crypto/openssh/kex.c

   1 /* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 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 <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 #include "roaming.h"
  52 #include "canohost.h"
  53
  54 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
  55 # if defined(HAVE_EVP_SHA256)
  56 # define evp_ssh_sha256 EVP_sha256
  57 # else
  58 extern const EVP_MD *evp_ssh_sha256(void);
  59 # endif
  60 #endif
  61
  62 /* prototype */
  63 static void kex_kexinit_finish(Kex *);
  64 static void kex_choose_conf(Kex *);
  65
  66 /* Validate KEX method name list */
  67 int
  68 kex_names_valid(const char *names)
  69 {
  70         char *s, *cp, *p;
  71
  72         if (names == NULL || strcmp(names, "") == 0)
  73                 return 0;
  74         s = cp = xstrdup(names);
  75         for ((p = strsep(&cp, ",")); p && *p != '\0';
  76             (p = strsep(&cp, ","))) {
  77                 if (strcmp(p, KEX_DHGEX_SHA256) != 0 &&
  78                     strcmp(p, KEX_DHGEX_SHA1) != 0 &&
  79                     strcmp(p, KEX_DH14) != 0 &&
  80                     strcmp(p, KEX_DH1) != 0 &&
  81                     (strncmp(p, KEX_ECDH_SHA2_STEM,
  82                     sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 ||
  83                     kex_ecdh_name_to_nid(p) == -1)) {
  84                         error("Unsupported KEX algorithm \"%.100s\"", p);
  85                         xfree(s);
  86                         return 0;
  87                 }
  88         }
  89         debug3("kex names ok: [%s]", names);
  90         xfree(s);
  91         return 1;
  92 }
  93
  94 /* put algorithm proposal into buffer */
  95 /* used in sshconnect.c as well as kex.c */
  96 void
  97 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
  98 {
  99         u_int i;
 100
 101         buffer_clear(b);
 102         /*
 103          * add a dummy cookie, the cookie will be overwritten by
 104          * kex_send_kexinit(), each time a kexinit is set
 105          */
 106         for (i = 0; i < KEX_COOKIE_LEN; i++)
 107                 buffer_put_char(b, 0);
 108         for (i = 0; i < PROPOSAL_MAX; i++)
 109                 buffer_put_cstring(b, proposal[i]);
 110         buffer_put_char(b, 0);                  /* first_kex_packet_follows */
 111         buffer_put_int(b, 0);                   /* uint32 reserved */
 112 }
 113
 114 /* parse buffer and return algorithm proposal */
 115 static char **
 116 kex_buf2prop(Buffer *raw, int *first_kex_follows)
 117 {
 118         Buffer b;
 119         u_int i;
 120         char **proposal;
 121
 122         proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
 123
 124         buffer_init(&b);
 125         buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
 126         /* skip cookie */
 127         for (i = 0; i < KEX_COOKIE_LEN; i++)
 128                 buffer_get_char(&b);
 129         /* extract kex init proposal strings */
 130         for (i = 0; i < PROPOSAL_MAX; i++) {
 131                 proposal[i] = buffer_get_cstring(&b,NULL);
 132                 debug2("kex_parse_kexinit: %s", proposal[i]);
 133         }
 134         /* first kex follows / reserved */
 135         i = buffer_get_char(&b);
 136         if (first_kex_follows != NULL)
 137                 *first_kex_follows = i;
 138         debug2("kex_parse_kexinit: first_kex_follows %d ", i);
 139         i = buffer_get_int(&b);
 140         debug2("kex_parse_kexinit: reserved %u ", i);
 141         buffer_free(&b);
 142         return proposal;
 143 }
 144
 145 static void
 146 kex_prop_free(char **proposal)
 147 {
 148         u_int i;
 149
 150         for (i = 0; i < PROPOSAL_MAX; i++)
 151                 xfree(proposal[i]);
 152         xfree(proposal);
 153 }
 154
 155 /* ARGSUSED */
 156 static void
 157 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 158 {
 159         error("Hm, kex protocol error: type %d seq %u", type, seq);
 160 }
 161
 162 static void
 163 kex_reset_dispatch(void)
 164 {
 165         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 166             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 167         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 168 }
 169
 170 void
 171 kex_finish(Kex *kex)
 172 {
 173         kex_reset_dispatch();
 174
 175         packet_start(SSH2_MSG_NEWKEYS);
 176         packet_send();
 177         /* packet_write_wait(); */
 178         debug("SSH2_MSG_NEWKEYS sent");
 179
 180         debug("expecting SSH2_MSG_NEWKEYS");
 181         packet_read_expect(SSH2_MSG_NEWKEYS);
 182         packet_check_eom();
 183         debug("SSH2_MSG_NEWKEYS received");
 184
 185         kex->done = 1;
 186         buffer_clear(&kex->peer);
 187         /* buffer_clear(&kex->my); */
 188         kex->flags &= ~KEX_INIT_SENT;
 189         xfree(kex->name);
 190         kex->name = NULL;
 191 }
 192
 193 void
 194 kex_send_kexinit(Kex *kex)
 195 {
 196         u_int32_t rnd = 0;
 197         u_char *cookie;
 198         u_int i;
 199
 200         if (kex == NULL) {
 201                 error("kex_send_kexinit: no kex, cannot rekey");
 202                 return;
 203         }
 204         if (kex->flags & KEX_INIT_SENT) {
 205                 debug("KEX_INIT_SENT");
 206                 return;
 207         }
 208         kex->done = 0;
 209
 210         /* generate a random cookie */
 211         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 212                 fatal("kex_send_kexinit: kex proposal too short");
 213         cookie = buffer_ptr(&kex->my);
 214         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 215                 if (i % 4 == 0)
 216                         rnd = arc4random();
 217                 cookie[i] = rnd;
 218                 rnd >>= 8;
 219         }
 220         packet_start(SSH2_MSG_KEXINIT);
 221         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 222         packet_send();
 223         debug("SSH2_MSG_KEXINIT sent");
 224         kex->flags |= KEX_INIT_SENT;
 225 }
 226
 227 /* ARGSUSED */
 228 void
 229 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 230 {
 231         char *ptr;
 232         u_int i, dlen;
 233         Kex *kex = (Kex *)ctxt;
 234
 235         debug("SSH2_MSG_KEXINIT received");
 236         if (kex == NULL)
 237                 fatal("kex_input_kexinit: no kex, cannot rekey");
 238
 239         ptr = packet_get_raw(&dlen);
 240         buffer_append(&kex->peer, ptr, dlen);
 241
 242         /* discard packet */
 243         for (i = 0; i < KEX_COOKIE_LEN; i++)
 244                 packet_get_char();
 245         for (i = 0; i < PROPOSAL_MAX; i++)
 246                 xfree(packet_get_string(NULL));
 247         (void) packet_get_char();
 248         (void) packet_get_int();
 249         packet_check_eom();
 250
 251         kex_kexinit_finish(kex);
 252 }
 253
 254 Kex *
 255 kex_setup(char *proposal[PROPOSAL_MAX])
 256 {
 257         Kex *kex;
 258
 259         kex = xcalloc(1, sizeof(*kex));
 260         buffer_init(&kex->peer);
 261         buffer_init(&kex->my);
 262         kex_prop2buf(&kex->my, proposal);
 263         kex->done = 0;
 264
 265         kex_send_kexinit(kex);                                  /* we start */
 266         kex_reset_dispatch();
 267
 268         return kex;
 269 }
 270
 271 static void
 272 kex_kexinit_finish(Kex *kex)
 273 {
 274         if (!(kex->flags & KEX_INIT_SENT))
 275                 kex_send_kexinit(kex);
 276
 277         kex_choose_conf(kex);
 278
 279         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 280             kex->kex[kex->kex_type] != NULL) {
 281                 (kex->kex[kex->kex_type])(kex);
 282         } else {
 283                 fatal("Unsupported key exchange %d", kex->kex_type);
 284         }
 285 }
 286
 287 static void
 288 choose_enc(Enc *enc, char *client, char *server)
 289 {
 290         char *name = match_list(client, server, NULL);
 291         if (name == NULL)
 292                 fatal("no matching cipher found: client %s server %s",
 293                     client, server);
 294         if ((enc->cipher = cipher_by_name(name)) == NULL)
 295                 fatal("matching cipher is not supported: %s", name);
 296         enc->name = name;
 297         enc->enabled = 0;
 298         enc->iv = NULL;
 299         enc->key = NULL;
 300         enc->key_len = cipher_keylen(enc->cipher);
 301         enc->block_size = cipher_blocksize(enc->cipher);
 302 }
 303
 304 static void
 305 choose_mac(Mac *mac, char *client, char *server)
 306 {
 307         char *name = match_list(client, server, NULL);
 308         if (name == NULL)
 309                 fatal("no matching mac found: client %s server %s",
 310                     client, server);
 311         if (mac_setup(mac, name) < 0)
 312                 fatal("unsupported mac %s", name);
 313         /* truncate the key */
 314         if (datafellows & SSH_BUG_HMAC)
 315                 mac->key_len = 16;
 316         mac->name = name;
 317         mac->key = NULL;
 318         mac->enabled = 0;
 319 }
 320
 321 static void
 322 choose_comp(Comp *comp, char *client, char *server)
 323 {
 324         char *name = match_list(client, server, NULL);
 325         if (name == NULL)
 326                 fatal("no matching comp found: client %s server %s", client, server);
 327         if (strcmp(name, "zlib@openssh.com") == 0) {
 328                 comp->type = COMP_DELAYED;
 329         } else if (strcmp(name, "zlib") == 0) {
 330                 comp->type = COMP_ZLIB;
 331         } else if (strcmp(name, "none") == 0) {
 332                 comp->type = COMP_NONE;
 333         } else {
 334                 fatal("unsupported comp %s", name);
 335         }
 336         comp->name = name;
 337 }
 338
 339 static void
 340 choose_kex(Kex *k, char *client, char *server)
 341 {
 342         k->name = match_list(client, server, NULL);
 343         if (k->name == NULL)
 344                 fatal("Unable to negotiate a key exchange method");
 345         if (strcmp(k->name, KEX_DH1) == 0) {
 346                 k->kex_type = KEX_DH_GRP1_SHA1;
 347                 k->evp_md = EVP_sha1();
 348         } else if (strcmp(k->name, KEX_DH14) == 0) {
 349                 k->kex_type = KEX_DH_GRP14_SHA1;
 350                 k->evp_md = EVP_sha1();
 351         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 352                 k->kex_type = KEX_DH_GEX_SHA1;
 353                 k->evp_md = EVP_sha1();
 354 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 355         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 356                 k->kex_type = KEX_DH_GEX_SHA256;
 357                 k->evp_md = evp_ssh_sha256();
 358         } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM,
 359             sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) {
 360                 k->kex_type = KEX_ECDH_SHA2;
 361                 k->evp_md = kex_ecdh_name_to_evpmd(k->name);
 362 #endif
 363         } else
 364                 fatal("bad kex alg %s", k->name);
 365 }
 366
 367 static void
 368 choose_hostkeyalg(Kex *k, char *client, char *server)
 369 {
 370         char *hostkeyalg = match_list(client, server, NULL);
 371         if (hostkeyalg == NULL)
 372                 fatal("no hostkey alg");
 373         k->hostkey_type = key_type_from_name(hostkeyalg);
 374         if (k->hostkey_type == KEY_UNSPEC)
 375                 fatal("bad hostkey alg '%s'", hostkeyalg);
 376         xfree(hostkeyalg);
 377 }
 378
 379 static int
 380 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 381 {
 382         static int check[] = {
 383                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 384         };
 385         int *idx;
 386         char *p;
 387
 388         for (idx = &check[0]; *idx != -1; idx++) {
 389                 if ((p = strchr(my[*idx], ',')) != NULL)
 390                         *p = '\0';
 391                 if ((p = strchr(peer[*idx], ',')) != NULL)
 392                         *p = '\0';
 393                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 394                         debug2("proposal mismatch: my %s peer %s",
 395                             my[*idx], peer[*idx]);
 396                         return (0);
 397                 }
 398         }
 399         debug2("proposals match");
 400         return (1);
 401 }
 402
 403 static void
 404 kex_choose_conf(Kex *kex)
 405 {
 406         Newkeys *newkeys;
 407         char **my, **peer;
 408         char **cprop, **sprop;
 409         int nenc, nmac, ncomp;
 410         u_int mode, ctos, need;
 411         int first_kex_follows, type;
 412         int log_flag = 0;
 413
 414         int auth_flag;
 415
 416         auth_flag = packet_authentication_state();
 417
 418         debug ("AUTH STATE IS %d", auth_flag);
 419
 420         my   = kex_buf2prop(&kex->my, NULL);
 421         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 422
 423         if (kex->server) {
 424                 cprop=peer;
 425                 sprop=my;
 426         } else {
 427                 cprop=my;
 428                 sprop=peer;
 429         }
 430
 431         /* Check whether server offers roaming */
 432         if (!kex->server) {
 433                 char *roaming;
 434                 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
 435                 if (roaming) {
 436                         kex->roaming = 1;
 437                         xfree(roaming);
 438                 }
 439         }
 440
 441         /* Algorithm Negotiation */
 442         for (mode = 0; mode < MODE_MAX; mode++) {
 443                 newkeys = xcalloc(1, sizeof(*newkeys));
 444                 kex->newkeys[mode] = newkeys;
 445                 ctos = (!kex->server && mode == MODE_OUT) ||
 446                     (kex->server && mode == MODE_IN);
 447                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 448                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 449                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 450                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 451                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 452                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 453                 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name);
 454                 if (strcmp(newkeys->enc.name, "none") == 0) {
 455                                 debug("Requesting NONE. Authflag is %d", auth_flag);
 456                         if (auth_flag == 1) {
 457                                 debug("None requested post authentication.");
 458                         } else {
 459                                 fatal("Pre-authentication none cipher requests are not allowed.");
 460                         }
 461                 }
 462                 debug("kex: %s %s %s %s",
 463                     ctos ? "client->server" : "server->client",
 464                     newkeys->enc.name,
 465                     newkeys->mac.name,
 466                     newkeys->comp.name);
 467                 /* client starts withctos = 0 && log flag = 0 and no log*/
 468                 /* 2nd client pass ctos=1 and flag = 1 so no log*/
 469                 /* server starts with ctos =1 && log_flag = 0 so log */
 470                 /* 2nd sever pass ctos = 1 && log flag = 1 so no log*/
 471                 /* -cjr*/
 472                 if (ctos && !log_flag) {
 473                         logit("SSH: Server;Ltype: Kex;Remote: %s-%d;Enc: %s;MAC: %s;Comp: %s",
 474                               get_remote_ipaddr(),
 475                               get_remote_port(),
 476                               newkeys->enc.name,
 477                               newkeys->mac.name,
 478                               newkeys->comp.name);
 479                 }
 480                 log_flag = 1;
 481         }
 482         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 483         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 484             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 485         need = 0;
 486         for (mode = 0; mode < MODE_MAX; mode++) {
 487                 newkeys = kex->newkeys[mode];
 488                 if (need < newkeys->enc.key_len)
 489                         need = newkeys->enc.key_len;
 490                 if (need < newkeys->enc.block_size)
 491                         need = newkeys->enc.block_size;
 492                 if (need < newkeys->mac.key_len)
 493                         need = newkeys->mac.key_len;
 494         }
 495         /* XXX need runden? */
 496         kex->we_need = need;
 497
 498         /* ignore the next message if the proposals do not match */
 499         if (first_kex_follows && !proposals_match(my, peer) &&
 500             !(datafellows & SSH_BUG_FIRSTKEX)) {
 501                 type = packet_read();
 502                 debug2("skipping next packet (type %u)", type);
 503         }
 504
 505         kex_prop_free(my);
 506         kex_prop_free(peer);
 507 }
 508
 509 static u_char *
 510 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 511     BIGNUM *shared_secret)
 512 {
 513         Buffer b;
 514         EVP_MD_CTX md;
 515         char c = id;
 516         u_int have;
 517         int mdsz;
 518         u_char *digest;
 519
 520         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 521                 fatal("bad kex md size %d", mdsz);
 522         digest = xmalloc(roundup(need, mdsz));
 523
 524         buffer_init(&b);
 525         buffer_put_bignum2(&b, shared_secret);
 526
 527         /* K1 = HASH(K || H || "A" || session_id) */
 528         EVP_DigestInit(&md, kex->evp_md);
 529         if (!(datafellows & SSH_BUG_DERIVEKEY))
 530                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 531         EVP_DigestUpdate(&md, hash, hashlen);
 532         EVP_DigestUpdate(&md, &c, 1);
 533         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 534         EVP_DigestFinal(&md, digest, NULL);
 535
 536         /*
 537          * expand key:
 538          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 539          * Key = K1 || K2 || ... || Kn
 540          */
 541         for (have = mdsz; need > have; have += mdsz) {
 542                 EVP_DigestInit(&md, kex->evp_md);
 543                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 544                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 545                 EVP_DigestUpdate(&md, hash, hashlen);
 546                 EVP_DigestUpdate(&md, digest, have);
 547                 EVP_DigestFinal(&md, digest + have, NULL);
 548         }
 549         buffer_free(&b);
 550 #ifdef DEBUG_KEX
 551         fprintf(stderr, "key '%c'== ", c);
 552         dump_digest("key", digest, need);
 553 #endif
 554         return digest;
 555 }
 556
 557 Newkeys *current_keys[MODE_MAX];
 558
 559 #define NKEYS   6
 560 void
 561 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 562 {
 563         u_char *keys[NKEYS];
 564         u_int i, mode, ctos;
 565
 566         for (i = 0; i < NKEYS; i++) {
 567                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 568                     shared_secret);
 569         }
 570
 571         debug2("kex_derive_keys");
 572         for (mode = 0; mode < MODE_MAX; mode++) {
 573                 current_keys[mode] = kex->newkeys[mode];
 574                 kex->newkeys[mode] = NULL;
 575                 ctos = (!kex->server && mode == MODE_OUT) ||
 576                     (kex->server && mode == MODE_IN);
 577                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 578                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 579                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 580         }
 581 }
 582
 583 Newkeys *
 584 kex_get_newkeys(int mode)
 585 {
 586         Newkeys *ret;
 587
 588         ret = current_keys[mode];
 589         current_keys[mode] = NULL;
 590         return ret;
 591 }
 592
 593 void
 594 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 595     u_int8_t cookie[8], u_int8_t id[16])
 596 {
 597         const EVP_MD *evp_md = EVP_md5();
 598         EVP_MD_CTX md;
 599         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 600         int len;
 601
 602         EVP_DigestInit(&md, evp_md);
 603
 604         len = BN_num_bytes(host_modulus);
 605         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 606                 fatal("%s: bad host modulus (len %d)", __func__, len);
 607         BN_bn2bin(host_modulus, nbuf);
 608         EVP_DigestUpdate(&md, nbuf, len);
 609
 610         len = BN_num_bytes(server_modulus);
 611         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 612                 fatal("%s: bad server modulus (len %d)", __func__, len);
 613         BN_bn2bin(server_modulus, nbuf);
 614         EVP_DigestUpdate(&md, nbuf, len);
 615
 616         EVP_DigestUpdate(&md, cookie, 8);
 617
 618         EVP_DigestFinal(&md, obuf, NULL);
 619         memcpy(id, obuf, 16);
 620
 621         memset(nbuf, 0, sizeof(nbuf));
 622         memset(obuf, 0, sizeof(obuf));
 623         memset(&md, 0, sizeof(md));
 624 }
 625
 626 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
 627 void
 628 dump_digest(char *msg, u_char *digest, int len)
 629 {
 630         int i;
 631
 632         fprintf(stderr, "%s\n", msg);
 633         for (i = 0; i < len; i++) {
 634                 fprintf(stderr, "%02x", digest[i]);
 635                 if (i%32 == 31)
 636                         fprintf(stderr, "\n");
 637                 else if (i%8 == 7)
 638                         fprintf(stderr, " ");
 639         }
 640         fprintf(stderr, "\n");
 641 }
 642 #endif