1 /* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 djm Exp $ */ 2 /* $FreeBSD$ */ 3 /* 4 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include "includes.h" 28 29 #include <sys/param.h> 30 31 #include <signal.h> 32 #include <stdarg.h> 33 #include <stdio.h> 34 #include <stdlib.h> 35 #include <string.h> 36 37 #include <openssl/crypto.h> 38 39 #include "xmalloc.h" 40 #include "ssh2.h" 41 #include "buffer.h" 42 #include "packet.h" 43 #include "compat.h" 44 #include "cipher.h" 45 #include "key.h" 46 #include "kex.h" 47 #include "log.h" 48 #include "mac.h" 49 #include "match.h" 50 #include "dispatch.h" 51 #include "monitor.h" 52 #include "roaming.h" 53 54 #if OPENSSL_VERSION_NUMBER >= 0x00907000L 55 # if defined(HAVE_EVP_SHA256) 56 # define evp_ssh_sha256 EVP_sha256 57 # else 58 extern const EVP_MD *evp_ssh_sha256(void); 59 # endif 60 #endif 61 62 /* prototype */ 63 static void kex_kexinit_finish(Kex *); 64 static void kex_choose_conf(Kex *); 65 66 /* Validate KEX method name list */ 67 int 68 kex_names_valid(const char *names) 69 { 70 char *s, *cp, *p; 71 72 if (names == NULL || strcmp(names, "") == 0) 73 return 0; 74 s = cp = xstrdup(names); 75 for ((p = strsep(&cp, ",")); p && *p != '\0'; 76 (p = strsep(&cp, ","))) { 77 if (strcmp(p, KEX_DHGEX_SHA256) != 0 && 78 strcmp(p, KEX_DHGEX_SHA1) != 0 && 79 strcmp(p, KEX_DH14) != 0 && 80 strcmp(p, KEX_DH1) != 0 && 81 (strncmp(p, KEX_ECDH_SHA2_STEM, 82 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 || 83 kex_ecdh_name_to_nid(p) == -1)) { 84 error("Unsupported KEX algorithm \"%.100s\"", p); 85 xfree(s); 86 return 0; 87 } 88 } 89 debug3("kex names ok: [%s]", names); 90 xfree(s); 91 return 1; 92 } 93 94 /* Put algorithm proposal into buffer. */ 95 #ifndef NONE_CIPHER_ENABLED 96 static void 97 #else 98 /* Also used in sshconnect2.c. */ 99 void 100 #endif 101 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 102 { 103 u_int i; 104 105 buffer_clear(b); 106 /* 107 * add a dummy cookie, the cookie will be overwritten by 108 * kex_send_kexinit(), each time a kexinit is set 109 */ 110 for (i = 0; i < KEX_COOKIE_LEN; i++) 111 buffer_put_char(b, 0); 112 for (i = 0; i < PROPOSAL_MAX; i++) 113 buffer_put_cstring(b, proposal[i]); 114 buffer_put_char(b, 0); /* first_kex_packet_follows */ 115 buffer_put_int(b, 0); /* uint32 reserved */ 116 } 117 118 /* parse buffer and return algorithm proposal */ 119 static char ** 120 kex_buf2prop(Buffer *raw, int *first_kex_follows) 121 { 122 Buffer b; 123 u_int i; 124 char **proposal; 125 126 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 127 128 buffer_init(&b); 129 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 130 /* skip cookie */ 131 for (i = 0; i < KEX_COOKIE_LEN; i++) 132 buffer_get_char(&b); 133 /* extract kex init proposal strings */ 134 for (i = 0; i < PROPOSAL_MAX; i++) { 135 proposal[i] = buffer_get_cstring(&b,NULL); 136 debug2("kex_parse_kexinit: %s", proposal[i]); 137 } 138 /* first kex follows / reserved */ 139 i = buffer_get_char(&b); 140 if (first_kex_follows != NULL) 141 *first_kex_follows = i; 142 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 143 i = buffer_get_int(&b); 144 debug2("kex_parse_kexinit: reserved %u ", i); 145 buffer_free(&b); 146 return proposal; 147 } 148 149 static void 150 kex_prop_free(char **proposal) 151 { 152 u_int i; 153 154 for (i = 0; i < PROPOSAL_MAX; i++) 155 xfree(proposal[i]); 156 xfree(proposal); 157 } 158 159 /* ARGSUSED */ 160 static void 161 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 162 { 163 error("Hm, kex protocol error: type %d seq %u", type, seq); 164 } 165 166 static void 167 kex_reset_dispatch(void) 168 { 169 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 170 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 171 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 172 } 173 174 void 175 kex_finish(Kex *kex) 176 { 177 kex_reset_dispatch(); 178 179 packet_start(SSH2_MSG_NEWKEYS); 180 packet_send(); 181 /* packet_write_wait(); */ 182 debug("SSH2_MSG_NEWKEYS sent"); 183 184 debug("expecting SSH2_MSG_NEWKEYS"); 185 packet_read_expect(SSH2_MSG_NEWKEYS); 186 packet_check_eom(); 187 debug("SSH2_MSG_NEWKEYS received"); 188 189 kex->done = 1; 190 buffer_clear(&kex->peer); 191 /* buffer_clear(&kex->my); */ 192 kex->flags &= ~KEX_INIT_SENT; 193 xfree(kex->name); 194 kex->name = NULL; 195 } 196 197 void 198 kex_send_kexinit(Kex *kex) 199 { 200 u_int32_t rnd = 0; 201 u_char *cookie; 202 u_int i; 203 204 if (kex == NULL) { 205 error("kex_send_kexinit: no kex, cannot rekey"); 206 return; 207 } 208 if (kex->flags & KEX_INIT_SENT) { 209 debug("KEX_INIT_SENT"); 210 return; 211 } 212 kex->done = 0; 213 214 /* generate a random cookie */ 215 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 216 fatal("kex_send_kexinit: kex proposal too short"); 217 cookie = buffer_ptr(&kex->my); 218 for (i = 0; i < KEX_COOKIE_LEN; i++) { 219 if (i % 4 == 0) 220 rnd = arc4random(); 221 cookie[i] = rnd; 222 rnd >>= 8; 223 } 224 packet_start(SSH2_MSG_KEXINIT); 225 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 226 packet_send(); 227 debug("SSH2_MSG_KEXINIT sent"); 228 kex->flags |= KEX_INIT_SENT; 229 } 230 231 /* ARGSUSED */ 232 void 233 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 234 { 235 char *ptr; 236 u_int i, dlen; 237 Kex *kex = (Kex *)ctxt; 238 239 debug("SSH2_MSG_KEXINIT received"); 240 if (kex == NULL) 241 fatal("kex_input_kexinit: no kex, cannot rekey"); 242 243 ptr = packet_get_raw(&dlen); 244 buffer_append(&kex->peer, ptr, dlen); 245 246 /* discard packet */ 247 for (i = 0; i < KEX_COOKIE_LEN; i++) 248 packet_get_char(); 249 for (i = 0; i < PROPOSAL_MAX; i++) 250 xfree(packet_get_string(NULL)); 251 (void) packet_get_char(); 252 (void) packet_get_int(); 253 packet_check_eom(); 254 255 kex_kexinit_finish(kex); 256 } 257 258 Kex * 259 kex_setup(char *proposal[PROPOSAL_MAX]) 260 { 261 Kex *kex; 262 263 kex = xcalloc(1, sizeof(*kex)); 264 buffer_init(&kex->peer); 265 buffer_init(&kex->my); 266 kex_prop2buf(&kex->my, proposal); 267 kex->done = 0; 268 269 kex_send_kexinit(kex); /* we start */ 270 kex_reset_dispatch(); 271 272 return kex; 273 } 274 275 static void 276 kex_kexinit_finish(Kex *kex) 277 { 278 if (!(kex->flags & KEX_INIT_SENT)) 279 kex_send_kexinit(kex); 280 281 kex_choose_conf(kex); 282 283 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 284 kex->kex[kex->kex_type] != NULL) { 285 (kex->kex[kex->kex_type])(kex); 286 } else { 287 fatal("Unsupported key exchange %d", kex->kex_type); 288 } 289 } 290 291 static void 292 choose_enc(Enc *enc, char *client, char *server) 293 { 294 char *name = match_list(client, server, NULL); 295 if (name == NULL) 296 fatal("no matching cipher found: client %s server %s", 297 client, server); 298 if ((enc->cipher = cipher_by_name(name)) == NULL) 299 fatal("matching cipher is not supported: %s", name); 300 enc->name = name; 301 enc->enabled = 0; 302 enc->iv = NULL; 303 enc->key = NULL; 304 enc->key_len = cipher_keylen(enc->cipher); 305 enc->block_size = cipher_blocksize(enc->cipher); 306 } 307 308 static void 309 choose_mac(Mac *mac, char *client, char *server) 310 { 311 char *name = match_list(client, server, NULL); 312 if (name == NULL) 313 fatal("no matching mac found: client %s server %s", 314 client, server); 315 if (mac_setup(mac, name) < 0) 316 fatal("unsupported mac %s", name); 317 /* truncate the key */ 318 if (datafellows & SSH_BUG_HMAC) 319 mac->key_len = 16; 320 mac->name = name; 321 mac->key = NULL; 322 mac->enabled = 0; 323 } 324 325 static void 326 choose_comp(Comp *comp, char *client, char *server) 327 { 328 char *name = match_list(client, server, NULL); 329 if (name == NULL) 330 fatal("no matching comp found: client %s server %s", client, server); 331 if (strcmp(name, "zlib@openssh.com") == 0) { 332 comp->type = COMP_DELAYED; 333 } else if (strcmp(name, "zlib") == 0) { 334 comp->type = COMP_ZLIB; 335 } else if (strcmp(name, "none") == 0) { 336 comp->type = COMP_NONE; 337 } else { 338 fatal("unsupported comp %s", name); 339 } 340 comp->name = name; 341 } 342 343 static void 344 choose_kex(Kex *k, char *client, char *server) 345 { 346 k->name = match_list(client, server, NULL); 347 if (k->name == NULL) 348 fatal("Unable to negotiate a key exchange method"); 349 if (strcmp(k->name, KEX_DH1) == 0) { 350 k->kex_type = KEX_DH_GRP1_SHA1; 351 k->evp_md = EVP_sha1(); 352 } else if (strcmp(k->name, KEX_DH14) == 0) { 353 k->kex_type = KEX_DH_GRP14_SHA1; 354 k->evp_md = EVP_sha1(); 355 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 356 k->kex_type = KEX_DH_GEX_SHA1; 357 k->evp_md = EVP_sha1(); 358 #if OPENSSL_VERSION_NUMBER >= 0x00907000L 359 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 360 k->kex_type = KEX_DH_GEX_SHA256; 361 k->evp_md = evp_ssh_sha256(); 362 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM, 363 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) { 364 k->kex_type = KEX_ECDH_SHA2; 365 k->evp_md = kex_ecdh_name_to_evpmd(k->name); 366 #endif 367 } else 368 fatal("bad kex alg %s", k->name); 369 } 370 371 static void 372 choose_hostkeyalg(Kex *k, char *client, char *server) 373 { 374 char *hostkeyalg = match_list(client, server, NULL); 375 if (hostkeyalg == NULL) 376 fatal("no hostkey alg"); 377 k->hostkey_type = key_type_from_name(hostkeyalg); 378 if (k->hostkey_type == KEY_UNSPEC) 379 fatal("bad hostkey alg '%s'", hostkeyalg); 380 xfree(hostkeyalg); 381 } 382 383 static int 384 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 385 { 386 static int check[] = { 387 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 388 }; 389 int *idx; 390 char *p; 391 392 for (idx = &check[0]; *idx != -1; idx++) { 393 if ((p = strchr(my[*idx], ',')) != NULL) 394 *p = '\0'; 395 if ((p = strchr(peer[*idx], ',')) != NULL) 396 *p = '\0'; 397 if (strcmp(my[*idx], peer[*idx]) != 0) { 398 debug2("proposal mismatch: my %s peer %s", 399 my[*idx], peer[*idx]); 400 return (0); 401 } 402 } 403 debug2("proposals match"); 404 return (1); 405 } 406 407 static void 408 kex_choose_conf(Kex *kex) 409 { 410 Newkeys *newkeys; 411 char **my, **peer; 412 char **cprop, **sprop; 413 int nenc, nmac, ncomp; 414 u_int mode, ctos, need; 415 int first_kex_follows, type; 416 #ifdef NONE_CIPHER_ENABLED 417 int auth_flag; 418 #endif 419 420 my = kex_buf2prop(&kex->my, NULL); 421 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 422 423 if (kex->server) { 424 cprop=peer; 425 sprop=my; 426 } else { 427 cprop=my; 428 sprop=peer; 429 } 430 431 /* Check whether server offers roaming */ 432 if (!kex->server) { 433 char *roaming; 434 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 435 if (roaming) { 436 kex->roaming = 1; 437 xfree(roaming); 438 } 439 } 440 441 /* Algorithm Negotiation */ 442 #ifdef NONE_CIPHER_ENABLED 443 auth_flag = packet_get_authentication_state(); 444 debug ("AUTH STATE is %d", auth_flag); 445 #endif 446 for (mode = 0; mode < MODE_MAX; mode++) { 447 newkeys = xcalloc(1, sizeof(*newkeys)); 448 kex->newkeys[mode] = newkeys; 449 ctos = (!kex->server && mode == MODE_OUT) || 450 (kex->server && mode == MODE_IN); 451 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 452 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 453 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 454 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 455 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 456 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 457 #ifdef NONE_CIPHER_ENABLED 458 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name); 459 if (strcmp(newkeys->enc.name, "none") == 0) { 460 debug("Requesting NONE. Authflag is %d", auth_flag); 461 if (auth_flag == 1) 462 debug("None requested post authentication."); 463 else 464 fatal("Pre-authentication none cipher requests " 465 "are not allowed."); 466 } 467 #endif 468 debug("kex: %s %s %s %s", 469 ctos ? "client->server" : "server->client", 470 newkeys->enc.name, 471 newkeys->mac.name, 472 newkeys->comp.name); 473 } 474 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 475 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 476 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 477 need = 0; 478 for (mode = 0; mode < MODE_MAX; mode++) { 479 newkeys = kex->newkeys[mode]; 480 if (need < newkeys->enc.key_len) 481 need = newkeys->enc.key_len; 482 if (need < newkeys->enc.block_size) 483 need = newkeys->enc.block_size; 484 if (need < newkeys->mac.key_len) 485 need = newkeys->mac.key_len; 486 } 487 /* XXX need runden? */ 488 kex->we_need = need; 489 490 /* ignore the next message if the proposals do not match */ 491 if (first_kex_follows && !proposals_match(my, peer) && 492 !(datafellows & SSH_BUG_FIRSTKEX)) { 493 type = packet_read(); 494 debug2("skipping next packet (type %u)", type); 495 } 496 497 kex_prop_free(my); 498 kex_prop_free(peer); 499 } 500 501 static u_char * 502 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 503 BIGNUM *shared_secret) 504 { 505 Buffer b; 506 EVP_MD_CTX md; 507 char c = id; 508 u_int have; 509 int mdsz; 510 u_char *digest; 511 512 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 513 fatal("bad kex md size %d", mdsz); 514 digest = xmalloc(roundup(need, mdsz)); 515 516 buffer_init(&b); 517 buffer_put_bignum2(&b, shared_secret); 518 519 /* K1 = HASH(K || H || "A" || session_id) */ 520 EVP_DigestInit(&md, kex->evp_md); 521 if (!(datafellows & SSH_BUG_DERIVEKEY)) 522 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 523 EVP_DigestUpdate(&md, hash, hashlen); 524 EVP_DigestUpdate(&md, &c, 1); 525 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 526 EVP_DigestFinal(&md, digest, NULL); 527 528 /* 529 * expand key: 530 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 531 * Key = K1 || K2 || ... || Kn 532 */ 533 for (have = mdsz; need > have; have += mdsz) { 534 EVP_DigestInit(&md, kex->evp_md); 535 if (!(datafellows & SSH_BUG_DERIVEKEY)) 536 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 537 EVP_DigestUpdate(&md, hash, hashlen); 538 EVP_DigestUpdate(&md, digest, have); 539 EVP_DigestFinal(&md, digest + have, NULL); 540 } 541 buffer_free(&b); 542 #ifdef DEBUG_KEX 543 fprintf(stderr, "key '%c'== ", c); 544 dump_digest("key", digest, need); 545 #endif 546 return digest; 547 } 548 549 Newkeys *current_keys[MODE_MAX]; 550 551 #define NKEYS 6 552 void 553 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 554 { 555 u_char *keys[NKEYS]; 556 u_int i, mode, ctos; 557 558 for (i = 0; i < NKEYS; i++) { 559 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 560 shared_secret); 561 } 562 563 debug2("kex_derive_keys"); 564 for (mode = 0; mode < MODE_MAX; mode++) { 565 current_keys[mode] = kex->newkeys[mode]; 566 kex->newkeys[mode] = NULL; 567 ctos = (!kex->server && mode == MODE_OUT) || 568 (kex->server && mode == MODE_IN); 569 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 570 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 571 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 572 } 573 } 574 575 Newkeys * 576 kex_get_newkeys(int mode) 577 { 578 Newkeys *ret; 579 580 ret = current_keys[mode]; 581 current_keys[mode] = NULL; 582 return ret; 583 } 584 585 void 586 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 587 u_int8_t cookie[8], u_int8_t id[16]) 588 { 589 const EVP_MD *evp_md = EVP_md5(); 590 EVP_MD_CTX md; 591 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 592 int len; 593 594 EVP_DigestInit(&md, evp_md); 595 596 len = BN_num_bytes(host_modulus); 597 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 598 fatal("%s: bad host modulus (len %d)", __func__, len); 599 BN_bn2bin(host_modulus, nbuf); 600 EVP_DigestUpdate(&md, nbuf, len); 601 602 len = BN_num_bytes(server_modulus); 603 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 604 fatal("%s: bad server modulus (len %d)", __func__, len); 605 BN_bn2bin(server_modulus, nbuf); 606 EVP_DigestUpdate(&md, nbuf, len); 607 608 EVP_DigestUpdate(&md, cookie, 8); 609 610 EVP_DigestFinal(&md, obuf, NULL); 611 memcpy(id, obuf, 16); 612 613 memset(nbuf, 0, sizeof(nbuf)); 614 memset(obuf, 0, sizeof(obuf)); 615 memset(&md, 0, sizeof(md)); 616 } 617 618 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) 619 void 620 dump_digest(char *msg, u_char *digest, int len) 621 { 622 int i; 623 624 fprintf(stderr, "%s\n", msg); 625 for (i = 0; i < len; i++) { 626 fprintf(stderr, "%02x", digest[i]); 627 if (i%32 == 31) 628 fprintf(stderr, "\n"); 629 else if (i%8 == 7) 630 fprintf(stderr, " "); 631 } 632 fprintf(stderr, "\n"); 633 } 634 #endif 635