1 /* $OpenBSD: kex.c,v 1.81 2009/05/27 06:34:36 andreas 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 <sys/param.h> 27 28 #include <signal.h> 29 #include <stdio.h> 30 #include <stdlib.h> 31 #include <string.h> 32 33 #include <openssl/crypto.h> 34 35 #include "xmalloc.h" 36 #include "ssh2.h" 37 #include "buffer.h" 38 #include "packet.h" 39 #include "compat.h" 40 #include "cipher.h" 41 #include "key.h" 42 #include "kex.h" 43 #include "log.h" 44 #include "mac.h" 45 #include "match.h" 46 #include "dispatch.h" 47 #include "monitor.h" 48 49 /* prototype */ 50 static void kex_kexinit_finish(Kex *); 51 static void kex_choose_conf(Kex *); 52 53 /* put algorithm proposal into buffer */ 54 static void 55 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 56 { 57 u_int i; 58 59 buffer_clear(b); 60 /* 61 * add a dummy cookie, the cookie will be overwritten by 62 * kex_send_kexinit(), each time a kexinit is set 63 */ 64 for (i = 0; i < KEX_COOKIE_LEN; i++) 65 buffer_put_char(b, 0); 66 for (i = 0; i < PROPOSAL_MAX; i++) 67 buffer_put_cstring(b, proposal[i]); 68 buffer_put_char(b, 0); /* first_kex_packet_follows */ 69 buffer_put_int(b, 0); /* uint32 reserved */ 70 } 71 72 /* parse buffer and return algorithm proposal */ 73 static char ** 74 kex_buf2prop(Buffer *raw, int *first_kex_follows) 75 { 76 Buffer b; 77 u_int i; 78 char **proposal; 79 80 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 81 82 buffer_init(&b); 83 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 84 /* skip cookie */ 85 for (i = 0; i < KEX_COOKIE_LEN; i++) 86 buffer_get_char(&b); 87 /* extract kex init proposal strings */ 88 for (i = 0; i < PROPOSAL_MAX; i++) { 89 proposal[i] = buffer_get_string(&b,NULL); 90 debug2("kex_parse_kexinit: %s", proposal[i]); 91 } 92 /* first kex follows / reserved */ 93 i = buffer_get_char(&b); 94 if (first_kex_follows != NULL) 95 *first_kex_follows = i; 96 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 97 i = buffer_get_int(&b); 98 debug2("kex_parse_kexinit: reserved %u ", i); 99 buffer_free(&b); 100 return proposal; 101 } 102 103 static void 104 kex_prop_free(char **proposal) 105 { 106 u_int i; 107 108 for (i = 0; i < PROPOSAL_MAX; i++) 109 xfree(proposal[i]); 110 xfree(proposal); 111 } 112 113 /* ARGSUSED */ 114 static void 115 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 116 { 117 error("Hm, kex protocol error: type %d seq %u", type, seq); 118 } 119 120 static void 121 kex_reset_dispatch(void) 122 { 123 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 124 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 125 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 126 } 127 128 void 129 kex_finish(Kex *kex) 130 { 131 kex_reset_dispatch(); 132 133 packet_start(SSH2_MSG_NEWKEYS); 134 packet_send(); 135 /* packet_write_wait(); */ 136 debug("SSH2_MSG_NEWKEYS sent"); 137 138 debug("expecting SSH2_MSG_NEWKEYS"); 139 packet_read_expect(SSH2_MSG_NEWKEYS); 140 packet_check_eom(); 141 debug("SSH2_MSG_NEWKEYS received"); 142 143 kex->done = 1; 144 buffer_clear(&kex->peer); 145 /* buffer_clear(&kex->my); */ 146 kex->flags &= ~KEX_INIT_SENT; 147 xfree(kex->name); 148 kex->name = NULL; 149 } 150 151 void 152 kex_send_kexinit(Kex *kex) 153 { 154 u_int32_t rnd = 0; 155 u_char *cookie; 156 u_int i; 157 158 if (kex == NULL) { 159 error("kex_send_kexinit: no kex, cannot rekey"); 160 return; 161 } 162 if (kex->flags & KEX_INIT_SENT) { 163 debug("KEX_INIT_SENT"); 164 return; 165 } 166 kex->done = 0; 167 168 /* generate a random cookie */ 169 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 170 fatal("kex_send_kexinit: kex proposal too short"); 171 cookie = buffer_ptr(&kex->my); 172 for (i = 0; i < KEX_COOKIE_LEN; i++) { 173 if (i % 4 == 0) 174 rnd = arc4random(); 175 cookie[i] = rnd; 176 rnd >>= 8; 177 } 178 packet_start(SSH2_MSG_KEXINIT); 179 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 180 packet_send(); 181 debug("SSH2_MSG_KEXINIT sent"); 182 kex->flags |= KEX_INIT_SENT; 183 } 184 185 /* ARGSUSED */ 186 void 187 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 188 { 189 char *ptr; 190 u_int i, dlen; 191 Kex *kex = (Kex *)ctxt; 192 193 debug("SSH2_MSG_KEXINIT received"); 194 if (kex == NULL) 195 fatal("kex_input_kexinit: no kex, cannot rekey"); 196 197 ptr = packet_get_raw(&dlen); 198 buffer_append(&kex->peer, ptr, dlen); 199 200 /* discard packet */ 201 for (i = 0; i < KEX_COOKIE_LEN; i++) 202 packet_get_char(); 203 for (i = 0; i < PROPOSAL_MAX; i++) 204 xfree(packet_get_string(NULL)); 205 (void) packet_get_char(); 206 (void) packet_get_int(); 207 packet_check_eom(); 208 209 kex_kexinit_finish(kex); 210 } 211 212 Kex * 213 kex_setup(char *proposal[PROPOSAL_MAX]) 214 { 215 Kex *kex; 216 217 kex = xcalloc(1, sizeof(*kex)); 218 buffer_init(&kex->peer); 219 buffer_init(&kex->my); 220 kex_prop2buf(&kex->my, proposal); 221 kex->done = 0; 222 223 kex_send_kexinit(kex); /* we start */ 224 kex_reset_dispatch(); 225 226 return kex; 227 } 228 229 static void 230 kex_kexinit_finish(Kex *kex) 231 { 232 if (!(kex->flags & KEX_INIT_SENT)) 233 kex_send_kexinit(kex); 234 235 kex_choose_conf(kex); 236 237 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 238 kex->kex[kex->kex_type] != NULL) { 239 (kex->kex[kex->kex_type])(kex); 240 } else { 241 fatal("Unsupported key exchange %d", kex->kex_type); 242 } 243 } 244 245 static void 246 choose_enc(Enc *enc, char *client, char *server) 247 { 248 char *name = match_list(client, server, NULL); 249 if (name == NULL) 250 fatal("no matching cipher found: client %s server %s", 251 client, server); 252 if ((enc->cipher = cipher_by_name(name)) == NULL) 253 fatal("matching cipher is not supported: %s", name); 254 enc->name = name; 255 enc->enabled = 0; 256 enc->iv = NULL; 257 enc->key = NULL; 258 enc->key_len = cipher_keylen(enc->cipher); 259 enc->block_size = cipher_blocksize(enc->cipher); 260 } 261 262 static void 263 choose_mac(Mac *mac, char *client, char *server) 264 { 265 char *name = match_list(client, server, NULL); 266 if (name == NULL) 267 fatal("no matching mac found: client %s server %s", 268 client, server); 269 if (mac_setup(mac, name) < 0) 270 fatal("unsupported mac %s", name); 271 /* truncate the key */ 272 if (datafellows & SSH_BUG_HMAC) 273 mac->key_len = 16; 274 mac->name = name; 275 mac->key = NULL; 276 mac->enabled = 0; 277 } 278 279 static void 280 choose_comp(Comp *comp, char *client, char *server) 281 { 282 char *name = match_list(client, server, NULL); 283 if (name == NULL) 284 fatal("no matching comp found: client %s server %s", client, server); 285 if (strcmp(name, "zlib@openssh.com") == 0) { 286 comp->type = COMP_DELAYED; 287 } else if (strcmp(name, "zlib") == 0) { 288 comp->type = COMP_ZLIB; 289 } else if (strcmp(name, "none") == 0) { 290 comp->type = COMP_NONE; 291 } else { 292 fatal("unsupported comp %s", name); 293 } 294 comp->name = name; 295 } 296 297 static void 298 choose_kex(Kex *k, char *client, char *server) 299 { 300 k->name = match_list(client, server, NULL); 301 if (k->name == NULL) 302 fatal("Unable to negotiate a key exchange method"); 303 if (strcmp(k->name, KEX_DH1) == 0) { 304 k->kex_type = KEX_DH_GRP1_SHA1; 305 k->evp_md = EVP_sha1(); 306 } else if (strcmp(k->name, KEX_DH14) == 0) { 307 k->kex_type = KEX_DH_GRP14_SHA1; 308 k->evp_md = EVP_sha1(); 309 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 310 k->kex_type = KEX_DH_GEX_SHA1; 311 k->evp_md = EVP_sha1(); 312 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 313 k->kex_type = KEX_DH_GEX_SHA256; 314 k->evp_md = EVP_sha256(); 315 } else 316 fatal("bad kex alg %s", k->name); 317 } 318 319 static void 320 choose_hostkeyalg(Kex *k, char *client, char *server) 321 { 322 char *hostkeyalg = match_list(client, server, NULL); 323 if (hostkeyalg == NULL) 324 fatal("no hostkey alg"); 325 k->hostkey_type = key_type_from_name(hostkeyalg); 326 if (k->hostkey_type == KEY_UNSPEC) 327 fatal("bad hostkey alg '%s'", hostkeyalg); 328 xfree(hostkeyalg); 329 } 330 331 static int 332 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 333 { 334 static int check[] = { 335 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 336 }; 337 int *idx; 338 char *p; 339 340 for (idx = &check[0]; *idx != -1; idx++) { 341 if ((p = strchr(my[*idx], ',')) != NULL) 342 *p = '\0'; 343 if ((p = strchr(peer[*idx], ',')) != NULL) 344 *p = '\0'; 345 if (strcmp(my[*idx], peer[*idx]) != 0) { 346 debug2("proposal mismatch: my %s peer %s", 347 my[*idx], peer[*idx]); 348 return (0); 349 } 350 } 351 debug2("proposals match"); 352 return (1); 353 } 354 355 static void 356 kex_choose_conf(Kex *kex) 357 { 358 Newkeys *newkeys; 359 char **my, **peer; 360 char **cprop, **sprop; 361 int nenc, nmac, ncomp; 362 u_int mode, ctos, need; 363 int first_kex_follows, type; 364 365 my = kex_buf2prop(&kex->my, NULL); 366 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 367 368 if (kex->server) { 369 cprop=peer; 370 sprop=my; 371 } else { 372 cprop=my; 373 sprop=peer; 374 } 375 376 /* Algorithm Negotiation */ 377 for (mode = 0; mode < MODE_MAX; mode++) { 378 newkeys = xcalloc(1, sizeof(*newkeys)); 379 kex->newkeys[mode] = newkeys; 380 ctos = (!kex->server && mode == MODE_OUT) || 381 (kex->server && mode == MODE_IN); 382 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 383 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 384 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 385 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 386 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 387 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 388 debug("kex: %s %s %s %s", 389 ctos ? "client->server" : "server->client", 390 newkeys->enc.name, 391 newkeys->mac.name, 392 newkeys->comp.name); 393 } 394 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 395 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 396 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 397 need = 0; 398 for (mode = 0; mode < MODE_MAX; mode++) { 399 newkeys = kex->newkeys[mode]; 400 if (need < newkeys->enc.key_len) 401 need = newkeys->enc.key_len; 402 if (need < newkeys->enc.block_size) 403 need = newkeys->enc.block_size; 404 if (need < newkeys->mac.key_len) 405 need = newkeys->mac.key_len; 406 } 407 /* XXX need runden? */ 408 kex->we_need = need; 409 410 /* ignore the next message if the proposals do not match */ 411 if (first_kex_follows && !proposals_match(my, peer) && 412 !(datafellows & SSH_BUG_FIRSTKEX)) { 413 type = packet_read(); 414 debug2("skipping next packet (type %u)", type); 415 } 416 417 kex_prop_free(my); 418 kex_prop_free(peer); 419 } 420 421 static u_char * 422 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 423 BIGNUM *shared_secret) 424 { 425 Buffer b; 426 EVP_MD_CTX md; 427 char c = id; 428 u_int have; 429 int mdsz; 430 u_char *digest; 431 432 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 433 fatal("bad kex md size %d", mdsz); 434 digest = xmalloc(roundup(need, mdsz)); 435 436 buffer_init(&b); 437 buffer_put_bignum2(&b, shared_secret); 438 439 /* K1 = HASH(K || H || "A" || session_id) */ 440 EVP_DigestInit(&md, kex->evp_md); 441 if (!(datafellows & SSH_BUG_DERIVEKEY)) 442 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 443 EVP_DigestUpdate(&md, hash, hashlen); 444 EVP_DigestUpdate(&md, &c, 1); 445 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 446 EVP_DigestFinal(&md, digest, NULL); 447 448 /* 449 * expand key: 450 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 451 * Key = K1 || K2 || ... || Kn 452 */ 453 for (have = mdsz; need > have; have += mdsz) { 454 EVP_DigestInit(&md, kex->evp_md); 455 if (!(datafellows & SSH_BUG_DERIVEKEY)) 456 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 457 EVP_DigestUpdate(&md, hash, hashlen); 458 EVP_DigestUpdate(&md, digest, have); 459 EVP_DigestFinal(&md, digest + have, NULL); 460 } 461 buffer_free(&b); 462 #ifdef DEBUG_KEX 463 fprintf(stderr, "key '%c'== ", c); 464 dump_digest("key", digest, need); 465 #endif 466 return digest; 467 } 468 469 Newkeys *current_keys[MODE_MAX]; 470 471 #define NKEYS 6 472 void 473 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 474 { 475 u_char *keys[NKEYS]; 476 u_int i, mode, ctos; 477 478 for (i = 0; i < NKEYS; i++) { 479 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 480 shared_secret); 481 } 482 483 debug2("kex_derive_keys"); 484 for (mode = 0; mode < MODE_MAX; mode++) { 485 current_keys[mode] = kex->newkeys[mode]; 486 kex->newkeys[mode] = NULL; 487 ctos = (!kex->server && mode == MODE_OUT) || 488 (kex->server && mode == MODE_IN); 489 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 490 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 491 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 492 } 493 } 494 495 Newkeys * 496 kex_get_newkeys(int mode) 497 { 498 Newkeys *ret; 499 500 ret = current_keys[mode]; 501 current_keys[mode] = NULL; 502 return ret; 503 } 504 505 void 506 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 507 u_int8_t cookie[8], u_int8_t id[16]) 508 { 509 const EVP_MD *evp_md = EVP_md5(); 510 EVP_MD_CTX md; 511 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 512 int len; 513 514 EVP_DigestInit(&md, evp_md); 515 516 len = BN_num_bytes(host_modulus); 517 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 518 fatal("%s: bad host modulus (len %d)", __func__, len); 519 BN_bn2bin(host_modulus, nbuf); 520 EVP_DigestUpdate(&md, nbuf, len); 521 522 len = BN_num_bytes(server_modulus); 523 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 524 fatal("%s: bad server modulus (len %d)", __func__, len); 525 BN_bn2bin(server_modulus, nbuf); 526 EVP_DigestUpdate(&md, nbuf, len); 527 528 EVP_DigestUpdate(&md, cookie, 8); 529 530 EVP_DigestFinal(&md, obuf, NULL); 531 memcpy(id, obuf, 16); 532 533 memset(nbuf, 0, sizeof(nbuf)); 534 memset(obuf, 0, sizeof(obuf)); 535 memset(&md, 0, sizeof(md)); 536 } 537 538 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 539 void 540 dump_digest(char *msg, u_char *digest, int len) 541 { 542 u_int i; 543 544 fprintf(stderr, "%s\n", msg); 545 for (i = 0; i < len; i++) { 546 fprintf(stderr, "%02x", digest[i]); 547 if (i%32 == 31) 548 fprintf(stderr, "\n"); 549 else if (i%8 == 7) 550 fprintf(stderr, " "); 551 } 552 fprintf(stderr, "\n"); 553 } 554 #endif 555