1 /* $NetBSD: kex.c,v 1.6 2011/07/25 03:03:10 christos Exp $ */ 2 /* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 djm Exp $ */ 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 __RCSID("$NetBSD: kex.c,v 1.6 2011/07/25 03:03:10 christos Exp $"); 29 #include <sys/param.h> 30 31 #include <signal.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 "canohost.h" 52 #include "roaming.h" 53 54 /* prototype */ 55 static void kex_kexinit_finish(Kex *); 56 static void kex_choose_conf(Kex *); 57 58 /* Validate KEX method name list */ 59 int 60 kex_names_valid(const char *names) 61 { 62 char *s, *cp, *p; 63 64 if (names == NULL || strcmp(names, "") == 0) 65 return 0; 66 s = cp = xstrdup(names); 67 for ((p = strsep(&cp, ",")); p && *p != '\0'; 68 (p = strsep(&cp, ","))) { 69 if (strcmp(p, KEX_DHGEX_SHA256) != 0 && 70 strcmp(p, KEX_DHGEX_SHA1) != 0 && 71 strcmp(p, KEX_DH14) != 0 && 72 strcmp(p, KEX_DH1) != 0 && 73 (strncmp(p, KEX_ECDH_SHA2_STEM, 74 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 || 75 kex_ecdh_name_to_nid(p) == -1)) { 76 error("Unsupported KEX algorithm \"%.100s\"", p); 77 xfree(s); 78 return 0; 79 } 80 } 81 debug3("kex names ok: [%s]", names); 82 xfree(s); 83 return 1; 84 } 85 86 /* put algorithm proposal into buffer */ 87 /* used in sshconnect.c as well as kex.c */ 88 void 89 kex_prop2buf(Buffer *b, const char *proposal[PROPOSAL_MAX]) 90 { 91 u_int i; 92 93 buffer_clear(b); 94 /* 95 * add a dummy cookie, the cookie will be overwritten by 96 * kex_send_kexinit(), each time a kexinit is set 97 */ 98 for (i = 0; i < KEX_COOKIE_LEN; i++) 99 buffer_put_char(b, 0); 100 for (i = 0; i < PROPOSAL_MAX; i++) 101 buffer_put_cstring(b, proposal[i]); 102 buffer_put_char(b, 0); /* first_kex_packet_follows */ 103 buffer_put_int(b, 0); /* uint32 reserved */ 104 } 105 106 /* parse buffer and return algorithm proposal */ 107 static char ** 108 kex_buf2prop(Buffer *raw, int *first_kex_follows) 109 { 110 Buffer b; 111 u_int i; 112 char **proposal; 113 114 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 115 116 buffer_init(&b); 117 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 118 /* skip cookie */ 119 for (i = 0; i < KEX_COOKIE_LEN; i++) 120 buffer_get_char(&b); 121 /* extract kex init proposal strings */ 122 for (i = 0; i < PROPOSAL_MAX; i++) { 123 proposal[i] = buffer_get_cstring(&b,NULL); 124 debug2("kex_parse_kexinit: %s", proposal[i]); 125 } 126 /* first kex follows / reserved */ 127 i = buffer_get_char(&b); 128 if (first_kex_follows != NULL) 129 *first_kex_follows = i; 130 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 131 i = buffer_get_int(&b); 132 debug2("kex_parse_kexinit: reserved %u ", i); 133 buffer_free(&b); 134 return proposal; 135 } 136 137 static void 138 kex_prop_free(char **proposal) 139 { 140 u_int i; 141 142 for (i = 0; i < PROPOSAL_MAX; i++) 143 xfree(proposal[i]); 144 xfree(proposal); 145 } 146 147 /* ARGSUSED */ 148 static void 149 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 150 { 151 error("Hm, kex protocol error: type %d seq %u", type, seq); 152 } 153 154 static void 155 kex_reset_dispatch(void) 156 { 157 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 158 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 159 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 160 } 161 162 void 163 kex_finish(Kex *kex) 164 { 165 kex_reset_dispatch(); 166 167 packet_start(SSH2_MSG_NEWKEYS); 168 packet_send(); 169 /* packet_write_wait(); */ 170 debug("SSH2_MSG_NEWKEYS sent"); 171 172 debug("expecting SSH2_MSG_NEWKEYS"); 173 packet_read_expect(SSH2_MSG_NEWKEYS); 174 packet_check_eom(); 175 debug("SSH2_MSG_NEWKEYS received"); 176 177 kex->done = 1; 178 buffer_clear(&kex->peer); 179 /* buffer_clear(&kex->my); */ 180 kex->flags &= ~KEX_INIT_SENT; 181 xfree(kex->name); 182 kex->name = NULL; 183 } 184 185 void 186 kex_send_kexinit(Kex *kex) 187 { 188 u_int32_t rnd = 0; 189 u_char *cookie; 190 u_int i; 191 192 if (kex == NULL) { 193 error("kex_send_kexinit: no kex, cannot rekey"); 194 return; 195 } 196 if (kex->flags & KEX_INIT_SENT) { 197 debug("KEX_INIT_SENT"); 198 return; 199 } 200 kex->done = 0; 201 202 /* generate a random cookie */ 203 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 204 fatal("kex_send_kexinit: kex proposal too short"); 205 cookie = buffer_ptr(&kex->my); 206 for (i = 0; i < KEX_COOKIE_LEN; i++) { 207 if (i % 4 == 0) 208 rnd = arc4random(); 209 cookie[i] = rnd; 210 rnd >>= 8; 211 } 212 packet_start(SSH2_MSG_KEXINIT); 213 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 214 packet_send(); 215 debug("SSH2_MSG_KEXINIT sent"); 216 kex->flags |= KEX_INIT_SENT; 217 } 218 219 /* ARGSUSED */ 220 void 221 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 222 { 223 char *ptr; 224 u_int i, dlen; 225 Kex *kex = (Kex *)ctxt; 226 227 debug("SSH2_MSG_KEXINIT received"); 228 if (kex == NULL) 229 fatal("kex_input_kexinit: no kex, cannot rekey"); 230 231 ptr = packet_get_raw(&dlen); 232 buffer_append(&kex->peer, ptr, dlen); 233 234 /* discard packet */ 235 for (i = 0; i < KEX_COOKIE_LEN; i++) 236 packet_get_char(); 237 for (i = 0; i < PROPOSAL_MAX; i++) 238 xfree(packet_get_string(NULL)); 239 (void) packet_get_char(); 240 (void) packet_get_int(); 241 packet_check_eom(); 242 243 kex_kexinit_finish(kex); 244 } 245 246 Kex * 247 kex_setup(const char *proposal[PROPOSAL_MAX]) 248 { 249 Kex *kex; 250 251 kex = xcalloc(1, sizeof(*kex)); 252 buffer_init(&kex->peer); 253 buffer_init(&kex->my); 254 kex_prop2buf(&kex->my, proposal); 255 kex->done = 0; 256 257 kex_send_kexinit(kex); /* we start */ 258 kex_reset_dispatch(); 259 260 return kex; 261 } 262 263 static void 264 kex_kexinit_finish(Kex *kex) 265 { 266 if (!(kex->flags & KEX_INIT_SENT)) 267 kex_send_kexinit(kex); 268 269 kex_choose_conf(kex); 270 271 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 272 kex->kex[kex->kex_type] != NULL) { 273 (kex->kex[kex->kex_type])(kex); 274 } else { 275 fatal("Unsupported key exchange %d", kex->kex_type); 276 } 277 } 278 279 static void 280 choose_enc(Enc *enc, char *client, char *server) 281 { 282 char *name = match_list(client, server, NULL); 283 if (name == NULL) 284 fatal("no matching cipher found: client %s server %s", 285 client, server); 286 if ((enc->cipher = cipher_by_name(name)) == NULL) 287 fatal("matching cipher is not supported: %s", name); 288 enc->name = name; 289 enc->enabled = 0; 290 enc->iv = NULL; 291 enc->key = NULL; 292 enc->key_len = cipher_keylen(enc->cipher); 293 enc->block_size = cipher_blocksize(enc->cipher); 294 } 295 296 static void 297 choose_mac(Mac *mac, char *client, char *server) 298 { 299 char *name = match_list(client, server, NULL); 300 if (name == NULL) 301 fatal("no matching mac found: client %s server %s", 302 client, server); 303 if (mac_setup(mac, name) < 0) 304 fatal("unsupported mac %s", name); 305 /* truncate the key */ 306 if (datafellows & SSH_BUG_HMAC) 307 mac->key_len = 16; 308 mac->name = name; 309 mac->key = NULL; 310 mac->enabled = 0; 311 } 312 313 static void 314 choose_comp(Comp *comp, char *client, char *server) 315 { 316 char *name = match_list(client, server, NULL); 317 if (name == NULL) 318 fatal("no matching comp found: client %s server %s", client, server); 319 if (strcmp(name, "zlib@openssh.com") == 0) { 320 comp->type = COMP_DELAYED; 321 } else if (strcmp(name, "zlib") == 0) { 322 comp->type = COMP_ZLIB; 323 } else if (strcmp(name, "none") == 0) { 324 comp->type = COMP_NONE; 325 } else { 326 fatal("unsupported comp %s", name); 327 } 328 comp->name = name; 329 } 330 331 static void 332 choose_kex(Kex *k, char *client, char *server) 333 { 334 k->name = match_list(client, server, NULL); 335 if (k->name == NULL) 336 fatal("Unable to negotiate a key exchange method"); 337 if (strcmp(k->name, KEX_DH1) == 0) { 338 k->kex_type = KEX_DH_GRP1_SHA1; 339 k->evp_md = EVP_sha1(); 340 } else if (strcmp(k->name, KEX_DH14) == 0) { 341 k->kex_type = KEX_DH_GRP14_SHA1; 342 k->evp_md = EVP_sha1(); 343 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 344 k->kex_type = KEX_DH_GEX_SHA1; 345 k->evp_md = EVP_sha1(); 346 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 347 k->kex_type = KEX_DH_GEX_SHA256; 348 k->evp_md = EVP_sha256(); 349 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM, 350 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) { 351 k->kex_type = KEX_ECDH_SHA2; 352 k->evp_md = kex_ecdh_name_to_evpmd(k->name); 353 } else 354 fatal("bad kex alg %s", k->name); 355 } 356 357 static void 358 choose_hostkeyalg(Kex *k, char *client, char *server) 359 { 360 char *hostkeyalg = match_list(client, server, NULL); 361 if (hostkeyalg == NULL) 362 fatal("no hostkey alg"); 363 k->hostkey_type = key_type_from_name(hostkeyalg); 364 if (k->hostkey_type == KEY_UNSPEC) 365 fatal("bad hostkey alg '%s'", hostkeyalg); 366 xfree(hostkeyalg); 367 } 368 369 static int 370 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 371 { 372 static int check[] = { 373 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 374 }; 375 int *idx; 376 char *p; 377 378 for (idx = &check[0]; *idx != -1; idx++) { 379 if ((p = strchr(my[*idx], ',')) != NULL) 380 *p = '\0'; 381 if ((p = strchr(peer[*idx], ',')) != NULL) 382 *p = '\0'; 383 if (strcmp(my[*idx], peer[*idx]) != 0) { 384 debug2("proposal mismatch: my %s peer %s", 385 my[*idx], peer[*idx]); 386 return (0); 387 } 388 } 389 debug2("proposals match"); 390 return (1); 391 } 392 393 static void 394 kex_choose_conf(Kex *kex) 395 { 396 Newkeys *newkeys; 397 char **my, **peer; 398 char **cprop, **sprop; 399 int nenc, nmac, ncomp; 400 u_int mode, ctos, need; 401 int first_kex_follows, type; 402 int log_flag = 0; 403 404 int auth_flag; 405 406 auth_flag = packet_authentication_state(); 407 408 debug ("AUTH STATE IS %d", auth_flag); 409 410 my = kex_buf2prop(&kex->my, NULL); 411 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 412 413 if (kex->server) { 414 cprop=peer; 415 sprop=my; 416 } else { 417 cprop=my; 418 sprop=peer; 419 } 420 421 /* Check whether server offers roaming */ 422 if (!kex->server) { 423 char *roaming; 424 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 425 if (roaming) { 426 kex->roaming = 1; 427 xfree(roaming); 428 } 429 } 430 431 /* Algorithm Negotiation */ 432 for (mode = 0; mode < MODE_MAX; mode++) { 433 newkeys = xcalloc(1, sizeof(*newkeys)); 434 kex->newkeys[mode] = newkeys; 435 ctos = (!kex->server && mode == MODE_OUT) || 436 (kex->server && mode == MODE_IN); 437 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 438 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 439 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 440 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 441 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 442 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 443 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name); 444 if (strcmp(newkeys->enc.name, "none") == 0) { 445 debug("Requesting NONE. Authflag is %d", auth_flag); 446 if (auth_flag == 1) { 447 debug("None requested post authentication."); 448 } else { 449 fatal("Pre-authentication none cipher requests are not allowed."); 450 } 451 } 452 debug("kex: %s %s %s %s", 453 ctos ? "client->server" : "server->client", 454 newkeys->enc.name, 455 newkeys->mac.name, 456 newkeys->comp.name); 457 /* client starts withctos = 0 && log flag = 0 and no log*/ 458 /* 2nd client pass ctos=1 and flag = 1 so no log*/ 459 /* server starts with ctos =1 && log_flag = 0 so log */ 460 /* 2nd sever pass ctos = 1 && log flag = 1 so no log*/ 461 /* -cjr*/ 462 if (ctos && !log_flag) { 463 logit("SSH: Server;Ltype: Kex;Remote: %s-%d;Enc: %s;MAC: %s;Comp: %s", 464 get_remote_ipaddr(), 465 get_remote_port(), 466 newkeys->enc.name, 467 newkeys->mac.name, 468 newkeys->comp.name); 469 } 470 log_flag = 1; 471 } 472 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 473 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 474 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 475 need = 0; 476 for (mode = 0; mode < MODE_MAX; mode++) { 477 newkeys = kex->newkeys[mode]; 478 if (need < newkeys->enc.key_len) 479 need = newkeys->enc.key_len; 480 if (need < newkeys->enc.block_size) 481 need = newkeys->enc.block_size; 482 if (need < newkeys->mac.key_len) 483 need = newkeys->mac.key_len; 484 } 485 /* XXX need runden? */ 486 kex->we_need = need; 487 488 /* ignore the next message if the proposals do not match */ 489 if (first_kex_follows && !proposals_match(my, peer) && 490 !(datafellows & SSH_BUG_FIRSTKEX)) { 491 type = packet_read(); 492 debug2("skipping next packet (type %u)", type); 493 } 494 495 kex_prop_free(my); 496 kex_prop_free(peer); 497 } 498 499 static u_char * 500 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 501 BIGNUM *shared_secret) 502 { 503 Buffer b; 504 EVP_MD_CTX md; 505 char c = id; 506 u_int have; 507 int mdsz; 508 u_char *digest; 509 510 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 511 fatal("bad kex md size %d", mdsz); 512 digest = xmalloc(roundup(need, mdsz)); 513 514 buffer_init(&b); 515 buffer_put_bignum2(&b, shared_secret); 516 517 /* K1 = HASH(K || H || "A" || session_id) */ 518 EVP_DigestInit(&md, kex->evp_md); 519 if (!(datafellows & SSH_BUG_DERIVEKEY)) 520 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 521 EVP_DigestUpdate(&md, hash, hashlen); 522 EVP_DigestUpdate(&md, &c, 1); 523 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 524 EVP_DigestFinal(&md, digest, NULL); 525 526 /* 527 * expand key: 528 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 529 * Key = K1 || K2 || ... || Kn 530 */ 531 for (have = mdsz; need > have; have += mdsz) { 532 EVP_DigestInit(&md, kex->evp_md); 533 if (!(datafellows & SSH_BUG_DERIVEKEY)) 534 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 535 EVP_DigestUpdate(&md, hash, hashlen); 536 EVP_DigestUpdate(&md, digest, have); 537 EVP_DigestFinal(&md, digest + have, NULL); 538 } 539 buffer_free(&b); 540 #ifdef DEBUG_KEX 541 fprintf(stderr, "key '%c'== ", c); 542 dump_digest("key", digest, need); 543 #endif 544 return digest; 545 } 546 547 Newkeys *current_keys[MODE_MAX]; 548 549 #define NKEYS 6 550 void 551 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 552 { 553 u_char *keys[NKEYS]; 554 u_int i, mode, ctos; 555 556 for (i = 0; i < NKEYS; i++) { 557 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 558 shared_secret); 559 } 560 561 debug2("kex_derive_keys"); 562 for (mode = 0; mode < MODE_MAX; mode++) { 563 current_keys[mode] = kex->newkeys[mode]; 564 kex->newkeys[mode] = NULL; 565 ctos = (!kex->server && mode == MODE_OUT) || 566 (kex->server && mode == MODE_IN); 567 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 568 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 569 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 570 } 571 } 572 573 Newkeys * 574 kex_get_newkeys(int mode) 575 { 576 Newkeys *ret; 577 578 ret = current_keys[mode]; 579 current_keys[mode] = NULL; 580 return ret; 581 } 582 583 void 584 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 585 u_int8_t cookie[8], u_int8_t id[16]) 586 { 587 const EVP_MD *evp_md = EVP_md5(); 588 EVP_MD_CTX md; 589 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 590 int len; 591 592 EVP_DigestInit(&md, evp_md); 593 594 len = BN_num_bytes(host_modulus); 595 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 596 fatal("%s: bad host modulus (len %d)", __func__, len); 597 BN_bn2bin(host_modulus, nbuf); 598 EVP_DigestUpdate(&md, nbuf, len); 599 600 len = BN_num_bytes(server_modulus); 601 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 602 fatal("%s: bad server modulus (len %d)", __func__, len); 603 BN_bn2bin(server_modulus, nbuf); 604 EVP_DigestUpdate(&md, nbuf, len); 605 606 EVP_DigestUpdate(&md, cookie, 8); 607 608 EVP_DigestFinal(&md, obuf, NULL); 609 memcpy(id, obuf, 16); 610 611 memset(nbuf, 0, sizeof(nbuf)); 612 memset(obuf, 0, sizeof(obuf)); 613 memset(&md, 0, sizeof(md)); 614 } 615 616 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) 617 void 618 dump_digest(char *msg, u_char *digest, int len) 619 { 620 int i; 621 622 fprintf(stderr, "%s\n", msg); 623 for (i = 0; i < len; i++) { 624 fprintf(stderr, "%02x", digest[i]); 625 if (i%32 == 31) 626 fprintf(stderr, "\n"); 627 else if (i%8 == 7) 628 fprintf(stderr, " "); 629 } 630 fprintf(stderr, "\n"); 631 } 632 #endif 633