kex.c

   1 /* $OpenBSD: kex.c,v 1.72 2006/07/22 20:48:23 stevesk 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 <openssl/crypto.h>
  29
  30 #include <string.h>
  31
  32 #include "ssh2.h"
  33 #include "xmalloc.h"
  34 #include "buffer.h"
  35 #include "bufaux.h"
  36 #include "packet.h"
  37 #include "compat.h"
  38 #include "cipher.h"
  39 #include "kex.h"
  40 #include "key.h"
  41 #include "log.h"
  42 #include "mac.h"
  43 #include "match.h"
  44 #include "dispatch.h"
  45 #include "monitor.h"
  46
  47 #define KEX_COOKIE_LEN  16
  48
  49 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
  50 # if defined(HAVE_EVP_SHA256)
  51 # define evp_ssh_sha256 EVP_sha256
  52 # else
  53 extern const EVP_MD *evp_ssh_sha256(void);
  54 # endif
  55 #endif
  56
  57 /* prototype */
  58 static void kex_kexinit_finish(Kex *);
  59 static void kex_choose_conf(Kex *);
  60
  61 /* put algorithm proposal into buffer */
  62 static void
  63 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
  64 {
  65         u_int i;
  66
  67         buffer_clear(b);
  68         /*
  69          * add a dummy cookie, the cookie will be overwritten by
  70          * kex_send_kexinit(), each time a kexinit is set
  71          */
  72         for (i = 0; i < KEX_COOKIE_LEN; i++)
  73                 buffer_put_char(b, 0);
  74         for (i = 0; i < PROPOSAL_MAX; i++)
  75                 buffer_put_cstring(b, proposal[i]);
  76         buffer_put_char(b, 0);                  /* first_kex_packet_follows */
  77         buffer_put_int(b, 0);                   /* uint32 reserved */
  78 }
  79
  80 /* parse buffer and return algorithm proposal */
  81 static char **
  82 kex_buf2prop(Buffer *raw, int *first_kex_follows)
  83 {
  84         Buffer b;
  85         int i;
  86         char **proposal;
  87
  88         proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
  89
  90         buffer_init(&b);
  91         buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
  92         /* skip cookie */
  93         for (i = 0; i < KEX_COOKIE_LEN; i++)
  94                 buffer_get_char(&b);
  95         /* extract kex init proposal strings */
  96         for (i = 0; i < PROPOSAL_MAX; i++) {
  97                 proposal[i] = buffer_get_string(&b,NULL);
  98                 debug2("kex_parse_kexinit: %s", proposal[i]);
  99         }
 100         /* first kex follows / reserved */
 101         i = buffer_get_char(&b);
 102         if (first_kex_follows != NULL)
 103                 *first_kex_follows = i;
 104         debug2("kex_parse_kexinit: first_kex_follows %d ", i);
 105         i = buffer_get_int(&b);
 106         debug2("kex_parse_kexinit: reserved %d ", i);
 107         buffer_free(&b);
 108         return proposal;
 109 }
 110
 111 static void
 112 kex_prop_free(char **proposal)
 113 {
 114         u_int i;
 115
 116         for (i = 0; i < PROPOSAL_MAX; i++)
 117                 xfree(proposal[i]);
 118         xfree(proposal);
 119 }
 120
 121 static void
 122 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 123 {
 124         error("Hm, kex protocol error: type %d seq %u", type, seq);
 125 }
 126
 127 static void
 128 kex_reset_dispatch(void)
 129 {
 130         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 131             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 132         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 133 }
 134
 135 void
 136 kex_finish(Kex *kex)
 137 {
 138         kex_reset_dispatch();
 139
 140         packet_start(SSH2_MSG_NEWKEYS);
 141         packet_send();
 142         /* packet_write_wait(); */
 143         debug("SSH2_MSG_NEWKEYS sent");
 144
 145         debug("expecting SSH2_MSG_NEWKEYS");
 146         packet_read_expect(SSH2_MSG_NEWKEYS);
 147         packet_check_eom();
 148         debug("SSH2_MSG_NEWKEYS received");
 149
 150         kex->done = 1;
 151         buffer_clear(&kex->peer);
 152         /* buffer_clear(&kex->my); */
 153         kex->flags &= ~KEX_INIT_SENT;
 154         xfree(kex->name);
 155         kex->name = NULL;
 156 }
 157
 158 void
 159 kex_send_kexinit(Kex *kex)
 160 {
 161         u_int32_t rnd = 0;
 162         u_char *cookie;
 163         u_int i;
 164
 165         if (kex == NULL) {
 166                 error("kex_send_kexinit: no kex, cannot rekey");
 167                 return;
 168         }
 169         if (kex->flags & KEX_INIT_SENT) {
 170                 debug("KEX_INIT_SENT");
 171                 return;
 172         }
 173         kex->done = 0;
 174
 175         /* generate a random cookie */
 176         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 177                 fatal("kex_send_kexinit: kex proposal too short");
 178         cookie = buffer_ptr(&kex->my);
 179         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 180                 if (i % 4 == 0)
 181                         rnd = arc4random();
 182                 cookie[i] = rnd;
 183                 rnd >>= 8;
 184         }
 185         packet_start(SSH2_MSG_KEXINIT);
 186         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 187         packet_send();
 188         debug("SSH2_MSG_KEXINIT sent");
 189         kex->flags |= KEX_INIT_SENT;
 190 }
 191
 192 void
 193 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 194 {
 195         char *ptr;
 196         u_int i, dlen;
 197         Kex *kex = (Kex *)ctxt;
 198
 199         debug("SSH2_MSG_KEXINIT received");
 200         if (kex == NULL)
 201                 fatal("kex_input_kexinit: no kex, cannot rekey");
 202
 203         ptr = packet_get_raw(&dlen);
 204         buffer_append(&kex->peer, ptr, dlen);
 205
 206         /* discard packet */
 207         for (i = 0; i < KEX_COOKIE_LEN; i++)
 208                 packet_get_char();
 209         for (i = 0; i < PROPOSAL_MAX; i++)
 210                 xfree(packet_get_string(NULL));
 211         (void) packet_get_char();
 212         (void) packet_get_int();
 213         packet_check_eom();
 214
 215         kex_kexinit_finish(kex);
 216 }
 217
 218 Kex *
 219 kex_setup(char *proposal[PROPOSAL_MAX])
 220 {
 221         Kex *kex;
 222
 223         kex = xcalloc(1, sizeof(*kex));
 224         buffer_init(&kex->peer);
 225         buffer_init(&kex->my);
 226         kex_prop2buf(&kex->my, proposal);
 227         kex->done = 0;
 228
 229         kex_send_kexinit(kex);                                  /* we start */
 230         kex_reset_dispatch();
 231
 232         return kex;
 233 }
 234
 235 static void
 236 kex_kexinit_finish(Kex *kex)
 237 {
 238         if (!(kex->flags & KEX_INIT_SENT))
 239                 kex_send_kexinit(kex);
 240
 241         kex_choose_conf(kex);
 242
 243         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 244             kex->kex[kex->kex_type] != NULL) {
 245                 (kex->kex[kex->kex_type])(kex);
 246         } else {
 247                 fatal("Unsupported key exchange %d", kex->kex_type);
 248         }
 249 }
 250
 251 static void
 252 choose_enc(Enc *enc, char *client, char *server)
 253 {
 254         char *name = match_list(client, server, NULL);
 255         if (name == NULL)
 256                 fatal("no matching cipher found: client %s server %s", client, server);
 257         if ((enc->cipher = cipher_by_name(name)) == NULL)
 258                 fatal("matching cipher is not supported: %s", name);
 259         enc->name = name;
 260         enc->enabled = 0;
 261         enc->iv = NULL;
 262         enc->key = NULL;
 263         enc->key_len = cipher_keylen(enc->cipher);
 264         enc->block_size = cipher_blocksize(enc->cipher);
 265 }
 266
 267 static void
 268 choose_mac(Mac *mac, char *client, char *server)
 269 {
 270         char *name = match_list(client, server, NULL);
 271         if (name == NULL)
 272                 fatal("no matching mac found: client %s server %s", client, server);
 273         if (mac_init(mac, name) < 0)
 274                 fatal("unsupported mac %s", name);
 275         /* truncate the key */
 276         if (datafellows & SSH_BUG_HMAC)
 277                 mac->key_len = 16;
 278         mac->name = name;
 279         mac->key = NULL;
 280         mac->enabled = 0;
 281 }
 282
 283 static void
 284 choose_comp(Comp *comp, char *client, char *server)
 285 {
 286         char *name = match_list(client, server, NULL);
 287         if (name == NULL)
 288                 fatal("no matching comp found: client %s server %s", client, server);
 289         if (strcmp(name, "zlib@openssh.com") == 0) {
 290                 comp->type = COMP_DELAYED;
 291         } else if (strcmp(name, "zlib") == 0) {
 292                 comp->type = COMP_ZLIB;
 293         } else if (strcmp(name, "none") == 0) {
 294                 comp->type = COMP_NONE;
 295         } else {
 296                 fatal("unsupported comp %s", name);
 297         }
 298         comp->name = name;
 299 }
 300
 301 static void
 302 choose_kex(Kex *k, char *client, char *server)
 303 {
 304         k->name = match_list(client, server, NULL);
 305         if (k->name == NULL)
 306                 fatal("no kex alg");
 307         if (strcmp(k->name, KEX_DH1) == 0) {
 308                 k->kex_type = KEX_DH_GRP1_SHA1;
 309                 k->evp_md = EVP_sha1();
 310         } else if (strcmp(k->name, KEX_DH14) == 0) {
 311                 k->kex_type = KEX_DH_GRP14_SHA1;
 312                 k->evp_md = EVP_sha1();
 313         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 314                 k->kex_type = KEX_DH_GEX_SHA1;
 315                 k->evp_md = EVP_sha1();
 316 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 317         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 318                 k->kex_type = KEX_DH_GEX_SHA256;
 319                 k->evp_md = evp_ssh_sha256();
 320 #endif
 321         } else
 322                 fatal("bad kex alg %s", k->name);
 323 }
 324
 325 static void
 326 choose_hostkeyalg(Kex *k, char *client, char *server)
 327 {
 328         char *hostkeyalg = match_list(client, server, NULL);
 329         if (hostkeyalg == NULL)
 330                 fatal("no hostkey alg");
 331         k->hostkey_type = key_type_from_name(hostkeyalg);
 332         if (k->hostkey_type == KEY_UNSPEC)
 333                 fatal("bad hostkey alg '%s'", hostkeyalg);
 334         xfree(hostkeyalg);
 335 }
 336
 337 static int
 338 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 339 {
 340         static int check[] = {
 341                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 342         };
 343         int *idx;
 344         char *p;
 345
 346         for (idx = &check[0]; *idx != -1; idx++) {
 347                 if ((p = strchr(my[*idx], ',')) != NULL)
 348                         *p = '\0';
 349                 if ((p = strchr(peer[*idx], ',')) != NULL)
 350                         *p = '\0';
 351                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 352                         debug2("proposal mismatch: my %s peer %s",
 353                             my[*idx], peer[*idx]);
 354                         return (0);
 355                 }
 356         }
 357         debug2("proposals match");
 358         return (1);
 359 }
 360
 361 static void
 362 kex_choose_conf(Kex *kex)
 363 {
 364         Newkeys *newkeys;
 365         char **my, **peer;
 366         char **cprop, **sprop;
 367         int nenc, nmac, ncomp;
 368         u_int mode, ctos, need;
 369         int first_kex_follows, type;
 370
 371         my   = kex_buf2prop(&kex->my, NULL);
 372         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 373
 374         if (kex->server) {
 375                 cprop=peer;
 376                 sprop=my;
 377         } else {
 378                 cprop=my;
 379                 sprop=peer;
 380         }
 381
 382         /* Algorithm Negotiation */
 383         for (mode = 0; mode < MODE_MAX; mode++) {
 384                 newkeys = xcalloc(1, sizeof(*newkeys));
 385                 kex->newkeys[mode] = newkeys;
 386                 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
 387                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 388                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 389                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 390                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 391                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 392                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 393                 debug("kex: %s %s %s %s",
 394                     ctos ? "client->server" : "server->client",
 395                     newkeys->enc.name,
 396                     newkeys->mac.name,
 397                     newkeys->comp.name);
 398         }
 399         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 400         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 401             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 402         need = 0;
 403         for (mode = 0; mode < MODE_MAX; mode++) {
 404                 newkeys = kex->newkeys[mode];
 405                 if (need < newkeys->enc.key_len)
 406                         need = newkeys->enc.key_len;
 407                 if (need < newkeys->enc.block_size)
 408                         need = newkeys->enc.block_size;
 409                 if (need < newkeys->mac.key_len)
 410                         need = newkeys->mac.key_len;
 411         }
 412         /* XXX need runden? */
 413         kex->we_need = need;
 414
 415         /* ignore the next message if the proposals do not match */
 416         if (first_kex_follows && !proposals_match(my, peer) &&
 417             !(datafellows & SSH_BUG_FIRSTKEX)) {
 418                 type = packet_read();
 419                 debug2("skipping next packet (type %u)", type);
 420         }
 421
 422         kex_prop_free(my);
 423         kex_prop_free(peer);
 424 }
 425
 426 static u_char *
 427 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 428     BIGNUM *shared_secret)
 429 {
 430         Buffer b;
 431         EVP_MD_CTX md;
 432         char c = id;
 433         u_int have;
 434         int mdsz;
 435         u_char *digest;
 436
 437         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 438                 fatal("bad kex md size %d", mdsz);
 439         digest = xmalloc(roundup(need, mdsz));
 440
 441         buffer_init(&b);
 442         buffer_put_bignum2(&b, shared_secret);
 443
 444         /* K1 = HASH(K || H || "A" || session_id) */
 445         EVP_DigestInit(&md, kex->evp_md);
 446         if (!(datafellows & SSH_BUG_DERIVEKEY))
 447                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 448         EVP_DigestUpdate(&md, hash, hashlen);
 449         EVP_DigestUpdate(&md, &c, 1);
 450         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 451         EVP_DigestFinal(&md, digest, NULL);
 452
 453         /*
 454          * expand key:
 455          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 456          * Key = K1 || K2 || ... || Kn
 457          */
 458         for (have = mdsz; need > have; have += mdsz) {
 459                 EVP_DigestInit(&md, kex->evp_md);
 460                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 461                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 462                 EVP_DigestUpdate(&md, hash, hashlen);
 463                 EVP_DigestUpdate(&md, digest, have);
 464                 EVP_DigestFinal(&md, digest + have, NULL);
 465         }
 466         buffer_free(&b);
 467 #ifdef DEBUG_KEX
 468         fprintf(stderr, "key '%c'== ", c);
 469         dump_digest("key", digest, need);
 470 #endif
 471         return digest;
 472 }
 473
 474 Newkeys *current_keys[MODE_MAX];
 475
 476 #define NKEYS   6
 477 void
 478 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 479 {
 480         u_char *keys[NKEYS];
 481         u_int i, mode, ctos;
 482
 483         for (i = 0; i < NKEYS; i++) {
 484                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 485                     shared_secret);
 486         }
 487
 488         debug2("kex_derive_keys");
 489         for (mode = 0; mode < MODE_MAX; mode++) {
 490                 current_keys[mode] = kex->newkeys[mode];
 491                 kex->newkeys[mode] = NULL;
 492                 ctos = (!kex->server && mode == MODE_OUT) ||
 493                     (kex->server && mode == MODE_IN);
 494                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 495                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 496                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 497         }
 498 }
 499
 500 Newkeys *
 501 kex_get_newkeys(int mode)
 502 {
 503         Newkeys *ret;
 504
 505         ret = current_keys[mode];
 506         current_keys[mode] = NULL;
 507         return ret;
 508 }
 509
 510 void
 511 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 512     u_int8_t cookie[8], u_int8_t id[16])
 513 {
 514         const EVP_MD *evp_md = EVP_md5();
 515         EVP_MD_CTX md;
 516         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 517         int len;
 518
 519         EVP_DigestInit(&md, evp_md);
 520
 521         len = BN_num_bytes(host_modulus);
 522         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 523                 fatal("%s: bad host modulus (len %d)", __func__, len);
 524         BN_bn2bin(host_modulus, nbuf);
 525         EVP_DigestUpdate(&md, nbuf, len);
 526
 527         len = BN_num_bytes(server_modulus);
 528         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 529                 fatal("%s: bad server modulus (len %d)", __func__, len);
 530         BN_bn2bin(server_modulus, nbuf);
 531         EVP_DigestUpdate(&md, nbuf, len);
 532
 533         EVP_DigestUpdate(&md, cookie, 8);
 534
 535         EVP_DigestFinal(&md, obuf, NULL);
 536         memcpy(id, obuf, 16);
 537
 538         memset(nbuf, 0, sizeof(nbuf));
 539         memset(obuf, 0, sizeof(obuf));
 540         memset(&md, 0, sizeof(md));
 541 }
 542
 543 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 544 void
 545 dump_digest(char *msg, u_char *digest, int len)
 546 {
 547         u_int i;
 548
 549         fprintf(stderr, "%s\n", msg);
 550         for (i = 0; i< len; i++) {
 551                 fprintf(stderr, "%02x", digest[i]);
 552                 if (i%32 == 31)
 553                         fprintf(stderr, "\n");
 554                 else if (i%8 == 7)
 555                         fprintf(stderr, " ");
 556         }
 557         fprintf(stderr, "\n");
 558 }
 559 #endif