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 "includes.h" 27 28 #include <sys/param.h> 29 30 #include <signal.h> 31 #include <stdarg.h> 32 #include <stdio.h> 33 #include <stdlib.h> 34 #include <string.h> 35 36 #include <openssl/crypto.h> 37 38 #include "xmalloc.h" 39 #include "ssh2.h" 40 #include "buffer.h" 41 #include "packet.h" 42 #include "compat.h" 43 #include "cipher.h" 44 #include "key.h" 45 #include "kex.h" 46 #include "log.h" 47 #include "mac.h" 48 #include "match.h" 49 #include "dispatch.h" 50 #include "monitor.h" 51 #include "roaming.h" 52 53 #if OPENSSL_VERSION_NUMBER >= 0x00907000L 54 # if defined(HAVE_EVP_SHA256) 55 # define evp_ssh_sha256 EVP_sha256 56 # else 57 extern const EVP_MD *evp_ssh_sha256(void); 58 # endif 59 #endif 60 61 /* prototype */ 62 static void kex_kexinit_finish(Kex *); 63 static void kex_choose_conf(Kex *); 64 65 /* put algorithm proposal into buffer */ 66 static void 67 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 68 { 69 u_int i; 70 71 buffer_clear(b); 72 /* 73 * add a dummy cookie, the cookie will be overwritten by 74 * kex_send_kexinit(), each time a kexinit is set 75 */ 76 for (i = 0; i < KEX_COOKIE_LEN; i++) 77 buffer_put_char(b, 0); 78 for (i = 0; i < PROPOSAL_MAX; i++) 79 buffer_put_cstring(b, proposal[i]); 80 buffer_put_char(b, 0); /* first_kex_packet_follows */ 81 buffer_put_int(b, 0); /* uint32 reserved */ 82 } 83 84 /* parse buffer and return algorithm proposal */ 85 static char ** 86 kex_buf2prop(Buffer *raw, int *first_kex_follows) 87 { 88 Buffer b; 89 u_int i; 90 char **proposal; 91 92 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 93 94 buffer_init(&b); 95 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 96 /* skip cookie */ 97 for (i = 0; i < KEX_COOKIE_LEN; i++) 98 buffer_get_char(&b); 99 /* extract kex init proposal strings */ 100 for (i = 0; i < PROPOSAL_MAX; i++) { 101 proposal[i] = buffer_get_string(&b,NULL); 102 debug2("kex_parse_kexinit: %s", proposal[i]); 103 } 104 /* first kex follows / reserved */ 105 i = buffer_get_char(&b); 106 if (first_kex_follows != NULL) 107 *first_kex_follows = i; 108 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 109 i = buffer_get_int(&b); 110 debug2("kex_parse_kexinit: reserved %u ", i); 111 buffer_free(&b); 112 return proposal; 113 } 114 115 static void 116 kex_prop_free(char **proposal) 117 { 118 u_int i; 119 120 for (i = 0; i < PROPOSAL_MAX; i++) 121 xfree(proposal[i]); 122 xfree(proposal); 123 } 124 125 /* ARGSUSED */ 126 static void 127 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 128 { 129 error("Hm, kex protocol error: type %d seq %u", type, seq); 130 } 131 132 static void 133 kex_reset_dispatch(void) 134 { 135 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 136 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 137 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 138 } 139 140 void 141 kex_finish(Kex *kex) 142 { 143 kex_reset_dispatch(); 144 145 packet_start(SSH2_MSG_NEWKEYS); 146 packet_send(); 147 /* packet_write_wait(); */ 148 debug("SSH2_MSG_NEWKEYS sent"); 149 150 debug("expecting SSH2_MSG_NEWKEYS"); 151 packet_read_expect(SSH2_MSG_NEWKEYS); 152 packet_check_eom(); 153 debug("SSH2_MSG_NEWKEYS received"); 154 155 kex->done = 1; 156 buffer_clear(&kex->peer); 157 /* buffer_clear(&kex->my); */ 158 kex->flags &= ~KEX_INIT_SENT; 159 xfree(kex->name); 160 kex->name = NULL; 161 } 162 163 void 164 kex_send_kexinit(Kex *kex) 165 { 166 u_int32_t rnd = 0; 167 u_char *cookie; 168 u_int i; 169 170 if (kex == NULL) { 171 error("kex_send_kexinit: no kex, cannot rekey"); 172 return; 173 } 174 if (kex->flags & KEX_INIT_SENT) { 175 debug("KEX_INIT_SENT"); 176 return; 177 } 178 kex->done = 0; 179 180 /* generate a random cookie */ 181 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 182 fatal("kex_send_kexinit: kex proposal too short"); 183 cookie = buffer_ptr(&kex->my); 184 for (i = 0; i < KEX_COOKIE_LEN; i++) { 185 if (i % 4 == 0) 186 rnd = arc4random(); 187 cookie[i] = rnd; 188 rnd >>= 8; 189 } 190 packet_start(SSH2_MSG_KEXINIT); 191 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 192 packet_send(); 193 debug("SSH2_MSG_KEXINIT sent"); 194 kex->flags |= KEX_INIT_SENT; 195 } 196 197 /* ARGSUSED */ 198 void 199 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 200 { 201 char *ptr; 202 u_int i, dlen; 203 Kex *kex = (Kex *)ctxt; 204 205 debug("SSH2_MSG_KEXINIT received"); 206 if (kex == NULL) 207 fatal("kex_input_kexinit: no kex, cannot rekey"); 208 209 ptr = packet_get_raw(&dlen); 210 buffer_append(&kex->peer, ptr, dlen); 211 212 /* discard packet */ 213 for (i = 0; i < KEX_COOKIE_LEN; i++) 214 packet_get_char(); 215 for (i = 0; i < PROPOSAL_MAX; i++) 216 xfree(packet_get_string(NULL)); 217 (void) packet_get_char(); 218 (void) packet_get_int(); 219 packet_check_eom(); 220 221 kex_kexinit_finish(kex); 222 } 223 224 Kex * 225 kex_setup(char *proposal[PROPOSAL_MAX]) 226 { 227 Kex *kex; 228 229 kex = xcalloc(1, sizeof(*kex)); 230 buffer_init(&kex->peer); 231 buffer_init(&kex->my); 232 kex_prop2buf(&kex->my, proposal); 233 kex->done = 0; 234 235 kex_send_kexinit(kex); /* we start */ 236 kex_reset_dispatch(); 237 238 return kex; 239 } 240 241 static void 242 kex_kexinit_finish(Kex *kex) 243 { 244 if (!(kex->flags & KEX_INIT_SENT)) 245 kex_send_kexinit(kex); 246 247 kex_choose_conf(kex); 248 249 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 250 kex->kex[kex->kex_type] != NULL) { 251 (kex->kex[kex->kex_type])(kex); 252 } else { 253 fatal("Unsupported key exchange %d", kex->kex_type); 254 } 255 } 256 257 static void 258 choose_enc(Enc *enc, char *client, char *server) 259 { 260 char *name = match_list(client, server, NULL); 261 if (name == NULL) 262 fatal("no matching cipher found: client %s server %s", 263 client, server); 264 if ((enc->cipher = cipher_by_name(name)) == NULL) 265 fatal("matching cipher is not supported: %s", name); 266 enc->name = name; 267 enc->enabled = 0; 268 enc->iv = NULL; 269 enc->key = NULL; 270 enc->key_len = cipher_keylen(enc->cipher); 271 enc->block_size = cipher_blocksize(enc->cipher); 272 } 273 274 static void 275 choose_mac(Mac *mac, char *client, char *server) 276 { 277 char *name = match_list(client, server, NULL); 278 if (name == NULL) 279 fatal("no matching mac found: client %s server %s", 280 client, server); 281 if (mac_setup(mac, name) < 0) 282 fatal("unsupported mac %s", name); 283 /* truncate the key */ 284 if (datafellows & SSH_BUG_HMAC) 285 mac->key_len = 16; 286 mac->name = name; 287 mac->key = NULL; 288 mac->enabled = 0; 289 } 290 291 static void 292 choose_comp(Comp *comp, char *client, char *server) 293 { 294 char *name = match_list(client, server, NULL); 295 if (name == NULL) 296 fatal("no matching comp found: client %s server %s", client, server); 297 if (strcmp(name, "zlib@openssh.com") == 0) { 298 comp->type = COMP_DELAYED; 299 } else if (strcmp(name, "zlib") == 0) { 300 comp->type = COMP_ZLIB; 301 } else if (strcmp(name, "none") == 0) { 302 comp->type = COMP_NONE; 303 } else { 304 fatal("unsupported comp %s", name); 305 } 306 comp->name = name; 307 } 308 309 static void 310 choose_kex(Kex *k, char *client, char *server) 311 { 312 k->name = match_list(client, server, NULL); 313 if (k->name == NULL) 314 fatal("Unable to negotiate a key exchange method"); 315 if (strcmp(k->name, KEX_DH1) == 0) { 316 k->kex_type = KEX_DH_GRP1_SHA1; 317 k->evp_md = EVP_sha1(); 318 } else if (strcmp(k->name, KEX_DH14) == 0) { 319 k->kex_type = KEX_DH_GRP14_SHA1; 320 k->evp_md = EVP_sha1(); 321 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 322 k->kex_type = KEX_DH_GEX_SHA1; 323 k->evp_md = EVP_sha1(); 324 #if OPENSSL_VERSION_NUMBER >= 0x00907000L 325 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 326 k->kex_type = KEX_DH_GEX_SHA256; 327 k->evp_md = evp_ssh_sha256(); 328 #endif 329 } else 330 fatal("bad kex alg %s", k->name); 331 } 332 333 static void 334 choose_hostkeyalg(Kex *k, char *client, char *server) 335 { 336 char *hostkeyalg = match_list(client, server, NULL); 337 if (hostkeyalg == NULL) 338 fatal("no hostkey alg"); 339 k->hostkey_type = key_type_from_name(hostkeyalg); 340 if (k->hostkey_type == KEY_UNSPEC) 341 fatal("bad hostkey alg '%s'", hostkeyalg); 342 xfree(hostkeyalg); 343 } 344 345 static int 346 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 347 { 348 static int check[] = { 349 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 350 }; 351 int *idx; 352 char *p; 353 354 for (idx = &check[0]; *idx != -1; idx++) { 355 if ((p = strchr(my[*idx], ',')) != NULL) 356 *p = '\0'; 357 if ((p = strchr(peer[*idx], ',')) != NULL) 358 *p = '\0'; 359 if (strcmp(my[*idx], peer[*idx]) != 0) { 360 debug2("proposal mismatch: my %s peer %s", 361 my[*idx], peer[*idx]); 362 return (0); 363 } 364 } 365 debug2("proposals match"); 366 return (1); 367 } 368 369 static void 370 kex_choose_conf(Kex *kex) 371 { 372 Newkeys *newkeys; 373 char **my, **peer; 374 char **cprop, **sprop; 375 int nenc, nmac, ncomp; 376 u_int mode, ctos, need; 377 int first_kex_follows, type; 378 379 my = kex_buf2prop(&kex->my, NULL); 380 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 381 382 if (kex->server) { 383 cprop=peer; 384 sprop=my; 385 } else { 386 cprop=my; 387 sprop=peer; 388 } 389 390 /* Check whether server offers roaming */ 391 if (!kex->server) { 392 char *roaming; 393 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 394 if (roaming) { 395 kex->roaming = 1; 396 xfree(roaming); 397 } 398 } 399 400 /* Algorithm Negotiation */ 401 for (mode = 0; mode < MODE_MAX; mode++) { 402 newkeys = xcalloc(1, sizeof(*newkeys)); 403 kex->newkeys[mode] = newkeys; 404 ctos = (!kex->server && mode == MODE_OUT) || 405 (kex->server && mode == MODE_IN); 406 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 407 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 408 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 409 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 410 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 411 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 412 debug("kex: %s %s %s %s", 413 ctos ? "client->server" : "server->client", 414 newkeys->enc.name, 415 newkeys->mac.name, 416 newkeys->comp.name); 417 } 418 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 419 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 420 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 421 need = 0; 422 for (mode = 0; mode < MODE_MAX; mode++) { 423 newkeys = kex->newkeys[mode]; 424 if (need < newkeys->enc.key_len) 425 need = newkeys->enc.key_len; 426 if (need < newkeys->enc.block_size) 427 need = newkeys->enc.block_size; 428 if (need < newkeys->mac.key_len) 429 need = newkeys->mac.key_len; 430 } 431 /* XXX need runden? */ 432 kex->we_need = need; 433 434 /* ignore the next message if the proposals do not match */ 435 if (first_kex_follows && !proposals_match(my, peer) && 436 !(datafellows & SSH_BUG_FIRSTKEX)) { 437 type = packet_read(); 438 debug2("skipping next packet (type %u)", type); 439 } 440 441 kex_prop_free(my); 442 kex_prop_free(peer); 443 } 444 445 static u_char * 446 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 447 BIGNUM *shared_secret) 448 { 449 Buffer b; 450 EVP_MD_CTX md; 451 char c = id; 452 u_int have; 453 int mdsz; 454 u_char *digest; 455 456 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 457 fatal("bad kex md size %d", mdsz); 458 digest = xmalloc(roundup(need, mdsz)); 459 460 buffer_init(&b); 461 buffer_put_bignum2(&b, shared_secret); 462 463 /* K1 = HASH(K || H || "A" || session_id) */ 464 EVP_DigestInit(&md, kex->evp_md); 465 if (!(datafellows & SSH_BUG_DERIVEKEY)) 466 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 467 EVP_DigestUpdate(&md, hash, hashlen); 468 EVP_DigestUpdate(&md, &c, 1); 469 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 470 EVP_DigestFinal(&md, digest, NULL); 471 472 /* 473 * expand key: 474 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 475 * Key = K1 || K2 || ... || Kn 476 */ 477 for (have = mdsz; need > have; have += mdsz) { 478 EVP_DigestInit(&md, kex->evp_md); 479 if (!(datafellows & SSH_BUG_DERIVEKEY)) 480 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 481 EVP_DigestUpdate(&md, hash, hashlen); 482 EVP_DigestUpdate(&md, digest, have); 483 EVP_DigestFinal(&md, digest + have, NULL); 484 } 485 buffer_free(&b); 486 #ifdef DEBUG_KEX 487 fprintf(stderr, "key '%c'== ", c); 488 dump_digest("key", digest, need); 489 #endif 490 return digest; 491 } 492 493 Newkeys *current_keys[MODE_MAX]; 494 495 #define NKEYS 6 496 void 497 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 498 { 499 u_char *keys[NKEYS]; 500 u_int i, mode, ctos; 501 502 for (i = 0; i < NKEYS; i++) { 503 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 504 shared_secret); 505 } 506 507 debug2("kex_derive_keys"); 508 for (mode = 0; mode < MODE_MAX; mode++) { 509 current_keys[mode] = kex->newkeys[mode]; 510 kex->newkeys[mode] = NULL; 511 ctos = (!kex->server && mode == MODE_OUT) || 512 (kex->server && mode == MODE_IN); 513 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 514 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 515 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 516 } 517 } 518 519 Newkeys * 520 kex_get_newkeys(int mode) 521 { 522 Newkeys *ret; 523 524 ret = current_keys[mode]; 525 current_keys[mode] = NULL; 526 return ret; 527 } 528 529 void 530 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 531 u_int8_t cookie[8], u_int8_t id[16]) 532 { 533 const EVP_MD *evp_md = EVP_md5(); 534 EVP_MD_CTX md; 535 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 536 int len; 537 538 EVP_DigestInit(&md, evp_md); 539 540 len = BN_num_bytes(host_modulus); 541 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 542 fatal("%s: bad host modulus (len %d)", __func__, len); 543 BN_bn2bin(host_modulus, nbuf); 544 EVP_DigestUpdate(&md, nbuf, len); 545 546 len = BN_num_bytes(server_modulus); 547 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 548 fatal("%s: bad server modulus (len %d)", __func__, len); 549 BN_bn2bin(server_modulus, nbuf); 550 EVP_DigestUpdate(&md, nbuf, len); 551 552 EVP_DigestUpdate(&md, cookie, 8); 553 554 EVP_DigestFinal(&md, obuf, NULL); 555 memcpy(id, obuf, 16); 556 557 memset(nbuf, 0, sizeof(nbuf)); 558 memset(obuf, 0, sizeof(obuf)); 559 memset(&md, 0, sizeof(md)); 560 } 561 562 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 563 void 564 dump_digest(char *msg, u_char *digest, int len) 565 { 566 u_int i; 567 568 fprintf(stderr, "%s\n", msg); 569 for (i = 0; i < len; i++) { 570 fprintf(stderr, "%02x", digest[i]); 571 if (i%32 == 31) 572 fprintf(stderr, "\n"); 573 else if (i%8 == 7) 574 fprintf(stderr, " "); 575 } 576 fprintf(stderr, "\n"); 577 } 578 #endif 579