kex.c revision 221420
1/* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 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 "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#include "roaming.h" 52 53#if OPENSSL_VERSION_NUMBER >= 0x00907000L 54# if defined(HAVE_EVP_SHA256) 55# define evp_ssh_sha256 EVP_sha256 56# else 57extern const EVP_MD *evp_ssh_sha256(void); 58# endif 59#endif 60 61/* prototype */ 62static void kex_kexinit_finish(Kex *); 63static void kex_choose_conf(Kex *); 64 65/* Validate KEX method name list */ 66int 67kex_names_valid(const char *names) 68{ 69 char *s, *cp, *p; 70 71 if (names == NULL || strcmp(names, "") == 0) 72 return 0; 73 s = cp = xstrdup(names); 74 for ((p = strsep(&cp, ",")); p && *p != '\0'; 75 (p = strsep(&cp, ","))) { 76 if (strcmp(p, KEX_DHGEX_SHA256) != 0 && 77 strcmp(p, KEX_DHGEX_SHA1) != 0 && 78 strcmp(p, KEX_DH14) != 0 && 79 strcmp(p, KEX_DH1) != 0 && 80 (strncmp(p, KEX_ECDH_SHA2_STEM, 81 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 || 82 kex_ecdh_name_to_nid(p) == -1)) { 83 error("Unsupported KEX algorithm \"%.100s\"", p); 84 xfree(s); 85 return 0; 86 } 87 } 88 debug3("kex names ok: [%s]", names); 89 xfree(s); 90 return 1; 91} 92 93/* put algorithm proposal into buffer */ 94static void 95kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 96{ 97 u_int i; 98 99 buffer_clear(b); 100 /* 101 * add a dummy cookie, the cookie will be overwritten by 102 * kex_send_kexinit(), each time a kexinit is set 103 */ 104 for (i = 0; i < KEX_COOKIE_LEN; i++) 105 buffer_put_char(b, 0); 106 for (i = 0; i < PROPOSAL_MAX; i++) 107 buffer_put_cstring(b, proposal[i]); 108 buffer_put_char(b, 0); /* first_kex_packet_follows */ 109 buffer_put_int(b, 0); /* uint32 reserved */ 110} 111 112/* parse buffer and return algorithm proposal */ 113static char ** 114kex_buf2prop(Buffer *raw, int *first_kex_follows) 115{ 116 Buffer b; 117 u_int i; 118 char **proposal; 119 120 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *)); 121 122 buffer_init(&b); 123 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 124 /* skip cookie */ 125 for (i = 0; i < KEX_COOKIE_LEN; i++) 126 buffer_get_char(&b); 127 /* extract kex init proposal strings */ 128 for (i = 0; i < PROPOSAL_MAX; i++) { 129 proposal[i] = buffer_get_cstring(&b,NULL); 130 debug2("kex_parse_kexinit: %s", proposal[i]); 131 } 132 /* first kex follows / reserved */ 133 i = buffer_get_char(&b); 134 if (first_kex_follows != NULL) 135 *first_kex_follows = i; 136 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 137 i = buffer_get_int(&b); 138 debug2("kex_parse_kexinit: reserved %u ", i); 139 buffer_free(&b); 140 return proposal; 141} 142 143static void 144kex_prop_free(char **proposal) 145{ 146 u_int i; 147 148 for (i = 0; i < PROPOSAL_MAX; i++) 149 xfree(proposal[i]); 150 xfree(proposal); 151} 152 153/* ARGSUSED */ 154static void 155kex_protocol_error(int type, u_int32_t seq, void *ctxt) 156{ 157 error("Hm, kex protocol error: type %d seq %u", type, seq); 158} 159 160static void 161kex_reset_dispatch(void) 162{ 163 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 164 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 165 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 166} 167 168void 169kex_finish(Kex *kex) 170{ 171 kex_reset_dispatch(); 172 173 packet_start(SSH2_MSG_NEWKEYS); 174 packet_send(); 175 /* packet_write_wait(); */ 176 debug("SSH2_MSG_NEWKEYS sent"); 177 178 debug("expecting SSH2_MSG_NEWKEYS"); 179 packet_read_expect(SSH2_MSG_NEWKEYS); 180 packet_check_eom(); 181 debug("SSH2_MSG_NEWKEYS received"); 182 183 kex->done = 1; 184 buffer_clear(&kex->peer); 185 /* buffer_clear(&kex->my); */ 186 kex->flags &= ~KEX_INIT_SENT; 187 xfree(kex->name); 188 kex->name = NULL; 189} 190 191void 192kex_send_kexinit(Kex *kex) 193{ 194 u_int32_t rnd = 0; 195 u_char *cookie; 196 u_int i; 197 198 if (kex == NULL) { 199 error("kex_send_kexinit: no kex, cannot rekey"); 200 return; 201 } 202 if (kex->flags & KEX_INIT_SENT) { 203 debug("KEX_INIT_SENT"); 204 return; 205 } 206 kex->done = 0; 207 208 /* generate a random cookie */ 209 if (buffer_len(&kex->my) < KEX_COOKIE_LEN) 210 fatal("kex_send_kexinit: kex proposal too short"); 211 cookie = buffer_ptr(&kex->my); 212 for (i = 0; i < KEX_COOKIE_LEN; i++) { 213 if (i % 4 == 0) 214 rnd = arc4random(); 215 cookie[i] = rnd; 216 rnd >>= 8; 217 } 218 packet_start(SSH2_MSG_KEXINIT); 219 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 220 packet_send(); 221 debug("SSH2_MSG_KEXINIT sent"); 222 kex->flags |= KEX_INIT_SENT; 223} 224 225/* ARGSUSED */ 226void 227kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 228{ 229 char *ptr; 230 u_int i, dlen; 231 Kex *kex = (Kex *)ctxt; 232 233 debug("SSH2_MSG_KEXINIT received"); 234 if (kex == NULL) 235 fatal("kex_input_kexinit: no kex, cannot rekey"); 236 237 ptr = packet_get_raw(&dlen); 238 buffer_append(&kex->peer, ptr, dlen); 239 240 /* discard packet */ 241 for (i = 0; i < KEX_COOKIE_LEN; i++) 242 packet_get_char(); 243 for (i = 0; i < PROPOSAL_MAX; i++) 244 xfree(packet_get_string(NULL)); 245 (void) packet_get_char(); 246 (void) packet_get_int(); 247 packet_check_eom(); 248 249 kex_kexinit_finish(kex); 250} 251 252Kex * 253kex_setup(char *proposal[PROPOSAL_MAX]) 254{ 255 Kex *kex; 256 257 kex = xcalloc(1, sizeof(*kex)); 258 buffer_init(&kex->peer); 259 buffer_init(&kex->my); 260 kex_prop2buf(&kex->my, proposal); 261 kex->done = 0; 262 263 kex_send_kexinit(kex); /* we start */ 264 kex_reset_dispatch(); 265 266 return kex; 267} 268 269static void 270kex_kexinit_finish(Kex *kex) 271{ 272 if (!(kex->flags & KEX_INIT_SENT)) 273 kex_send_kexinit(kex); 274 275 kex_choose_conf(kex); 276 277 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 278 kex->kex[kex->kex_type] != NULL) { 279 (kex->kex[kex->kex_type])(kex); 280 } else { 281 fatal("Unsupported key exchange %d", kex->kex_type); 282 } 283} 284 285static void 286choose_enc(Enc *enc, char *client, char *server) 287{ 288 char *name = match_list(client, server, NULL); 289 if (name == NULL) 290 fatal("no matching cipher found: client %s server %s", 291 client, server); 292 if ((enc->cipher = cipher_by_name(name)) == NULL) 293 fatal("matching cipher is not supported: %s", name); 294 enc->name = name; 295 enc->enabled = 0; 296 enc->iv = NULL; 297 enc->key = NULL; 298 enc->key_len = cipher_keylen(enc->cipher); 299 enc->block_size = cipher_blocksize(enc->cipher); 300} 301 302static void 303choose_mac(Mac *mac, char *client, char *server) 304{ 305 char *name = match_list(client, server, NULL); 306 if (name == NULL) 307 fatal("no matching mac found: client %s server %s", 308 client, server); 309 if (mac_setup(mac, name) < 0) 310 fatal("unsupported mac %s", name); 311 /* truncate the key */ 312 if (datafellows & SSH_BUG_HMAC) 313 mac->key_len = 16; 314 mac->name = name; 315 mac->key = NULL; 316 mac->enabled = 0; 317} 318 319static void 320choose_comp(Comp *comp, char *client, char *server) 321{ 322 char *name = match_list(client, server, NULL); 323 if (name == NULL) 324 fatal("no matching comp found: client %s server %s", client, server); 325 if (strcmp(name, "zlib@openssh.com") == 0) { 326 comp->type = COMP_DELAYED; 327 } else if (strcmp(name, "zlib") == 0) { 328 comp->type = COMP_ZLIB; 329 } else if (strcmp(name, "none") == 0) { 330 comp->type = COMP_NONE; 331 } else { 332 fatal("unsupported comp %s", name); 333 } 334 comp->name = name; 335} 336 337static void 338choose_kex(Kex *k, char *client, char *server) 339{ 340 k->name = match_list(client, server, NULL); 341 if (k->name == NULL) 342 fatal("Unable to negotiate a key exchange method"); 343 if (strcmp(k->name, KEX_DH1) == 0) { 344 k->kex_type = KEX_DH_GRP1_SHA1; 345 k->evp_md = EVP_sha1(); 346 } else if (strcmp(k->name, KEX_DH14) == 0) { 347 k->kex_type = KEX_DH_GRP14_SHA1; 348 k->evp_md = EVP_sha1(); 349 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) { 350 k->kex_type = KEX_DH_GEX_SHA1; 351 k->evp_md = EVP_sha1(); 352#if OPENSSL_VERSION_NUMBER >= 0x00907000L 353 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) { 354 k->kex_type = KEX_DH_GEX_SHA256; 355 k->evp_md = evp_ssh_sha256(); 356 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM, 357 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) { 358 k->kex_type = KEX_ECDH_SHA2; 359 k->evp_md = kex_ecdh_name_to_evpmd(k->name); 360#endif 361 } else 362 fatal("bad kex alg %s", k->name); 363} 364 365static void 366choose_hostkeyalg(Kex *k, char *client, char *server) 367{ 368 char *hostkeyalg = match_list(client, server, NULL); 369 if (hostkeyalg == NULL) 370 fatal("no hostkey alg"); 371 k->hostkey_type = key_type_from_name(hostkeyalg); 372 if (k->hostkey_type == KEY_UNSPEC) 373 fatal("bad hostkey alg '%s'", hostkeyalg); 374 xfree(hostkeyalg); 375} 376 377static int 378proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 379{ 380 static int check[] = { 381 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 382 }; 383 int *idx; 384 char *p; 385 386 for (idx = &check[0]; *idx != -1; idx++) { 387 if ((p = strchr(my[*idx], ',')) != NULL) 388 *p = '\0'; 389 if ((p = strchr(peer[*idx], ',')) != NULL) 390 *p = '\0'; 391 if (strcmp(my[*idx], peer[*idx]) != 0) { 392 debug2("proposal mismatch: my %s peer %s", 393 my[*idx], peer[*idx]); 394 return (0); 395 } 396 } 397 debug2("proposals match"); 398 return (1); 399} 400 401static void 402kex_choose_conf(Kex *kex) 403{ 404 Newkeys *newkeys; 405 char **my, **peer; 406 char **cprop, **sprop; 407 int nenc, nmac, ncomp; 408 u_int mode, ctos, need; 409 int first_kex_follows, type; 410 411 my = kex_buf2prop(&kex->my, NULL); 412 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 413 414 if (kex->server) { 415 cprop=peer; 416 sprop=my; 417 } else { 418 cprop=my; 419 sprop=peer; 420 } 421 422 /* Check whether server offers roaming */ 423 if (!kex->server) { 424 char *roaming; 425 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL); 426 if (roaming) { 427 kex->roaming = 1; 428 xfree(roaming); 429 } 430 } 431 432 /* Algorithm Negotiation */ 433 for (mode = 0; mode < MODE_MAX; mode++) { 434 newkeys = xcalloc(1, sizeof(*newkeys)); 435 kex->newkeys[mode] = newkeys; 436 ctos = (!kex->server && mode == MODE_OUT) || 437 (kex->server && mode == MODE_IN); 438 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 439 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 440 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 441 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 442 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 443 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 444 debug("kex: %s %s %s %s", 445 ctos ? "client->server" : "server->client", 446 newkeys->enc.name, 447 newkeys->mac.name, 448 newkeys->comp.name); 449 } 450 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 451 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 452 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 453 need = 0; 454 for (mode = 0; mode < MODE_MAX; mode++) { 455 newkeys = kex->newkeys[mode]; 456 if (need < newkeys->enc.key_len) 457 need = newkeys->enc.key_len; 458 if (need < newkeys->enc.block_size) 459 need = newkeys->enc.block_size; 460 if (need < newkeys->mac.key_len) 461 need = newkeys->mac.key_len; 462 } 463 /* XXX need runden? */ 464 kex->we_need = need; 465 466 /* ignore the next message if the proposals do not match */ 467 if (first_kex_follows && !proposals_match(my, peer) && 468 !(datafellows & SSH_BUG_FIRSTKEX)) { 469 type = packet_read(); 470 debug2("skipping next packet (type %u)", type); 471 } 472 473 kex_prop_free(my); 474 kex_prop_free(peer); 475} 476 477static u_char * 478derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen, 479 BIGNUM *shared_secret) 480{ 481 Buffer b; 482 EVP_MD_CTX md; 483 char c = id; 484 u_int have; 485 int mdsz; 486 u_char *digest; 487 488 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0) 489 fatal("bad kex md size %d", mdsz); 490 digest = xmalloc(roundup(need, mdsz)); 491 492 buffer_init(&b); 493 buffer_put_bignum2(&b, shared_secret); 494 495 /* K1 = HASH(K || H || "A" || session_id) */ 496 EVP_DigestInit(&md, kex->evp_md); 497 if (!(datafellows & SSH_BUG_DERIVEKEY)) 498 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 499 EVP_DigestUpdate(&md, hash, hashlen); 500 EVP_DigestUpdate(&md, &c, 1); 501 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 502 EVP_DigestFinal(&md, digest, NULL); 503 504 /* 505 * expand key: 506 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 507 * Key = K1 || K2 || ... || Kn 508 */ 509 for (have = mdsz; need > have; have += mdsz) { 510 EVP_DigestInit(&md, kex->evp_md); 511 if (!(datafellows & SSH_BUG_DERIVEKEY)) 512 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 513 EVP_DigestUpdate(&md, hash, hashlen); 514 EVP_DigestUpdate(&md, digest, have); 515 EVP_DigestFinal(&md, digest + have, NULL); 516 } 517 buffer_free(&b); 518#ifdef DEBUG_KEX 519 fprintf(stderr, "key '%c'== ", c); 520 dump_digest("key", digest, need); 521#endif 522 return digest; 523} 524 525Newkeys *current_keys[MODE_MAX]; 526 527#define NKEYS 6 528void 529kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret) 530{ 531 u_char *keys[NKEYS]; 532 u_int i, mode, ctos; 533 534 for (i = 0; i < NKEYS; i++) { 535 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen, 536 shared_secret); 537 } 538 539 debug2("kex_derive_keys"); 540 for (mode = 0; mode < MODE_MAX; mode++) { 541 current_keys[mode] = kex->newkeys[mode]; 542 kex->newkeys[mode] = NULL; 543 ctos = (!kex->server && mode == MODE_OUT) || 544 (kex->server && mode == MODE_IN); 545 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 546 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 547 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 548 } 549} 550 551Newkeys * 552kex_get_newkeys(int mode) 553{ 554 Newkeys *ret; 555 556 ret = current_keys[mode]; 557 current_keys[mode] = NULL; 558 return ret; 559} 560 561void 562derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus, 563 u_int8_t cookie[8], u_int8_t id[16]) 564{ 565 const EVP_MD *evp_md = EVP_md5(); 566 EVP_MD_CTX md; 567 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE]; 568 int len; 569 570 EVP_DigestInit(&md, evp_md); 571 572 len = BN_num_bytes(host_modulus); 573 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 574 fatal("%s: bad host modulus (len %d)", __func__, len); 575 BN_bn2bin(host_modulus, nbuf); 576 EVP_DigestUpdate(&md, nbuf, len); 577 578 len = BN_num_bytes(server_modulus); 579 if (len < (512 / 8) || (u_int)len > sizeof(nbuf)) 580 fatal("%s: bad server modulus (len %d)", __func__, len); 581 BN_bn2bin(server_modulus, nbuf); 582 EVP_DigestUpdate(&md, nbuf, len); 583 584 EVP_DigestUpdate(&md, cookie, 8); 585 586 EVP_DigestFinal(&md, obuf, NULL); 587 memcpy(id, obuf, 16); 588 589 memset(nbuf, 0, sizeof(nbuf)); 590 memset(obuf, 0, sizeof(obuf)); 591 memset(&md, 0, sizeof(md)); 592} 593 594#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH) 595void 596dump_digest(char *msg, u_char *digest, int len) 597{ 598 int i; 599 600 fprintf(stderr, "%s\n", msg); 601 for (i = 0; i < len; i++) { 602 fprintf(stderr, "%02x", digest[i]); 603 if (i%32 == 31) 604 fprintf(stderr, "\n"); 605 else if (i%8 == 7) 606 fprintf(stderr, " "); 607 } 608 fprintf(stderr, "\n"); 609} 610#endif 611