1 /* $OpenBSD: kex.c,v 1.76 2006/08/03 03:34:42 deraadt 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 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 %d ", 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 static void 127 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 128 { 129 error("Hm, kex protocol error: type %d seq %u", type, seq); 130 } 131 132 static void 133 kex_reset_dispatch(void) 134 { 135 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 136 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 137 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 138 } 139 140 void 141 kex_finish(Kex *kex) 142 { 143 kex_reset_dispatch(); 144 145 packet_start(SSH2_MSG_NEWKEYS); 146 packet_send(); 147 /* packet_write_wait(); */ 148 debug("SSH2_MSG_NEWKEYS sent"); 149 150 debug("expecting SSH2_MSG_NEWKEYS"); 151 packet_read_expect(SSH2_MSG_NEWKEYS); 152 packet_check_eom(); 153 debug("SSH2_MSG_NEWKEYS received"); 154 155 kex->done = 1; 156 buffer_clear(&kex->peer); 157 /* buffer_clear(&kex->my); */ 158 kex->flags &= ~KEX_INIT_SENT; 159 xfree(kex->name); 160 kex->name = NULL; 161 } 162 163 void 164 kex_send_kexinit(Kex *kex) 165 { 166 u_int32_t rnd = 0; 167 u_char *cookie; 168 u_int i; 169 170 if (kex == NULL) { 171 error("kex_send_kexinit: no kex, cannot rekey"); 172 return; 173 } 174 if (kex->flags & KEX_INIT_SENT) { 175 debug("KEX_INIT_SENT"); 176 return; 177 } 178 kex->done = 0; 179 180 /* generate a random cookie */ 181 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 182 fatal("kex_send_kexinit: kex proposal too short"); 183 cookie = buffer_ptr(&kex->my); 184 for (i = 0; i < KEX_COOKIE_LEN; i++) { 185 if (i % 4 == 0) 186 rnd = arc4random(); 187 cookie[i] = rnd; 188 rnd >>= 8; 189 } 190 packet_start(SSH2_MSG_KEXINIT); 191 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 192 packet_send(); 193 debug("SSH2_MSG_KEXINIT sent"); 194 kex->flags |= KEX_INIT_SENT; 195 } 196 197 void 198 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 199 { 200 char *ptr; 201 u_int i, dlen; 202 Kex *kex = (Kex *)ctxt; 203 204 debug("SSH2_MSG_KEXINIT received"); 205 if (kex == NULL) 206 fatal("kex_input_kexinit: no kex, cannot rekey"); 207 208 ptr = packet_get_raw(&dlen); 209 buffer_append(&kex->peer, ptr, dlen); 210 211 /* discard packet */ 212 for (i = 0; i < KEX_COOKIE_LEN; i++) 213 packet_get_char(); 214 for (i = 0; i < PROPOSAL_MAX; i++) 215 xfree(packet_get_string(NULL)); 216 (void) packet_get_char(); 217 (void) packet_get_int(); 218 packet_check_eom(); 219 220 kex_kexinit_finish(kex); 221 } 222 223 Kex * 224 kex_setup(char *proposal[PROPOSAL_MAX]) 225 { 226 Kex *kex; 227 228 kex = xcalloc(1, sizeof(*kex)); 229 buffer_init(&kex->peer); 230 buffer_init(&kex->my); 231 kex_prop2buf(&kex->my, proposal); 232 kex->done = 0; 233 234 kex_send_kexinit(kex); /* we start */ 235 kex_reset_dispatch(); 236 237 return kex; 238 } 239 240 static void 241 kex_kexinit_finish(Kex *kex) 242 { 243 if (!(kex->flags & KEX_INIT_SENT)) 244 kex_send_kexinit(kex); 245 246 kex_choose_conf(kex); 247 248 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 249 kex->kex[kex->kex_type] != NULL) { 250 (kex->kex[kex->kex_type])(kex); 251 } else { 252 fatal("Unsupported key exchange %d", kex->kex_type); 253 } 254 } 255 256 static void 257 choose_enc(Enc *enc, char *client, char *server) 258 { 259 char *name = match_list(client, server, NULL); 260 if (name == NULL) 261 fatal("no matching cipher found: client %s server %s", client, server); 262 if ((enc->cipher = cipher_by_name(name)) == NULL) 263 fatal("matching cipher is not supported: %s", name); 264 enc->name = name; 265 enc->enabled = 0; 266 enc->iv = NULL; 267 enc->key = NULL; 268 enc->key_len = cipher_keylen(enc->cipher); 269 enc->block_size = cipher_blocksize(enc->cipher); 270 } 271 272 static void 273 choose_mac(Mac *mac, char *client, char *server) 274 { 275 char *name = match_list(client, server, NULL); 276 if (name == NULL) 277 fatal("no matching mac found: client %s server %s", client, server); 278 if (mac_init(mac, name) < 0) 279 fatal("unsupported mac %s", name); 280 /* truncate the key */ 281 if (datafellows & SSH_BUG_HMAC) 282 mac->key_len = 16; 283 mac->name = name; 284 mac->key = NULL; 285 mac->enabled = 0; 286 } 287 288 static void 289 choose_comp(Comp *comp, char *client, char *server) 290 { 291 char *name = match_list(client, server, NULL); 292 if (name == NULL) 293 fatal("no matching comp found: client %s server %s", client, server); 294 if (strcmp(name, "zlib@openssh.com") == 0) { 295 comp->type = COMP_DELAYED; 296 } else if (strcmp(name, "zlib") == 0) { 297 comp->type = COMP_ZLIB; 298 } else if (strcmp(name, "none") == 0) { 299 comp->type = COMP_NONE; 300 } else { 301 fatal("unsupported comp %s", name); 302 } 303 comp->name = name; 304 } 305 306 static void 307 choose_kex(Kex *k, char *client, char *server) 308 { 309 k->name = match_list(client, server, NULL); 310 if (k->name == NULL) 311 fatal("no kex alg"); 312 if (strcmp(k->name, KEX_DH1) == 0) { 313 k->kex_type = KEX_DH_GRP1_SHA1; 314 k->evp_md = EVP_sha1(); 315 } else if (strcmp(k->name, KEX_DH14) == 0) { 316 k->kex_type = KEX_DH_GRP14_SHA1; 317 k->evp_md = EVP_sha1(); 318 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 319 k->kex_type = KEX_DH_GEX_SHA1; 320 k->evp_md = EVP_sha1(); 321 #if OPENSSL_VERSION_NUMBER >= 0x00907000L 322 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 323 k->kex_type = KEX_DH_GEX_SHA256; 324 k->evp_md = evp_ssh_sha256(); 325 #endif 326 } else 327 fatal("bad kex alg %s", k->name); 328 } 329 330 static void 331 choose_hostkeyalg(Kex *k, char *client, char *server) 332 { 333 char *hostkeyalg = match_list(client, server, NULL); 334 if (hostkeyalg == NULL) 335 fatal("no hostkey alg"); 336 k->hostkey_type = key_type_from_name(hostkeyalg); 337 if (k->hostkey_type == KEY_UNSPEC) 338 fatal("bad hostkey alg '%s'", hostkeyalg); 339 xfree(hostkeyalg); 340 } 341 342 static int 343 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 344 { 345 static int check[] = { 346 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 347 }; 348 int *idx; 349 char *p; 350 351 for (idx = &check[0]; *idx != -1; idx++) { 352 if ((p = strchr(my[*idx], ',')) != NULL) 353 *p = '\0'; 354 if ((p = strchr(peer[*idx], ',')) != NULL) 355 *p = '\0'; 356 if (strcmp(my[*idx], peer[*idx]) != 0) { 357 debug2("proposal mismatch: my %s peer %s", 358 my[*idx], peer[*idx]); 359 return (0); 360 } 361 } 362 debug2("proposals match"); 363 return (1); 364 } 365 366 static void 367 kex_choose_conf(Kex *kex) 368 { 369 Newkeys *newkeys; 370 char **my, **peer; 371 char **cprop, **sprop; 372 int nenc, nmac, ncomp; 373 u_int mode, ctos, need; 374 int first_kex_follows, type; 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) || (kex->server && mode == MODE_IN); 392 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 393 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 394 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 395 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 396 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 397 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 398 debug("kex: %s %s %s %s", 399 ctos ? "client->server" : "server->client", 400 newkeys->enc.name, 401 newkeys->mac.name, 402 newkeys->comp.name); 403 } 404 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 405 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 406 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 407 need = 0; 408 for (mode = 0; mode < MODE_MAX; mode++) { 409 newkeys = kex->newkeys[mode]; 410 if (need < newkeys->enc.key_len) 411 need = newkeys->enc.key_len; 412 if (need < newkeys->enc.block_size) 413 need = newkeys->enc.block_size; 414 if (need < newkeys->mac.key_len) 415 need = newkeys->mac.key_len; 416 } 417 /* XXX need runden? */ 418 kex->we_need = need; 419 420 /* ignore the next message if the proposals do not match */ 421 if (first_kex_follows && !proposals_match(my, peer) && 422 !(datafellows & SSH_BUG_FIRSTKEX)) { 423 type = packet_read(); 424 debug2("skipping next packet (type %u)", type); 425 } 426 427 kex_prop_free(my); 428 kex_prop_free(peer); 429 } 430 431 static u_char * 432 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 433 BIGNUM *shared_secret) 434 { 435 Buffer b; 436 EVP_MD_CTX md; 437 char c = id; 438 u_int have; 439 int mdsz; 440 u_char *digest; 441 442 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 443 fatal("bad kex md size %d", mdsz); 444 digest = xmalloc(roundup(need, mdsz)); 445 446 buffer_init(&b); 447 buffer_put_bignum2(&b, shared_secret); 448 449 /* K1 = HASH(K || H || "A" || session_id) */ 450 EVP_DigestInit(&md, kex->evp_md); 451 if (!(datafellows & SSH_BUG_DERIVEKEY)) 452 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 453 EVP_DigestUpdate(&md, hash, hashlen); 454 EVP_DigestUpdate(&md, &c, 1); 455 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 456 EVP_DigestFinal(&md, digest, NULL); 457 458 /* 459 * expand key: 460 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 461 * Key = K1 || K2 || ... || Kn 462 */ 463 for (have = mdsz; need > have; have += mdsz) { 464 EVP_DigestInit(&md, kex->evp_md); 465 if (!(datafellows & SSH_BUG_DERIVEKEY)) 466 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 467 EVP_DigestUpdate(&md, hash, hashlen); 468 EVP_DigestUpdate(&md, digest, have); 469 EVP_DigestFinal(&md, digest + have, NULL); 470 } 471 buffer_free(&b); 472 #ifdef DEBUG_KEX 473 fprintf(stderr, "key '%c'== ", c); 474 dump_digest("key", digest, need); 475 #endif 476 return digest; 477 } 478 479 Newkeys *current_keys[MODE_MAX]; 480 481 #define NKEYS 6 482 void 483 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 484 { 485 u_char *keys[NKEYS]; 486 u_int i, mode, ctos; 487 488 for (i = 0; i < NKEYS; i++) { 489 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 490 shared_secret); 491 } 492 493 debug2("kex_derive_keys"); 494 for (mode = 0; mode < MODE_MAX; mode++) { 495 current_keys[mode] = kex->newkeys[mode]; 496 kex->newkeys[mode] = NULL; 497 ctos = (!kex->server && mode == MODE_OUT) || 498 (kex->server && mode == MODE_IN); 499 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 500 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 501 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 502 } 503 } 504 505 Newkeys * 506 kex_get_newkeys(int mode) 507 { 508 Newkeys *ret; 509 510 ret = current_keys[mode]; 511 current_keys[mode] = NULL; 512 return ret; 513 } 514 515 void 516 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 517 u_int8_t cookie[8], u_int8_t id[16]) 518 { 519 const EVP_MD *evp_md = EVP_md5(); 520 EVP_MD_CTX md; 521 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 522 int len; 523 524 EVP_DigestInit(&md, evp_md); 525 526 len = BN_num_bytes(host_modulus); 527 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 528 fatal("%s: bad host modulus (len %d)", __func__, len); 529 BN_bn2bin(host_modulus, nbuf); 530 EVP_DigestUpdate(&md, nbuf, len); 531 532 len = BN_num_bytes(server_modulus); 533 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 534 fatal("%s: bad server modulus (len %d)", __func__, len); 535 BN_bn2bin(server_modulus, nbuf); 536 EVP_DigestUpdate(&md, nbuf, len); 537 538 EVP_DigestUpdate(&md, cookie, 8); 539 540 EVP_DigestFinal(&md, obuf, NULL); 541 memcpy(id, obuf, 16); 542 543 memset(nbuf, 0, sizeof(nbuf)); 544 memset(obuf, 0, sizeof(obuf)); 545 memset(&md, 0, sizeof(md)); 546 } 547 548 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 549 void 550 dump_digest(char *msg, u_char *digest, int len) 551 { 552 u_int i; 553 554 fprintf(stderr, "%s\n", msg); 555 for (i = 0; i< len; i++) { 556 fprintf(stderr, "%02x", digest[i]); 557 if (i%32 == 31) 558 fprintf(stderr, "\n"); 559 else if (i%8 == 7) 560 fprintf(stderr, " "); 561 } 562 fprintf(stderr, "\n"); 563 } 564 #endif 565