1 /* $OpenBSD: kex.c,v 1.82 2009/10/24 11:13:54 andreas Exp $ */ 2 /* 3 * Copyright (c) 2000, 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 <sys/param.h> 27 28 #include <signal.h> 29 #include <stdio.h> 30 #include <stdlib.h> 31 #include <string.h> 32 33 #include <openssl/crypto.h> 34 35 #include "xmalloc.h" 36 #include "ssh2.h" 37 #include "buffer.h" 38 #include "packet.h" 39 #include "compat.h" 40 #include "cipher.h" 41 #include "key.h" 42 #include "kex.h" 43 #include "log.h" 44 #include "mac.h" 45 #include "match.h" 46 #include "dispatch.h" 47 #include "monitor.h" 48 #include "roaming.h" 49 50 /* prototype */ 51 static void kex_kexinit_finish(Kex *); 52 static void kex_choose_conf(Kex *); 53 54 /* put algorithm proposal into buffer */ 55 static void 56 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 57 { 58 u_int i; 59 60 buffer_clear(b); 61 /* 62 * add a dummy cookie, the cookie will be overwritten by 63 * kex_send_kexinit(), each time a kexinit is set 64 */ 65 for (i = 0; i < KEX_COOKIE_LEN; i++) 66 buffer_put_char(b, 0); 67 for (i = 0; i < PROPOSAL_MAX; i++) 68 buffer_put_cstring(b, proposal[i]); 69 buffer_put_char(b, 0); /* first_kex_packet_follows */ 70 buffer_put_int(b, 0); /* uint32 reserved */ 71 } 72 73 /* parse buffer and return algorithm proposal */ 74 static char ** 75 kex_buf2prop(Buffer *raw, int *first_kex_follows) 76 { 77 Buffer b; 78 u_int i; 79 char **proposal; 80 81 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 82 83 buffer_init(&b); 84 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 85 /* skip cookie */ 86 for (i = 0; i < KEX_COOKIE_LEN; i++) 87 buffer_get_char(&b); 88 /* extract kex init proposal strings */ 89 for (i = 0; i < PROPOSAL_MAX; i++) { 90 proposal[i] = buffer_get_string(&b,NULL); 91 debug2("kex_parse_kexinit: %s", proposal[i]); 92 } 93 /* first kex follows / reserved */ 94 i = buffer_get_char(&b); 95 if (first_kex_follows != NULL) 96 *first_kex_follows = i; 97 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 98 i = buffer_get_int(&b); 99 debug2("kex_parse_kexinit: reserved %u ", i); 100 buffer_free(&b); 101 return proposal; 102 } 103 104 static void 105 kex_prop_free(char **proposal) 106 { 107 u_int i; 108 109 for (i = 0; i < PROPOSAL_MAX; i++) 110 xfree(proposal[i]); 111 xfree(proposal); 112 } 113 114 /* ARGSUSED */ 115 static void 116 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 117 { 118 error("Hm, kex protocol error: type %d seq %u", type, seq); 119 } 120 121 static void 122 kex_reset_dispatch(void) 123 { 124 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 125 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 126 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 127 } 128 129 void 130 kex_finish(Kex *kex) 131 { 132 kex_reset_dispatch(); 133 134 packet_start(SSH2_MSG_NEWKEYS); 135 packet_send(); 136 /* packet_write_wait(); */ 137 debug("SSH2_MSG_NEWKEYS sent"); 138 139 debug("expecting SSH2_MSG_NEWKEYS"); 140 packet_read_expect(SSH2_MSG_NEWKEYS); 141 packet_check_eom(); 142 debug("SSH2_MSG_NEWKEYS received"); 143 144 kex->done = 1; 145 buffer_clear(&kex->peer); 146 /* buffer_clear(&kex->my); */ 147 kex->flags &= ~KEX_INIT_SENT; 148 xfree(kex->name); 149 kex->name = NULL; 150 } 151 152 void 153 kex_send_kexinit(Kex *kex) 154 { 155 u_int32_t rnd = 0; 156 u_char *cookie; 157 u_int i; 158 159 if (kex == NULL) { 160 error("kex_send_kexinit: no kex, cannot rekey"); 161 return; 162 } 163 if (kex->flags & KEX_INIT_SENT) { 164 debug("KEX_INIT_SENT"); 165 return; 166 } 167 kex->done = 0; 168 169 /* generate a random cookie */ 170 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 171 fatal("kex_send_kexinit: kex proposal too short"); 172 cookie = buffer_ptr(&kex->my); 173 for (i = 0; i < KEX_COOKIE_LEN; i++) { 174 if (i % 4 == 0) 175 rnd = arc4random(); 176 cookie[i] = rnd; 177 rnd >>= 8; 178 } 179 packet_start(SSH2_MSG_KEXINIT); 180 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 181 packet_send(); 182 debug("SSH2_MSG_KEXINIT sent"); 183 kex->flags |= KEX_INIT_SENT; 184 } 185 186 /* ARGSUSED */ 187 void 188 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 189 { 190 char *ptr; 191 u_int i, dlen; 192 Kex *kex = (Kex *)ctxt; 193 194 debug("SSH2_MSG_KEXINIT received"); 195 if (kex == NULL) 196 fatal("kex_input_kexinit: no kex, cannot rekey"); 197 198 ptr = packet_get_raw(&dlen); 199 buffer_append(&kex->peer, ptr, dlen); 200 201 /* discard packet */ 202 for (i = 0; i < KEX_COOKIE_LEN; i++) 203 packet_get_char(); 204 for (i = 0; i < PROPOSAL_MAX; i++) 205 xfree(packet_get_string(NULL)); 206 (void) packet_get_char(); 207 (void) packet_get_int(); 208 packet_check_eom(); 209 210 kex_kexinit_finish(kex); 211 } 212 213 Kex * 214 kex_setup(char *proposal[PROPOSAL_MAX]) 215 { 216 Kex *kex; 217 218 kex = xcalloc(1, sizeof(*kex)); 219 buffer_init(&kex->peer); 220 buffer_init(&kex->my); 221 kex_prop2buf(&kex->my, proposal); 222 kex->done = 0; 223 224 kex_send_kexinit(kex); /* we start */ 225 kex_reset_dispatch(); 226 227 return kex; 228 } 229 230 static void 231 kex_kexinit_finish(Kex *kex) 232 { 233 if (!(kex->flags & KEX_INIT_SENT)) 234 kex_send_kexinit(kex); 235 236 kex_choose_conf(kex); 237 238 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 239 kex->kex[kex->kex_type] != NULL) { 240 (kex->kex[kex->kex_type])(kex); 241 } else { 242 fatal("Unsupported key exchange %d", kex->kex_type); 243 } 244 } 245 246 static void 247 choose_enc(Enc *enc, char *client, char *server) 248 { 249 char *name = match_list(client, server, NULL); 250 if (name == NULL) 251 fatal("no matching cipher found: client %s server %s", 252 client, server); 253 if ((enc->cipher = cipher_by_name(name)) == NULL) 254 fatal("matching cipher is not supported: %s", name); 255 enc->name = name; 256 enc->enabled = 0; 257 enc->iv = NULL; 258 enc->key = NULL; 259 enc->key_len = cipher_keylen(enc->cipher); 260 enc->block_size = cipher_blocksize(enc->cipher); 261 } 262 263 static void 264 choose_mac(Mac *mac, char *client, char *server) 265 { 266 char *name = match_list(client, server, NULL); 267 if (name == NULL) 268 fatal("no matching mac found: client %s server %s", 269 client, server); 270 if (mac_setup(mac, name) < 0) 271 fatal("unsupported mac %s", name); 272 /* truncate the key */ 273 if (datafellows & SSH_BUG_HMAC) 274 mac->key_len = 16; 275 mac->name = name; 276 mac->key = NULL; 277 mac->enabled = 0; 278 } 279 280 static void 281 choose_comp(Comp *comp, char *client, char *server) 282 { 283 char *name = match_list(client, server, NULL); 284 if (name == NULL) 285 fatal("no matching comp found: client %s server %s", client, server); 286 if (strcmp(name, "zlib@openssh.com") == 0) { 287 comp->type = COMP_DELAYED; 288 } else if (strcmp(name, "zlib") == 0) { 289 comp->type = COMP_ZLIB; 290 } else if (strcmp(name, "none") == 0) { 291 comp->type = COMP_NONE; 292 } else { 293 fatal("unsupported comp %s", name); 294 } 295 comp->name = name; 296 } 297 298 static void 299 choose_kex(Kex *k, char *client, char *server) 300 { 301 k->name = match_list(client, server, NULL); 302 if (k->name == NULL) 303 fatal("Unable to negotiate a key exchange method"); 304 if (strcmp(k->name, KEX_DH1) == 0) { 305 k->kex_type = KEX_DH_GRP1_SHA1; 306 k->evp_md = EVP_sha1(); 307 } else if (strcmp(k->name, KEX_DH14) == 0) { 308 k->kex_type = KEX_DH_GRP14_SHA1; 309 k->evp_md = EVP_sha1(); 310 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 311 k->kex_type = KEX_DH_GEX_SHA1; 312 k->evp_md = EVP_sha1(); 313 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 314 k->kex_type = KEX_DH_GEX_SHA256; 315 k->evp_md = EVP_sha256(); 316 } else 317 fatal("bad kex alg %s", k->name); 318 } 319 320 static void 321 choose_hostkeyalg(Kex *k, char *client, char *server) 322 { 323 char *hostkeyalg = match_list(client, server, NULL); 324 if (hostkeyalg == NULL) 325 fatal("no hostkey alg"); 326 k->hostkey_type = key_type_from_name(hostkeyalg); 327 if (k->hostkey_type == KEY_UNSPEC) 328 fatal("bad hostkey alg '%s'", hostkeyalg); 329 xfree(hostkeyalg); 330 } 331 332 static int 333 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 334 { 335 static int check[] = { 336 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 337 }; 338 int *idx; 339 char *p; 340 341 for (idx = &check[0]; *idx != -1; idx++) { 342 if ((p = strchr(my[*idx], ',')) != NULL) 343 *p = '\0'; 344 if ((p = strchr(peer[*idx], ',')) != NULL) 345 *p = '\0'; 346 if (strcmp(my[*idx], peer[*idx]) != 0) { 347 debug2("proposal mismatch: my %s peer %s", 348 my[*idx], peer[*idx]); 349 return (0); 350 } 351 } 352 debug2("proposals match"); 353 return (1); 354 } 355 356 static void 357 kex_choose_conf(Kex *kex) 358 { 359 Newkeys *newkeys; 360 char **my, **peer; 361 char **cprop, **sprop; 362 int nenc, nmac, ncomp; 363 u_int mode, ctos, need; 364 int first_kex_follows, type; 365 366 my = kex_buf2prop(&kex->my, NULL); 367 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 368 369 if (kex->server) { 370 cprop=peer; 371 sprop=my; 372 } else { 373 cprop=my; 374 sprop=peer; 375 } 376 377 /* Check whether server offers roaming */ 378 if (!kex->server) { 379 char *roaming; 380 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 381 if (roaming) { 382 kex->roaming = 1; 383 xfree(roaming); 384 } 385 } 386 387 /* Algorithm Negotiation */ 388 for (mode = 0; mode < MODE_MAX; mode++) { 389 newkeys = xcalloc(1, sizeof(*newkeys)); 390 kex->newkeys[mode] = newkeys; 391 ctos = (!kex->server && mode == MODE_OUT) || 392 (kex->server && mode == MODE_IN); 393 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 394 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 395 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 396 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 397 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 398 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 399 debug("kex: %s %s %s %s", 400 ctos ? "client->server" : "server->client", 401 newkeys->enc.name, 402 newkeys->mac.name, 403 newkeys->comp.name); 404 } 405 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 406 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 407 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 408 need = 0; 409 for (mode = 0; mode < MODE_MAX; mode++) { 410 newkeys = kex->newkeys[mode]; 411 if (need < newkeys->enc.key_len) 412 need = newkeys->enc.key_len; 413 if (need < newkeys->enc.block_size) 414 need = newkeys->enc.block_size; 415 if (need < newkeys->mac.key_len) 416 need = newkeys->mac.key_len; 417 } 418 /* XXX need runden? */ 419 kex->we_need = need; 420 421 /* ignore the next message if the proposals do not match */ 422 if (first_kex_follows && !proposals_match(my, peer) && 423 !(datafellows & SSH_BUG_FIRSTKEX)) { 424 type = packet_read(); 425 debug2("skipping next packet (type %u)", type); 426 } 427 428 kex_prop_free(my); 429 kex_prop_free(peer); 430 } 431 432 static u_char * 433 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 434 BIGNUM *shared_secret) 435 { 436 Buffer b; 437 EVP_MD_CTX md; 438 char c = id; 439 u_int have; 440 int mdsz; 441 u_char *digest; 442 443 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 444 fatal("bad kex md size %d", mdsz); 445 digest = xmalloc(roundup(need, mdsz)); 446 447 buffer_init(&b); 448 buffer_put_bignum2(&b, shared_secret); 449 450 /* K1 = HASH(K || H || "A" || session_id) */ 451 EVP_DigestInit(&md, kex->evp_md); 452 if (!(datafellows & SSH_BUG_DERIVEKEY)) 453 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 454 EVP_DigestUpdate(&md, hash, hashlen); 455 EVP_DigestUpdate(&md, &c, 1); 456 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 457 EVP_DigestFinal(&md, digest, NULL); 458 459 /* 460 * expand key: 461 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 462 * Key = K1 || K2 || ... || Kn 463 */ 464 for (have = mdsz; need > have; have += mdsz) { 465 EVP_DigestInit(&md, kex->evp_md); 466 if (!(datafellows & SSH_BUG_DERIVEKEY)) 467 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 468 EVP_DigestUpdate(&md, hash, hashlen); 469 EVP_DigestUpdate(&md, digest, have); 470 EVP_DigestFinal(&md, digest + have, NULL); 471 } 472 buffer_free(&b); 473 #ifdef DEBUG_KEX 474 fprintf(stderr, "key '%c'== ", c); 475 dump_digest("key", digest, need); 476 #endif 477 return digest; 478 } 479 480 Newkeys *current_keys[MODE_MAX]; 481 482 #define NKEYS 6 483 void 484 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 485 { 486 u_char *keys[NKEYS]; 487 u_int i, mode, ctos; 488 489 for (i = 0; i < NKEYS; i++) { 490 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 491 shared_secret); 492 } 493 494 debug2("kex_derive_keys"); 495 for (mode = 0; mode < MODE_MAX; mode++) { 496 current_keys[mode] = kex->newkeys[mode]; 497 kex->newkeys[mode] = NULL; 498 ctos = (!kex->server && mode == MODE_OUT) || 499 (kex->server && mode == MODE_IN); 500 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 501 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 502 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 503 } 504 } 505 506 Newkeys * 507 kex_get_newkeys(int mode) 508 { 509 Newkeys *ret; 510 511 ret = current_keys[mode]; 512 current_keys[mode] = NULL; 513 return ret; 514 } 515 516 void 517 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 518 u_int8_t cookie[8], u_int8_t id[16]) 519 { 520 const EVP_MD *evp_md = EVP_md5(); 521 EVP_MD_CTX md; 522 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 523 int len; 524 525 EVP_DigestInit(&md, evp_md); 526 527 len = BN_num_bytes(host_modulus); 528 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 529 fatal("%s: bad host modulus (len %d)", __func__, len); 530 BN_bn2bin(host_modulus, nbuf); 531 EVP_DigestUpdate(&md, nbuf, len); 532 533 len = BN_num_bytes(server_modulus); 534 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 535 fatal("%s: bad server modulus (len %d)", __func__, len); 536 BN_bn2bin(server_modulus, nbuf); 537 EVP_DigestUpdate(&md, nbuf, len); 538 539 EVP_DigestUpdate(&md, cookie, 8); 540 541 EVP_DigestFinal(&md, obuf, NULL); 542 memcpy(id, obuf, 16); 543 544 memset(nbuf, 0, sizeof(nbuf)); 545 memset(obuf, 0, sizeof(obuf)); 546 memset(&md, 0, sizeof(md)); 547 } 548 549 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 550 void 551 dump_digest(char *msg, u_char *digest, int len) 552 { 553 u_int i; 554 555 fprintf(stderr, "%s\n", msg); 556 for (i = 0; i < len; i++) { 557 fprintf(stderr, "%02x", digest[i]); 558 if (i%32 == 31) 559 fprintf(stderr, "\n"); 560 else if (i%8 == 7) 561 fprintf(stderr, " "); 562 } 563 fprintf(stderr, "\n"); 564 } 565 #endif 566