kex.c

   1 /* $OpenBSD: kex.c,v 1.71 2006/03/25 13:17:02 djm 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 "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 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
  48 # if defined(HAVE_EVP_SHA256)
  49 # define evp_ssh_sha256 EVP_sha256
  50 # else
  51 extern const EVP_MD *evp_ssh_sha256(void);
  52 # endif
  53 #endif
  54
  55 /* prototype */
  56 static void kex_kexinit_finish(Kex *);
  57 static void kex_choose_conf(Kex *);
  58
  59 /* put algorithm proposal into buffer */
  60 static void
  61 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
  62 {
  63         u_int i;
  64
  65         buffer_clear(b);
  66         /*
  67          * add a dummy cookie, the cookie will be overwritten by
  68          * kex_send_kexinit(), each time a kexinit is set
  69          */
  70         for (i = 0; i < KEX_COOKIE_LEN; i++)
  71                 buffer_put_char(b, 0);
  72         for (i = 0; i < PROPOSAL_MAX; i++)
  73                 buffer_put_cstring(b, proposal[i]);
  74         buffer_put_char(b, 0);                  /* first_kex_packet_follows */
  75         buffer_put_int(b, 0);                   /* uint32 reserved */
  76 }
  77
  78 /* parse buffer and return algorithm proposal */
  79 static char **
  80 kex_buf2prop(Buffer *raw, int *first_kex_follows)
  81 {
  82         Buffer b;
  83         int i;
  84         char **proposal;
  85
  86         proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
  87
  88         buffer_init(&b);
  89         buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
  90         /* skip cookie */
  91         for (i = 0; i < KEX_COOKIE_LEN; i++)
  92                 buffer_get_char(&b);
  93         /* extract kex init proposal strings */
  94         for (i = 0; i < PROPOSAL_MAX; i++) {
  95                 proposal[i] = buffer_get_string(&b,NULL);
  96                 debug2("kex_parse_kexinit: %s", proposal[i]);
  97         }
  98         /* first kex follows / reserved */
  99         i = buffer_get_char(&b);
 100         if (first_kex_follows != NULL)
 101                 *first_kex_follows = i;
 102         debug2("kex_parse_kexinit: first_kex_follows %d ", i);
 103         i = buffer_get_int(&b);
 104         debug2("kex_parse_kexinit: reserved %d ", i);
 105         buffer_free(&b);
 106         return proposal;
 107 }
 108
 109 static void
 110 kex_prop_free(char **proposal)
 111 {
 112         u_int i;
 113
 114         for (i = 0; i < PROPOSAL_MAX; i++)
 115                 xfree(proposal[i]);
 116         xfree(proposal);
 117 }
 118
 119 static void
 120 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 121 {
 122         error("Hm, kex protocol error: type %d seq %u", type, seq);
 123 }
 124
 125 static void
 126 kex_reset_dispatch(void)
 127 {
 128         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 129             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 130         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 131 }
 132
 133 void
 134 kex_finish(Kex *kex)
 135 {
 136         kex_reset_dispatch();
 137
 138         packet_start(SSH2_MSG_NEWKEYS);
 139         packet_send();
 140         /* packet_write_wait(); */
 141         debug("SSH2_MSG_NEWKEYS sent");
 142
 143         debug("expecting SSH2_MSG_NEWKEYS");
 144         packet_read_expect(SSH2_MSG_NEWKEYS);
 145         packet_check_eom();
 146         debug("SSH2_MSG_NEWKEYS received");
 147
 148         kex->done = 1;
 149         buffer_clear(&kex->peer);
 150         /* buffer_clear(&kex->my); */
 151         kex->flags &= ~KEX_INIT_SENT;
 152         xfree(kex->name);
 153         kex->name = NULL;
 154 }
 155
 156 void
 157 kex_send_kexinit(Kex *kex)
 158 {
 159         u_int32_t rnd = 0;
 160         u_char *cookie;
 161         u_int i;
 162
 163         if (kex == NULL) {
 164                 error("kex_send_kexinit: no kex, cannot rekey");
 165                 return;
 166         }
 167         if (kex->flags & KEX_INIT_SENT) {
 168                 debug("KEX_INIT_SENT");
 169                 return;
 170         }
 171         kex->done = 0;
 172
 173         /* generate a random cookie */
 174         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 175                 fatal("kex_send_kexinit: kex proposal too short");
 176         cookie = buffer_ptr(&kex->my);
 177         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 178                 if (i % 4 == 0)
 179                         rnd = arc4random();
 180                 cookie[i] = rnd;
 181                 rnd >>= 8;
 182         }
 183         packet_start(SSH2_MSG_KEXINIT);
 184         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 185         packet_send();
 186         debug("SSH2_MSG_KEXINIT sent");
 187         kex->flags |= KEX_INIT_SENT;
 188 }
 189
 190 void
 191 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 192 {
 193         char *ptr;
 194         u_int i, dlen;
 195         Kex *kex = (Kex *)ctxt;
 196
 197         debug("SSH2_MSG_KEXINIT received");
 198         if (kex == NULL)
 199                 fatal("kex_input_kexinit: no kex, cannot rekey");
 200
 201         ptr = packet_get_raw(&dlen);
 202         buffer_append(&kex->peer, ptr, dlen);
 203
 204         /* discard packet */
 205         for (i = 0; i < KEX_COOKIE_LEN; i++)
 206                 packet_get_char();
 207         for (i = 0; i < PROPOSAL_MAX; i++)
 208                 xfree(packet_get_string(NULL));
 209         (void) packet_get_char();
 210         (void) packet_get_int();
 211         packet_check_eom();
 212
 213         kex_kexinit_finish(kex);
 214 }
 215
 216 Kex *
 217 kex_setup(char *proposal[PROPOSAL_MAX])
 218 {
 219         Kex *kex;
 220
 221         kex = xcalloc(1, sizeof(*kex));
 222         buffer_init(&kex->peer);
 223         buffer_init(&kex->my);
 224         kex_prop2buf(&kex->my, proposal);
 225         kex->done = 0;
 226
 227         kex_send_kexinit(kex);                                  /* we start */
 228         kex_reset_dispatch();
 229
 230         return kex;
 231 }
 232
 233 static void
 234 kex_kexinit_finish(Kex *kex)
 235 {
 236         if (!(kex->flags & KEX_INIT_SENT))
 237                 kex_send_kexinit(kex);
 238
 239         kex_choose_conf(kex);
 240
 241         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 242             kex->kex[kex->kex_type] != NULL) {
 243                 (kex->kex[kex->kex_type])(kex);
 244         } else {
 245                 fatal("Unsupported key exchange %d", kex->kex_type);
 246         }
 247 }
 248
 249 static void
 250 choose_enc(Enc *enc, char *client, char *server)
 251 {
 252         char *name = match_list(client, server, NULL);
 253         if (name == NULL)
 254                 fatal("no matching cipher found: client %s server %s", client, server);
 255         if ((enc->cipher = cipher_by_name(name)) == NULL)
 256                 fatal("matching cipher is not supported: %s", name);
 257         enc->name = name;
 258         enc->enabled = 0;
 259         enc->iv = NULL;
 260         enc->key = NULL;
 261         enc->key_len = cipher_keylen(enc->cipher);
 262         enc->block_size = cipher_blocksize(enc->cipher);
 263 }
 264
 265 static void
 266 choose_mac(Mac *mac, char *client, char *server)
 267 {
 268         char *name = match_list(client, server, NULL);
 269         if (name == NULL)
 270                 fatal("no matching mac found: client %s server %s", client, server);
 271         if (mac_init(mac, name) < 0)
 272                 fatal("unsupported mac %s", name);
 273         /* truncate the key */
 274         if (datafellows & SSH_BUG_HMAC)
 275                 mac->key_len = 16;
 276         mac->name = name;
 277         mac->key = NULL;
 278         mac->enabled = 0;
 279 }
 280
 281 static void
 282 choose_comp(Comp *comp, char *client, char *server)
 283 {
 284         char *name = match_list(client, server, NULL);
 285         if (name == NULL)
 286                 fatal("no matching comp found: client %s server %s", client, server);
 287         if (strcmp(name, "zlib@openssh.com") == 0) {
 288                 comp->type = COMP_DELAYED;
 289         } else if (strcmp(name, "zlib") == 0) {
 290                 comp->type = COMP_ZLIB;
 291         } else if (strcmp(name, "none") == 0) {
 292                 comp->type = COMP_NONE;
 293         } else {
 294                 fatal("unsupported comp %s", name);
 295         }
 296         comp->name = name;
 297 }
 298
 299 static void
 300 choose_kex(Kex *k, char *client, char *server)
 301 {
 302         k->name = match_list(client, server, NULL);
 303         if (k->name == NULL)
 304                 fatal("no kex alg");
 305         if (strcmp(k->name, KEX_DH1) == 0) {
 306                 k->kex_type = KEX_DH_GRP1_SHA1;
 307                 k->evp_md = EVP_sha1();
 308         } else if (strcmp(k->name, KEX_DH14) == 0) {
 309                 k->kex_type = KEX_DH_GRP14_SHA1;
 310                 k->evp_md = EVP_sha1();
 311         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 312                 k->kex_type = KEX_DH_GEX_SHA1;
 313                 k->evp_md = EVP_sha1();
 314 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 315         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 316                 k->kex_type = KEX_DH_GEX_SHA256;
 317                 k->evp_md = evp_ssh_sha256();
 318 #endif
 319         } else
 320                 fatal("bad kex alg %s", k->name);
 321 }
 322
 323 static void
 324 choose_hostkeyalg(Kex *k, char *client, char *server)
 325 {
 326         char *hostkeyalg = match_list(client, server, NULL);
 327         if (hostkeyalg == NULL)
 328                 fatal("no hostkey alg");
 329         k->hostkey_type = key_type_from_name(hostkeyalg);
 330         if (k->hostkey_type == KEY_UNSPEC)
 331                 fatal("bad hostkey alg '%s'", hostkeyalg);
 332         xfree(hostkeyalg);
 333 }
 334
 335 static int
 336 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 337 {
 338         static int check[] = {
 339                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 340         };
 341         int *idx;
 342         char *p;
 343
 344         for (idx = &check[0]; *idx != -1; idx++) {
 345                 if ((p = strchr(my[*idx], ',')) != NULL)
 346                         *p = '\0';
 347                 if ((p = strchr(peer[*idx], ',')) != NULL)
 348                         *p = '\0';
 349                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 350                         debug2("proposal mismatch: my %s peer %s",
 351                             my[*idx], peer[*idx]);
 352                         return (0);
 353                 }
 354         }
 355         debug2("proposals match");
 356         return (1);
 357 }
 358
 359 static void
 360 kex_choose_conf(Kex *kex)
 361 {
 362         Newkeys *newkeys;
 363         char **my, **peer;
 364         char **cprop, **sprop;
 365         int nenc, nmac, ncomp;
 366         u_int mode, ctos, need;
 367         int first_kex_follows, type;
 368
 369         my   = kex_buf2prop(&kex->my, NULL);
 370         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 371
 372         if (kex->server) {
 373                 cprop=peer;
 374                 sprop=my;
 375         } else {
 376                 cprop=my;
 377                 sprop=peer;
 378         }
 379
 380         /* Algorithm Negotiation */
 381         for (mode = 0; mode < MODE_MAX; mode++) {
 382                 newkeys = xcalloc(1, sizeof(*newkeys));
 383                 kex->newkeys[mode] = newkeys;
 384                 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
 385                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 386                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 387                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 388                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 389                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 390                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 391                 debug("kex: %s %s %s %s",
 392                     ctos ? "client->server" : "server->client",
 393                     newkeys->enc.name,
 394                     newkeys->mac.name,
 395                     newkeys->comp.name);
 396         }
 397         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 398         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 399             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 400         need = 0;
 401         for (mode = 0; mode < MODE_MAX; mode++) {
 402                 newkeys = kex->newkeys[mode];
 403                 if (need < newkeys->enc.key_len)
 404                         need = newkeys->enc.key_len;
 405                 if (need < newkeys->enc.block_size)
 406                         need = newkeys->enc.block_size;
 407                 if (need < newkeys->mac.key_len)
 408                         need = newkeys->mac.key_len;
 409         }
 410         /* XXX need runden? */
 411         kex->we_need = need;
 412
 413         /* ignore the next message if the proposals do not match */
 414         if (first_kex_follows && !proposals_match(my, peer) &&
 415             !(datafellows & SSH_BUG_FIRSTKEX)) {
 416                 type = packet_read();
 417                 debug2("skipping next packet (type %u)", type);
 418         }
 419
 420         kex_prop_free(my);
 421         kex_prop_free(peer);
 422 }
 423
 424 static u_char *
 425 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 426     BIGNUM *shared_secret)
 427 {
 428         Buffer b;
 429         EVP_MD_CTX md;
 430         char c = id;
 431         u_int have;
 432         int mdsz;
 433         u_char *digest;
 434
 435         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 436                 fatal("bad kex md size %d", mdsz);
 437         digest = xmalloc(roundup(need, mdsz));
 438
 439         buffer_init(&b);
 440         buffer_put_bignum2(&b, shared_secret);
 441
 442         /* K1 = HASH(K || H || "A" || session_id) */
 443         EVP_DigestInit(&md, kex->evp_md);
 444         if (!(datafellows & SSH_BUG_DERIVEKEY))
 445                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 446         EVP_DigestUpdate(&md, hash, hashlen);
 447         EVP_DigestUpdate(&md, &c, 1);
 448         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 449         EVP_DigestFinal(&md, digest, NULL);
 450
 451         /*
 452          * expand key:
 453          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 454          * Key = K1 || K2 || ... || Kn
 455          */
 456         for (have = mdsz; need > have; have += mdsz) {
 457                 EVP_DigestInit(&md, kex->evp_md);
 458                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 459                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 460                 EVP_DigestUpdate(&md, hash, hashlen);
 461                 EVP_DigestUpdate(&md, digest, have);
 462                 EVP_DigestFinal(&md, digest + have, NULL);
 463         }
 464         buffer_free(&b);
 465 #ifdef DEBUG_KEX
 466         fprintf(stderr, "key '%c'== ", c);
 467         dump_digest("key", digest, need);
 468 #endif
 469         return digest;
 470 }
 471
 472 Newkeys *current_keys[MODE_MAX];
 473
 474 #define NKEYS   6
 475 void
 476 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 477 {
 478         u_char *keys[NKEYS];
 479         u_int i, mode, ctos;
 480
 481         for (i = 0; i < NKEYS; i++) {
 482                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 483                     shared_secret);
 484         }
 485
 486         debug2("kex_derive_keys");
 487         for (mode = 0; mode < MODE_MAX; mode++) {
 488                 current_keys[mode] = kex->newkeys[mode];
 489                 kex->newkeys[mode] = NULL;
 490                 ctos = (!kex->server && mode == MODE_OUT) ||
 491                     (kex->server && mode == MODE_IN);
 492                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 493                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 494                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 495         }
 496 }
 497
 498 Newkeys *
 499 kex_get_newkeys(int mode)
 500 {
 501         Newkeys *ret;
 502
 503         ret = current_keys[mode];
 504         current_keys[mode] = NULL;
 505         return ret;
 506 }
 507
 508 void
 509 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 510     u_int8_t cookie[8], u_int8_t id[16])
 511 {
 512         const EVP_MD *evp_md = EVP_md5();
 513         EVP_MD_CTX md;
 514         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 515         int len;
 516
 517         EVP_DigestInit(&md, evp_md);
 518
 519         len = BN_num_bytes(host_modulus);
 520         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 521                 fatal("%s: bad host modulus (len %d)", __func__, len);
 522         BN_bn2bin(host_modulus, nbuf);
 523         EVP_DigestUpdate(&md, nbuf, len);
 524
 525         len = BN_num_bytes(server_modulus);
 526         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 527                 fatal("%s: bad server modulus (len %d)", __func__, len);
 528         BN_bn2bin(server_modulus, nbuf);
 529         EVP_DigestUpdate(&md, nbuf, len);
 530
 531         EVP_DigestUpdate(&md, cookie, 8);
 532
 533         EVP_DigestFinal(&md, obuf, NULL);
 534         memcpy(id, obuf, 16);
 535
 536         memset(nbuf, 0, sizeof(nbuf));
 537         memset(obuf, 0, sizeof(obuf));
 538         memset(&md, 0, sizeof(md));
 539 }
 540
 541 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 542 void
 543 dump_digest(char *msg, u_char *digest, int len)
 544 {
 545         u_int i;
 546
 547         fprintf(stderr, "%s\n", msg);
 548         for (i = 0; i< len; i++) {
 549                 fprintf(stderr, "%02x", digest[i]);
 550                 if (i%32 == 31)
 551                         fprintf(stderr, "\n");
 552                 else if (i%8 == 7)
 553                         fprintf(stderr, " ");
 554         }
 555         fprintf(stderr, "\n");
 556 }
 557 #endif