1 /* $OpenBSD: kex.c,v 1.80 2008/09/06 12:24:13 djm 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 52 #define KEX_COOKIE_LEN 16 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 /* put algorithm proposal into buffer */ 67 static void 68 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 69 { 70 u_int i; 71 72 buffer_clear(b); 73 /* 74 * add a dummy cookie, the cookie will be overwritten by 75 * kex_send_kexinit(), each time a kexinit is set 76 */ 77 for (i = 0; i < KEX_COOKIE_LEN; i++) 78 buffer_put_char(b, 0); 79 for (i = 0; i < PROPOSAL_MAX; i++) 80 buffer_put_cstring(b, proposal[i]); 81 buffer_put_char(b, 0); /* first_kex_packet_follows */ 82 buffer_put_int(b, 0); /* uint32 reserved */ 83 } 84 85 /* parse buffer and return algorithm proposal */ 86 static char ** 87 kex_buf2prop(Buffer *raw, int *first_kex_follows) 88 { 89 Buffer b; 90 u_int i; 91 char **proposal; 92 93 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 94 95 buffer_init(&b); 96 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 97 /* skip cookie */ 98 for (i = 0; i < KEX_COOKIE_LEN; i++) 99 buffer_get_char(&b); 100 /* extract kex init proposal strings */ 101 for (i = 0; i < PROPOSAL_MAX; i++) { 102 proposal[i] = buffer_get_string(&b,NULL); 103 debug2("kex_parse_kexinit: %s", proposal[i]); 104 } 105 /* first kex follows / reserved */ 106 i = buffer_get_char(&b); 107 if (first_kex_follows != NULL) 108 *first_kex_follows = i; 109 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 110 i = buffer_get_int(&b); 111 debug2("kex_parse_kexinit: reserved %u ", i); 112 buffer_free(&b); 113 return proposal; 114 } 115 116 static void 117 kex_prop_free(char **proposal) 118 { 119 u_int i; 120 121 for (i = 0; i < PROPOSAL_MAX; i++) 122 xfree(proposal[i]); 123 xfree(proposal); 124 } 125 126 /* ARGSUSED */ 127 static void 128 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 129 { 130 error("Hm, kex protocol error: type %d seq %u", type, seq); 131 } 132 133 static void 134 kex_reset_dispatch(void) 135 { 136 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 137 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 138 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 139 } 140 141 void 142 kex_finish(Kex *kex) 143 { 144 kex_reset_dispatch(); 145 146 packet_start(SSH2_MSG_NEWKEYS); 147 packet_send(); 148 /* packet_write_wait(); */ 149 debug("SSH2_MSG_NEWKEYS sent"); 150 151 debug("expecting SSH2_MSG_NEWKEYS"); 152 packet_read_expect(SSH2_MSG_NEWKEYS); 153 packet_check_eom(); 154 debug("SSH2_MSG_NEWKEYS received"); 155 156 kex->done = 1; 157 buffer_clear(&kex->peer); 158 /* buffer_clear(&kex->my); */ 159 kex->flags &= ~KEX_INIT_SENT; 160 xfree(kex->name); 161 kex->name = NULL; 162 } 163 164 void 165 kex_send_kexinit(Kex *kex) 166 { 167 u_int32_t rnd = 0; 168 u_char *cookie; 169 u_int i; 170 171 if (kex == NULL) { 172 error("kex_send_kexinit: no kex, cannot rekey"); 173 return; 174 } 175 if (kex->flags & KEX_INIT_SENT) { 176 debug("KEX_INIT_SENT"); 177 return; 178 } 179 kex->done = 0; 180 181 /* generate a random cookie */ 182 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 183 fatal("kex_send_kexinit: kex proposal too short"); 184 cookie = buffer_ptr(&kex->my); 185 for (i = 0; i < KEX_COOKIE_LEN; i++) { 186 if (i % 4 == 0) 187 rnd = arc4random(); 188 cookie[i] = rnd; 189 rnd >>= 8; 190 } 191 packet_start(SSH2_MSG_KEXINIT); 192 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 193 packet_send(); 194 debug("SSH2_MSG_KEXINIT sent"); 195 kex->flags |= KEX_INIT_SENT; 196 } 197 198 /* ARGSUSED */ 199 void 200 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 201 { 202 char *ptr; 203 u_int i, dlen; 204 Kex *kex = (Kex *)ctxt; 205 206 debug("SSH2_MSG_KEXINIT received"); 207 if (kex == NULL) 208 fatal("kex_input_kexinit: no kex, cannot rekey"); 209 210 ptr = packet_get_raw(&dlen); 211 buffer_append(&kex->peer, ptr, dlen); 212 213 /* discard packet */ 214 for (i = 0; i < KEX_COOKIE_LEN; i++) 215 packet_get_char(); 216 for (i = 0; i < PROPOSAL_MAX; i++) 217 xfree(packet_get_string(NULL)); 218 (void) packet_get_char(); 219 (void) packet_get_int(); 220 packet_check_eom(); 221 222 kex_kexinit_finish(kex); 223 } 224 225 Kex * 226 kex_setup(char *proposal[PROPOSAL_MAX]) 227 { 228 Kex *kex; 229 230 kex = xcalloc(1, sizeof(*kex)); 231 buffer_init(&kex->peer); 232 buffer_init(&kex->my); 233 kex_prop2buf(&kex->my, proposal); 234 kex->done = 0; 235 236 kex_send_kexinit(kex); /* we start */ 237 kex_reset_dispatch(); 238 239 return kex; 240 } 241 242 static void 243 kex_kexinit_finish(Kex *kex) 244 { 245 if (!(kex->flags & KEX_INIT_SENT)) 246 kex_send_kexinit(kex); 247 248 kex_choose_conf(kex); 249 250 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 251 kex->kex[kex->kex_type] != NULL) { 252 (kex->kex[kex->kex_type])(kex); 253 } else { 254 fatal("Unsupported key exchange %d", kex->kex_type); 255 } 256 } 257 258 static void 259 choose_enc(Enc *enc, char *client, char *server) 260 { 261 char *name = match_list(client, server, NULL); 262 if (name == NULL) 263 fatal("no matching cipher found: client %s server %s", 264 client, server); 265 if ((enc->cipher = cipher_by_name(name)) == NULL) 266 fatal("matching cipher is not supported: %s", name); 267 enc->name = name; 268 enc->enabled = 0; 269 enc->iv = NULL; 270 enc->key = NULL; 271 enc->key_len = cipher_keylen(enc->cipher); 272 enc->block_size = cipher_blocksize(enc->cipher); 273 } 274 275 static void 276 choose_mac(Mac *mac, char *client, char *server) 277 { 278 char *name = match_list(client, server, NULL); 279 if (name == NULL) 280 fatal("no matching mac found: client %s server %s", 281 client, server); 282 if (mac_setup(mac, name) < 0) 283 fatal("unsupported mac %s", name); 284 /* truncate the key */ 285 if (datafellows & SSH_BUG_HMAC) 286 mac->key_len = 16; 287 mac->name = name; 288 mac->key = NULL; 289 mac->enabled = 0; 290 } 291 292 static void 293 choose_comp(Comp *comp, char *client, char *server) 294 { 295 char *name = match_list(client, server, NULL); 296 if (name == NULL) 297 fatal("no matching comp found: client %s server %s", client, server); 298 if (strcmp(name, "zlib@openssh.com") == 0) { 299 comp->type = COMP_DELAYED; 300 } else if (strcmp(name, "zlib") == 0) { 301 comp->type = COMP_ZLIB; 302 } else if (strcmp(name, "none") == 0) { 303 comp->type = COMP_NONE; 304 } else { 305 fatal("unsupported comp %s", name); 306 } 307 comp->name = name; 308 } 309 310 static void 311 choose_kex(Kex *k, char *client, char *server) 312 { 313 k->name = match_list(client, server, NULL); 314 if (k->name == NULL) 315 fatal("Unable to negotiate a key exchange method"); 316 if (strcmp(k->name, KEX_DH1) == 0) { 317 k->kex_type = KEX_DH_GRP1_SHA1; 318 k->evp_md = EVP_sha1(); 319 } else if (strcmp(k->name, KEX_DH14) == 0) { 320 k->kex_type = KEX_DH_GRP14_SHA1; 321 k->evp_md = EVP_sha1(); 322 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 323 k->kex_type = KEX_DH_GEX_SHA1; 324 k->evp_md = EVP_sha1(); 325 #if OPENSSL_VERSION_NUMBER >= 0x00907000L 326 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 327 k->kex_type = KEX_DH_GEX_SHA256; 328 k->evp_md = evp_ssh_sha256(); 329 #endif 330 } else 331 fatal("bad kex alg %s", k->name); 332 } 333 334 static void 335 choose_hostkeyalg(Kex *k, char *client, char *server) 336 { 337 char *hostkeyalg = match_list(client, server, NULL); 338 if (hostkeyalg == NULL) 339 fatal("no hostkey alg"); 340 k->hostkey_type = key_type_from_name(hostkeyalg); 341 if (k->hostkey_type == KEY_UNSPEC) 342 fatal("bad hostkey alg '%s'", hostkeyalg); 343 xfree(hostkeyalg); 344 } 345 346 static int 347 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 348 { 349 static int check[] = { 350 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 351 }; 352 int *idx; 353 char *p; 354 355 for (idx = &check[0]; *idx != -1; idx++) { 356 if ((p = strchr(my[*idx], ',')) != NULL) 357 *p = '\0'; 358 if ((p = strchr(peer[*idx], ',')) != NULL) 359 *p = '\0'; 360 if (strcmp(my[*idx], peer[*idx]) != 0) { 361 debug2("proposal mismatch: my %s peer %s", 362 my[*idx], peer[*idx]); 363 return (0); 364 } 365 } 366 debug2("proposals match"); 367 return (1); 368 } 369 370 static void 371 kex_choose_conf(Kex *kex) 372 { 373 Newkeys *newkeys; 374 char **my, **peer; 375 char **cprop, **sprop; 376 int nenc, nmac, ncomp; 377 u_int mode, ctos, need; 378 int first_kex_follows, type; 379 380 my = kex_buf2prop(&kex->my, NULL); 381 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 382 383 if (kex->server) { 384 cprop=peer; 385 sprop=my; 386 } else { 387 cprop=my; 388 sprop=peer; 389 } 390 391 /* Algorithm Negotiation */ 392 for (mode = 0; mode < MODE_MAX; mode++) { 393 newkeys = xcalloc(1, sizeof(*newkeys)); 394 kex->newkeys[mode] = newkeys; 395 ctos = (!kex->server && mode == MODE_OUT) || 396 (kex->server && mode == MODE_IN); 397 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 398 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 399 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 400 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 401 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 402 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 403 debug("kex: %s %s %s %s", 404 ctos ? "client->server" : "server->client", 405 newkeys->enc.name, 406 newkeys->mac.name, 407 newkeys->comp.name); 408 } 409 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 410 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 411 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 412 need = 0; 413 for (mode = 0; mode < MODE_MAX; mode++) { 414 newkeys = kex->newkeys[mode]; 415 if (need < newkeys->enc.key_len) 416 need = newkeys->enc.key_len; 417 if (need < newkeys->enc.block_size) 418 need = newkeys->enc.block_size; 419 if (need < newkeys->mac.key_len) 420 need = newkeys->mac.key_len; 421 } 422 /* XXX need runden? */ 423 kex->we_need = need; 424 425 /* ignore the next message if the proposals do not match */ 426 if (first_kex_follows && !proposals_match(my, peer) && 427 !(datafellows & SSH_BUG_FIRSTKEX)) { 428 type = packet_read(); 429 debug2("skipping next packet (type %u)", type); 430 } 431 432 kex_prop_free(my); 433 kex_prop_free(peer); 434 } 435 436 static u_char * 437 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 438 BIGNUM *shared_secret) 439 { 440 Buffer b; 441 EVP_MD_CTX md; 442 char c = id; 443 u_int have; 444 int mdsz; 445 u_char *digest; 446 447 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 448 fatal("bad kex md size %d", mdsz); 449 digest = xmalloc(roundup(need, mdsz)); 450 451 buffer_init(&b); 452 buffer_put_bignum2(&b, shared_secret); 453 454 /* K1 = HASH(K || H || "A" || session_id) */ 455 EVP_DigestInit(&md, kex->evp_md); 456 if (!(datafellows & SSH_BUG_DERIVEKEY)) 457 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 458 EVP_DigestUpdate(&md, hash, hashlen); 459 EVP_DigestUpdate(&md, &c, 1); 460 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 461 EVP_DigestFinal(&md, digest, NULL); 462 463 /* 464 * expand key: 465 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 466 * Key = K1 || K2 || ... || Kn 467 */ 468 for (have = mdsz; need > have; have += mdsz) { 469 EVP_DigestInit(&md, kex->evp_md); 470 if (!(datafellows & SSH_BUG_DERIVEKEY)) 471 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 472 EVP_DigestUpdate(&md, hash, hashlen); 473 EVP_DigestUpdate(&md, digest, have); 474 EVP_DigestFinal(&md, digest + have, NULL); 475 } 476 buffer_free(&b); 477 #ifdef DEBUG_KEX 478 fprintf(stderr, "key '%c'== ", c); 479 dump_digest("key", digest, need); 480 #endif 481 return digest; 482 } 483 484 Newkeys *current_keys[MODE_MAX]; 485 486 #define NKEYS 6 487 void 488 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 489 { 490 u_char *keys[NKEYS]; 491 u_int i, mode, ctos; 492 493 for (i = 0; i < NKEYS; i++) { 494 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 495 shared_secret); 496 } 497 498 debug2("kex_derive_keys"); 499 for (mode = 0; mode < MODE_MAX; mode++) { 500 current_keys[mode] = kex->newkeys[mode]; 501 kex->newkeys[mode] = NULL; 502 ctos = (!kex->server && mode == MODE_OUT) || 503 (kex->server && mode == MODE_IN); 504 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 505 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 506 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 507 } 508 } 509 510 Newkeys * 511 kex_get_newkeys(int mode) 512 { 513 Newkeys *ret; 514 515 ret = current_keys[mode]; 516 current_keys[mode] = NULL; 517 return ret; 518 } 519 520 void 521 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 522 u_int8_t cookie[8], u_int8_t id[16]) 523 { 524 const EVP_MD *evp_md = EVP_md5(); 525 EVP_MD_CTX md; 526 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 527 int len; 528 529 EVP_DigestInit(&md, evp_md); 530 531 len = BN_num_bytes(host_modulus); 532 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 533 fatal("%s: bad host modulus (len %d)", __func__, len); 534 BN_bn2bin(host_modulus, nbuf); 535 EVP_DigestUpdate(&md, nbuf, len); 536 537 len = BN_num_bytes(server_modulus); 538 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 539 fatal("%s: bad server modulus (len %d)", __func__, len); 540 BN_bn2bin(server_modulus, nbuf); 541 EVP_DigestUpdate(&md, nbuf, len); 542 543 EVP_DigestUpdate(&md, cookie, 8); 544 545 EVP_DigestFinal(&md, obuf, NULL); 546 memcpy(id, obuf, 16); 547 548 memset(nbuf, 0, sizeof(nbuf)); 549 memset(obuf, 0, sizeof(obuf)); 550 memset(&md, 0, sizeof(md)); 551 } 552 553 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 554 void 555 dump_digest(char *msg, u_char *digest, int len) 556 { 557 u_int i; 558 559 fprintf(stderr, "%s\n", msg); 560 for (i = 0; i < len; i++) { 561 fprintf(stderr, "%02x", digest[i]); 562 if (i%32 == 31) 563 fprintf(stderr, "\n"); 564 else if (i%8 == 7) 565 fprintf(stderr, " "); 566 } 567 fprintf(stderr, "\n"); 568 } 569 #endif 570