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 1.47 2002/02/28 15:46:33 markus 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 44 #define KEX_COOKIE_LEN 16 45 46 /* prototype */ 47 static void kex_kexinit_finish(Kex *); 48 static void kex_choose_conf(Kex *); 49 50 /* put algorithm proposal into buffer */ 51 static void 52 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 53 { 54 u_int32_t rand = 0; 55 int i; 56 57 buffer_clear(b); 58 for (i = 0; i < KEX_COOKIE_LEN; i++) { 59 if (i % 4 == 0) 60 rand = arc4random(); 61 buffer_put_char(b, rand & 0xff); 62 rand >>= 8; 63 } 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) 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 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 93 i = buffer_get_int(&b); 94 debug2("kex_parse_kexinit: reserved %d ", i); 95 buffer_free(&b); 96 return proposal; 97 } 98 99 static void 100 kex_prop_free(char **proposal) 101 { 102 int i; 103 104 for (i = 0; i < PROPOSAL_MAX; i++) 105 xfree(proposal[i]); 106 xfree(proposal); 107 } 108 109 static void 110 kex_protocol_error(int type, u_int32_t seq, void *ctxt) 111 { 112 error("Hm, kex protocol error: type %d seq %u", type, seq); 113 } 114 115 static void 116 kex_reset_dispatch(void) 117 { 118 dispatch_range(SSH2_MSG_TRANSPORT_MIN, 119 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); 120 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 121 } 122 123 void 124 kex_finish(Kex *kex) 125 { 126 kex_reset_dispatch(); 127 128 packet_start(SSH2_MSG_NEWKEYS); 129 packet_send(); 130 /* packet_write_wait(); */ 131 debug("SSH2_MSG_NEWKEYS sent"); 132 133 debug("waiting for SSH2_MSG_NEWKEYS"); 134 packet_read_expect(SSH2_MSG_NEWKEYS); 135 packet_check_eom(); 136 debug("SSH2_MSG_NEWKEYS received"); 137 138 kex->done = 1; 139 buffer_clear(&kex->peer); 140 /* buffer_clear(&kex->my); */ 141 kex->flags &= ~KEX_INIT_SENT; 142 xfree(kex->name); 143 kex->name = NULL; 144 } 145 146 void 147 kex_send_kexinit(Kex *kex) 148 { 149 if (kex == NULL) { 150 error("kex_send_kexinit: no kex, cannot rekey"); 151 return; 152 } 153 if (kex->flags & KEX_INIT_SENT) { 154 debug("KEX_INIT_SENT"); 155 return; 156 } 157 kex->done = 0; 158 packet_start(SSH2_MSG_KEXINIT); 159 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 160 packet_send(); 161 debug("SSH2_MSG_KEXINIT sent"); 162 kex->flags |= KEX_INIT_SENT; 163 } 164 165 void 166 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 167 { 168 char *ptr; 169 int dlen; 170 int i; 171 Kex *kex = (Kex *)ctxt; 172 173 debug("SSH2_MSG_KEXINIT received"); 174 if (kex == NULL) 175 fatal("kex_input_kexinit: no kex, cannot rekey"); 176 177 ptr = packet_get_raw(&dlen); 178 buffer_append(&kex->peer, ptr, dlen); 179 180 /* discard packet */ 181 for (i = 0; i < KEX_COOKIE_LEN; i++) 182 packet_get_char(); 183 for (i = 0; i < PROPOSAL_MAX; i++) 184 xfree(packet_get_string(NULL)); 185 packet_get_char(); 186 packet_get_int(); 187 packet_check_eom(); 188 189 kex_kexinit_finish(kex); 190 } 191 192 Kex * 193 kex_setup(char *proposal[PROPOSAL_MAX]) 194 { 195 Kex *kex; 196 197 kex = xmalloc(sizeof(*kex)); 198 memset(kex, 0, sizeof(*kex)); 199 buffer_init(&kex->peer); 200 buffer_init(&kex->my); 201 kex_prop2buf(&kex->my, proposal); 202 kex->done = 0; 203 204 kex_send_kexinit(kex); /* we start */ 205 kex_reset_dispatch(); 206 207 return kex; 208 } 209 210 static void 211 kex_kexinit_finish(Kex *kex) 212 { 213 if (!(kex->flags & KEX_INIT_SENT)) 214 kex_send_kexinit(kex); 215 216 kex_choose_conf(kex); 217 218 switch (kex->kex_type) { 219 case DH_GRP1_SHA1: 220 kexdh(kex); 221 break; 222 case DH_GEX_SHA1: 223 kexgex(kex); 224 break; 225 default: 226 fatal("Unsupported key exchange %d", kex->kex_type); 227 } 228 } 229 230 static void 231 choose_enc(Enc *enc, char *client, char *server) 232 { 233 char *name = match_list(client, server, NULL); 234 if (name == NULL) 235 fatal("no matching cipher found: client %s server %s", client, server); 236 if ((enc->cipher = cipher_by_name(name)) == NULL) 237 fatal("matching cipher is not supported: %s", name); 238 enc->name = name; 239 enc->enabled = 0; 240 enc->iv = NULL; 241 enc->key = NULL; 242 enc->key_len = cipher_keylen(enc->cipher); 243 enc->block_size = cipher_blocksize(enc->cipher); 244 } 245 static void 246 choose_mac(Mac *mac, char *client, char *server) 247 { 248 char *name = match_list(client, server, NULL); 249 if (name == NULL) 250 fatal("no matching mac found: client %s server %s", client, server); 251 if (mac_init(mac, name) < 0) 252 fatal("unsupported mac %s", name); 253 /* truncate the key */ 254 if (datafellows & SSH_BUG_HMAC) 255 mac->key_len = 16; 256 mac->name = name; 257 mac->key = NULL; 258 mac->enabled = 0; 259 } 260 static void 261 choose_comp(Comp *comp, char *client, char *server) 262 { 263 char *name = match_list(client, server, NULL); 264 if (name == NULL) 265 fatal("no matching comp found: client %s server %s", client, server); 266 if (strcmp(name, "zlib") == 0) { 267 comp->type = 1; 268 } else if (strcmp(name, "none") == 0) { 269 comp->type = 0; 270 } else { 271 fatal("unsupported comp %s", name); 272 } 273 comp->name = name; 274 } 275 static void 276 choose_kex(Kex *k, char *client, char *server) 277 { 278 k->name = match_list(client, server, NULL); 279 if (k->name == NULL) 280 fatal("no kex alg"); 281 if (strcmp(k->name, KEX_DH1) == 0) { 282 k->kex_type = DH_GRP1_SHA1; 283 } else if (strcmp(k->name, KEX_DHGEX) == 0) { 284 k->kex_type = DH_GEX_SHA1; 285 } else 286 fatal("bad kex alg %s", k->name); 287 } 288 static void 289 choose_hostkeyalg(Kex *k, char *client, char *server) 290 { 291 char *hostkeyalg = match_list(client, server, NULL); 292 if (hostkeyalg == NULL) 293 fatal("no hostkey alg"); 294 k->hostkey_type = key_type_from_name(hostkeyalg); 295 if (k->hostkey_type == KEY_UNSPEC) 296 fatal("bad hostkey alg '%s'", hostkeyalg); 297 xfree(hostkeyalg); 298 } 299 300 static void 301 kex_choose_conf(Kex *kex) 302 { 303 Newkeys *newkeys; 304 char **my, **peer; 305 char **cprop, **sprop; 306 int nenc, nmac, ncomp; 307 int mode; 308 int ctos; /* direction: if true client-to-server */ 309 int need; 310 311 my = kex_buf2prop(&kex->my); 312 peer = kex_buf2prop(&kex->peer); 313 314 if (kex->server) { 315 cprop=peer; 316 sprop=my; 317 } else { 318 cprop=my; 319 sprop=peer; 320 } 321 322 /* Algorithm Negotiation */ 323 for (mode = 0; mode < MODE_MAX; mode++) { 324 newkeys = xmalloc(sizeof(*newkeys)); 325 memset(newkeys, 0, sizeof(*newkeys)); 326 kex->newkeys[mode] = newkeys; 327 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 328 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 329 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 330 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 331 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 332 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 333 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 334 debug("kex: %s %s %s %s", 335 ctos ? "client->server" : "server->client", 336 newkeys->enc.name, 337 newkeys->mac.name, 338 newkeys->comp.name); 339 } 340 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 341 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 342 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 343 need = 0; 344 for (mode = 0; mode < MODE_MAX; mode++) { 345 newkeys = kex->newkeys[mode]; 346 if (need < newkeys->enc.key_len) 347 need = newkeys->enc.key_len; 348 if (need < newkeys->enc.block_size) 349 need = newkeys->enc.block_size; 350 if (need < newkeys->mac.key_len) 351 need = newkeys->mac.key_len; 352 } 353 /* XXX need runden? */ 354 kex->we_need = need; 355 356 kex_prop_free(my); 357 kex_prop_free(peer); 358 } 359 360 static u_char * 361 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) 362 { 363 Buffer b; 364 const EVP_MD *evp_md = EVP_sha1(); 365 EVP_MD_CTX md; 366 char c = id; 367 int have; 368 int mdsz = EVP_MD_size(evp_md); 369 u_char *digest = xmalloc(roundup(need, mdsz)); 370 371 buffer_init(&b); 372 buffer_put_bignum2(&b, shared_secret); 373 374 /* K1 = HASH(K || H || "A" || session_id) */ 375 EVP_DigestInit(&md, evp_md); 376 if (!(datafellows & SSH_BUG_DERIVEKEY)) 377 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 378 EVP_DigestUpdate(&md, hash, mdsz); 379 EVP_DigestUpdate(&md, &c, 1); 380 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 381 EVP_DigestFinal(&md, digest, NULL); 382 383 /* 384 * expand key: 385 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 386 * Key = K1 || K2 || ... || Kn 387 */ 388 for (have = mdsz; need > have; have += mdsz) { 389 EVP_DigestInit(&md, evp_md); 390 if (!(datafellows & SSH_BUG_DERIVEKEY)) 391 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 392 EVP_DigestUpdate(&md, hash, mdsz); 393 EVP_DigestUpdate(&md, digest, have); 394 EVP_DigestFinal(&md, digest + have, NULL); 395 } 396 buffer_free(&b); 397 #ifdef DEBUG_KEX 398 fprintf(stderr, "key '%c'== ", c); 399 dump_digest("key", digest, need); 400 #endif 401 return digest; 402 } 403 404 Newkeys *current_keys[MODE_MAX]; 405 406 #define NKEYS 6 407 void 408 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) 409 { 410 u_char *keys[NKEYS]; 411 int i, mode, ctos; 412 413 for (i = 0; i < NKEYS; i++) 414 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); 415 416 debug("kex_derive_keys"); 417 for (mode = 0; mode < MODE_MAX; mode++) { 418 current_keys[mode] = kex->newkeys[mode]; 419 kex->newkeys[mode] = NULL; 420 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 421 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 422 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 423 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 424 } 425 } 426 427 Newkeys * 428 kex_get_newkeys(int mode) 429 { 430 Newkeys *ret; 431 432 ret = current_keys[mode]; 433 current_keys[mode] = NULL; 434 return ret; 435 } 436 437 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 438 void 439 dump_digest(char *msg, u_char *digest, int len) 440 { 441 int i; 442 443 fprintf(stderr, "%s\n", msg); 444 for (i = 0; i< len; i++) { 445 fprintf(stderr, "%02x", digest[i]); 446 if (i%32 == 31) 447 fprintf(stderr, "\n"); 448 else if (i%8 == 7) 449 fprintf(stderr, " "); 450 } 451 fprintf(stderr, "\n"); 452 } 453 #endif 454