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 1.45 2002/02/14 23:41:01 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 debug("SSH2_MSG_NEWKEYS received"); 136 137 kex->done = 1; 138 buffer_clear(&kex->peer); 139 /* buffer_clear(&kex->my); */ 140 kex->flags &= ~KEX_INIT_SENT; 141 xfree(kex->name); 142 kex->name = NULL; 143 } 144 145 void 146 kex_send_kexinit(Kex *kex) 147 { 148 if (kex == NULL) { 149 error("kex_send_kexinit: no kex, cannot rekey"); 150 return; 151 } 152 if (kex->flags & KEX_INIT_SENT) { 153 debug("KEX_INIT_SENT"); 154 return; 155 } 156 kex->done = 0; 157 packet_start(SSH2_MSG_KEXINIT); 158 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 159 packet_send(); 160 debug("SSH2_MSG_KEXINIT sent"); 161 kex->flags |= KEX_INIT_SENT; 162 } 163 164 void 165 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 166 { 167 char *ptr; 168 int dlen; 169 int i; 170 Kex *kex = (Kex *)ctxt; 171 172 debug("SSH2_MSG_KEXINIT received"); 173 if (kex == NULL) 174 fatal("kex_input_kexinit: no kex, cannot rekey"); 175 176 ptr = packet_get_raw(&dlen); 177 buffer_append(&kex->peer, ptr, dlen); 178 179 /* discard packet */ 180 for (i = 0; i < KEX_COOKIE_LEN; i++) 181 packet_get_char(); 182 for (i = 0; i < PROPOSAL_MAX; i++) 183 xfree(packet_get_string(NULL)); 184 packet_get_char(); 185 packet_get_int(); 186 packet_check_eom(); 187 188 kex_kexinit_finish(kex); 189 } 190 191 Kex * 192 kex_setup(char *proposal[PROPOSAL_MAX]) 193 { 194 Kex *kex; 195 196 kex = xmalloc(sizeof(*kex)); 197 memset(kex, 0, sizeof(*kex)); 198 buffer_init(&kex->peer); 199 buffer_init(&kex->my); 200 kex_prop2buf(&kex->my, proposal); 201 kex->done = 0; 202 203 kex_send_kexinit(kex); /* we start */ 204 kex_reset_dispatch(); 205 206 return kex; 207 } 208 209 static void 210 kex_kexinit_finish(Kex *kex) 211 { 212 if (!(kex->flags & KEX_INIT_SENT)) 213 kex_send_kexinit(kex); 214 215 kex_choose_conf(kex); 216 217 switch (kex->kex_type) { 218 case DH_GRP1_SHA1: 219 kexdh(kex); 220 break; 221 case DH_GEX_SHA1: 222 kexgex(kex); 223 break; 224 default: 225 fatal("Unsupported key exchange %d", kex->kex_type); 226 } 227 } 228 229 static void 230 choose_enc(Enc *enc, char *client, char *server) 231 { 232 char *name = match_list(client, server, NULL); 233 if (name == NULL) 234 fatal("no matching cipher found: client %s server %s", client, server); 235 if ((enc->cipher = cipher_by_name(name)) == NULL) 236 fatal("matching cipher is not supported: %s", name); 237 enc->name = name; 238 enc->enabled = 0; 239 enc->iv = NULL; 240 enc->key = NULL; 241 enc->key_len = cipher_keylen(enc->cipher); 242 enc->block_size = cipher_blocksize(enc->cipher); 243 } 244 static void 245 choose_mac(Mac *mac, char *client, char *server) 246 { 247 char *name = match_list(client, server, NULL); 248 if (name == NULL) 249 fatal("no matching mac found: client %s server %s", client, server); 250 if (mac_init(mac, name) < 0) 251 fatal("unsupported mac %s", name); 252 /* truncate the key */ 253 if (datafellows & SSH_BUG_HMAC) 254 mac->key_len = 16; 255 mac->name = name; 256 mac->key = NULL; 257 mac->enabled = 0; 258 } 259 static void 260 choose_comp(Comp *comp, char *client, char *server) 261 { 262 char *name = match_list(client, server, NULL); 263 if (name == NULL) 264 fatal("no matching comp found: client %s server %s", client, server); 265 if (strcmp(name, "zlib") == 0) { 266 comp->type = 1; 267 } else if (strcmp(name, "none") == 0) { 268 comp->type = 0; 269 } else { 270 fatal("unsupported comp %s", name); 271 } 272 comp->name = name; 273 } 274 static void 275 choose_kex(Kex *k, char *client, char *server) 276 { 277 k->name = match_list(client, server, NULL); 278 if (k->name == NULL) 279 fatal("no kex alg"); 280 if (strcmp(k->name, KEX_DH1) == 0) { 281 k->kex_type = DH_GRP1_SHA1; 282 } else if (strcmp(k->name, KEX_DHGEX) == 0) { 283 k->kex_type = DH_GEX_SHA1; 284 } else 285 fatal("bad kex alg %s", k->name); 286 } 287 static void 288 choose_hostkeyalg(Kex *k, char *client, char *server) 289 { 290 char *hostkeyalg = match_list(client, server, NULL); 291 if (hostkeyalg == NULL) 292 fatal("no hostkey alg"); 293 k->hostkey_type = key_type_from_name(hostkeyalg); 294 if (k->hostkey_type == KEY_UNSPEC) 295 fatal("bad hostkey alg '%s'", hostkeyalg); 296 xfree(hostkeyalg); 297 } 298 299 static void 300 kex_choose_conf(Kex *kex) 301 { 302 Newkeys *newkeys; 303 char **my, **peer; 304 char **cprop, **sprop; 305 int nenc, nmac, ncomp; 306 int mode; 307 int ctos; /* direction: if true client-to-server */ 308 int need; 309 310 my = kex_buf2prop(&kex->my); 311 peer = kex_buf2prop(&kex->peer); 312 313 if (kex->server) { 314 cprop=peer; 315 sprop=my; 316 } else { 317 cprop=my; 318 sprop=peer; 319 } 320 321 /* Algorithm Negotiation */ 322 for (mode = 0; mode < MODE_MAX; mode++) { 323 newkeys = xmalloc(sizeof(*newkeys)); 324 memset(newkeys, 0, sizeof(*newkeys)); 325 kex->newkeys[mode] = newkeys; 326 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 327 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 328 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 329 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 330 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 331 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 332 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 333 debug("kex: %s %s %s %s", 334 ctos ? "client->server" : "server->client", 335 newkeys->enc.name, 336 newkeys->mac.name, 337 newkeys->comp.name); 338 } 339 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 340 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 341 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 342 need = 0; 343 for (mode = 0; mode < MODE_MAX; mode++) { 344 newkeys = kex->newkeys[mode]; 345 if (need < newkeys->enc.key_len) 346 need = newkeys->enc.key_len; 347 if (need < newkeys->enc.block_size) 348 need = newkeys->enc.block_size; 349 if (need < newkeys->mac.key_len) 350 need = newkeys->mac.key_len; 351 } 352 /* XXX need runden? */ 353 kex->we_need = need; 354 355 kex_prop_free(my); 356 kex_prop_free(peer); 357 } 358 359 static u_char * 360 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) 361 { 362 Buffer b; 363 EVP_MD *evp_md = EVP_sha1(); 364 EVP_MD_CTX md; 365 char c = id; 366 int have; 367 int mdsz = EVP_MD_size(evp_md); 368 u_char *digest = xmalloc(roundup(need, mdsz)); 369 370 buffer_init(&b); 371 buffer_put_bignum2(&b, shared_secret); 372 373 /* K1 = HASH(K || H || "A" || session_id) */ 374 EVP_DigestInit(&md, evp_md); 375 if (!(datafellows & SSH_BUG_DERIVEKEY)) 376 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 377 EVP_DigestUpdate(&md, hash, mdsz); 378 EVP_DigestUpdate(&md, &c, 1); 379 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 380 EVP_DigestFinal(&md, digest, NULL); 381 382 /* 383 * expand key: 384 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 385 * Key = K1 || K2 || ... || Kn 386 */ 387 for (have = mdsz; need > have; have += mdsz) { 388 EVP_DigestInit(&md, evp_md); 389 if (!(datafellows & SSH_BUG_DERIVEKEY)) 390 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 391 EVP_DigestUpdate(&md, hash, mdsz); 392 EVP_DigestUpdate(&md, digest, have); 393 EVP_DigestFinal(&md, digest + have, NULL); 394 } 395 buffer_free(&b); 396 #ifdef DEBUG_KEX 397 fprintf(stderr, "key '%c'== ", c); 398 dump_digest("key", digest, need); 399 #endif 400 return digest; 401 } 402 403 Newkeys *current_keys[MODE_MAX]; 404 405 #define NKEYS 6 406 void 407 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) 408 { 409 u_char *keys[NKEYS]; 410 int i, mode, ctos; 411 412 for (i = 0; i < NKEYS; i++) 413 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); 414 415 debug("kex_derive_keys"); 416 for (mode = 0; mode < MODE_MAX; mode++) { 417 current_keys[mode] = kex->newkeys[mode]; 418 kex->newkeys[mode] = NULL; 419 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 420 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 421 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 422 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 423 } 424 } 425 426 Newkeys * 427 kex_get_newkeys(int mode) 428 { 429 Newkeys *ret; 430 431 ret = current_keys[mode]; 432 current_keys[mode] = NULL; 433 return ret; 434 } 435 436 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 437 void 438 dump_digest(char *msg, u_char *digest, int len) 439 { 440 int i; 441 442 fprintf(stderr, "%s\n", msg); 443 for (i = 0; i< len; i++) { 444 fprintf(stderr, "%02x", digest[i]); 445 if (i%32 == 31) 446 fprintf(stderr, "\n"); 447 else if (i%8 == 7) 448 fprintf(stderr, " "); 449 } 450 fprintf(stderr, "\n"); 451 } 452 #endif 453