1 /* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 djm 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 /* Validate KEX method name list */ 55 int 56 kex_names_valid(const char *names) 57 { 58 char *s, *cp, *p; 59 60 if (names == NULL || strcmp(names, "") == 0) 61 return 0; 62 s = cp = xstrdup(names); 63 for ((p = strsep(&cp, ",")); p && *p != '\0'; 64 (p = strsep(&cp, ","))) { 65 if (strcmp(p, KEX_DHGEX_SHA256) != 0 && 66 strcmp(p, KEX_DHGEX_SHA1) != 0 && 67 strcmp(p, KEX_DH14) != 0 && 68 strcmp(p, KEX_DH1) != 0 && 69 (strncmp(p, KEX_ECDH_SHA2_STEM, 70 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 || 71 kex_ecdh_name_to_nid(p) == -1)) { 72 error("Unsupported KEX algorithm \"%.100s\"", p); 73 xfree(s); 74 return 0; 75 } 76 } 77 debug3("kex names ok: [%s]", names); 78 xfree(s); 79 return 1; 80 } 81 82 /* put algorithm proposal into buffer */ 83 static void 84 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 85 { 86 u_int i; 87 88 buffer_clear(b); 89 /* 90 * add a dummy cookie, the cookie will be overwritten by 91 * kex_send_kexinit(), each time a kexinit is set 92 */ 93 for (i = 0; i < KEX_COOKIE_LEN; i++) 94 buffer_put_char(b, 0); 95 for (i = 0; i < PROPOSAL_MAX; i++) 96 buffer_put_cstring(b, proposal[i]); 97 buffer_put_char(b, 0); /* first_kex_packet_follows */ 98 buffer_put_int(b, 0); /* uint32 reserved */ 99 } 100 101 /* parse buffer and return algorithm proposal */ 102 static char ** 103 kex_buf2prop(Buffer *raw, int *first_kex_follows) 104 { 105 Buffer b; 106 u_int i; 107 char **proposal; 108 109 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 110 111 buffer_init(&b); 112 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 113 /* skip cookie */ 114 for (i = 0; i < KEX_COOKIE_LEN; i++) 115 buffer_get_char(&b); 116 /* extract kex init proposal strings */ 117 for (i = 0; i < PROPOSAL_MAX; i++) { 118 proposal[i] = buffer_get_cstring(&b,NULL); 119 debug2("kex_parse_kexinit: %s", proposal[i]); 120 } 121 /* first kex follows / reserved */ 122 i = buffer_get_char(&b); 123 if (first_kex_follows != NULL) 124 *first_kex_follows = i; 125 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 126 i = buffer_get_int(&b); 127 debug2("kex_parse_kexinit: reserved %u ", i); 128 buffer_free(&b); 129 return proposal; 130 } 131 132 static void 133 kex_prop_free(char **proposal) 134 { 135 u_int i; 136 137 for (i = 0; i < PROPOSAL_MAX; i++) 138 xfree(proposal[i]); 139 xfree(proposal); 140 } 141 142 /* ARGSUSED */ 143 static void 144 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 145 { 146 error("Hm, kex protocol error: type %d seq %u", type, seq); 147 } 148 149 static void 150 kex_reset_dispatch(void) 151 { 152 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 153 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 154 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 155 } 156 157 void 158 kex_finish(Kex *kex) 159 { 160 kex_reset_dispatch(); 161 162 packet_start(SSH2_MSG_NEWKEYS); 163 packet_send(); 164 /* packet_write_wait(); */ 165 debug("SSH2_MSG_NEWKEYS sent"); 166 167 debug("expecting SSH2_MSG_NEWKEYS"); 168 packet_read_expect(SSH2_MSG_NEWKEYS); 169 packet_check_eom(); 170 debug("SSH2_MSG_NEWKEYS received"); 171 172 kex->done = 1; 173 buffer_clear(&kex->peer); 174 /* buffer_clear(&kex->my); */ 175 kex->flags &= ~KEX_INIT_SENT; 176 xfree(kex->name); 177 kex->name = NULL; 178 } 179 180 void 181 kex_send_kexinit(Kex *kex) 182 { 183 u_int32_t rnd = 0; 184 u_char *cookie; 185 u_int i; 186 187 if (kex == NULL) { 188 error("kex_send_kexinit: no kex, cannot rekey"); 189 return; 190 } 191 if (kex->flags & KEX_INIT_SENT) { 192 debug("KEX_INIT_SENT"); 193 return; 194 } 195 kex->done = 0; 196 197 /* generate a random cookie */ 198 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 199 fatal("kex_send_kexinit: kex proposal too short"); 200 cookie = buffer_ptr(&kex->my); 201 for (i = 0; i < KEX_COOKIE_LEN; i++) { 202 if (i % 4 == 0) 203 rnd = arc4random(); 204 cookie[i] = rnd; 205 rnd >>= 8; 206 } 207 packet_start(SSH2_MSG_KEXINIT); 208 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 209 packet_send(); 210 debug("SSH2_MSG_KEXINIT sent"); 211 kex->flags |= KEX_INIT_SENT; 212 } 213 214 /* ARGSUSED */ 215 void 216 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 217 { 218 char *ptr; 219 u_int i, dlen; 220 Kex *kex = (Kex *)ctxt; 221 222 debug("SSH2_MSG_KEXINIT received"); 223 if (kex == NULL) 224 fatal("kex_input_kexinit: no kex, cannot rekey"); 225 226 ptr = packet_get_raw(&dlen); 227 buffer_append(&kex->peer, ptr, dlen); 228 229 /* discard packet */ 230 for (i = 0; i < KEX_COOKIE_LEN; i++) 231 packet_get_char(); 232 for (i = 0; i < PROPOSAL_MAX; i++) 233 xfree(packet_get_string(NULL)); 234 (void) packet_get_char(); 235 (void) packet_get_int(); 236 packet_check_eom(); 237 238 kex_kexinit_finish(kex); 239 } 240 241 Kex * 242 kex_setup(char *proposal[PROPOSAL_MAX]) 243 { 244 Kex *kex; 245 246 kex = xcalloc(1, sizeof(*kex)); 247 buffer_init(&kex->peer); 248 buffer_init(&kex->my); 249 kex_prop2buf(&kex->my, proposal); 250 kex->done = 0; 251 252 kex_send_kexinit(kex); /* we start */ 253 kex_reset_dispatch(); 254 255 return kex; 256 } 257 258 static void 259 kex_kexinit_finish(Kex *kex) 260 { 261 if (!(kex->flags & KEX_INIT_SENT)) 262 kex_send_kexinit(kex); 263 264 kex_choose_conf(kex); 265 266 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 267 kex->kex[kex->kex_type] != NULL) { 268 (kex->kex[kex->kex_type])(kex); 269 } else { 270 fatal("Unsupported key exchange %d", kex->kex_type); 271 } 272 } 273 274 static void 275 choose_enc(Enc *enc, char *client, char *server) 276 { 277 char *name = match_list(client, server, NULL); 278 if (name == NULL) 279 fatal("no matching cipher found: client %s server %s", 280 client, server); 281 if ((enc->cipher = cipher_by_name(name)) == NULL) 282 fatal("matching cipher is not supported: %s", name); 283 enc->name = name; 284 enc->enabled = 0; 285 enc->iv = NULL; 286 enc->key = NULL; 287 enc->key_len = cipher_keylen(enc->cipher); 288 enc->block_size = cipher_blocksize(enc->cipher); 289 } 290 291 static void 292 choose_mac(Mac *mac, char *client, char *server) 293 { 294 char *name = match_list(client, server, NULL); 295 if (name == NULL) 296 fatal("no matching mac found: client %s server %s", 297 client, server); 298 if (mac_setup(mac, name) < 0) 299 fatal("unsupported mac %s", name); 300 /* truncate the key */ 301 if (datafellows & SSH_BUG_HMAC) 302 mac->key_len = 16; 303 mac->name = name; 304 mac->key = NULL; 305 mac->enabled = 0; 306 } 307 308 static void 309 choose_comp(Comp *comp, char *client, char *server) 310 { 311 char *name = match_list(client, server, NULL); 312 if (name == NULL) 313 fatal("no matching comp found: client %s server %s", client, server); 314 if (strcmp(name, "zlib@openssh.com") == 0) { 315 comp->type = COMP_DELAYED; 316 } else if (strcmp(name, "zlib") == 0) { 317 comp->type = COMP_ZLIB; 318 } else if (strcmp(name, "none") == 0) { 319 comp->type = COMP_NONE; 320 } else { 321 fatal("unsupported comp %s", name); 322 } 323 comp->name = name; 324 } 325 326 static void 327 choose_kex(Kex *k, char *client, char *server) 328 { 329 k->name = match_list(client, server, NULL); 330 if (k->name == NULL) 331 fatal("Unable to negotiate a key exchange method"); 332 if (strcmp(k->name, KEX_DH1) == 0) { 333 k->kex_type = KEX_DH_GRP1_SHA1; 334 k->evp_md = EVP_sha1(); 335 } else if (strcmp(k->name, KEX_DH14) == 0) { 336 k->kex_type = KEX_DH_GRP14_SHA1; 337 k->evp_md = EVP_sha1(); 338 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 339 k->kex_type = KEX_DH_GEX_SHA1; 340 k->evp_md = EVP_sha1(); 341 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 342 k->kex_type = KEX_DH_GEX_SHA256; 343 k->evp_md = EVP_sha256(); 344 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM, 345 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) { 346 k->kex_type = KEX_ECDH_SHA2; 347 k->evp_md = kex_ecdh_name_to_evpmd(k->name); 348 } else 349 fatal("bad kex alg %s", k->name); 350 } 351 352 static void 353 choose_hostkeyalg(Kex *k, char *client, char *server) 354 { 355 char *hostkeyalg = match_list(client, server, NULL); 356 if (hostkeyalg == NULL) 357 fatal("no hostkey alg"); 358 k->hostkey_type = key_type_from_name(hostkeyalg); 359 if (k->hostkey_type == KEY_UNSPEC) 360 fatal("bad hostkey alg '%s'", hostkeyalg); 361 xfree(hostkeyalg); 362 } 363 364 static int 365 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 366 { 367 static int check[] = { 368 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 369 }; 370 int *idx; 371 char *p; 372 373 for (idx = &check[0]; *idx != -1; idx++) { 374 if ((p = strchr(my[*idx], ',')) != NULL) 375 *p = '\0'; 376 if ((p = strchr(peer[*idx], ',')) != NULL) 377 *p = '\0'; 378 if (strcmp(my[*idx], peer[*idx]) != 0) { 379 debug2("proposal mismatch: my %s peer %s", 380 my[*idx], peer[*idx]); 381 return (0); 382 } 383 } 384 debug2("proposals match"); 385 return (1); 386 } 387 388 static void 389 kex_choose_conf(Kex *kex) 390 { 391 Newkeys *newkeys; 392 char **my, **peer; 393 char **cprop, **sprop; 394 int nenc, nmac, ncomp; 395 u_int mode, ctos, need; 396 int first_kex_follows, type; 397 398 my = kex_buf2prop(&kex->my, NULL); 399 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 400 401 if (kex->server) { 402 cprop=peer; 403 sprop=my; 404 } else { 405 cprop=my; 406 sprop=peer; 407 } 408 409 /* Check whether server offers roaming */ 410 if (!kex->server) { 411 char *roaming; 412 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 413 if (roaming) { 414 kex->roaming = 1; 415 xfree(roaming); 416 } 417 } 418 419 /* Algorithm Negotiation */ 420 for (mode = 0; mode < MODE_MAX; mode++) { 421 newkeys = xcalloc(1, sizeof(*newkeys)); 422 kex->newkeys[mode] = newkeys; 423 ctos = (!kex->server && mode == MODE_OUT) || 424 (kex->server && mode == MODE_IN); 425 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 426 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 427 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 428 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 429 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 430 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 431 debug("kex: %s %s %s %s", 432 ctos ? "client->server" : "server->client", 433 newkeys->enc.name, 434 newkeys->mac.name, 435 newkeys->comp.name); 436 } 437 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 438 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 439 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 440 need = 0; 441 for (mode = 0; mode < MODE_MAX; mode++) { 442 newkeys = kex->newkeys[mode]; 443 if (need < newkeys->enc.key_len) 444 need = newkeys->enc.key_len; 445 if (need < newkeys->enc.block_size) 446 need = newkeys->enc.block_size; 447 if (need < newkeys->mac.key_len) 448 need = newkeys->mac.key_len; 449 } 450 /* XXX need runden? */ 451 kex->we_need = need; 452 453 /* ignore the next message if the proposals do not match */ 454 if (first_kex_follows && !proposals_match(my, peer) && 455 !(datafellows & SSH_BUG_FIRSTKEX)) { 456 type = packet_read(); 457 debug2("skipping next packet (type %u)", type); 458 } 459 460 kex_prop_free(my); 461 kex_prop_free(peer); 462 } 463 464 static u_char * 465 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 466 BIGNUM *shared_secret) 467 { 468 Buffer b; 469 EVP_MD_CTX md; 470 char c = id; 471 u_int have; 472 int mdsz; 473 u_char *digest; 474 475 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 476 fatal("bad kex md size %d", mdsz); 477 digest = xmalloc(roundup(need, mdsz)); 478 479 buffer_init(&b); 480 buffer_put_bignum2(&b, shared_secret); 481 482 /* K1 = HASH(K || H || "A" || session_id) */ 483 EVP_DigestInit(&md, kex->evp_md); 484 if (!(datafellows & SSH_BUG_DERIVEKEY)) 485 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 486 EVP_DigestUpdate(&md, hash, hashlen); 487 EVP_DigestUpdate(&md, &c, 1); 488 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 489 EVP_DigestFinal(&md, digest, NULL); 490 491 /* 492 * expand key: 493 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 494 * Key = K1 || K2 || ... || Kn 495 */ 496 for (have = mdsz; need > have; have += mdsz) { 497 EVP_DigestInit(&md, kex->evp_md); 498 if (!(datafellows & SSH_BUG_DERIVEKEY)) 499 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 500 EVP_DigestUpdate(&md, hash, hashlen); 501 EVP_DigestUpdate(&md, digest, have); 502 EVP_DigestFinal(&md, digest + have, NULL); 503 } 504 buffer_free(&b); 505 #ifdef DEBUG_KEX 506 fprintf(stderr, "key '%c'== ", c); 507 dump_digest("key", digest, need); 508 #endif 509 return digest; 510 } 511 512 Newkeys *current_keys[MODE_MAX]; 513 514 #define NKEYS 6 515 void 516 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 517 { 518 u_char *keys[NKEYS]; 519 u_int i, mode, ctos; 520 521 for (i = 0; i < NKEYS; i++) { 522 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 523 shared_secret); 524 } 525 526 debug2("kex_derive_keys"); 527 for (mode = 0; mode < MODE_MAX; mode++) { 528 current_keys[mode] = kex->newkeys[mode]; 529 kex->newkeys[mode] = NULL; 530 ctos = (!kex->server && mode == MODE_OUT) || 531 (kex->server && mode == MODE_IN); 532 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 533 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 534 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 535 } 536 } 537 538 Newkeys * 539 kex_get_newkeys(int mode) 540 { 541 Newkeys *ret; 542 543 ret = current_keys[mode]; 544 current_keys[mode] = NULL; 545 return ret; 546 } 547 548 void 549 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 550 u_int8_t cookie[8], u_int8_t id[16]) 551 { 552 const EVP_MD *evp_md = EVP_md5(); 553 EVP_MD_CTX md; 554 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 555 int len; 556 557 EVP_DigestInit(&md, evp_md); 558 559 len = BN_num_bytes(host_modulus); 560 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 561 fatal("%s: bad host modulus (len %d)", __func__, len); 562 BN_bn2bin(host_modulus, nbuf); 563 EVP_DigestUpdate(&md, nbuf, len); 564 565 len = BN_num_bytes(server_modulus); 566 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 567 fatal("%s: bad server modulus (len %d)", __func__, len); 568 BN_bn2bin(server_modulus, nbuf); 569 EVP_DigestUpdate(&md, nbuf, len); 570 571 EVP_DigestUpdate(&md, cookie, 8); 572 573 EVP_DigestFinal(&md, obuf, NULL); 574 memcpy(id, obuf, 16); 575 576 memset(nbuf, 0, sizeof(nbuf)); 577 memset(obuf, 0, sizeof(obuf)); 578 memset(&md, 0, sizeof(md)); 579 } 580 581 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) 582 void 583 dump_digest(char *msg, u_char *digest, int len) 584 { 585 int i; 586 587 fprintf(stderr, "%s\n", msg); 588 for (i = 0; i < len; i++) { 589 fprintf(stderr, "%02x", digest[i]); 590 if (i%32 == 31) 591 fprintf(stderr, "\n"); 592 else if (i%8 == 7) 593 fprintf(stderr, " "); 594 } 595 fprintf(stderr, "\n"); 596 } 597 #endif 598