1 /* 2 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23 */ 24 25 #include "includes.h" 26 RCSID("$OpenBSD: kex.c,v 1.65 2005/11/04 05:15:59 djm Exp $"); 27 28 #include <openssl/crypto.h> 29 30 #include "ssh2.h" 31 #include "xmalloc.h" 32 #include "buffer.h" 33 #include "bufaux.h" 34 #include "packet.h" 35 #include "compat.h" 36 #include "cipher.h" 37 #include "kex.h" 38 #include "key.h" 39 #include "log.h" 40 #include "mac.h" 41 #include "match.h" 42 #include "dispatch.h" 43 #include "monitor.h" 44 45 #define KEX_COOKIE_LEN 16 46 47 /* prototype */ 48 static void kex_kexinit_finish(Kex *); 49 static void kex_choose_conf(Kex *); 50 51 /* put algorithm proposal into buffer */ 52 static void 53 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 54 { 55 u_int i; 56 57 buffer_clear(b); 58 /* 59 * add a dummy cookie, the cookie will be overwritten by 60 * kex_send_kexinit(), each time a kexinit is set 61 */ 62 for (i = 0; i < KEX_COOKIE_LEN; i++) 63 buffer_put_char(b, 0); 64 for (i = 0; i < PROPOSAL_MAX; i++) 65 buffer_put_cstring(b, proposal[i]); 66 buffer_put_char(b, 0); /* first_kex_packet_follows */ 67 buffer_put_int(b, 0); /* uint32 reserved */ 68 } 69 70 /* parse buffer and return algorithm proposal */ 71 static char ** 72 kex_buf2prop(Buffer *raw, int *first_kex_follows) 73 { 74 Buffer b; 75 int i; 76 char **proposal; 77 78 proposal = xmalloc(PROPOSAL_MAX * sizeof(char *)); 79 80 buffer_init(&b); 81 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 82 /* skip cookie */ 83 for (i = 0; i < KEX_COOKIE_LEN; i++) 84 buffer_get_char(&b); 85 /* extract kex init proposal strings */ 86 for (i = 0; i < PROPOSAL_MAX; i++) { 87 proposal[i] = buffer_get_string(&b,NULL); 88 debug2("kex_parse_kexinit: %s", proposal[i]); 89 } 90 /* first kex follows / reserved */ 91 i = buffer_get_char(&b); 92 if (first_kex_follows != NULL) 93 *first_kex_follows = i; 94 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 95 i = buffer_get_int(&b); 96 debug2("kex_parse_kexinit: reserved %d ", i); 97 buffer_free(&b); 98 return proposal; 99 } 100 101 static void 102 kex_prop_free(char **proposal) 103 { 104 u_int i; 105 106 for (i = 0; i < PROPOSAL_MAX; i++) 107 xfree(proposal[i]); 108 xfree(proposal); 109 } 110 111 static void 112 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 113 { 114 error("Hm, kex protocol error: type %d seq %u", type, seq); 115 } 116 117 static void 118 kex_reset_dispatch(void) 119 { 120 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 121 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 122 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 123 } 124 125 void 126 kex_finish(Kex *kex) 127 { 128 kex_reset_dispatch(); 129 130 packet_start(SSH2_MSG_NEWKEYS); 131 packet_send(); 132 /* packet_write_wait(); */ 133 debug("SSH2_MSG_NEWKEYS sent"); 134 135 debug("expecting SSH2_MSG_NEWKEYS"); 136 packet_read_expect(SSH2_MSG_NEWKEYS); 137 packet_check_eom(); 138 debug("SSH2_MSG_NEWKEYS received"); 139 140 kex->done = 1; 141 buffer_clear(&kex->peer); 142 /* buffer_clear(&kex->my); */ 143 kex->flags &= ~KEX_INIT_SENT; 144 xfree(kex->name); 145 kex->name = NULL; 146 } 147 148 void 149 kex_send_kexinit(Kex *kex) 150 { 151 u_int32_t rnd = 0; 152 u_char *cookie; 153 u_int i; 154 155 if (kex == NULL) { 156 error("kex_send_kexinit: no kex, cannot rekey"); 157 return; 158 } 159 if (kex->flags & KEX_INIT_SENT) { 160 debug("KEX_INIT_SENT"); 161 return; 162 } 163 kex->done = 0; 164 165 /* generate a random cookie */ 166 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 167 fatal("kex_send_kexinit: kex proposal too short"); 168 cookie = buffer_ptr(&kex->my); 169 for (i = 0; i < KEX_COOKIE_LEN; i++) { 170 if (i % 4 == 0) 171 rnd = arc4random(); 172 cookie[i] = rnd; 173 rnd >>= 8; 174 } 175 packet_start(SSH2_MSG_KEXINIT); 176 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 177 packet_send(); 178 debug("SSH2_MSG_KEXINIT sent"); 179 kex->flags |= KEX_INIT_SENT; 180 } 181 182 void 183 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 184 { 185 char *ptr; 186 u_int i, dlen; 187 Kex *kex = (Kex *)ctxt; 188 189 debug("SSH2_MSG_KEXINIT received"); 190 if (kex == NULL) 191 fatal("kex_input_kexinit: no kex, cannot rekey"); 192 193 ptr = packet_get_raw(&dlen); 194 buffer_append(&kex->peer, ptr, dlen); 195 196 /* discard packet */ 197 for (i = 0; i < KEX_COOKIE_LEN; i++) 198 packet_get_char(); 199 for (i = 0; i < PROPOSAL_MAX; i++) 200 xfree(packet_get_string(NULL)); 201 (void) packet_get_char(); 202 (void) packet_get_int(); 203 packet_check_eom(); 204 205 kex_kexinit_finish(kex); 206 } 207 208 Kex * 209 kex_setup(char *proposal[PROPOSAL_MAX]) 210 { 211 Kex *kex; 212 213 kex = xmalloc(sizeof(*kex)); 214 memset(kex, 0, sizeof(*kex)); 215 buffer_init(&kex->peer); 216 buffer_init(&kex->my); 217 kex_prop2buf(&kex->my, proposal); 218 kex->done = 0; 219 220 kex_send_kexinit(kex); /* we start */ 221 kex_reset_dispatch(); 222 223 return kex; 224 } 225 226 static void 227 kex_kexinit_finish(Kex *kex) 228 { 229 if (!(kex->flags & KEX_INIT_SENT)) 230 kex_send_kexinit(kex); 231 232 kex_choose_conf(kex); 233 234 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 235 kex->kex[kex->kex_type] != NULL) { 236 (kex->kex[kex->kex_type])(kex); 237 } else { 238 fatal("Unsupported key exchange %d", kex->kex_type); 239 } 240 } 241 242 static void 243 choose_enc(Enc *enc, char *client, char *server) 244 { 245 char *name = match_list(client, server, NULL); 246 if (name == NULL) 247 fatal("no matching cipher found: client %s server %s", client, server); 248 if ((enc->cipher = cipher_by_name(name)) == NULL) 249 fatal("matching cipher is not supported: %s", name); 250 enc->name = name; 251 enc->enabled = 0; 252 enc->iv = NULL; 253 enc->key = NULL; 254 enc->key_len = cipher_keylen(enc->cipher); 255 enc->block_size = cipher_blocksize(enc->cipher); 256 } 257 static void 258 choose_mac(Mac *mac, char *client, char *server) 259 { 260 char *name = match_list(client, server, NULL); 261 if (name == NULL) 262 fatal("no matching mac found: client %s server %s", client, server); 263 if (mac_init(mac, name) < 0) 264 fatal("unsupported mac %s", name); 265 /* truncate the key */ 266 if (datafellows & SSH_BUG_HMAC) 267 mac->key_len = 16; 268 mac->name = name; 269 mac->key = NULL; 270 mac->enabled = 0; 271 } 272 static void 273 choose_comp(Comp *comp, char *client, char *server) 274 { 275 char *name = match_list(client, server, NULL); 276 if (name == NULL) 277 fatal("no matching comp found: client %s server %s", client, server); 278 if (strcmp(name, "zlib@openssh.com") == 0) { 279 comp->type = COMP_DELAYED; 280 } else if (strcmp(name, "zlib") == 0) { 281 comp->type = COMP_ZLIB; 282 } else if (strcmp(name, "none") == 0) { 283 comp->type = COMP_NONE; 284 } else { 285 fatal("unsupported comp %s", name); 286 } 287 comp->name = name; 288 } 289 static void 290 choose_kex(Kex *k, char *client, char *server) 291 { 292 k->name = match_list(client, server, NULL); 293 if (k->name == NULL) 294 fatal("no kex alg"); 295 if (strcmp(k->name, KEX_DH1) == 0) { 296 k->kex_type = KEX_DH_GRP1_SHA1; 297 k->evp_md = EVP_sha1(); 298 } else if (strcmp(k->name, KEX_DH14) == 0) { 299 k->kex_type = KEX_DH_GRP14_SHA1; 300 k->evp_md = EVP_sha1(); 301 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 302 k->kex_type = KEX_DH_GEX_SHA1; 303 k->evp_md = EVP_sha1(); 304 } else 305 fatal("bad kex alg %s", k->name); 306 } 307 308 static void 309 choose_hostkeyalg(Kex *k, char *client, char *server) 310 { 311 char *hostkeyalg = match_list(client, server, NULL); 312 if (hostkeyalg == NULL) 313 fatal("no hostkey alg"); 314 k->hostkey_type = key_type_from_name(hostkeyalg); 315 if (k->hostkey_type == KEY_UNSPEC) 316 fatal("bad hostkey alg '%s'", hostkeyalg); 317 xfree(hostkeyalg); 318 } 319 320 static int 321 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 322 { 323 static int check[] = { 324 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 325 }; 326 int *idx; 327 char *p; 328 329 for (idx = &check[0]; *idx != -1; idx++) { 330 if ((p = strchr(my[*idx], ',')) != NULL) 331 *p = '\0'; 332 if ((p = strchr(peer[*idx], ',')) != NULL) 333 *p = '\0'; 334 if (strcmp(my[*idx], peer[*idx]) != 0) { 335 debug2("proposal mismatch: my %s peer %s", 336 my[*idx], peer[*idx]); 337 return (0); 338 } 339 } 340 debug2("proposals match"); 341 return (1); 342 } 343 344 static void 345 kex_choose_conf(Kex *kex) 346 { 347 Newkeys *newkeys; 348 char **my, **peer; 349 char **cprop, **sprop; 350 int nenc, nmac, ncomp; 351 u_int mode, ctos, need; 352 int first_kex_follows, type; 353 354 my = kex_buf2prop(&kex->my, NULL); 355 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 356 357 if (kex->server) { 358 cprop=peer; 359 sprop=my; 360 } else { 361 cprop=my; 362 sprop=peer; 363 } 364 365 /* Algorithm Negotiation */ 366 for (mode = 0; mode < MODE_MAX; mode++) { 367 newkeys = xmalloc(sizeof(*newkeys)); 368 memset(newkeys, 0, sizeof(*newkeys)); 369 kex->newkeys[mode] = newkeys; 370 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 371 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 372 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 373 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 374 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 375 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 376 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 377 debug("kex: %s %s %s %s", 378 ctos ? "client->server" : "server->client", 379 newkeys->enc.name, 380 newkeys->mac.name, 381 newkeys->comp.name); 382 } 383 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 384 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 385 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 386 need = 0; 387 for (mode = 0; mode < MODE_MAX; mode++) { 388 newkeys = kex->newkeys[mode]; 389 if (need < newkeys->enc.key_len) 390 need = newkeys->enc.key_len; 391 if (need < newkeys->enc.block_size) 392 need = newkeys->enc.block_size; 393 if (need < newkeys->mac.key_len) 394 need = newkeys->mac.key_len; 395 } 396 /* XXX need runden? */ 397 kex->we_need = need; 398 399 /* ignore the next message if the proposals do not match */ 400 if (first_kex_follows && !proposals_match(my, peer) && 401 !(datafellows & SSH_BUG_FIRSTKEX)) { 402 type = packet_read(); 403 debug2("skipping next packet (type %u)", type); 404 } 405 406 kex_prop_free(my); 407 kex_prop_free(peer); 408 } 409 410 static u_char * 411 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 412 BIGNUM *shared_secret) 413 { 414 Buffer b; 415 EVP_MD_CTX md; 416 char c = id; 417 u_int have; 418 int mdsz; 419 u_char *digest; 420 421 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 422 fatal("bad kex md size %d", mdsz); 423 digest = xmalloc(roundup(need, mdsz)); 424 425 buffer_init(&b); 426 buffer_put_bignum2(&b, shared_secret); 427 428 /* K1 = HASH(K || H || "A" || session_id) */ 429 EVP_DigestInit(&md, kex->evp_md); 430 if (!(datafellows & SSH_BUG_DERIVEKEY)) 431 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 432 EVP_DigestUpdate(&md, hash, hashlen); 433 EVP_DigestUpdate(&md, &c, 1); 434 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 435 EVP_DigestFinal(&md, digest, NULL); 436 437 /* 438 * expand key: 439 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 440 * Key = K1 || K2 || ... || Kn 441 */ 442 for (have = mdsz; need > have; have += mdsz) { 443 EVP_DigestInit(&md, kex->evp_md); 444 if (!(datafellows & SSH_BUG_DERIVEKEY)) 445 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 446 EVP_DigestUpdate(&md, hash, hashlen); 447 EVP_DigestUpdate(&md, digest, have); 448 EVP_DigestFinal(&md, digest + have, NULL); 449 } 450 buffer_free(&b); 451 #ifdef DEBUG_KEX 452 fprintf(stderr, "key '%c'== ", c); 453 dump_digest("key", digest, need); 454 #endif 455 return digest; 456 } 457 458 Newkeys *current_keys[MODE_MAX]; 459 460 #define NKEYS 6 461 void 462 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 463 { 464 u_char *keys[NKEYS]; 465 u_int i, mode, ctos; 466 467 for (i = 0; i < NKEYS; i++) { 468 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 469 shared_secret); 470 } 471 472 debug2("kex_derive_keys"); 473 for (mode = 0; mode < MODE_MAX; mode++) { 474 current_keys[mode] = kex->newkeys[mode]; 475 kex->newkeys[mode] = NULL; 476 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 477 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 478 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 479 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 480 } 481 } 482 483 Newkeys * 484 kex_get_newkeys(int mode) 485 { 486 Newkeys *ret; 487 488 ret = current_keys[mode]; 489 current_keys[mode] = NULL; 490 return ret; 491 } 492 493 void 494 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 495 u_int8_t cookie[8], u_int8_t id[16]) 496 { 497 const EVP_MD *evp_md = EVP_md5(); 498 EVP_MD_CTX md; 499 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 500 int len; 501 502 EVP_DigestInit(&md, evp_md); 503 504 len = BN_num_bytes(host_modulus); 505 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 506 fatal("%s: bad host modulus (len %d)", __func__, len); 507 BN_bn2bin(host_modulus, nbuf); 508 EVP_DigestUpdate(&md, nbuf, len); 509 510 len = BN_num_bytes(server_modulus); 511 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 512 fatal("%s: bad server modulus (len %d)", __func__, len); 513 BN_bn2bin(server_modulus, nbuf); 514 EVP_DigestUpdate(&md, nbuf, len); 515 516 EVP_DigestUpdate(&md, cookie, 8); 517 518 EVP_DigestFinal(&md, obuf, NULL); 519 memcpy(id, obuf, 16); 520 521 memset(nbuf, 0, sizeof(nbuf)); 522 memset(obuf, 0, sizeof(obuf)); 523 memset(&md, 0, sizeof(md)); 524 } 525 526 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 527 void 528 dump_digest(char *msg, u_char *digest, int len) 529 { 530 u_int i; 531 532 fprintf(stderr, "%s\n", msg); 533 for (i = 0; i< len; i++) { 534 fprintf(stderr, "%02x", digest[i]); 535 if (i%32 == 31) 536 fprintf(stderr, "\n"); 537 else if (i%8 == 7) 538 fprintf(stderr, " "); 539 } 540 fprintf(stderr, "\n"); 541 } 542 #endif 543