1 /* $NetBSD: kex.c,v 1.3 2009/12/27 01:40:47 christos Exp $ */ 2 /* $OpenBSD: kex.c,v 1.81 2009/05/27 06:34:36 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 1.3 2009/12/27 01:40:47 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 53 /* prototype */ 54 static void kex_kexinit_finish(Kex *); 55 static void kex_choose_conf(Kex *); 56 57 /* put algorithm proposal into buffer */ 58 void 59 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 60 { 61 u_int i; 62 63 buffer_clear(b); 64 /* 65 * add a dummy cookie, the cookie will be overwritten by 66 * kex_send_kexinit(), each time a kexinit is set 67 */ 68 for (i = 0; i < KEX_COOKIE_LEN; i++) 69 buffer_put_char(b, 0); 70 for (i = 0; i < PROPOSAL_MAX; i++) 71 buffer_put_cstring(b, proposal[i]); 72 buffer_put_char(b, 0); /* first_kex_packet_follows */ 73 buffer_put_int(b, 0); /* uint32 reserved */ 74 } 75 76 /* parse buffer and return algorithm proposal */ 77 static char ** 78 kex_buf2prop(Buffer *raw, int *first_kex_follows) 79 { 80 Buffer b; 81 u_int i; 82 char **proposal; 83 84 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 85 86 buffer_init(&b); 87 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 88 /* skip cookie */ 89 for (i = 0; i < KEX_COOKIE_LEN; i++) 90 buffer_get_char(&b); 91 /* extract kex init proposal strings */ 92 for (i = 0; i < PROPOSAL_MAX; i++) { 93 proposal[i] = buffer_get_string(&b,NULL); 94 debug2("kex_parse_kexinit: %s", proposal[i]); 95 } 96 /* first kex follows / reserved */ 97 i = buffer_get_char(&b); 98 if (first_kex_follows != NULL) 99 *first_kex_follows = i; 100 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 101 i = buffer_get_int(&b); 102 debug2("kex_parse_kexinit: reserved %u ", i); 103 buffer_free(&b); 104 return proposal; 105 } 106 107 static void 108 kex_prop_free(char **proposal) 109 { 110 u_int i; 111 112 for (i = 0; i < PROPOSAL_MAX; i++) 113 xfree(proposal[i]); 114 xfree(proposal); 115 } 116 117 /* ARGSUSED */ 118 static void 119 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 120 { 121 error("Hm, kex protocol error: type %d seq %u", type, seq); 122 } 123 124 static void 125 kex_reset_dispatch(void) 126 { 127 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 128 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 129 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 130 } 131 132 void 133 kex_finish(Kex *kex) 134 { 135 kex_reset_dispatch(); 136 137 packet_start(SSH2_MSG_NEWKEYS); 138 packet_send(); 139 /* packet_write_wait(); */ 140 debug("SSH2_MSG_NEWKEYS sent"); 141 142 debug("expecting SSH2_MSG_NEWKEYS"); 143 packet_read_expect(SSH2_MSG_NEWKEYS); 144 packet_check_eom(); 145 debug("SSH2_MSG_NEWKEYS received"); 146 147 kex->done = 1; 148 buffer_clear(&kex->peer); 149 /* buffer_clear(&kex->my); */ 150 kex->flags &= ~KEX_INIT_SENT; 151 xfree(kex->name); 152 kex->name = NULL; 153 } 154 155 void 156 kex_send_kexinit(Kex *kex) 157 { 158 u_int32_t rnd = 0; 159 u_char *cookie; 160 u_int i; 161 162 if (kex == NULL) { 163 error("kex_send_kexinit: no kex, cannot rekey"); 164 return; 165 } 166 if (kex->flags & KEX_INIT_SENT) { 167 debug("KEX_INIT_SENT"); 168 return; 169 } 170 kex->done = 0; 171 172 /* generate a random cookie */ 173 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 174 fatal("kex_send_kexinit: kex proposal too short"); 175 cookie = buffer_ptr(&kex->my); 176 for (i = 0; i < KEX_COOKIE_LEN; i++) { 177 if (i % 4 == 0) 178 rnd = arc4random(); 179 cookie[i] = rnd; 180 rnd >>= 8; 181 } 182 packet_start(SSH2_MSG_KEXINIT); 183 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 184 packet_send(); 185 debug("SSH2_MSG_KEXINIT sent"); 186 kex->flags |= KEX_INIT_SENT; 187 } 188 189 /* ARGSUSED */ 190 void 191 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 192 { 193 char *ptr; 194 u_int i, dlen; 195 Kex *kex = (Kex *)ctxt; 196 197 debug("SSH2_MSG_KEXINIT received"); 198 if (kex == NULL) 199 fatal("kex_input_kexinit: no kex, cannot rekey"); 200 201 ptr = packet_get_raw(&dlen); 202 buffer_append(&kex->peer, ptr, dlen); 203 204 /* discard packet */ 205 for (i = 0; i < KEX_COOKIE_LEN; i++) 206 packet_get_char(); 207 for (i = 0; i < PROPOSAL_MAX; i++) 208 xfree(packet_get_string(NULL)); 209 (void) packet_get_char(); 210 (void) packet_get_int(); 211 packet_check_eom(); 212 213 kex_kexinit_finish(kex); 214 } 215 216 Kex * 217 kex_setup(char *proposal[PROPOSAL_MAX]) 218 { 219 Kex *kex; 220 221 kex = xcalloc(1, sizeof(*kex)); 222 buffer_init(&kex->peer); 223 buffer_init(&kex->my); 224 kex_prop2buf(&kex->my, proposal); 225 kex->done = 0; 226 227 kex_send_kexinit(kex); /* we start */ 228 kex_reset_dispatch(); 229 230 return kex; 231 } 232 233 static void 234 kex_kexinit_finish(Kex *kex) 235 { 236 if (!(kex->flags & KEX_INIT_SENT)) 237 kex_send_kexinit(kex); 238 239 kex_choose_conf(kex); 240 241 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 242 kex->kex[kex->kex_type] != NULL) { 243 (kex->kex[kex->kex_type])(kex); 244 } else { 245 fatal("Unsupported key exchange %d", kex->kex_type); 246 } 247 } 248 249 static void 250 choose_enc(Enc *enc, char *client, char *server) 251 { 252 char *name = match_list(client, server, NULL); 253 if (name == NULL) 254 fatal("no matching cipher found: client %s server %s", 255 client, server); 256 if ((enc->cipher = cipher_by_name(name)) == NULL) 257 fatal("matching cipher is not supported: %s", name); 258 enc->name = name; 259 enc->enabled = 0; 260 enc->iv = NULL; 261 enc->key = NULL; 262 enc->key_len = cipher_keylen(enc->cipher); 263 enc->block_size = cipher_blocksize(enc->cipher); 264 } 265 266 static void 267 choose_mac(Mac *mac, char *client, char *server) 268 { 269 char *name = match_list(client, server, NULL); 270 if (name == NULL) 271 fatal("no matching mac found: client %s server %s", 272 client, server); 273 if (mac_setup(mac, name) < 0) 274 fatal("unsupported mac %s", name); 275 /* truncate the key */ 276 if (datafellows & SSH_BUG_HMAC) 277 mac->key_len = 16; 278 mac->name = name; 279 mac->key = NULL; 280 mac->enabled = 0; 281 } 282 283 static void 284 choose_comp(Comp *comp, char *client, char *server) 285 { 286 char *name = match_list(client, server, NULL); 287 if (name == NULL) 288 fatal("no matching comp found: client %s server %s", client, server); 289 if (strcmp(name, "zlib@openssh.com") == 0) { 290 comp->type = COMP_DELAYED; 291 } else if (strcmp(name, "zlib") == 0) { 292 comp->type = COMP_ZLIB; 293 } else if (strcmp(name, "none") == 0) { 294 comp->type = COMP_NONE; 295 } else { 296 fatal("unsupported comp %s", name); 297 } 298 comp->name = name; 299 } 300 301 static void 302 choose_kex(Kex *k, char *client, char *server) 303 { 304 k->name = match_list(client, server, NULL); 305 if (k->name == NULL) 306 fatal("Unable to negotiate a key exchange method"); 307 if (strcmp(k->name, KEX_DH1) == 0) { 308 k->kex_type = KEX_DH_GRP1_SHA1; 309 k->evp_md = EVP_sha1(); 310 } else if (strcmp(k->name, KEX_DH14) == 0) { 311 k->kex_type = KEX_DH_GRP14_SHA1; 312 k->evp_md = EVP_sha1(); 313 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 314 k->kex_type = KEX_DH_GEX_SHA1; 315 k->evp_md = EVP_sha1(); 316 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 317 k->kex_type = KEX_DH_GEX_SHA256; 318 k->evp_md = EVP_sha256(); 319 } else 320 fatal("bad kex alg %s", k->name); 321 } 322 323 static void 324 choose_hostkeyalg(Kex *k, char *client, char *server) 325 { 326 char *hostkeyalg = match_list(client, server, NULL); 327 if (hostkeyalg == NULL) 328 fatal("no hostkey alg"); 329 k->hostkey_type = key_type_from_name(hostkeyalg); 330 if (k->hostkey_type == KEY_UNSPEC) 331 fatal("bad hostkey alg '%s'", hostkeyalg); 332 xfree(hostkeyalg); 333 } 334 335 static int 336 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 337 { 338 static int check[] = { 339 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 340 }; 341 int *idx; 342 char *p; 343 344 for (idx = &check[0]; *idx != -1; idx++) { 345 if ((p = strchr(my[*idx], ',')) != NULL) 346 *p = '\0'; 347 if ((p = strchr(peer[*idx], ',')) != NULL) 348 *p = '\0'; 349 if (strcmp(my[*idx], peer[*idx]) != 0) { 350 debug2("proposal mismatch: my %s peer %s", 351 my[*idx], peer[*idx]); 352 return (0); 353 } 354 } 355 debug2("proposals match"); 356 return (1); 357 } 358 359 static void 360 kex_choose_conf(Kex *kex) 361 { 362 Newkeys *newkeys; 363 char **my, **peer; 364 char **cprop, **sprop; 365 int nenc, nmac, ncomp; 366 u_int mode, ctos, need; 367 int first_kex_follows, type; 368 int log_flag = 0; 369 370 int auth_flag; 371 372 auth_flag = packet_authentication_state(); 373 374 debug ("AUTH STATE IS %d", auth_flag); 375 376 my = kex_buf2prop(&kex->my, NULL); 377 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 378 379 if (kex->server) { 380 cprop=peer; 381 sprop=my; 382 } else { 383 cprop=my; 384 sprop=peer; 385 } 386 387 /* Algorithm Negotiation */ 388 for (mode = 0; mode < MODE_MAX; mode++) { 389 newkeys = xcalloc(1, sizeof(*newkeys)); 390 kex->newkeys[mode] = newkeys; 391 ctos = (!kex->server && mode == MODE_OUT) || 392 (kex->server && mode == MODE_IN); 393 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 394 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 395 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 396 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 397 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 398 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 399 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name); 400 if (strcmp(newkeys->enc.name, "none") == 0) { 401 debug("Requesting NONE. Authflag is %d", auth_flag); 402 if (auth_flag == 1) { 403 debug("None requested post authentication."); 404 } else { 405 fatal("Pre-authentication none cipher requests are not allowed."); 406 } 407 } 408 debug("kex: %s %s %s %s", 409 ctos ? "client->server" : "server->client", 410 newkeys->enc.name, 411 newkeys->mac.name, 412 newkeys->comp.name); 413 /* client starts withctos = 0 && log flag = 0 and no log*/ 414 /* 2nd client pass ctos=1 and flag = 1 so no log*/ 415 /* server starts with ctos =1 && log_flag = 0 so log */ 416 /* 2nd sever pass ctos = 1 && log flag = 1 so no log*/ 417 /* -cjr*/ 418 if (ctos && !log_flag) { 419 logit("SSH: Server;Ltype: Kex;Remote: %s-%d;Enc: %s;MAC: %s;Comp: %s", 420 get_remote_ipaddr(), 421 get_remote_port(), 422 newkeys->enc.name, 423 newkeys->mac.name, 424 newkeys->comp.name); 425 } 426 log_flag = 1; 427 } 428 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 429 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 430 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 431 need = 0; 432 for (mode = 0; mode < MODE_MAX; mode++) { 433 newkeys = kex->newkeys[mode]; 434 if (need < newkeys->enc.key_len) 435 need = newkeys->enc.key_len; 436 if (need < newkeys->enc.block_size) 437 need = newkeys->enc.block_size; 438 if (need < newkeys->mac.key_len) 439 need = newkeys->mac.key_len; 440 } 441 /* XXX need runden? */ 442 kex->we_need = need; 443 444 /* ignore the next message if the proposals do not match */ 445 if (first_kex_follows && !proposals_match(my, peer) && 446 !(datafellows & SSH_BUG_FIRSTKEX)) { 447 type = packet_read(); 448 debug2("skipping next packet (type %u)", type); 449 } 450 451 kex_prop_free(my); 452 kex_prop_free(peer); 453 } 454 455 static u_char * 456 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 457 BIGNUM *shared_secret) 458 { 459 Buffer b; 460 EVP_MD_CTX md; 461 char c = id; 462 u_int have; 463 int mdsz; 464 u_char *digest; 465 466 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 467 fatal("bad kex md size %d", mdsz); 468 digest = xmalloc(roundup(need, mdsz)); 469 470 buffer_init(&b); 471 buffer_put_bignum2(&b, shared_secret); 472 473 /* K1 = HASH(K || H || "A" || session_id) */ 474 EVP_DigestInit(&md, kex->evp_md); 475 if (!(datafellows & SSH_BUG_DERIVEKEY)) 476 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 477 EVP_DigestUpdate(&md, hash, hashlen); 478 EVP_DigestUpdate(&md, &c, 1); 479 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 480 EVP_DigestFinal(&md, digest, NULL); 481 482 /* 483 * expand key: 484 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 485 * Key = K1 || K2 || ... || Kn 486 */ 487 for (have = mdsz; need > have; have += mdsz) { 488 EVP_DigestInit(&md, kex->evp_md); 489 if (!(datafellows & SSH_BUG_DERIVEKEY)) 490 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 491 EVP_DigestUpdate(&md, hash, hashlen); 492 EVP_DigestUpdate(&md, digest, have); 493 EVP_DigestFinal(&md, digest + have, NULL); 494 } 495 buffer_free(&b); 496 #ifdef DEBUG_KEX 497 fprintf(stderr, "key '%c'== ", c); 498 dump_digest("key", digest, need); 499 #endif 500 return digest; 501 } 502 503 Newkeys *current_keys[MODE_MAX]; 504 505 #define NKEYS 6 506 void 507 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 508 { 509 u_char *keys[NKEYS]; 510 u_int i, mode, ctos; 511 512 for (i = 0; i < NKEYS; i++) { 513 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 514 shared_secret); 515 } 516 517 debug2("kex_derive_keys"); 518 for (mode = 0; mode < MODE_MAX; mode++) { 519 current_keys[mode] = kex->newkeys[mode]; 520 kex->newkeys[mode] = NULL; 521 ctos = (!kex->server && mode == MODE_OUT) || 522 (kex->server && mode == MODE_IN); 523 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 524 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 525 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 526 } 527 } 528 529 Newkeys * 530 kex_get_newkeys(int mode) 531 { 532 Newkeys *ret; 533 534 ret = current_keys[mode]; 535 current_keys[mode] = NULL; 536 return ret; 537 } 538 539 void 540 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 541 u_int8_t cookie[8], u_int8_t id[16]) 542 { 543 const EVP_MD *evp_md = EVP_md5(); 544 EVP_MD_CTX md; 545 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 546 int len; 547 548 EVP_DigestInit(&md, evp_md); 549 550 len = BN_num_bytes(host_modulus); 551 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 552 fatal("%s: bad host modulus (len %d)", __func__, len); 553 BN_bn2bin(host_modulus, nbuf); 554 EVP_DigestUpdate(&md, nbuf, len); 555 556 len = BN_num_bytes(server_modulus); 557 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 558 fatal("%s: bad server modulus (len %d)", __func__, len); 559 BN_bn2bin(server_modulus, nbuf); 560 EVP_DigestUpdate(&md, nbuf, len); 561 562 EVP_DigestUpdate(&md, cookie, 8); 563 564 EVP_DigestFinal(&md, obuf, NULL); 565 memcpy(id, obuf, 16); 566 567 memset(nbuf, 0, sizeof(nbuf)); 568 memset(obuf, 0, sizeof(obuf)); 569 memset(&md, 0, sizeof(md)); 570 } 571 572 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 573 void 574 dump_digest(char *msg, u_char *digest, int len) 575 { 576 u_int i; 577 578 fprintf(stderr, "%s\n", msg); 579 for (i = 0; i < len; i++) { 580 fprintf(stderr, "%02x", digest[i]); 581 if (i%32 == 31) 582 fprintf(stderr, "\n"); 583 else if (i%8 == 7) 584 fprintf(stderr, " "); 585 } 586 fprintf(stderr, "\n"); 587 } 588 #endif 589