kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.11 2006/11/06 21:25:28 markus 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 <stdarg.h>
  32 #include <stdio.h>
  33 #include <string.h>
  34 #include <signal.h>
  35
  36 #include "xmalloc.h"
  37 #include "buffer.h"
  38 #include "key.h"
  39 #include "cipher.h"
  40 #include "kex.h"
  41 #include "log.h"
  42 #include "packet.h"
  43 #include "dh.h"
  44 #include "ssh2.h"
  45 #include "compat.h"
  46
  47 void
  48 kexgex_client(Kex *kex)
  49 {
  50         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  51         BIGNUM *p = NULL, *g = NULL;
  52         Key *server_host_key;
  53         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  54         u_int klen, slen, sbloblen, hashlen;
  55         int kout;
  56         int min, max, nbits;
  57         DH *dh;
  58
  59         nbits = dh_estimate(kex->we_need * 8);
  60
  61         if (datafellows & SSH_OLD_DHGEX) {
  62                 /* Old GEX request */
  63                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
  64                 packet_put_int(nbits);
  65                 min = DH_GRP_MIN;
  66                 max = DH_GRP_MAX;
  67
  68                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
  69         } else {
  70                 /* New GEX request */
  71                 min = DH_GRP_MIN;
  72                 max = DH_GRP_MAX;
  73                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
  74                 packet_put_int(min);
  75                 packet_put_int(nbits);
  76                 packet_put_int(max);
  77
  78                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  79                     min, nbits, max);
  80         }
  81 #ifdef DEBUG_KEXDH
  82         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  83             min, nbits, max);
  84 #endif
  85         packet_send();
  86
  87         debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  88         packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
  89
  90         if ((p = BN_new()) == NULL)
  91                 fatal("BN_new");
  92         packet_get_bignum2(p);
  93         if ((g = BN_new()) == NULL)
  94                 fatal("BN_new");
  95         packet_get_bignum2(g);
  96         packet_check_eom();
  97
  98         if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  99                 fatal("DH_GEX group out of range: %d !< %d !< %d",
 100                     min, BN_num_bits(p), max);
 101
 102         dh = dh_new_group(g, p);
 103         dh_gen_key(dh, kex->we_need * 8);
 104
 105 #ifdef DEBUG_KEXDH
 106         DHparams_print_fp(stderr, dh);
 107         fprintf(stderr, "pub= ");
 108         BN_print_fp(stderr, dh->pub_key);
 109         fprintf(stderr, "\n");
 110 #endif
 111
 112         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 113         /* generate and send 'e', client DH public key */
 114         packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
 115         packet_put_bignum2(dh->pub_key);
 116         packet_send();
 117
 118         debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
 119         packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
 120
 121         /* key, cert */
 122         server_host_key_blob = packet_get_string(&sbloblen);
 123         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
 124         if (server_host_key == NULL)
 125                 fatal("cannot decode server_host_key_blob");
 126         if (server_host_key->type != kex->hostkey_type)
 127                 fatal("type mismatch for decoded server_host_key_blob");
 128         if (kex->verify_host_key == NULL)
 129                 fatal("cannot verify server_host_key");
 130         if (kex->verify_host_key(server_host_key) == -1)
 131                 fatal("server_host_key verification failed");
 132
 133         /* DH parameter f, server public DH key */
 134         if ((dh_server_pub = BN_new()) == NULL)
 135                 fatal("dh_server_pub == NULL");
 136         packet_get_bignum2(dh_server_pub);
 137
 138 #ifdef DEBUG_KEXDH
 139         fprintf(stderr, "dh_server_pub= ");
 140         BN_print_fp(stderr, dh_server_pub);
 141         fprintf(stderr, "\n");
 142         debug("bits %d", BN_num_bits(dh_server_pub));
 143 #endif
 144
 145         /* signed H */
 146         signature = packet_get_string(&slen);
 147         packet_check_eom();
 148
 149         if (!dh_pub_is_valid(dh, dh_server_pub))
 150                 packet_disconnect("bad server public DH value");
 151
 152         klen = DH_size(dh);
 153         kbuf = xmalloc(klen);
 154         if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0)
 155                 fatal("DH_compute_key: failed");
 156 #ifdef DEBUG_KEXDH
 157         dump_digest("shared secret", kbuf, kout);
 158 #endif
 159         if ((shared_secret = BN_new()) == NULL)
 160                 fatal("kexgex_client: BN_new failed");
 161         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 162                 fatal("kexgex_client: BN_bin2bn failed");
 163         memset(kbuf, 0, klen);
 164         xfree(kbuf);
 165
 166         if (datafellows & SSH_OLD_DHGEX)
 167                 min = max = -1;
 168
 169         /* calc and verify H */
 170         kexgex_hash(
 171             kex->evp_md,
 172             kex->client_version_string,
 173             kex->server_version_string,
 174             buffer_ptr(&kex->my), buffer_len(&kex->my),
 175             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 176             server_host_key_blob, sbloblen,
 177             min, nbits, max,
 178             dh->p, dh->g,
 179             dh->pub_key,
 180             dh_server_pub,
 181             shared_secret,
 182             &hash, &hashlen
 183         );
 184
 185         /* have keys, free DH */
 186         DH_free(dh);
 187         xfree(server_host_key_blob);
 188         BN_clear_free(dh_server_pub);
 189
 190         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 191                 fatal("key_verify failed for server_host_key");
 192         key_free(server_host_key);
 193         xfree(signature);
 194
 195         /* save session id */
 196         if (kex->session_id == NULL) {
 197                 kex->session_id_len = hashlen;
 198                 kex->session_id = xmalloc(kex->session_id_len);
 199                 memcpy(kex->session_id, hash, kex->session_id_len);
 200         }
 201         kex_derive_keys(kex, hash, hashlen, shared_secret);
 202         BN_clear_free(shared_secret);
 203
 204         kex_finish(kex);
 205 }