crypto/openssh-4/kex.c

   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 1.60 2004/06/21 17:36:31 avsm 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 rnd = 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                         rnd = arc4random();
 172                 cookie[i] = rnd;
 173                 rnd >>= 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_DH14) == 0) {
 297                 k->kex_type = KEX_DH_GRP14_SHA1;
 298         } else if (strcmp(k->name, KEX_DHGEX) == 0) {
 299                 k->kex_type = KEX_DH_GEX_SHA1;
 300         } else
 301                 fatal("bad kex alg %s", k->name);
 302 }
 303 static void
 304 choose_hostkeyalg(Kex *k, char *client, char *server)
 305 {
 306         char *hostkeyalg = match_list(client, server, NULL);
 307         if (hostkeyalg == NULL)
 308                 fatal("no hostkey alg");
 309         k->hostkey_type = key_type_from_name(hostkeyalg);
 310         if (k->hostkey_type == KEY_UNSPEC)
 311                 fatal("bad hostkey alg '%s'", hostkeyalg);
 312         xfree(hostkeyalg);
 313 }
 314
 315 static int
 316 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 317 {
 318         static int check[] = {
 319                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 320         };
 321         int *idx;
 322         char *p;
 323
 324         for (idx = &check[0]; *idx != -1; idx++) {
 325                 if ((p = strchr(my[*idx], ',')) != NULL)
 326                         *p = '\0';
 327                 if ((p = strchr(peer[*idx], ',')) != NULL)
 328                         *p = '\0';
 329                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 330                         debug2("proposal mismatch: my %s peer %s",
 331                             my[*idx], peer[*idx]);
 332                         return (0);
 333                 }
 334         }
 335         debug2("proposals match");
 336         return (1);
 337 }
 338
 339 static void
 340 kex_choose_conf(Kex *kex)
 341 {
 342         Newkeys *newkeys;
 343         char **my, **peer;
 344         char **cprop, **sprop;
 345         int nenc, nmac, ncomp;
 346         int mode;
 347         int ctos;                               /* direction: if true client-to-server */
 348         int need;
 349         int first_kex_follows, type;
 350
 351         my   = kex_buf2prop(&kex->my, NULL);
 352         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 353
 354         if (kex->server) {
 355                 cprop=peer;
 356                 sprop=my;
 357         } else {
 358                 cprop=my;
 359                 sprop=peer;
 360         }
 361
 362         /* Algorithm Negotiation */
 363         for (mode = 0; mode < MODE_MAX; mode++) {
 364                 newkeys = xmalloc(sizeof(*newkeys));
 365                 memset(newkeys, 0, sizeof(*newkeys));
 366                 kex->newkeys[mode] = newkeys;
 367                 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
 368                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 369                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 370                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 371                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 372                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 373                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 374                 debug("kex: %s %s %s %s",
 375                     ctos ? "client->server" : "server->client",
 376                     newkeys->enc.name,
 377                     newkeys->mac.name,
 378                     newkeys->comp.name);
 379         }
 380         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 381         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 382             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 383         need = 0;
 384         for (mode = 0; mode < MODE_MAX; mode++) {
 385                 newkeys = kex->newkeys[mode];
 386                 if (need < newkeys->enc.key_len)
 387                         need = newkeys->enc.key_len;
 388                 if (need < newkeys->enc.block_size)
 389                         need = newkeys->enc.block_size;
 390                 if (need < newkeys->mac.key_len)
 391                         need = newkeys->mac.key_len;
 392         }
 393         /* XXX need runden? */
 394         kex->we_need = need;
 395
 396         /* ignore the next message if the proposals do not match */
 397         if (first_kex_follows && !proposals_match(my, peer) &&
 398            !(datafellows & SSH_BUG_FIRSTKEX)) {
 399                 type = packet_read();
 400                 debug2("skipping next packet (type %u)", type);
 401         }
 402
 403         kex_prop_free(my);
 404         kex_prop_free(peer);
 405 }
 406
 407 static u_char *
 408 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
 409 {
 410         Buffer b;
 411         const EVP_MD *evp_md = EVP_sha1();
 412         EVP_MD_CTX md;
 413         char c = id;
 414         int have;
 415         int mdsz = EVP_MD_size(evp_md);
 416         u_char *digest = xmalloc(roundup(need, mdsz));
 417
 418         buffer_init(&b);
 419         buffer_put_bignum2(&b, shared_secret);
 420
 421         /* K1 = HASH(K || H || "A" || session_id) */
 422         EVP_DigestInit(&md, evp_md);
 423         if (!(datafellows & SSH_BUG_DERIVEKEY))
 424                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 425         EVP_DigestUpdate(&md, hash, mdsz);
 426         EVP_DigestUpdate(&md, &c, 1);
 427         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 428         EVP_DigestFinal(&md, digest, NULL);
 429
 430         /*
 431          * expand key:
 432          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 433          * Key = K1 || K2 || ... || Kn
 434          */
 435         for (have = mdsz; need > have; have += mdsz) {
 436                 EVP_DigestInit(&md, evp_md);
 437                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 438                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 439                 EVP_DigestUpdate(&md, hash, mdsz);
 440                 EVP_DigestUpdate(&md, digest, have);
 441                 EVP_DigestFinal(&md, digest + have, NULL);
 442         }
 443         buffer_free(&b);
 444 #ifdef DEBUG_KEX
 445         fprintf(stderr, "key '%c'== ", c);
 446         dump_digest("key", digest, need);
 447 #endif
 448         return digest;
 449 }
 450
 451 Newkeys *current_keys[MODE_MAX];
 452
 453 #define NKEYS   6
 454 void
 455 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
 456 {
 457         u_char *keys[NKEYS];
 458         int i, mode, ctos;
 459
 460         for (i = 0; i < NKEYS; i++)
 461                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
 462
 463         debug2("kex_derive_keys");
 464         for (mode = 0; mode < MODE_MAX; mode++) {
 465                 current_keys[mode] = kex->newkeys[mode];
 466                 kex->newkeys[mode] = NULL;
 467                 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
 468                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 469                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 470                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 471         }
 472 }
 473
 474 Newkeys *
 475 kex_get_newkeys(int mode)
 476 {
 477         Newkeys *ret;
 478
 479         ret = current_keys[mode];
 480         current_keys[mode] = NULL;
 481         return ret;
 482 }
 483
 484 void
 485 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 486     u_int8_t cookie[8], u_int8_t id[16])
 487 {
 488         const EVP_MD *evp_md = EVP_md5();
 489         EVP_MD_CTX md;
 490         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 491         int len;
 492
 493         EVP_DigestInit(&md, evp_md);
 494
 495         len = BN_num_bytes(host_modulus);
 496         if (len < (512 / 8) || len > sizeof(nbuf))
 497                 fatal("%s: bad host modulus (len %d)", __func__, len);
 498         BN_bn2bin(host_modulus, nbuf);
 499         EVP_DigestUpdate(&md, nbuf, len);
 500
 501         len = BN_num_bytes(server_modulus);
 502         if (len < (512 / 8) || len > sizeof(nbuf))
 503                 fatal("%s: bad server modulus (len %d)", __func__, len);
 504         BN_bn2bin(server_modulus, nbuf);
 505         EVP_DigestUpdate(&md, nbuf, len);
 506
 507         EVP_DigestUpdate(&md, cookie, 8);
 508
 509         EVP_DigestFinal(&md, obuf, NULL);
 510         memcpy(id, obuf, 16);
 511
 512         memset(nbuf, 0, sizeof(nbuf));
 513         memset(obuf, 0, sizeof(obuf));
 514         memset(&md, 0, sizeof(md));
 515 }
 516
 517 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 518 void
 519 dump_digest(char *msg, u_char *digest, int len)
 520 {
 521         int i;
 522
 523         fprintf(stderr, "%s\n", msg);
 524         for (i = 0; i< len; i++) {
 525                 fprintf(stderr, "%02x", digest[i]);
 526                 if (i%32 == 31)
 527                         fprintf(stderr, "\n");
 528                 else if (i%8 == 7)
 529                         fprintf(stderr, " ");
 530         }
 531         fprintf(stderr, "\n");
 532 }
 533 #endif