kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.7 2006/07/22 20:48:23 stevesk 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 <string.h>
  30
  31 #include "xmalloc.h"
  32 #include "key.h"
  33 #include "kex.h"
  34 #include "log.h"
  35 #include "packet.h"
  36 #include "dh.h"
  37 #include "ssh2.h"
  38 #include "compat.h"
  39
  40 void
  41 kexgex_client(Kex *kex)
  42 {
  43         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  44         BIGNUM *p = NULL, *g = NULL;
  45         Key *server_host_key;
  46         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  47         u_int klen, kout, slen, sbloblen, hashlen;
  48         int min, max, nbits;
  49         DH *dh;
  50
  51         nbits = dh_estimate(kex->we_need * 8);
  52
  53         if (datafellows & SSH_OLD_DHGEX) {
  54                 /* Old GEX request */
  55                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
  56                 packet_put_int(nbits);
  57                 min = DH_GRP_MIN;
  58                 max = DH_GRP_MAX;
  59
  60                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
  61         } else {
  62                 /* New GEX request */
  63                 min = DH_GRP_MIN;
  64                 max = DH_GRP_MAX;
  65                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
  66                 packet_put_int(min);
  67                 packet_put_int(nbits);
  68                 packet_put_int(max);
  69
  70                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  71                     min, nbits, max);
  72         }
  73 #ifdef DEBUG_KEXDH
  74         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  75             min, nbits, max);
  76 #endif
  77         packet_send();
  78
  79         debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  80         packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
  81
  82         if ((p = BN_new()) == NULL)
  83                 fatal("BN_new");
  84         packet_get_bignum2(p);
  85         if ((g = BN_new()) == NULL)
  86                 fatal("BN_new");
  87         packet_get_bignum2(g);
  88         packet_check_eom();
  89
  90         if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  91                 fatal("DH_GEX group out of range: %d !< %d !< %d",
  92                     min, BN_num_bits(p), max);
  93
  94         dh = dh_new_group(g, p);
  95         dh_gen_key(dh, kex->we_need * 8);
  96
  97 #ifdef DEBUG_KEXDH
  98         DHparams_print_fp(stderr, dh);
  99         fprintf(stderr, "pub= ");
 100         BN_print_fp(stderr, dh->pub_key);
 101         fprintf(stderr, "\n");
 102 #endif
 103
 104         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 105         /* generate and send 'e', client DH public key */
 106         packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
 107         packet_put_bignum2(dh->pub_key);
 108         packet_send();
 109
 110         debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
 111         packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
 112
 113         /* key, cert */
 114         server_host_key_blob = packet_get_string(&sbloblen);
 115         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
 116         if (server_host_key == NULL)
 117                 fatal("cannot decode server_host_key_blob");
 118         if (server_host_key->type != kex->hostkey_type)
 119                 fatal("type mismatch for decoded server_host_key_blob");
 120         if (kex->verify_host_key == NULL)
 121                 fatal("cannot verify server_host_key");
 122         if (kex->verify_host_key(server_host_key) == -1)
 123                 fatal("server_host_key verification failed");
 124
 125         /* DH parameter f, server public DH key */
 126         if ((dh_server_pub = BN_new()) == NULL)
 127                 fatal("dh_server_pub == NULL");
 128         packet_get_bignum2(dh_server_pub);
 129
 130 #ifdef DEBUG_KEXDH
 131         fprintf(stderr, "dh_server_pub= ");
 132         BN_print_fp(stderr, dh_server_pub);
 133         fprintf(stderr, "\n");
 134         debug("bits %d", BN_num_bits(dh_server_pub));
 135 #endif
 136
 137         /* signed H */
 138         signature = packet_get_string(&slen);
 139         packet_check_eom();
 140
 141         if (!dh_pub_is_valid(dh, dh_server_pub))
 142                 packet_disconnect("bad server public DH value");
 143
 144         klen = DH_size(dh);
 145         kbuf = xmalloc(klen);
 146         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 147 #ifdef DEBUG_KEXDH
 148         dump_digest("shared secret", kbuf, kout);
 149 #endif
 150         if ((shared_secret = BN_new()) == NULL)
 151                 fatal("kexgex_client: BN_new failed");
 152         BN_bin2bn(kbuf, kout, shared_secret);
 153         memset(kbuf, 0, klen);
 154         xfree(kbuf);
 155
 156         if (datafellows & SSH_OLD_DHGEX)
 157                 min = max = -1;
 158
 159         /* calc and verify H */
 160         kexgex_hash(
 161             kex->evp_md,
 162             kex->client_version_string,
 163             kex->server_version_string,
 164             buffer_ptr(&kex->my), buffer_len(&kex->my),
 165             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 166             server_host_key_blob, sbloblen,
 167             min, nbits, max,
 168             dh->p, dh->g,
 169             dh->pub_key,
 170             dh_server_pub,
 171             shared_secret,
 172             &hash, &hashlen
 173         );
 174
 175         /* have keys, free DH */
 176         DH_free(dh);
 177         xfree(server_host_key_blob);
 178         BN_clear_free(dh_server_pub);
 179
 180         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 181                 fatal("key_verify failed for server_host_key");
 182         key_free(server_host_key);
 183         xfree(signature);
 184
 185         /* save session id */
 186         if (kex->session_id == NULL) {
 187                 kex->session_id_len = hashlen;
 188                 kex->session_id = xmalloc(kex->session_id_len);
 189                 memcpy(kex->session_id, hash, kex->session_id_len);
 190         }
 191         kex_derive_keys(kex, hash, hashlen, shared_secret);
 192         BN_clear_free(shared_secret);
 193
 194         kex_finish(kex);
 195 }