kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.6 2006/05/18 21:27:25 miod 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 "xmalloc.h"
  30 #include "key.h"
  31 #include "kex.h"
  32 #include "log.h"
  33 #include "packet.h"
  34 #include "dh.h"
  35 #include "ssh2.h"
  36 #include "compat.h"
  37
  38 void
  39 kexgex_client(Kex *kex)
  40 {
  41         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  42         BIGNUM *p = NULL, *g = NULL;
  43         Key *server_host_key;
  44         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  45         u_int klen, kout, slen, sbloblen, hashlen;
  46         int min, max, nbits;
  47         DH *dh;
  48
  49         nbits = dh_estimate(kex->we_need * 8);
  50
  51         if (datafellows & SSH_OLD_DHGEX) {
  52                 /* Old GEX request */
  53                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
  54                 packet_put_int(nbits);
  55                 min = DH_GRP_MIN;
  56                 max = DH_GRP_MAX;
  57
  58                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
  59         } else {
  60                 /* New GEX request */
  61                 min = DH_GRP_MIN;
  62                 max = DH_GRP_MAX;
  63                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
  64                 packet_put_int(min);
  65                 packet_put_int(nbits);
  66                 packet_put_int(max);
  67
  68                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  69                     min, nbits, max);
  70         }
  71 #ifdef DEBUG_KEXDH
  72         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  73             min, nbits, max);
  74 #endif
  75         packet_send();
  76
  77         debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  78         packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
  79
  80         if ((p = BN_new()) == NULL)
  81                 fatal("BN_new");
  82         packet_get_bignum2(p);
  83         if ((g = BN_new()) == NULL)
  84                 fatal("BN_new");
  85         packet_get_bignum2(g);
  86         packet_check_eom();
  87
  88         if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  89                 fatal("DH_GEX group out of range: %d !< %d !< %d",
  90                     min, BN_num_bits(p), max);
  91
  92         dh = dh_new_group(g, p);
  93         dh_gen_key(dh, kex->we_need * 8);
  94
  95 #ifdef DEBUG_KEXDH
  96         DHparams_print_fp(stderr, dh);
  97         fprintf(stderr, "pub= ");
  98         BN_print_fp(stderr, dh->pub_key);
  99         fprintf(stderr, "\n");
 100 #endif
 101
 102         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 103         /* generate and send 'e', client DH public key */
 104         packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
 105         packet_put_bignum2(dh->pub_key);
 106         packet_send();
 107
 108         debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
 109         packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
 110
 111         /* key, cert */
 112         server_host_key_blob = packet_get_string(&sbloblen);
 113         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
 114         if (server_host_key == NULL)
 115                 fatal("cannot decode server_host_key_blob");
 116         if (server_host_key->type != kex->hostkey_type)
 117                 fatal("type mismatch for decoded server_host_key_blob");
 118         if (kex->verify_host_key == NULL)
 119                 fatal("cannot verify server_host_key");
 120         if (kex->verify_host_key(server_host_key) == -1)
 121                 fatal("server_host_key verification failed");
 122
 123         /* DH parameter f, server public DH key */
 124         if ((dh_server_pub = BN_new()) == NULL)
 125                 fatal("dh_server_pub == NULL");
 126         packet_get_bignum2(dh_server_pub);
 127
 128 #ifdef DEBUG_KEXDH
 129         fprintf(stderr, "dh_server_pub= ");
 130         BN_print_fp(stderr, dh_server_pub);
 131         fprintf(stderr, "\n");
 132         debug("bits %d", BN_num_bits(dh_server_pub));
 133 #endif
 134
 135         /* signed H */
 136         signature = packet_get_string(&slen);
 137         packet_check_eom();
 138
 139         if (!dh_pub_is_valid(dh, dh_server_pub))
 140                 packet_disconnect("bad server public DH value");
 141
 142         klen = DH_size(dh);
 143         kbuf = xmalloc(klen);
 144         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 145 #ifdef DEBUG_KEXDH
 146         dump_digest("shared secret", kbuf, kout);
 147 #endif
 148         if ((shared_secret = BN_new()) == NULL)
 149                 fatal("kexgex_client: BN_new failed");
 150         BN_bin2bn(kbuf, kout, shared_secret);
 151         memset(kbuf, 0, klen);
 152         xfree(kbuf);
 153
 154         if (datafellows & SSH_OLD_DHGEX)
 155                 min = max = -1;
 156
 157         /* calc and verify H */
 158         kexgex_hash(
 159             kex->evp_md,
 160             kex->client_version_string,
 161             kex->server_version_string,
 162             buffer_ptr(&kex->my), buffer_len(&kex->my),
 163             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 164             server_host_key_blob, sbloblen,
 165             min, nbits, max,
 166             dh->p, dh->g,
 167             dh->pub_key,
 168             dh_server_pub,
 169             shared_secret,
 170             &hash, &hashlen
 171         );
 172
 173         /* have keys, free DH */
 174         DH_free(dh);
 175         xfree(server_host_key_blob);
 176         BN_clear_free(dh_server_pub);
 177
 178         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 179                 fatal("key_verify failed for server_host_key");
 180         key_free(server_host_key);
 181         xfree(signature);
 182
 183         /* save session id */
 184         if (kex->session_id == NULL) {
 185                 kex->session_id_len = hashlen;
 186                 kex->session_id = xmalloc(kex->session_id_len);
 187                 memcpy(kex->session_id, hash, kex->session_id_len);
 188         }
 189         kex_derive_keys(kex, hash, hashlen, shared_secret);
 190         BN_clear_free(shared_secret);
 191
 192         kex_finish(kex);
 193 }