->p, dh->g, 229 dh->pub_key, 230 dh_server_pub, 231 shared_secret 232 ); 233 /* have keys, free DH */ 234 DH_free(dh); 235 xfree(server_host_key_blob); 236 BN_clear_free(dh_server_pub); 237 238 if (key_verify(server_host_key, signature, slen, hash, 20) != 1) 239 fatal("key_verify failed for server_host_key"); 240 key_free(server_host_key); 241 xfree(signature); 242 243 /* save session id */ 244 if (kex->session_id == NULL) { 245 kex->session_id_len = 20; 246 kex->session_id = xmalloc(kex->session_id_len); 247 memcpy(kex->session_id, hash, kex->session_id_len); 248 } 249 kex_derive_keys(kex, hash, shared_secret); 250 BN_clear_free(shared_secret); 251 252 kex_finish(kex); 253 } 254 255 /* server */ 256 257 static void 258 kexgex_server(Kex *kex) 259 { 260 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 261 Key *server_host_key; 262 DH *dh = dh; 263 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 264 u_int sbloblen, klen, kout, slen; 265 int min = -1, max = -1, nbits = -1, type; 266 267 if (kex->load_host_key == NULL) 268 fatal("Cannot load hostkey"); 269 server_host_key = kex->load_host_key(kex->hostkey_type); 270 if (server_host_key == NULL) 271 fatal("Unsupported hostkey type %d", kex->hostkey_type); 272 273 type = packet_read(); 274 switch (type) { 275 case SSH2_MSG_KEX_DH_GEX_REQUEST: 276 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 277 min = packet_get_int(); 278 nbits = packet_get_int(); 279 max = packet_get_int(); 280 min = MAX(DH_GRP_MIN, min); 281 max = MIN(DH_GRP_MAX, max); 282 break; 283 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 284 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 285 nbits = packet_get_int(); 286 min = DH_GRP_MIN; 287 max = DH_GRP_MAX; 288 /* unused for old GEX */ 289 break; 290 default: 291 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 292 } 293 packet_check_eom(); 294 295 if (max < min || nbits < min || max < nbits) 296 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 297 min, nbits, max); 298 299 dh = choose_dh(min, nbits, max); 300 if (dh == NULL) 301 packet_disconnect("Protocol error: no matching DH grp found"); 302 303 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 304 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 305 packet_put_bignum2(dh->p); 306 packet_put_bignum2(dh->g); 307 packet_send(); 308 309 /* flush */ 310 packet_write_wait(); 311 312 /* Compute our exchange value in parallel with the client */ 313 dh_gen_key(dh, kex->we_need * 8); 314 315 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 316 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 317 318 /* key, cert */ 319 if ((dh_client_pub = BN_new()) == NULL) 320 fatal("dh_client_pub == NULL"); 321 packet_get_bignum2(dh_client_pub); 322 packet_check_eom(); 323 324 #ifdef DEBUG_KEXDH 325 fprintf(stderr, "dh_client_pub= "); 326 BN_print_fp(stderr, dh_client_pub); 327 fprintf(stderr, "\n"); 328 debug("bits %d", BN_num_bits(dh_client_pub)); 329 #endif 330 331 #ifdef DEBUG_KEXDH 332 DHparams_print_fp(stderr, dh); 333 fprintf(stderr, "pub= "); 334 BN_print_fp(stderr, dh->pub_key); 335 fprintf(stderr, "\n"); 336 #endif 337 if (!dh_pub_is_valid(dh, dh_client_pub)) 338 packet_disconnect("bad client public DH value"); 339 340 klen = DH_size(dh); 341 kbuf = xmalloc(klen); 342 kout = DH_compute_key(kbuf, dh_client_pub, dh); 343 #ifdef DEBUG_KEXDH 344 dump_digest("shared secret", kbuf, kout); 345 #endif 346 if ((shared_secret = BN_new()) == NULL) 347 fatal("kexgex_server: BN_new failed"); 348 BN_bin2bn(kbuf, kout, shared_secret); 349 memset(kbuf, 0, klen); 350 xfree(kbuf); 351 352 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 353 354 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 355 min = max = -1; 356 357 /* calc H */ /* XXX depends on 'kex' */ 358 hash = kexgex_hash( 359 kex->client_version_string, 360 kex->server_version_string, 361 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 362 buffer_ptr(&kex->my), buffer_len(&kex->my), 363 server_host_key_blob, sbloblen, 364 min, nbits, max, 365 dh->p, dh->g, 366 dh_client_pub, 367 dh->pub_key, 368 shared_secret 369 ); 370 BN_clear_free(dh_client_pub); 371 372 /* save session id := H */ 373 /* XXX hashlen depends on KEX */ 374 if (kex->session_id == NULL) { 375 kex->session_id_len = 20; 376 kex->session_id = xmalloc(kex->session_id_len); 377 memcpy(kex->session_id, hash, kex->session_id_len); 378 } 379 380 /* sign H */ 381 /* XXX hashlen depends on KEX */ 382 key_sign(server_host_key, &signature, &slen, hash, 20); 383 384 /* destroy_sensitive_data(); */ 385 386 /* send server hostkey, DH pubkey 'f' and singed H */ 387 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 388 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 389 packet_put_string(server_host_key_blob, sbloblen); 390 packet_put_bignum2(dh->pub_key); /* f */ 391 packet_put_string(signature, slen); 392 packet_send(); 393 xfree(signature); 394 xfree(server_host_key_blob); 395 /* have keys, free DH */ 396 DH_free(dh); 397 398 kex_derive_keys(kex, hash, shared_secret); 399 BN_clear_free(shared_secret); 400 401 kex_finish(kex); 402 } 403 404 void 405 kexgex(Kex *kex) 406 { 407 if (kex->server) 408 kexgex_server(kex); 409 else 410 kexgex_client(kex); 411 } 412