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 <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 #define KEX_COOKIE_LEN 16 50 51 /* prototype */ 52 static void kex_kexinit_finish(Kex *); 53 static void kex_choose_conf(Kex *); 54 55 /* put algorithm proposal into buffer */ 56 static void 57 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 58 { 59 u_int i; 60 61 buffer_clear(b); 62 /* 63 * add a dummy cookie, the cookie will be overwritten by 64 * kex_send_kexinit(), each time a kexinit is set 65 */ 66 for (i = 0; i < KEX_COOKIE_LEN; i++) 67 buffer_put_char(b, 0); 68 for (i = 0; i < PROPOSAL_MAX; i++) 69 buffer_put_cstring(b, proposal[i]); 70 buffer_put_char(b, 0); /* first_kex_packet_follows */ 71 buffer_put_int(b, 0); /* uint32 reserved */ 72 } 73 74 /* parse buffer and return algorithm proposal */ 75 static char ** 76 kex_buf2prop(Buffer *raw, int *first_kex_follows) 77 { 78 Buffer b; 79 u_int i; 80 char **proposal; 81 82 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 83 84 buffer_init(&b); 85 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 86 /* skip cookie */ 87 for (i = 0; i < KEX_COOKIE_LEN; i++) 88 buffer_get_char(&b); 89 /* extract kex init proposal strings */ 90 for (i = 0; i < PROPOSAL_MAX; i++) { 91 proposal[i] = buffer_get_string(&b,NULL); 92 debug2("kex_parse_kexinit: %s", proposal[i]); 93 } 94 /* first kex follows / reserved */ 95 i = buffer_get_char(&b); 96 if (first_kex_follows != NULL) 97 *first_kex_follows = i; 98 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 99 i = buffer_get_int(&b); 100 debug2("kex_parse_kexinit: reserved %u ", i); 101 buffer_free(&b); 102 return proposal; 103 } 104 105 static void 106 kex_prop_free(char **proposal) 107 { 108 u_int i; 109 110 for (i = 0; i < PROPOSAL_MAX; i++) 111 xfree(proposal[i]); 112 xfree(proposal); 113 } 114 115 /* ARGSUSED */ 116 static void 117 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 118 { 119 error("Hm, kex protocol error: type %d seq %u", type, seq); 120 } 121 122 static void 123 kex_reset_dispatch(void) 124 { 125 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 126 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 127 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 128 } 129 130 void 131 kex_finish(Kex *kex) 132 { 133 kex_reset_dispatch(); 134 135 packet_start(SSH2_MSG_NEWKEYS); 136 packet_send(); 137 /* packet_write_wait(); */ 138 debug("SSH2_MSG_NEWKEYS sent"); 139 140 debug("expecting SSH2_MSG_NEWKEYS"); 141 packet_read_expect(SSH2_MSG_NEWKEYS); 142 packet_check_eom(); 143 debug("SSH2_MSG_NEWKEYS received"); 144 145 kex->done = 1; 146 buffer_clear(&kex->peer); 147 /* buffer_clear(&kex->my); */ 148 kex->flags &= ~KEX_INIT_SENT; 149 xfree(kex->name); 150 kex->name = NULL; 151 } 152 153 void 154 kex_send_kexinit(Kex *kex) 155 { 156 u_int32_t rnd = 0; 157 u_char *cookie; 158 u_int i; 159 160 if (kex == NULL) { 161 error("kex_send_kexinit: no kex, cannot rekey"); 162 return; 163 } 164 if (kex->flags & KEX_INIT_SENT) { 165 debug("KEX_INIT_SENT"); 166 return; 167 } 168 kex->done = 0; 169 170 /* generate a random cookie */ 171 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 172 fatal("kex_send_kexinit: kex proposal too short"); 173 cookie = buffer_ptr(&kex->my); 174 for (i = 0; i < KEX_COOKIE_LEN; i++) { 175 if (i % 4 == 0) 176 rnd = arc4random(); 177 cookie[i] = rnd; 178 rnd >>= 8; 179 } 180 packet_start(SSH2_MSG_KEXINIT); 181 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 182 packet_send(); 183 debug("SSH2_MSG_KEXINIT sent"); 184 kex->flags |= KEX_INIT_SENT; 185 } 186 187 /* ARGSUSED */ 188 void 189 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 190 { 191 char *ptr; 192 u_int i, dlen; 193 Kex *kex = (Kex *)ctxt; 194 195 debug("SSH2_MSG_KEXINIT received"); 196 if (kex == NULL) 197 fatal("kex_input_kexinit: no kex, cannot rekey"); 198 199 ptr = packet_get_raw(&dlen); 200 buffer_append(&kex->peer, ptr, dlen); 201 202 /* discard packet */ 203 for (i = 0; i < KEX_COOKIE_LEN; i++) 204 packet_get_char(); 205 for (i = 0; i < PROPOSAL_MAX; i++) 206 xfree(packet_get_string(NULL)); 207 (void) packet_get_char(); 208 (void) packet_get_int(); 209 packet_check_eom(); 210 211 kex_kexinit_finish(kex); 212 } 213 214 Kex * 215 kex_setup(char *proposal[PROPOSAL_MAX]) 216 { 217 Kex *kex; 218 219 kex = xcalloc(1, sizeof(*kex)); 220 buffer_init(&kex->peer); 221 buffer_init(&kex->my); 222 kex_prop2buf(&kex->my, proposal); 223 kex->done = 0; 224 225 kex_send_kexinit(kex); /* we start */ 226 kex_reset_dispatch(); 227 228 return kex; 229 } 230 231 static void 232 kex_kexinit_finish(Kex *kex) 233 { 234 if (!(kex->flags & KEX_INIT_SENT)) 235 kex_send_kexinit(kex); 236 237 kex_choose_conf(kex); 238 239 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 240 kex->kex[kex->kex_type] != NULL) { 241 (kex->kex[kex->kex_type])(kex); 242 } else { 243 fatal("Unsupported key exchange %d", kex->kex_type); 244 } 245 } 246 247 static void 248 choose_enc(Enc *enc, char *client, char *server) 249 { 250 char *name = match_list(client, server, NULL); 251 if (name == NULL) 252 fatal("no matching cipher found: client %s server %s", 253 client, server); 254 if ((enc->cipher = cipher_by_name(name)) == NULL) 255 fatal("matching cipher is not supported: %s", name); 256 enc->name = name; 257 enc->enabled = 0; 258 enc->iv = NULL; 259 enc->key = NULL; 260 enc->key_len = cipher_keylen(enc->cipher); 261 enc->block_size = cipher_blocksize(enc->cipher); 262 } 263 264 static void 265 choose_mac(Mac *mac, char *client, char *server) 266 { 267 char *name = match_list(client, server, NULL); 268 if (name == NULL) 269 fatal("no matching mac found: client %s server %s", 270 client, server); 271 if (mac_setup(mac, name) < 0) 272 fatal("unsupported mac %s", name); 273 /* truncate the key */ 274 if (datafellows & SSH_BUG_HMAC) 275 mac->key_len = 16; 276 mac->name = name; 277 mac->key = NULL; 278 mac->enabled = 0; 279 } 280 281 static void 282 choose_comp(Comp *comp, char *client, char *server) 283 { 284 char *name = match_list(client, server, NULL); 285 if (name == NULL) 286 fatal("no matching comp found: client %s server %s", client, server); 287 if (strcmp(name, "zlib@openssh.com") == 0) { 288 comp->type = COMP_DELAYED; 289 } else if (strcmp(name, "zlib") == 0) { 290 comp->type = COMP_ZLIB; 291 } else if (strcmp(name, "none") == 0) { 292 comp->type = COMP_NONE; 293 } else { 294 fatal("unsupported comp %s", name); 295 } 296 comp->name = name; 297 } 298 299 static void 300 choose_kex(Kex *k, char *client, char *server) 301 { 302 k->name = match_list(client, server, NULL); 303 if (k->name == NULL) 304 fatal("Unable to negotiate a key exchange method"); 305 if (strcmp(k->name, KEX_DH1) == 0) { 306 k->kex_type = KEX_DH_GRP1_SHA1; 307 k->evp_md = EVP_sha1(); 308 } else if (strcmp(k->name, KEX_DH14) == 0) { 309 k->kex_type = KEX_DH_GRP14_SHA1; 310 k->evp_md = EVP_sha1(); 311 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 312 k->kex_type = KEX_DH_GEX_SHA1; 313 k->evp_md = EVP_sha1(); 314 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 315 k->kex_type = KEX_DH_GEX_SHA256; 316 k->evp_md = EVP_sha256(); 317 } else 318 fatal("bad kex alg %s", k->name); 319 } 320 321 static void 322 choose_hostkeyalg(Kex *k, char *client, char *server) 323 { 324 char *hostkeyalg = match_list(client, server, NULL); 325 if (hostkeyalg == NULL) 326 fatal("no hostkey alg"); 327 k->hostkey_type = key_type_from_name(hostkeyalg); 328 if (k->hostkey_type == KEY_UNSPEC) 329 fatal("bad hostkey alg '%s'", hostkeyalg); 330 xfree(hostkeyalg); 331 } 332 333 static int 334 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 335 { 336 static int check[] = { 337 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 338 }; 339 int *idx; 340 char *p; 341 342 for (idx = &check[0]; *idx != -1; idx++) { 343 if ((p = strchr(my[*idx], ',')) != NULL) 344 *p = '\0'; 345 if ((p = strchr(peer[*idx], ',')) != NULL) 346 *p = '\0'; 347 if (strcmp(my[*idx], peer[*idx]) != 0) { 348 debug2("proposal mismatch: my %s peer %s", 349 my[*idx], peer[*idx]); 350 return (0); 351 } 352 } 353 debug2("proposals match"); 354 return (1); 355 } 356 357 static void 358 kex_choose_conf(Kex *kex) 359 { 360 Newkeys *newkeys; 361 char **my, **peer; 362 char **cprop, **sprop; 363 int nenc, nmac, ncomp; 364 u_int mode, ctos, need; 365 int first_kex_follows, type; 366 367 my = kex_buf2prop(&kex->my, NULL); 368 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 369 370 if (kex->server) { 371 cprop=peer; 372 sprop=my; 373 } else { 374 cprop=my; 375 sprop=peer; 376 } 377 378 /* Algorithm Negotiation */ 379 for (mode = 0; mode < MODE_MAX; mode++) { 380 newkeys = xcalloc(1, sizeof(*newkeys)); 381 kex->newkeys[mode] = newkeys; 382 ctos = (!kex->server && mode == MODE_OUT) || 383 (kex->server && mode == MODE_IN); 384 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 385 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 386 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 387 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 388 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 389 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 390 debug("kex: %s %s %s %s", 391 ctos ? "client->server" : "server->client", 392 newkeys->enc.name, 393 newkeys->mac.name, 394 newkeys->comp.name); 395 } 396 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 397 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 398 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 399 need = 0; 400 for (mode = 0; mode < MODE_MAX; mode++) { 401 newkeys = kex->newkeys[mode]; 402 if (need < newkeys->enc.key_len) 403 need = newkeys->enc.key_len; 404 if (need < newkeys->enc.block_size) 405 need = newkeys->enc.block_size; 406 if (need < newkeys->mac.key_len) 407 need = newkeys->mac.key_len; 408 } 409 /* XXX need runden? */ 410 kex->we_need = need; 411 412 /* ignore the next message if the proposals do not match */ 413 if (first_kex_follows && !proposals_match(my, peer) && 414 !(datafellows & SSH_BUG_FIRSTKEX)) { 415 type = packet_read(); 416 debug2("skipping next packet (type %u)", type); 417 } 418 419 kex_prop_free(my); 420 kex_prop_free(peer); 421 } 422 423 static u_char * 424 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 425 BIGNUM *shared_secret) 426 { 427 Buffer b; 428 EVP_MD_CTX md; 429 char c = id; 430 u_int have; 431 int mdsz; 432 u_char *digest; 433 434 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 435 fatal("bad kex md size %d", mdsz); 436 digest = xmalloc(roundup(need, mdsz)); 437 438 buffer_init(&b); 439 buffer_put_bignum2(&b, shared_secret); 440 441 /* K1 = HASH(K || H || "A" || session_id) */ 442 EVP_DigestInit(&md, kex->evp_md); 443 if (!(datafellows & SSH_BUG_DERIVEKEY)) 444 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 445 EVP_DigestUpdate(&md, hash, hashlen); 446 EVP_DigestUpdate(&md, &c, 1); 447 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 448 EVP_DigestFinal(&md, digest, NULL); 449 450 /* 451 * expand key: 452 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 453 * Key = K1 || K2 || ... || Kn 454 */ 455 for (have = mdsz; need > have; have += mdsz) { 456 EVP_DigestInit(&md, kex->evp_md); 457 if (!(datafellows & SSH_BUG_DERIVEKEY)) 458 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 459 EVP_DigestUpdate(&md, hash, hashlen); 460 EVP_DigestUpdate(&md, digest, have); 461 EVP_DigestFinal(&md, digest + have, NULL); 462 } 463 buffer_free(&b); 464 #ifdef DEBUG_KEX 465 fprintf(stderr, "key '%c'== ", c); 466 dump_digest("key", digest, need); 467 #endif 468 return digest; 469 } 470 471 Newkeys *current_keys[MODE_MAX]; 472 473 #define NKEYS 6 474 void 475 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 476 { 477 u_char *keys[NKEYS]; 478 u_int i, mode, ctos; 479 480 for (i = 0; i < NKEYS; i++) { 481 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 482 shared_secret); 483 } 484 485 debug2("kex_derive_keys"); 486 for (mode = 0; mode < MODE_MAX; mode++) { 487 current_keys[mode] = kex->newkeys[mode]; 488 kex->newkeys[mode] = NULL; 489 ctos = (!kex->server && mode == MODE_OUT) || 490 (kex->server && mode == MODE_IN); 491 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 492 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 493 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 494 } 495 } 496 497 Newkeys * 498 kex_get_newkeys(int mode) 499 { 500 Newkeys *ret; 501 502 ret = current_keys[mode]; 503 current_keys[mode] = NULL; 504 return ret; 505 } 506 507 void 508 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 509 u_int8_t cookie[8], u_int8_t id[16]) 510 { 511 const EVP_MD *evp_md = EVP_md5(); 512 EVP_MD_CTX md; 513 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 514 int len; 515 516 EVP_DigestInit(&md, evp_md); 517 518 len = BN_num_bytes(host_modulus); 519 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 520 fatal("%s: bad host modulus (len %d)", __func__, len); 521 BN_bn2bin(host_modulus, nbuf); 522 EVP_DigestUpdate(&md, nbuf, len); 523 524 len = BN_num_bytes(server_modulus); 525 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 526 fatal("%s: bad server modulus (len %d)", __func__, len); 527 BN_bn2bin(server_modulus, nbuf); 528 EVP_DigestUpdate(&md, nbuf, len); 529 530 EVP_DigestUpdate(&md, cookie, 8); 531 532 EVP_DigestFinal(&md, obuf, NULL); 533 memcpy(id, obuf, 16); 534 535 memset(nbuf, 0, sizeof(nbuf)); 536 memset(obuf, 0, sizeof(obuf)); 537 memset(&md, 0, sizeof(md)); 538 } 539 540 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 541 void 542 dump_digest(char *msg, u_char *digest, int len) 543 { 544 u_int i; 545 546 fprintf(stderr, "%s\n", msg); 547 for (i = 0; i < len; i++) { 548 fprintf(stderr, "%02x", digest[i]); 549 if (i%32 == 31) 550 fprintf(stderr, "\n"); 551 else if (i%8 == 7) 552 fprintf(stderr, " "); 553 } 554 fprintf(stderr, "\n"); 555 } 556 #endif 557