kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.12 2010/11/10 01:33:07 djm Exp $ */
   2 /*
   3  * Copyright (c) 2000 Niels Provos.  All rights reserved.
   4  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "includes.h"
  28
  29 #include <sys/types.h>
  30
  31 #include <openssl/dh.h>
  32
  33 #include <stdarg.h>
  34 #include <stdio.h>
  35 #include <string.h>
  36 #include <signal.h>
  37
  38 #include "xmalloc.h"
  39 #include "buffer.h"
  40 #include "key.h"
  41 #include "cipher.h"
  42 #include "kex.h"
  43 #include "log.h"
  44 #include "packet.h"
  45 #include "dh.h"
  46 #include "ssh2.h"
  47 #include "compat.h"
  48
  49 void
  50 kexgex_client(Kex *kex)
  51 {
  52         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  53         BIGNUM *p = NULL, *g = NULL;
  54         Key *server_host_key;
  55         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  56         u_int klen, slen, sbloblen, hashlen;
  57         int kout;
  58         int min, max, nbits;
  59         DH *dh;
  60
  61         nbits = dh_estimate(kex->we_need * 8);
  62
  63         if (datafellows & SSH_OLD_DHGEX) {
  64                 /* Old GEX request */
  65                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
  66                 packet_put_int(nbits);
  67                 min = DH_GRP_MIN;
  68                 max = DH_GRP_MAX;
  69
  70                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
  71         } else {
  72                 /* New GEX request */
  73                 min = DH_GRP_MIN;
  74                 max = DH_GRP_MAX;
  75                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
  76                 packet_put_int(min);
  77                 packet_put_int(nbits);
  78                 packet_put_int(max);
  79
  80                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  81                     min, nbits, max);
  82         }
  83 #ifdef DEBUG_KEXDH
  84         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  85             min, nbits, max);
  86 #endif
  87         packet_send();
  88
  89         debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  90         packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
  91
  92         if ((p = BN_new()) == NULL)
  93                 fatal("BN_new");
  94         packet_get_bignum2(p);
  95         if ((g = BN_new()) == NULL)
  96                 fatal("BN_new");
  97         packet_get_bignum2(g);
  98         packet_check_eom();
  99
 100         if (BN_num_bits(p) < min || BN_num_bits(p) > max)
 101                 fatal("DH_GEX group out of range: %d !< %d !< %d",
 102                     min, BN_num_bits(p), max);
 103
 104         dh = dh_new_group(g, p);
 105         dh_gen_key(dh, kex->we_need * 8);
 106
 107 #ifdef DEBUG_KEXDH
 108         DHparams_print_fp(stderr, dh);
 109         fprintf(stderr, "pub= ");
 110         BN_print_fp(stderr, dh->pub_key);
 111         fprintf(stderr, "\n");
 112 #endif
 113
 114         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 115         /* generate and send 'e', client DH public key */
 116         packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
 117         packet_put_bignum2(dh->pub_key);
 118         packet_send();
 119
 120         debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
 121         packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
 122
 123         /* key, cert */
 124         server_host_key_blob = packet_get_string(&sbloblen);
 125         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
 126         if (server_host_key == NULL)
 127                 fatal("cannot decode server_host_key_blob");
 128         if (server_host_key->type != kex->hostkey_type)
 129                 fatal("type mismatch for decoded server_host_key_blob");
 130         if (kex->verify_host_key == NULL)
 131                 fatal("cannot verify server_host_key");
 132         if (kex->verify_host_key(server_host_key) == -1)
 133                 fatal("server_host_key verification failed");
 134
 135         /* DH parameter f, server public DH key */
 136         if ((dh_server_pub = BN_new()) == NULL)
 137                 fatal("dh_server_pub == NULL");
 138         packet_get_bignum2(dh_server_pub);
 139
 140 #ifdef DEBUG_KEXDH
 141         fprintf(stderr, "dh_server_pub= ");
 142         BN_print_fp(stderr, dh_server_pub);
 143         fprintf(stderr, "\n");
 144         debug("bits %d", BN_num_bits(dh_server_pub));
 145 #endif
 146
 147         /* signed H */
 148         signature = packet_get_string(&slen);
 149         packet_check_eom();
 150
 151         if (!dh_pub_is_valid(dh, dh_server_pub))
 152                 packet_disconnect("bad server public DH value");
 153
 154         klen = DH_size(dh);
 155         kbuf = xmalloc(klen);
 156         if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0)
 157                 fatal("DH_compute_key: failed");
 158 #ifdef DEBUG_KEXDH
 159         dump_digest("shared secret", kbuf, kout);
 160 #endif
 161         if ((shared_secret = BN_new()) == NULL)
 162                 fatal("kexgex_client: BN_new failed");
 163         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 164                 fatal("kexgex_client: BN_bin2bn failed");
 165         memset(kbuf, 0, klen);
 166         xfree(kbuf);
 167
 168         if (datafellows & SSH_OLD_DHGEX)
 169                 min = max = -1;
 170
 171         /* calc and verify H */
 172         kexgex_hash(
 173             kex->evp_md,
 174             kex->client_version_string,
 175             kex->server_version_string,
 176             buffer_ptr(&kex->my), buffer_len(&kex->my),
 177             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 178             server_host_key_blob, sbloblen,
 179             min, nbits, max,
 180             dh->p, dh->g,
 181             dh->pub_key,
 182             dh_server_pub,
 183             shared_secret,
 184             &hash, &hashlen
 185         );
 186
 187         /* have keys, free DH */
 188         DH_free(dh);
 189         xfree(server_host_key_blob);
 190         BN_clear_free(dh_server_pub);
 191
 192         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 193                 fatal("key_verify failed for server_host_key");
 194         key_free(server_host_key);
 195         xfree(signature);
 196
 197         /* save session id */
 198         if (kex->session_id == NULL) {
 199                 kex->session_id_len = hashlen;
 200                 kex->session_id = xmalloc(kex->session_id_len);
 201                 memcpy(kex->session_id, hash, kex->session_id_len);
 202         }
 203         kex_derive_keys(kex, hash, hashlen, shared_secret);
 204         BN_clear_free(shared_secret);
 205
 206         kex_finish(kex);
 207 }