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 1.56 2003/11/21 11:57:03 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 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 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 rand = 0; 152 u_char *cookie; 153 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 rand = arc4random(); 172 cookie[i] = rand; 173 rand >>= 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 int dlen; 187 int i; 188 Kex *kex = (Kex *)ctxt; 189 190 debug("SSH2_MSG_KEXINIT received"); 191 if (kex == NULL) 192 fatal("kex_input_kexinit: no kex, cannot rekey"); 193 194 ptr = packet_get_raw(&dlen); 195 buffer_append(&kex->peer, ptr, dlen); 196 197 /* discard packet */ 198 for (i = 0; i < KEX_COOKIE_LEN; i++) 199 packet_get_char(); 200 for (i = 0; i < PROPOSAL_MAX; i++) 201 xfree(packet_get_string(NULL)); 202 (void) packet_get_char(); 203 (void) packet_get_int(); 204 packet_check_eom(); 205 206 kex_kexinit_finish(kex); 207 } 208 209 Kex * 210 kex_setup(char *proposal[PROPOSAL_MAX]) 211 { 212 Kex *kex; 213 214 kex = xmalloc(sizeof(*kex)); 215 memset(kex, 0, sizeof(*kex)); 216 buffer_init(&kex->peer); 217 buffer_init(&kex->my); 218 kex_prop2buf(&kex->my, proposal); 219 kex->done = 0; 220 221 kex_send_kexinit(kex); /* we start */ 222 kex_reset_dispatch(); 223 224 return kex; 225 } 226 227 static void 228 kex_kexinit_finish(Kex *kex) 229 { 230 if (!(kex->flags & KEX_INIT_SENT)) 231 kex_send_kexinit(kex); 232 233 kex_choose_conf(kex); 234 235 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && 236 kex->kex[kex->kex_type] != NULL) { 237 (kex->kex[kex->kex_type])(kex); 238 } else { 239 fatal("Unsupported key exchange %d", kex->kex_type); 240 } 241 } 242 243 static void 244 choose_enc(Enc *enc, char *client, char *server) 245 { 246 char *name = match_list(client, server, NULL); 247 if (name == NULL) 248 fatal("no matching cipher found: client %s server %s", client, server); 249 if ((enc->cipher = cipher_by_name(name)) == NULL) 250 fatal("matching cipher is not supported: %s", name); 251 enc->name = name; 252 enc->enabled = 0; 253 enc->iv = NULL; 254 enc->key = NULL; 255 enc->key_len = cipher_keylen(enc->cipher); 256 enc->block_size = cipher_blocksize(enc->cipher); 257 } 258 static void 259 choose_mac(Mac *mac, char *client, char *server) 260 { 261 char *name = match_list(client, server, NULL); 262 if (name == NULL) 263 fatal("no matching mac found: client %s server %s", client, server); 264 if (mac_init(mac, name) < 0) 265 fatal("unsupported mac %s", name); 266 /* truncate the key */ 267 if (datafellows & SSH_BUG_HMAC) 268 mac->key_len = 16; 269 mac->name = name; 270 mac->key = NULL; 271 mac->enabled = 0; 272 } 273 static void 274 choose_comp(Comp *comp, char *client, char *server) 275 { 276 char *name = match_list(client, server, NULL); 277 if (name == NULL) 278 fatal("no matching comp found: client %s server %s", client, server); 279 if (strcmp(name, "zlib") == 0) { 280 comp->type = 1; 281 } else if (strcmp(name, "none") == 0) { 282 comp->type = 0; 283 } else { 284 fatal("unsupported comp %s", name); 285 } 286 comp->name = name; 287 } 288 static void 289 choose_kex(Kex *k, char *client, char *server) 290 { 291 k->name = match_list(client, server, NULL); 292 if (k->name == NULL) 293 fatal("no kex alg"); 294 if (strcmp(k->name, KEX_DH1) == 0) { 295 k->kex_type = KEX_DH_GRP1_SHA1; 296 } else if (strcmp(k->name, KEX_DHGEX) == 0) { 297 k->kex_type = KEX_DH_GEX_SHA1; 298 } else 299 fatal("bad kex alg %s", k->name); 300 } 301 static void 302 choose_hostkeyalg(Kex *k, char *client, char *server) 303 { 304 char *hostkeyalg = match_list(client, server, NULL); 305 if (hostkeyalg == NULL) 306 fatal("no hostkey alg"); 307 k->hostkey_type = key_type_from_name(hostkeyalg); 308 if (k->hostkey_type == KEY_UNSPEC) 309 fatal("bad hostkey alg '%s'", hostkeyalg); 310 xfree(hostkeyalg); 311 } 312 313 static int 314 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) 315 { 316 static int check[] = { 317 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 318 }; 319 int *idx; 320 char *p; 321 322 for (idx = &check[0]; *idx != -1; idx++) { 323 if ((p = strchr(my[*idx], ',')) != NULL) 324 *p = '\0'; 325 if ((p = strchr(peer[*idx], ',')) != NULL) 326 *p = '\0'; 327 if (strcmp(my[*idx], peer[*idx]) != 0) { 328 debug2("proposal mismatch: my %s peer %s", 329 my[*idx], peer[*idx]); 330 return (0); 331 } 332 } 333 debug2("proposals match"); 334 return (1); 335 } 336 337 static void 338 kex_choose_conf(Kex *kex) 339 { 340 Newkeys *newkeys; 341 char **my, **peer; 342 char **cprop, **sprop; 343 int nenc, nmac, ncomp; 344 int mode; 345 int ctos; /* direction: if true client-to-server */ 346 int need; 347 int first_kex_follows, type; 348 349 my = kex_buf2prop(&kex->my, NULL); 350 peer = kex_buf2prop(&kex->peer, &first_kex_follows); 351 352 if (kex->server) { 353 cprop=peer; 354 sprop=my; 355 } else { 356 cprop=my; 357 sprop=peer; 358 } 359 360 /* Algorithm Negotiation */ 361 for (mode = 0; mode < MODE_MAX; mode++) { 362 newkeys = xmalloc(sizeof(*newkeys)); 363 memset(newkeys, 0, sizeof(*newkeys)); 364 kex->newkeys[mode] = newkeys; 365 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 366 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 367 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 368 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 369 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 370 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 371 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 372 debug("kex: %s %s %s %s", 373 ctos ? "client->server" : "server->client", 374 newkeys->enc.name, 375 newkeys->mac.name, 376 newkeys->comp.name); 377 } 378 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 379 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 380 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 381 need = 0; 382 for (mode = 0; mode < MODE_MAX; mode++) { 383 newkeys = kex->newkeys[mode]; 384 if (need < newkeys->enc.key_len) 385 need = newkeys->enc.key_len; 386 if (need < newkeys->enc.block_size) 387 need = newkeys->enc.block_size; 388 if (need < newkeys->mac.key_len) 389 need = newkeys->mac.key_len; 390 } 391 /* XXX need runden? */ 392 kex->we_need = need; 393 394 /* ignore the next message if the proposals do not match */ 395 if (first_kex_follows && !proposals_match(my, peer) && 396 !(datafellows & SSH_BUG_FIRSTKEX)) { 397 type = packet_read(); 398 debug2("skipping next packet (type %u)", type); 399 } 400 401 kex_prop_free(my); 402 kex_prop_free(peer); 403 } 404 405 static u_char * 406 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) 407 { 408 Buffer b; 409 const EVP_MD *evp_md = EVP_sha1(); 410 EVP_MD_CTX md; 411 char c = id; 412 int have; 413 int mdsz = EVP_MD_size(evp_md); 414 u_char *digest = xmalloc(roundup(need, mdsz)); 415 416 buffer_init(&b); 417 buffer_put_bignum2(&b, shared_secret); 418 419 /* K1 = HASH(K || H || "A" || session_id) */ 420 EVP_DigestInit(&md, evp_md); 421 if (!(datafellows & SSH_BUG_DERIVEKEY)) 422 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 423 EVP_DigestUpdate(&md, hash, mdsz); 424 EVP_DigestUpdate(&md, &c, 1); 425 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 426 EVP_DigestFinal(&md, digest, NULL); 427 428 /* 429 * expand key: 430 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 431 * Key = K1 || K2 || ... || Kn 432 */ 433 for (have = mdsz; need > have; have += mdsz) { 434 EVP_DigestInit(&md, evp_md); 435 if (!(datafellows & SSH_BUG_DERIVEKEY)) 436 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 437 EVP_DigestUpdate(&md, hash, mdsz); 438 EVP_DigestUpdate(&md, digest, have); 439 EVP_DigestFinal(&md, digest + have, NULL); 440 } 441 buffer_free(&b); 442 #ifdef DEBUG_KEX 443 fprintf(stderr, "key '%c'== ", c); 444 dump_digest("key", digest, need); 445 #endif 446 return digest; 447 } 448 449 Newkeys *current_keys[MODE_MAX]; 450 451 #define NKEYS 6 452 void 453 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) 454 { 455 u_char *keys[NKEYS]; 456 int i, mode, ctos; 457 458 for (i = 0; i < NKEYS; i++) 459 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); 460 461 debug2("kex_derive_keys"); 462 for (mode = 0; mode < MODE_MAX; mode++) { 463 current_keys[mode] = kex->newkeys[mode]; 464 kex->newkeys[mode] = NULL; 465 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 466 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 467 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 468 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 469 } 470 } 471 472 Newkeys * 473 kex_get_newkeys(int mode) 474 { 475 Newkeys *ret; 476 477 ret = current_keys[mode]; 478 current_keys[mode] = NULL; 479 return ret; 480 } 481 482 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 483 void 484 dump_digest(char *msg, u_char *digest, int len) 485 { 486 int i; 487 488 fprintf(stderr, "%s\n", msg); 489 for (i = 0; i< len; i++) { 490 fprintf(stderr, "%02x", digest[i]); 491 if (i%32 == 31) 492 fprintf(stderr, "\n"); 493 else if (i%8 == 7) 494 fprintf(stderr, " "); 495 } 496 fprintf(stderr, "\n"); 497 } 498 #endif 499