kex.c

   1 /* $OpenBSD: kex.c,v 1.81 2009/05/27 06:34:36 andreas 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
  52 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
  53 # if defined(HAVE_EVP_SHA256)
  54 # define evp_ssh_sha256 EVP_sha256
  55 # else
  56 extern const EVP_MD *evp_ssh_sha256(void);
  57 # endif
  58 #endif
  59
  60 /* prototype */
  61 static void kex_kexinit_finish(Kex *);
  62 static void kex_choose_conf(Kex *);
  63
  64 /* put algorithm proposal into buffer */
  65 static void
  66 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
  67 {
  68         u_int i;
  69
  70         buffer_clear(b);
  71         /*
  72          * add a dummy cookie, the cookie will be overwritten by
  73          * kex_send_kexinit(), each time a kexinit is set
  74          */
  75         for (i = 0; i < KEX_COOKIE_LEN; i++)
  76                 buffer_put_char(b, 0);
  77         for (i = 0; i < PROPOSAL_MAX; i++)
  78                 buffer_put_cstring(b, proposal[i]);
  79         buffer_put_char(b, 0);                  /* first_kex_packet_follows */
  80         buffer_put_int(b, 0);                   /* uint32 reserved */
  81 }
  82
  83 /* parse buffer and return algorithm proposal */
  84 static char **
  85 kex_buf2prop(Buffer *raw, int *first_kex_follows)
  86 {
  87         Buffer b;
  88         u_int i;
  89         char **proposal;
  90
  91         proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
  92
  93         buffer_init(&b);
  94         buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
  95         /* skip cookie */
  96         for (i = 0; i < KEX_COOKIE_LEN; i++)
  97                 buffer_get_char(&b);
  98         /* extract kex init proposal strings */
  99         for (i = 0; i < PROPOSAL_MAX; i++) {
 100                 proposal[i] = buffer_get_string(&b,NULL);
 101                 debug2("kex_parse_kexinit: %s", proposal[i]);
 102         }
 103         /* first kex follows / reserved */
 104         i = buffer_get_char(&b);
 105         if (first_kex_follows != NULL)
 106                 *first_kex_follows = i;
 107         debug2("kex_parse_kexinit: first_kex_follows %d ", i);
 108         i = buffer_get_int(&b);
 109         debug2("kex_parse_kexinit: reserved %u ", i);
 110         buffer_free(&b);
 111         return proposal;
 112 }
 113
 114 static void
 115 kex_prop_free(char **proposal)
 116 {
 117         u_int i;
 118
 119         for (i = 0; i < PROPOSAL_MAX; i++)
 120                 xfree(proposal[i]);
 121         xfree(proposal);
 122 }
 123
 124 /* ARGSUSED */
 125 static void
 126 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 127 {
 128         error("Hm, kex protocol error: type %d seq %u", type, seq);
 129 }
 130
 131 static void
 132 kex_reset_dispatch(void)
 133 {
 134         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 135             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 136         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 137 }
 138
 139 void
 140 kex_finish(Kex *kex)
 141 {
 142         kex_reset_dispatch();
 143
 144         packet_start(SSH2_MSG_NEWKEYS);
 145         packet_send();
 146         /* packet_write_wait(); */
 147         debug("SSH2_MSG_NEWKEYS sent");
 148
 149         debug("expecting SSH2_MSG_NEWKEYS");
 150         packet_read_expect(SSH2_MSG_NEWKEYS);
 151         packet_check_eom();
 152         debug("SSH2_MSG_NEWKEYS received");
 153
 154         kex->done = 1;
 155         buffer_clear(&kex->peer);
 156         /* buffer_clear(&kex->my); */
 157         kex->flags &= ~KEX_INIT_SENT;
 158         xfree(kex->name);
 159         kex->name = NULL;
 160 }
 161
 162 void
 163 kex_send_kexinit(Kex *kex)
 164 {
 165         u_int32_t rnd = 0;
 166         u_char *cookie;
 167         u_int i;
 168
 169         if (kex == NULL) {
 170                 error("kex_send_kexinit: no kex, cannot rekey");
 171                 return;
 172         }
 173         if (kex->flags & KEX_INIT_SENT) {
 174                 debug("KEX_INIT_SENT");
 175                 return;
 176         }
 177         kex->done = 0;
 178
 179         /* generate a random cookie */
 180         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 181                 fatal("kex_send_kexinit: kex proposal too short");
 182         cookie = buffer_ptr(&kex->my);
 183         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 184                 if (i % 4 == 0)
 185                         rnd = arc4random();
 186                 cookie[i] = rnd;
 187                 rnd >>= 8;
 188         }
 189         packet_start(SSH2_MSG_KEXINIT);
 190         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 191         packet_send();
 192         debug("SSH2_MSG_KEXINIT sent");
 193         kex->flags |= KEX_INIT_SENT;
 194 }
 195
 196 /* ARGSUSED */
 197 void
 198 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 199 {
 200         char *ptr;
 201         u_int i, dlen;
 202         Kex *kex = (Kex *)ctxt;
 203
 204         debug("SSH2_MSG_KEXINIT received");
 205         if (kex == NULL)
 206                 fatal("kex_input_kexinit: no kex, cannot rekey");
 207
 208         ptr = packet_get_raw(&dlen);
 209         buffer_append(&kex->peer, ptr, dlen);
 210
 211         /* discard packet */
 212         for (i = 0; i < KEX_COOKIE_LEN; i++)
 213                 packet_get_char();
 214         for (i = 0; i < PROPOSAL_MAX; i++)
 215                 xfree(packet_get_string(NULL));
 216         (void) packet_get_char();
 217         (void) packet_get_int();
 218         packet_check_eom();
 219
 220         kex_kexinit_finish(kex);
 221 }
 222
 223 Kex *
 224 kex_setup(char *proposal[PROPOSAL_MAX])
 225 {
 226         Kex *kex;
 227
 228         kex = xcalloc(1, sizeof(*kex));
 229         buffer_init(&kex->peer);
 230         buffer_init(&kex->my);
 231         kex_prop2buf(&kex->my, proposal);
 232         kex->done = 0;
 233
 234         kex_send_kexinit(kex);                                  /* we start */
 235         kex_reset_dispatch();
 236
 237         return kex;
 238 }
 239
 240 static void
 241 kex_kexinit_finish(Kex *kex)
 242 {
 243         if (!(kex->flags & KEX_INIT_SENT))
 244                 kex_send_kexinit(kex);
 245
 246         kex_choose_conf(kex);
 247
 248         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 249             kex->kex[kex->kex_type] != NULL) {
 250                 (kex->kex[kex->kex_type])(kex);
 251         } else {
 252                 fatal("Unsupported key exchange %d", kex->kex_type);
 253         }
 254 }
 255
 256 static void
 257 choose_enc(Enc *enc, char *client, char *server)
 258 {
 259         char *name = match_list(client, server, NULL);
 260         if (name == NULL)
 261                 fatal("no matching cipher found: client %s server %s",
 262                     client, server);
 263         if ((enc->cipher = cipher_by_name(name)) == NULL)
 264                 fatal("matching cipher is not supported: %s", name);
 265         enc->name = name;
 266         enc->enabled = 0;
 267         enc->iv = NULL;
 268         enc->key = NULL;
 269         enc->key_len = cipher_keylen(enc->cipher);
 270         enc->block_size = cipher_blocksize(enc->cipher);
 271 }
 272
 273 static void
 274 choose_mac(Mac *mac, char *client, char *server)
 275 {
 276         char *name = match_list(client, server, NULL);
 277         if (name == NULL)
 278                 fatal("no matching mac found: client %s server %s",
 279                     client, server);
 280         if (mac_setup(mac, name) < 0)
 281                 fatal("unsupported mac %s", name);
 282         /* truncate the key */
 283         if (datafellows & SSH_BUG_HMAC)
 284                 mac->key_len = 16;
 285         mac->name = name;
 286         mac->key = NULL;
 287         mac->enabled = 0;
 288 }
 289
 290 static void
 291 choose_comp(Comp *comp, char *client, char *server)
 292 {
 293         char *name = match_list(client, server, NULL);
 294         if (name == NULL)
 295                 fatal("no matching comp found: client %s server %s", client, server);
 296         if (strcmp(name, "zlib@openssh.com") == 0) {
 297                 comp->type = COMP_DELAYED;
 298         } else if (strcmp(name, "zlib") == 0) {
 299                 comp->type = COMP_ZLIB;
 300         } else if (strcmp(name, "none") == 0) {
 301                 comp->type = COMP_NONE;
 302         } else {
 303                 fatal("unsupported comp %s", name);
 304         }
 305         comp->name = name;
 306 }
 307
 308 static void
 309 choose_kex(Kex *k, char *client, char *server)
 310 {
 311         k->name = match_list(client, server, NULL);
 312         if (k->name == NULL)
 313                 fatal("Unable to negotiate a key exchange method");
 314         if (strcmp(k->name, KEX_DH1) == 0) {
 315                 k->kex_type = KEX_DH_GRP1_SHA1;
 316                 k->evp_md = EVP_sha1();
 317         } else if (strcmp(k->name, KEX_DH14) == 0) {
 318                 k->kex_type = KEX_DH_GRP14_SHA1;
 319                 k->evp_md = EVP_sha1();
 320         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 321                 k->kex_type = KEX_DH_GEX_SHA1;
 322                 k->evp_md = EVP_sha1();
 323 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 324         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 325                 k->kex_type = KEX_DH_GEX_SHA256;
 326                 k->evp_md = evp_ssh_sha256();
 327 #endif
 328         } else
 329                 fatal("bad kex alg %s", k->name);
 330 }
 331
 332 static void
 333 choose_hostkeyalg(Kex *k, char *client, char *server)
 334 {
 335         char *hostkeyalg = match_list(client, server, NULL);
 336         if (hostkeyalg == NULL)
 337                 fatal("no hostkey alg");
 338         k->hostkey_type = key_type_from_name(hostkeyalg);
 339         if (k->hostkey_type == KEY_UNSPEC)
 340                 fatal("bad hostkey alg '%s'", hostkeyalg);
 341         xfree(hostkeyalg);
 342 }
 343
 344 static int
 345 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 346 {
 347         static int check[] = {
 348                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 349         };
 350         int *idx;
 351         char *p;
 352
 353         for (idx = &check[0]; *idx != -1; idx++) {
 354                 if ((p = strchr(my[*idx], ',')) != NULL)
 355                         *p = '\0';
 356                 if ((p = strchr(peer[*idx], ',')) != NULL)
 357                         *p = '\0';
 358                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 359                         debug2("proposal mismatch: my %s peer %s",
 360                             my[*idx], peer[*idx]);
 361                         return (0);
 362                 }
 363         }
 364         debug2("proposals match");
 365         return (1);
 366 }
 367
 368 static void
 369 kex_choose_conf(Kex *kex)
 370 {
 371         Newkeys *newkeys;
 372         char **my, **peer;
 373         char **cprop, **sprop;
 374         int nenc, nmac, ncomp;
 375         u_int mode, ctos, need;
 376         int first_kex_follows, type;
 377
 378         my   = kex_buf2prop(&kex->my, NULL);
 379         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 380
 381         if (kex->server) {
 382                 cprop=peer;
 383                 sprop=my;
 384         } else {
 385                 cprop=my;
 386                 sprop=peer;
 387         }
 388
 389         /* Algorithm Negotiation */
 390         for (mode = 0; mode < MODE_MAX; mode++) {
 391                 newkeys = xcalloc(1, sizeof(*newkeys));
 392                 kex->newkeys[mode] = newkeys;
 393                 ctos = (!kex->server && mode == MODE_OUT) ||
 394                     (kex->server && mode == MODE_IN);
 395                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 396                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 397                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 398                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 399                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 400                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 401                 debug("kex: %s %s %s %s",
 402                     ctos ? "client->server" : "server->client",
 403                     newkeys->enc.name,
 404                     newkeys->mac.name,
 405                     newkeys->comp.name);
 406         }
 407         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 408         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 409             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 410         need = 0;
 411         for (mode = 0; mode < MODE_MAX; mode++) {
 412                 newkeys = kex->newkeys[mode];
 413                 if (need < newkeys->enc.key_len)
 414                         need = newkeys->enc.key_len;
 415                 if (need < newkeys->enc.block_size)
 416                         need = newkeys->enc.block_size;
 417                 if (need < newkeys->mac.key_len)
 418                         need = newkeys->mac.key_len;
 419         }
 420         /* XXX need runden? */
 421         kex->we_need = need;
 422
 423         /* ignore the next message if the proposals do not match */
 424         if (first_kex_follows && !proposals_match(my, peer) &&
 425             !(datafellows & SSH_BUG_FIRSTKEX)) {
 426                 type = packet_read();
 427                 debug2("skipping next packet (type %u)", type);
 428         }
 429
 430         kex_prop_free(my);
 431         kex_prop_free(peer);
 432 }
 433
 434 static u_char *
 435 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 436     BIGNUM *shared_secret)
 437 {
 438         Buffer b;
 439         EVP_MD_CTX md;
 440         char c = id;
 441         u_int have;
 442         int mdsz;
 443         u_char *digest;
 444
 445         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 446                 fatal("bad kex md size %d", mdsz);
 447         digest = xmalloc(roundup(need, mdsz));
 448
 449         buffer_init(&b);
 450         buffer_put_bignum2(&b, shared_secret);
 451
 452         /* K1 = HASH(K || H || "A" || session_id) */
 453         EVP_DigestInit(&md, kex->evp_md);
 454         if (!(datafellows & SSH_BUG_DERIVEKEY))
 455                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 456         EVP_DigestUpdate(&md, hash, hashlen);
 457         EVP_DigestUpdate(&md, &c, 1);
 458         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 459         EVP_DigestFinal(&md, digest, NULL);
 460
 461         /*
 462          * expand key:
 463          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 464          * Key = K1 || K2 || ... || Kn
 465          */
 466         for (have = mdsz; need > have; have += mdsz) {
 467                 EVP_DigestInit(&md, kex->evp_md);
 468                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 469                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 470                 EVP_DigestUpdate(&md, hash, hashlen);
 471                 EVP_DigestUpdate(&md, digest, have);
 472                 EVP_DigestFinal(&md, digest + have, NULL);
 473         }
 474         buffer_free(&b);
 475 #ifdef DEBUG_KEX
 476         fprintf(stderr, "key '%c'== ", c);
 477         dump_digest("key", digest, need);
 478 #endif
 479         return digest;
 480 }
 481
 482 Newkeys *current_keys[MODE_MAX];
 483
 484 #define NKEYS   6
 485 void
 486 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 487 {
 488         u_char *keys[NKEYS];
 489         u_int i, mode, ctos;
 490
 491         for (i = 0; i < NKEYS; i++) {
 492                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 493                     shared_secret);
 494         }
 495
 496         debug2("kex_derive_keys");
 497         for (mode = 0; mode < MODE_MAX; mode++) {
 498                 current_keys[mode] = kex->newkeys[mode];
 499                 kex->newkeys[mode] = NULL;
 500                 ctos = (!kex->server && mode == MODE_OUT) ||
 501                     (kex->server && mode == MODE_IN);
 502                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 503                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 504                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 505         }
 506 }
 507
 508 Newkeys *
 509 kex_get_newkeys(int mode)
 510 {
 511         Newkeys *ret;
 512
 513         ret = current_keys[mode];
 514         current_keys[mode] = NULL;
 515         return ret;
 516 }
 517
 518 void
 519 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 520     u_int8_t cookie[8], u_int8_t id[16])
 521 {
 522         const EVP_MD *evp_md = EVP_md5();
 523         EVP_MD_CTX md;
 524         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 525         int len;
 526
 527         EVP_DigestInit(&md, evp_md);
 528
 529         len = BN_num_bytes(host_modulus);
 530         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 531                 fatal("%s: bad host modulus (len %d)", __func__, len);
 532         BN_bn2bin(host_modulus, nbuf);
 533         EVP_DigestUpdate(&md, nbuf, len);
 534
 535         len = BN_num_bytes(server_modulus);
 536         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 537                 fatal("%s: bad server modulus (len %d)", __func__, len);
 538         BN_bn2bin(server_modulus, nbuf);
 539         EVP_DigestUpdate(&md, nbuf, len);
 540
 541         EVP_DigestUpdate(&md, cookie, 8);
 542
 543         EVP_DigestFinal(&md, obuf, NULL);
 544         memcpy(id, obuf, 16);
 545
 546         memset(nbuf, 0, sizeof(nbuf));
 547         memset(obuf, 0, sizeof(obuf));
 548         memset(&md, 0, sizeof(md));
 549 }
 550
 551 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 552 void
 553 dump_digest(char *msg, u_char *digest, int len)
 554 {
 555         u_int i;
 556
 557         fprintf(stderr, "%s\n", msg);
 558         for (i = 0; i < len; i++) {
 559                 fprintf(stderr, "%02x", digest[i]);
 560                 if (i%32 == 31)
 561                         fprintf(stderr, "\n");
 562                 else if (i%8 == 7)
 563                         fprintf(stderr, " ");
 564         }
 565         fprintf(stderr, "\n");
 566 }
 567 #endif