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 1.22 2002/03/24 17:27:03 stevesk 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 #include "monitor_wrap.h" 42 43 static u_char * 44 kexgex_hash( 45 char *client_version_string, 46 char *server_version_string, 47 char *ckexinit, int ckexinitlen, 48 char *skexinit, int skexinitlen, 49 u_char *serverhostkeyblob, int sbloblen, 50 int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen, 51 BIGNUM *client_dh_pub, 52 BIGNUM *server_dh_pub, 53 BIGNUM *shared_secret) 54 { 55 Buffer b; 56 static u_char digest[EVP_MAX_MD_SIZE]; 57 const EVP_MD *evp_md = EVP_sha1(); 58 EVP_MD_CTX md; 59 60 buffer_init(&b); 61 buffer_put_cstring(&b, client_version_string); 62 buffer_put_cstring(&b, server_version_string); 63 64 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 65 buffer_put_int(&b, ckexinitlen+1); 66 buffer_put_char(&b, SSH2_MSG_KEXINIT); 67 buffer_append(&b, ckexinit, ckexinitlen); 68 buffer_put_int(&b, skexinitlen+1); 69 buffer_put_char(&b, SSH2_MSG_KEXINIT); 70 buffer_append(&b, skexinit, skexinitlen); 71 72 buffer_put_string(&b, serverhostkeyblob, sbloblen); 73 if (min == -1 || max == -1) 74 buffer_put_int(&b, wantbits); 75 else { 76 buffer_put_int(&b, min); 77 buffer_put_int(&b, wantbits); 78 buffer_put_int(&b, max); 79 } 80 buffer_put_bignum2(&b, prime); 81 buffer_put_bignum2(&b, gen); 82 buffer_put_bignum2(&b, client_dh_pub); 83 buffer_put_bignum2(&b, server_dh_pub); 84 buffer_put_bignum2(&b, shared_secret); 85 86 #ifdef DEBUG_KEXDH 87 buffer_dump(&b); 88 #endif 89 EVP_DigestInit(&md, evp_md); 90 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 91 EVP_DigestFinal(&md, digest, NULL); 92 93 buffer_free(&b); 94 95 #ifdef DEBUG_KEXDH 96 dump_digest("hash", digest, EVP_MD_size(evp_md)); 97 #endif 98 return digest; 99 } 100 101 /* client */ 102 103 static void 104 kexgex_client(Kex *kex) 105 { 106 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 107 BIGNUM *p = NULL, *g = NULL; 108 Key *server_host_key; 109 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 110 u_int klen, kout, slen, sbloblen; 111 int min, max, nbits; 112 DH *dh; 113 114 nbits = dh_estimate(kex->we_need * 8); 115 116 if (datafellows & SSH_OLD_DHGEX) { 117 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent"); 118 119 /* Old GEX request */ 120 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); 121 packet_put_int(nbits); 122 min = DH_GRP_MIN; 123 max = DH_GRP_MAX; 124 } else { 125 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent"); 126 127 /* New GEX request */ 128 min = DH_GRP_MIN; 129 max = DH_GRP_MAX; 130 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); 131 packet_put_int(min); 132 packet_put_int(nbits); 133 packet_put_int(max); 134 } 135 #ifdef DEBUG_KEXDH 136 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 137 min, nbits, max); 138 #endif 139 packet_send(); 140 141 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); 142 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP); 143 144 if ((p = BN_new()) == NULL) 145 fatal("BN_new"); 146 packet_get_bignum2(p); 147 if ((g = BN_new()) == NULL) 148 fatal("BN_new"); 149 packet_get_bignum2(g); 150 packet_check_eom(); 151 152 if (BN_num_bits(p) < min || BN_num_bits(p) > max) 153 fatal("DH_GEX group out of range: %d !< %d !< %d", 154 min, BN_num_bits(p), max); 155 156 dh = dh_new_group(g, p); 157 dh_gen_key(dh, kex->we_need * 8); 158 159 #ifdef DEBUG_KEXDH 160 DHparams_print_fp(stderr, dh); 161 fprintf(stderr, "pub= "); 162 BN_print_fp(stderr, dh->pub_key); 163 fprintf(stderr, "\n"); 164 #endif 165 166 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 167 /* generate and send 'e', client DH public key */ 168 packet_start(SSH2_MSG_KEX_DH_GEX_INIT); 169 packet_put_bignum2(dh->pub_key); 170 packet_send(); 171 172 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); 173 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY); 174 175 /* key, cert */ 176 server_host_key_blob = packet_get_string(&sbloblen); 177 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 178 if (server_host_key == NULL) 179 fatal("cannot decode server_host_key_blob"); 180 if (server_host_key->type != kex->hostkey_type) 181 fatal("type mismatch for decoded server_host_key_blob"); 182 if (kex->verify_host_key == NULL) 183 fatal("cannot verify server_host_key"); 184 if (kex->verify_host_key(server_host_key) == -1) 185 fatal("server_host_key verification failed"); 186 187 /* DH paramter f, server public DH key */ 188 if ((dh_server_pub = BN_new()) == NULL) 189 fatal("dh_server_pub == NULL"); 190 packet_get_bignum2(dh_server_pub); 191 192 #ifdef DEBUG_KEXDH 193 fprintf(stderr, "dh_server_pub= "); 194 BN_print_fp(stderr, dh_server_pub); 195 fprintf(stderr, "\n"); 196 debug("bits %d", BN_num_bits(dh_server_pub)); 197 #endif 198 199 /* signed H */ 200 signature = packet_get_string(&slen); 201 packet_check_eom(); 202 203 if (!dh_pub_is_valid(dh, dh_server_pub)) 204 packet_disconnect("bad server public DH value"); 205 206 klen = DH_size(dh); 207 kbuf = xmalloc(klen); 208 kout = DH_compute_key(kbuf, dh_server_pub, dh); 209 #ifdef DEBUG_KEXDH 210 dump_digest("shared secret", kbuf, kout); 211 #endif 212 if ((shared_secret = BN_new()) == NULL) 213 fatal("kexgex_client: BN_new failed"); 214 BN_bin2bn(kbuf, kout, shared_secret); 215 memset(kbuf, 0, klen); 216 xfree(kbuf); 217 218 if (datafellows & SSH_OLD_DHGEX) 219 min = max = -1; 220 221 /* calc and verify H */ 222 hash = kexgex_hash( 223 kex->client_version_string, 224 kex->server_version_string, 225 buffer_ptr(&kex->my), buffer_len(&kex->my), 226 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 227 server_host_key_blob, sbloblen, 228 min, nbits, max, 229 dh->p, dh->g, 230 dh->pub_key, 231 dh_server_pub, 232 shared_secret 233 ); 234 /* have keys, free DH */ 235 DH_free(dh); 236 xfree(server_host_key_blob); 237 BN_clear_free(dh_server_pub); 238 239 if (key_verify(server_host_key, signature, slen, hash, 20) != 1) 240 fatal("key_verify failed for server_host_key"); 241 key_free(server_host_key); 242 xfree(signature); 243 244 /* save session id */ 245 if (kex->session_id == NULL) { 246 kex->session_id_len = 20; 247 kex->session_id = xmalloc(kex->session_id_len); 248 memcpy(kex->session_id, hash, kex->session_id_len); 249 } 250 kex_derive_keys(kex, hash, shared_secret); 251 BN_clear_free(shared_secret); 252 253 kex_finish(kex); 254 } 255 256 /* server */ 257 258 static void 259 kexgex_server(Kex *kex) 260 { 261 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 262 Key *server_host_key; 263 DH *dh; 264 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 265 u_int sbloblen, klen, kout, slen; 266 int min = -1, max = -1, nbits = -1, type; 267 268 if (kex->load_host_key == NULL) 269 fatal("Cannot load hostkey"); 270 server_host_key = kex->load_host_key(kex->hostkey_type); 271 if (server_host_key == NULL) 272 fatal("Unsupported hostkey type %d", kex->hostkey_type); 273 274 type = packet_read(); 275 switch (type) { 276 case SSH2_MSG_KEX_DH_GEX_REQUEST: 277 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 278 min = packet_get_int(); 279 nbits = packet_get_int(); 280 max = packet_get_int(); 281 min = MAX(DH_GRP_MIN, min); 282 max = MIN(DH_GRP_MAX, max); 283 break; 284 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: 285 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); 286 nbits = packet_get_int(); 287 min = DH_GRP_MIN; 288 max = DH_GRP_MAX; 289 /* unused for old GEX */ 290 break; 291 default: 292 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); 293 } 294 packet_check_eom(); 295 296 if (max < min || nbits < min || max < nbits) 297 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", 298 min, nbits, max); 299 300 /* Contact privileged parent */ 301 dh = PRIVSEP(choose_dh(min, nbits, max)); 302 if (dh == NULL) 303 packet_disconnect("Protocol error: no matching DH grp found"); 304 305 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 306 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); 307 packet_put_bignum2(dh->p); 308 packet_put_bignum2(dh->g); 309 packet_send(); 310 311 /* flush */ 312 packet_write_wait(); 313 314 /* Compute our exchange value in parallel with the client */ 315 dh_gen_key(dh, kex->we_need * 8); 316 317 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 318 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT); 319 320 /* key, cert */ 321 if ((dh_client_pub = BN_new()) == NULL) 322 fatal("dh_client_pub == NULL"); 323 packet_get_bignum2(dh_client_pub); 324 packet_check_eom(); 325 326 #ifdef DEBUG_KEXDH 327 fprintf(stderr, "dh_client_pub= "); 328 BN_print_fp(stderr, dh_client_pub); 329 fprintf(stderr, "\n"); 330 debug("bits %d", BN_num_bits(dh_client_pub)); 331 #endif 332 333 #ifdef DEBUG_KEXDH 334 DHparams_print_fp(stderr, dh); 335 fprintf(stderr, "pub= "); 336 BN_print_fp(stderr, dh->pub_key); 337 fprintf(stderr, "\n"); 338 #endif 339 if (!dh_pub_is_valid(dh, dh_client_pub)) 340 packet_disconnect("bad client public DH value"); 341 342 klen = DH_size(dh); 343 kbuf = xmalloc(klen); 344 kout = DH_compute_key(kbuf, dh_client_pub, dh); 345 #ifdef DEBUG_KEXDH 346 dump_digest("shared secret", kbuf, kout); 347 #endif 348 if ((shared_secret = BN_new()) == NULL) 349 fatal("kexgex_server: BN_new failed"); 350 BN_bin2bn(kbuf, kout, shared_secret); 351 memset(kbuf, 0, klen); 352 xfree(kbuf); 353 354 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 355 356 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) 357 min = max = -1; 358 359 /* calc H */ /* XXX depends on 'kex' */ 360 hash = kexgex_hash( 361 kex->client_version_string, 362 kex->server_version_string, 363 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 364 buffer_ptr(&kex->my), buffer_len(&kex->my), 365 server_host_key_blob, sbloblen, 366 min, nbits, max, 367 dh->p, dh->g, 368 dh_client_pub, 369 dh->pub_key, 370 shared_secret 371 ); 372 BN_clear_free(dh_client_pub); 373 374 /* save session id := H */ 375 /* XXX hashlen depends on KEX */ 376 if (kex->session_id == NULL) { 377 kex->session_id_len = 20; 378 kex->session_id = xmalloc(kex->session_id_len); 379 memcpy(kex->session_id, hash, kex->session_id_len); 380 } 381 382 /* sign H */ 383 /* XXX hashlen depends on KEX */ 384 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20)); 385 386 /* destroy_sensitive_data(); */ 387 388 /* send server hostkey, DH pubkey 'f' and singed H */ 389 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); 390 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); 391 packet_put_string(server_host_key_blob, sbloblen); 392 packet_put_bignum2(dh->pub_key); /* f */ 393 packet_put_string(signature, slen); 394 packet_send(); 395 396 xfree(signature); 397 xfree(server_host_key_blob); 398 /* have keys, free DH */ 399 DH_free(dh); 400 401 kex_derive_keys(kex, hash, shared_secret); 402 BN_clear_free(shared_secret); 403 404 kex_finish(kex); 405 } 406 407 void 408 kexgex(Kex *kex) 409 { 410 if (kex->server) 411 kexgex_server(kex); 412 else 413 kexgex_client(kex); 414 } 415