1 /* $OpenBSD: kex.c,v 1.77 2007/01/21 01:41:54 stevesk 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 extern const EVP_MD *evp_ssh_sha256(void); 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 static 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 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 %d ", 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 static void 118 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 119 { 120 error("Hm, kex protocol error: type %d seq %u", type, seq); 121 } 122 123 static void 124 kex_reset_dispatch(void) 125 { 126 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 127 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 128 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 129 } 130 131 void 132 kex_finish(Kex *kex) 133 { 134 kex_reset_dispatch(); 135 136 packet_start(SSH2_MSG_NEWKEYS); 137 packet_send(); 138 /* packet_write_wait(); */ 139 debug("SSH2_MSG_NEWKEYS sent"); 140 141 debug("expecting SSH2_MSG_NEWKEYS"); 142 packet_read_expect(SSH2_MSG_NEWKEYS); 143 packet_check_eom(); 144 debug("SSH2_MSG_NEWKEYS received"); 145 146 kex->done = 1; 147 buffer_clear(&kex->peer); 148 /* buffer_clear(&kex->my); */ 149 kex->flags &= ~KEX_INIT_SENT; 150 xfree(kex->name); 151 kex->name = NULL; 152 } 153 154 void 155 kex_send_kexinit(Kex *kex) 156 { 157 u_int32_t rnd = 0; 158 u_char *cookie; 159 u_int i; 160 161 if (kex == NULL) { 162 error("kex_send_kexinit: no kex, cannot rekey"); 163 return; 164 } 165 if (kex->flags & KEX_INIT_SENT) { 166 debug("KEX_INIT_SENT"); 167 return; 168 } 169 kex->done = 0; 170 171 /* generate a random cookie */ 172 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 173 fatal("kex_send_kexinit: kex proposal too short"); 174 cookie = buffer_ptr(&kex->my); 175 for (i = 0; i < KEX_COOKIE_LEN; i++) { 176 if (i % 4 == 0) 177 rnd = arc4random(); 178 cookie[i] = rnd; 179 rnd >>= 8; 180 } 181 packet_start(SSH2_MSG_KEXINIT); 182 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 183 packet_send(); 184 debug("SSH2_MSG_KEXINIT sent"); 185 kex->flags |= KEX_INIT_SENT; 186 } 187 188 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", client, server); 253 if ((enc->cipher = cipher_by_name(name)) == NULL) 254 fatal("matching cipher is not supported: %s", name); 255 enc->name = name; 256 enc->enabled = 0; 257 enc->iv = NULL; 258 enc->key = NULL; 259 enc->key_len = cipher_keylen(enc->cipher); 260 enc->block_size = cipher_blocksize(enc->cipher); 261 } 262 263 static void 264 choose_mac(Mac *mac, char *client, char *server) 265 { 266 char *name = match_list(client, server, NULL); 267 if (name == NULL) 268 fatal("no matching mac found: client %s server %s", client, server); 269 if (mac_init(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("no kex alg"); 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_ssh_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) || (kex->server && mode == MODE_IN); 381 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 382 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 383 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 384 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 385 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 386 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 387 debug("kex: %s %s %s %s", 388 ctos ? "client->server" : "server->client", 389 newkeys->enc.name, 390 newkeys->mac.name, 391 newkeys->comp.name); 392 } 393 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 394 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 395 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 396 need = 0; 397 for (mode = 0; mode < MODE_MAX; mode++) { 398 newkeys = kex->newkeys[mode]; 399 if (need < newkeys->enc.key_len) 400 need = newkeys->enc.key_len; 401 if (need < newkeys->enc.block_size) 402 need = newkeys->enc.block_size; 403 if (need < newkeys->mac.key_len) 404 need = newkeys->mac.key_len; 405 } 406 /* XXX need runden? */ 407 kex->we_need = need; 408 409 /* ignore the next message if the proposals do not match */ 410 if (first_kex_follows && !proposals_match(my, peer) && 411 !(datafellows & SSH_BUG_FIRSTKEX)) { 412 type = packet_read(); 413 debug2("skipping next packet (type %u)", type); 414 } 415 416 kex_prop_free(my); 417 kex_prop_free(peer); 418 } 419 420 static u_char * 421 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 422 BIGNUM *shared_secret) 423 { 424 Buffer b; 425 EVP_MD_CTX md; 426 char c = id; 427 u_int have; 428 int mdsz; 429 u_char *digest; 430 431 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 432 fatal("bad kex md size %d", mdsz); 433 digest = xmalloc(roundup(need, mdsz)); 434 435 buffer_init(&b); 436 buffer_put_bignum2(&b, shared_secret); 437 438 /* K1 = HASH(K || H || "A" || session_id) */ 439 EVP_DigestInit(&md, kex->evp_md); 440 if (!(datafellows & SSH_BUG_DERIVEKEY)) 441 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 442 EVP_DigestUpdate(&md, hash, hashlen); 443 EVP_DigestUpdate(&md, &c, 1); 444 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 445 EVP_DigestFinal(&md, digest, NULL); 446 447 /* 448 * expand key: 449 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 450 * Key = K1 || K2 || ... || Kn 451 */ 452 for (have = mdsz; need > have; have += mdsz) { 453 EVP_DigestInit(&md, kex->evp_md); 454 if (!(datafellows & SSH_BUG_DERIVEKEY)) 455 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 456 EVP_DigestUpdate(&md, hash, hashlen); 457 EVP_DigestUpdate(&md, digest, have); 458 EVP_DigestFinal(&md, digest + have, NULL); 459 } 460 buffer_free(&b); 461 #ifdef DEBUG_KEX 462 fprintf(stderr, "key '%c'== ", c); 463 dump_digest("key", digest, need); 464 #endif 465 return digest; 466 } 467 468 Newkeys *current_keys[MODE_MAX]; 469 470 #define NKEYS 6 471 void 472 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 473 { 474 u_char *keys[NKEYS]; 475 u_int i, mode, ctos; 476 477 for (i = 0; i < NKEYS; i++) { 478 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 479 shared_secret); 480 } 481 482 debug2("kex_derive_keys"); 483 for (mode = 0; mode < MODE_MAX; mode++) { 484 current_keys[mode] = kex->newkeys[mode]; 485 kex->newkeys[mode] = NULL; 486 ctos = (!kex->server && mode == MODE_OUT) || 487 (kex->server && mode == MODE_IN); 488 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 489 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 490 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 491 } 492 } 493 494 Newkeys * 495 kex_get_newkeys(int mode) 496 { 497 Newkeys *ret; 498 499 ret = current_keys[mode]; 500 current_keys[mode] = NULL; 501 return ret; 502 } 503 504 void 505 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 506 u_int8_t cookie[8], u_int8_t id[16]) 507 { 508 const EVP_MD *evp_md = EVP_md5(); 509 EVP_MD_CTX md; 510 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 511 int len; 512 513 EVP_DigestInit(&md, evp_md); 514 515 len = BN_num_bytes(host_modulus); 516 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 517 fatal("%s: bad host modulus (len %d)", __func__, len); 518 BN_bn2bin(host_modulus, nbuf); 519 EVP_DigestUpdate(&md, nbuf, len); 520 521 len = BN_num_bytes(server_modulus); 522 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 523 fatal("%s: bad server modulus (len %d)", __func__, len); 524 BN_bn2bin(server_modulus, nbuf); 525 EVP_DigestUpdate(&md, nbuf, len); 526 527 EVP_DigestUpdate(&md, cookie, 8); 528 529 EVP_DigestFinal(&md, obuf, NULL); 530 memcpy(id, obuf, 16); 531 532 memset(nbuf, 0, sizeof(nbuf)); 533 memset(obuf, 0, sizeof(obuf)); 534 memset(&md, 0, sizeof(md)); 535 } 536 537 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 538 void 539 dump_digest(char *msg, u_char *digest, int len) 540 { 541 u_int i; 542 543 fprintf(stderr, "%s\n", msg); 544 for (i = 0; i < len; i++) { 545 fprintf(stderr, "%02x", digest[i]); 546 if (i%32 == 31) 547 fprintf(stderr, "\n"); 548 else if (i%8 == 7) 549 fprintf(stderr, " "); 550 } 551 fprintf(stderr, "\n"); 552 } 553 #endif 554