1 /* $NetBSD: kex.c,v 1.5 2010/11/21 18:59:04 adam Exp $ */ 2 /* $OpenBSD: kex.c,v 1.82 2009/10/24 11:13:54 andreas 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 1.5 2010/11/21 18:59:04 adam 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 /* put algorithm proposal into buffer */ 59 /* used in sshconnect.c as well as kex.c */ 60 void 61 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 62 { 63 u_int i; 64 65 buffer_clear(b); 66 /* 67 * add a dummy cookie, the cookie will be overwritten by 68 * kex_send_kexinit(), each time a kexinit is set 69 */ 70 for (i = 0; i < KEX_COOKIE_LEN; i++) 71 buffer_put_char(b, 0); 72 for (i = 0; i < PROPOSAL_MAX; i++) 73 buffer_put_cstring(b, proposal[i]); 74 buffer_put_char(b, 0); /* first_kex_packet_follows */ 75 buffer_put_int(b, 0); /* uint32 reserved */ 76 } 77 78 /* parse buffer and return algorithm proposal */ 79 static char ** 80 kex_buf2prop(Buffer *raw, int *first_kex_follows) 81 { 82 Buffer b; 83 u_int i; 84 char **proposal; 85 86 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 87 88 buffer_init(&b); 89 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 90 /* skip cookie */ 91 for (i = 0; i < KEX_COOKIE_LEN; i++) 92 buffer_get_char(&b); 93 /* extract kex init proposal strings */ 94 for (i = 0; i < PROPOSAL_MAX; i++) { 95 proposal[i] = buffer_get_string(&b,NULL); 96 debug2("kex_parse_kexinit: %s", proposal[i]); 97 } 98 /* first kex follows / reserved */ 99 i = buffer_get_char(&b); 100 if (first_kex_follows != NULL) 101 *first_kex_follows = i; 102 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 103 i = buffer_get_int(&b); 104 debug2("kex_parse_kexinit: reserved %u ", i); 105 buffer_free(&b); 106 return proposal; 107 } 108 109 static void 110 kex_prop_free(char **proposal) 111 { 112 u_int i; 113 114 for (i = 0; i < PROPOSAL_MAX; i++) 115 xfree(proposal[i]); 116 xfree(proposal); 117 } 118 119 /* ARGSUSED */ 120 static void 121 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 122 { 123 error("Hm, kex protocol error: type %d seq %u", type, seq); 124 } 125 126 static void 127 kex_reset_dispatch(void) 128 { 129 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 130 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 131 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 132 } 133 134 void 135 kex_finish(Kex *kex) 136 { 137 kex_reset_dispatch(); 138 139 packet_start(SSH2_MSG_NEWKEYS); 140 packet_send(); 141 /* packet_write_wait(); */ 142 debug("SSH2_MSG_NEWKEYS sent"); 143 144 debug("expecting SSH2_MSG_NEWKEYS"); 145 packet_read_expect(SSH2_MSG_NEWKEYS); 146 packet_check_eom(); 147 debug("SSH2_MSG_NEWKEYS received"); 148 149 kex->done = 1; 150 buffer_clear(&kex->peer); 151 /* buffer_clear(&kex->my); */ 152 kex->flags &= ~KEX_INIT_SENT; 153 xfree(kex->name); 154 kex->name = NULL; 155 } 156 157 void 158 kex_send_kexinit(Kex *kex) 159 { 160 u_int32_t rnd = 0; 161 u_char *cookie; 162 u_int i; 163 164 if (kex == NULL) { 165 error("kex_send_kexinit: no kex, cannot rekey"); 166 return; 167 } 168 if (kex->flags & KEX_INIT_SENT) { 169 debug("KEX_INIT_SENT"); 170 return; 171 } 172 kex->done = 0; 173 174 /* generate a random cookie */ 175 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 176 fatal("kex_send_kexinit: kex proposal too short"); 177 cookie = buffer_ptr(&kex->my); 178 for (i = 0; i < KEX_COOKIE_LEN; i++) { 179 if (i % 4 == 0) 180 rnd = arc4random(); 181 cookie[i] = rnd; 182 rnd >>= 8; 183 } 184 packet_start(SSH2_MSG_KEXINIT); 185 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 186 packet_send(); 187 debug("SSH2_MSG_KEXINIT sent"); 188 kex->flags |= KEX_INIT_SENT; 189 } 190 191 /* ARGSUSED */ 192 void 193 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 194 { 195 char *ptr; 196 u_int i, dlen; 197 Kex *kex = (Kex *)ctxt; 198 199 debug("SSH2_MSG_KEXINIT received"); 200 if (kex == NULL) 201 fatal("kex_input_kexinit: no kex, cannot rekey"); 202 203 ptr = packet_get_raw(&dlen); 204 buffer_append(&kex->peer, ptr, dlen); 205 206 /* discard packet */ 207 for (i = 0; i < KEX_COOKIE_LEN; i++) 208 packet_get_char(); 209 for (i = 0; i < PROPOSAL_MAX; i++) 210 xfree(packet_get_string(NULL)); 211 (void) packet_get_char(); 212 (void) packet_get_int(); 213 packet_check_eom(); 214 215 kex_kexinit_finish(kex); 216 } 217 218 Kex * 219 kex_setup(char *proposal[PROPOSAL_MAX]) 220 { 221 Kex *kex; 222 223 kex = xcalloc(1, sizeof(*kex)); 224 buffer_init(&kex->peer); 225 buffer_init(&kex->my); 226 kex_prop2buf(&kex->my, proposal); 227 kex->done = 0; 228 229 kex_send_kexinit(kex); /* we start */ 230 kex_reset_dispatch(); 231 232 return kex; 233 } 234 235 static void 236 kex_kexinit_finish(Kex *kex) 237 { 238 if (!(kex->flags & KEX_INIT_SENT)) 239 kex_send_kexinit(kex); 240 241 kex_choose_conf(kex); 242 243 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 244 kex->kex[kex->kex_type] != NULL) { 245 (kex->kex[kex->kex_type])(kex); 246 } else { 247 fatal("Unsupported key exchange %d", kex->kex_type); 248 } 249 } 250 251 static void 252 choose_enc(Enc *enc, char *client, char *server) 253 { 254 char *name = match_list(client, server, NULL); 255 if (name == NULL) 256 fatal("no matching cipher found: client %s server %s", 257 client, server); 258 if ((enc->cipher = cipher_by_name(name)) == NULL) 259 fatal("matching cipher is not supported: %s", name); 260 enc->name = name; 261 enc->enabled = 0; 262 enc->iv = NULL; 263 enc->key = NULL; 264 enc->key_len = cipher_keylen(enc->cipher); 265 enc->block_size = cipher_blocksize(enc->cipher); 266 } 267 268 static void 269 choose_mac(Mac *mac, char *client, char *server) 270 { 271 char *name = match_list(client, server, NULL); 272 if (name == NULL) 273 fatal("no matching mac found: client %s server %s", 274 client, server); 275 if (mac_setup(mac, name) < 0) 276 fatal("unsupported mac %s", name); 277 /* truncate the key */ 278 if (datafellows & SSH_BUG_HMAC) 279 mac->key_len = 16; 280 mac->name = name; 281 mac->key = NULL; 282 mac->enabled = 0; 283 } 284 285 static void 286 choose_comp(Comp *comp, char *client, char *server) 287 { 288 char *name = match_list(client, server, NULL); 289 if (name == NULL) 290 fatal("no matching comp found: client %s server %s", client, server); 291 if (strcmp(name, "zlib@openssh.com") == 0) { 292 comp->type = COMP_DELAYED; 293 } else if (strcmp(name, "zlib") == 0) { 294 comp->type = COMP_ZLIB; 295 } else if (strcmp(name, "none") == 0) { 296 comp->type = COMP_NONE; 297 } else { 298 fatal("unsupported comp %s", name); 299 } 300 comp->name = name; 301 } 302 303 static void 304 choose_kex(Kex *k, char *client, char *server) 305 { 306 k->name = match_list(client, server, NULL); 307 if (k->name == NULL) 308 fatal("Unable to negotiate a key exchange method"); 309 if (strcmp(k->name, KEX_DH1) == 0) { 310 k->kex_type = KEX_DH_GRP1_SHA1; 311 k->evp_md = EVP_sha1(); 312 } else if (strcmp(k->name, KEX_DH14) == 0) { 313 k->kex_type = KEX_DH_GRP14_SHA1; 314 k->evp_md = EVP_sha1(); 315 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 316 k->kex_type = KEX_DH_GEX_SHA1; 317 k->evp_md = EVP_sha1(); 318 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 319 k->kex_type = KEX_DH_GEX_SHA256; 320 k->evp_md = EVP_sha256(); 321 } else 322 fatal("bad kex alg %s", k->name); 323 } 324 325 static void 326 choose_hostkeyalg(Kex *k, char *client, char *server) 327 { 328 char *hostkeyalg = match_list(client, server, NULL); 329 if (hostkeyalg == NULL) 330 fatal("no hostkey alg"); 331 k->hostkey_type = key_type_from_name(hostkeyalg); 332 if (k->hostkey_type == KEY_UNSPEC) 333 fatal("bad hostkey alg '%s'", hostkeyalg); 334 xfree(hostkeyalg); 335 } 336 337 static int 338 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 339 { 340 static int check[] = { 341 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 342 }; 343 int *idx; 344 char *p; 345 346 for (idx = &check[0]; *idx != -1; idx++) { 347 if ((p = strchr(my[*idx], ',')) != NULL) 348 *p = '\0'; 349 if ((p = strchr(peer[*idx], ',')) != NULL) 350 *p = '\0'; 351 if (strcmp(my[*idx], peer[*idx]) != 0) { 352 debug2("proposal mismatch: my %s peer %s", 353 my[*idx], peer[*idx]); 354 return (0); 355 } 356 } 357 debug2("proposals match"); 358 return (1); 359 } 360 361 static void 362 kex_choose_conf(Kex *kex) 363 { 364 Newkeys *newkeys; 365 char **my, **peer; 366 char **cprop, **sprop; 367 int nenc, nmac, ncomp; 368 u_int mode, ctos, need; 369 int first_kex_follows, type; 370 int log_flag = 0; 371 372 int auth_flag; 373 374 auth_flag = packet_authentication_state(); 375 376 debug ("AUTH STATE IS %d", auth_flag); 377 378 my = kex_buf2prop(&kex->my, NULL); 379 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 380 381 if (kex->server) { 382 cprop=peer; 383 sprop=my; 384 } else { 385 cprop=my; 386 sprop=peer; 387 } 388 389 /* Check whether server offers roaming */ 390 if (!kex->server) { 391 char *roaming; 392 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 393 if (roaming) { 394 kex->roaming = 1; 395 xfree(roaming); 396 } 397 } 398 399 /* Algorithm Negotiation */ 400 for (mode = 0; mode < MODE_MAX; mode++) { 401 newkeys = xcalloc(1, sizeof(*newkeys)); 402 kex->newkeys[mode] = newkeys; 403 ctos = (!kex->server && mode == MODE_OUT) || 404 (kex->server && mode == MODE_IN); 405 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 406 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 407 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 408 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 409 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 410 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 411 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name); 412 if (strcmp(newkeys->enc.name, "none") == 0) { 413 debug("Requesting NONE. Authflag is %d", auth_flag); 414 if (auth_flag == 1) { 415 debug("None requested post authentication."); 416 } else { 417 fatal("Pre-authentication none cipher requests are not allowed."); 418 } 419 } 420 debug("kex: %s %s %s %s", 421 ctos ? "client->server" : "server->client", 422 newkeys->enc.name, 423 newkeys->mac.name, 424 newkeys->comp.name); 425 /* client starts withctos = 0 && log flag = 0 and no log*/ 426 /* 2nd client pass ctos=1 and flag = 1 so no log*/ 427 /* server starts with ctos =1 && log_flag = 0 so log */ 428 /* 2nd sever pass ctos = 1 && log flag = 1 so no log*/ 429 /* -cjr*/ 430 if (ctos && !log_flag) { 431 logit("SSH: Server;Ltype: Kex;Remote: %s-%d;Enc: %s;MAC: %s;Comp: %s", 432 get_remote_ipaddr(), 433 get_remote_port(), 434 newkeys->enc.name, 435 newkeys->mac.name, 436 newkeys->comp.name); 437 } 438 log_flag = 1; 439 } 440 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 441 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 442 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 443 need = 0; 444 for (mode = 0; mode < MODE_MAX; mode++) { 445 newkeys = kex->newkeys[mode]; 446 if (need < newkeys->enc.key_len) 447 need = newkeys->enc.key_len; 448 if (need < newkeys->enc.block_size) 449 need = newkeys->enc.block_size; 450 if (need < newkeys->mac.key_len) 451 need = newkeys->mac.key_len; 452 } 453 /* XXX need runden? */ 454 kex->we_need = need; 455 456 /* ignore the next message if the proposals do not match */ 457 if (first_kex_follows && !proposals_match(my, peer) && 458 !(datafellows & SSH_BUG_FIRSTKEX)) { 459 type = packet_read(); 460 debug2("skipping next packet (type %u)", type); 461 } 462 463 kex_prop_free(my); 464 kex_prop_free(peer); 465 } 466 467 static u_char * 468 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 469 BIGNUM *shared_secret) 470 { 471 Buffer b; 472 EVP_MD_CTX md; 473 char c = id; 474 u_int have; 475 int mdsz; 476 u_char *digest; 477 478 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 479 fatal("bad kex md size %d", mdsz); 480 digest = xmalloc(roundup(need, mdsz)); 481 482 buffer_init(&b); 483 buffer_put_bignum2(&b, shared_secret); 484 485 /* K1 = HASH(K || H || "A" || session_id) */ 486 EVP_DigestInit(&md, kex->evp_md); 487 if (!(datafellows & SSH_BUG_DERIVEKEY)) 488 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 489 EVP_DigestUpdate(&md, hash, hashlen); 490 EVP_DigestUpdate(&md, &c, 1); 491 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 492 EVP_DigestFinal(&md, digest, NULL); 493 494 /* 495 * expand key: 496 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 497 * Key = K1 || K2 || ... || Kn 498 */ 499 for (have = mdsz; need > have; have += mdsz) { 500 EVP_DigestInit(&md, kex->evp_md); 501 if (!(datafellows & SSH_BUG_DERIVEKEY)) 502 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 503 EVP_DigestUpdate(&md, hash, hashlen); 504 EVP_DigestUpdate(&md, digest, have); 505 EVP_DigestFinal(&md, digest + have, NULL); 506 } 507 buffer_free(&b); 508 #ifdef DEBUG_KEX 509 fprintf(stderr, "key '%c'== ", c); 510 dump_digest("key", digest, need); 511 #endif 512 return digest; 513 } 514 515 Newkeys *current_keys[MODE_MAX]; 516 517 #define NKEYS 6 518 void 519 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 520 { 521 u_char *keys[NKEYS]; 522 u_int i, mode, ctos; 523 524 for (i = 0; i < NKEYS; i++) { 525 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 526 shared_secret); 527 } 528 529 debug2("kex_derive_keys"); 530 for (mode = 0; mode < MODE_MAX; mode++) { 531 current_keys[mode] = kex->newkeys[mode]; 532 kex->newkeys[mode] = NULL; 533 ctos = (!kex->server && mode == MODE_OUT) || 534 (kex->server && mode == MODE_IN); 535 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 536 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 537 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 538 } 539 } 540 541 Newkeys * 542 kex_get_newkeys(int mode) 543 { 544 Newkeys *ret; 545 546 ret = current_keys[mode]; 547 current_keys[mode] = NULL; 548 return ret; 549 } 550 551 void 552 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 553 u_int8_t cookie[8], u_int8_t id[16]) 554 { 555 const EVP_MD *evp_md = EVP_md5(); 556 EVP_MD_CTX md; 557 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 558 int len; 559 560 EVP_DigestInit(&md, evp_md); 561 562 len = BN_num_bytes(host_modulus); 563 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 564 fatal("%s: bad host modulus (len %d)", __func__, len); 565 BN_bn2bin(host_modulus, nbuf); 566 EVP_DigestUpdate(&md, nbuf, len); 567 568 len = BN_num_bytes(server_modulus); 569 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 570 fatal("%s: bad server modulus (len %d)", __func__, len); 571 BN_bn2bin(server_modulus, nbuf); 572 EVP_DigestUpdate(&md, nbuf, len); 573 574 EVP_DigestUpdate(&md, cookie, 8); 575 576 EVP_DigestFinal(&md, obuf, NULL); 577 memcpy(id, obuf, 16); 578 579 memset(nbuf, 0, sizeof(nbuf)); 580 memset(obuf, 0, sizeof(obuf)); 581 memset(&md, 0, sizeof(md)); 582 } 583 584 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 585 void 586 dump_digest(char *msg, u_char *digest, int len) 587 { 588 u_int i; 589 590 fprintf(stderr, "%s\n", msg); 591 for (i = 0; i < len; i++) { 592 fprintf(stderr, "%02x", digest[i]); 593 if (i%32 == 31) 594 fprintf(stderr, "\n"); 595 else if (i%8 == 7) 596 fprintf(stderr, " "); 597 } 598 fprintf(stderr, "\n"); 599 } 600 #endif 601