kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.9 2006/08/03 03:34:42 deraadt 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, kout, slen, sbloblen, hashlen;
  55         int min, max, nbits;
  56         DH *dh;
  57
  58         nbits = dh_estimate(kex->we_need * 8);
  59
  60         if (datafellows & SSH_OLD_DHGEX) {
  61                 /* Old GEX request */
  62                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
  63                 packet_put_int(nbits);
  64                 min = DH_GRP_MIN;
  65                 max = DH_GRP_MAX;
  66
  67                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
  68         } else {
  69                 /* New GEX request */
  70                 min = DH_GRP_MIN;
  71                 max = DH_GRP_MAX;
  72                 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
  73                 packet_put_int(min);
  74                 packet_put_int(nbits);
  75                 packet_put_int(max);
  76
  77                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  78                     min, nbits, max);
  79         }
  80 #ifdef DEBUG_KEXDH
  81         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  82             min, nbits, max);
  83 #endif
  84         packet_send();
  85
  86         debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  87         packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
  88
  89         if ((p = BN_new()) == NULL)
  90                 fatal("BN_new");
  91         packet_get_bignum2(p);
  92         if ((g = BN_new()) == NULL)
  93                 fatal("BN_new");
  94         packet_get_bignum2(g);
  95         packet_check_eom();
  96
  97         if (BN_num_bits(p) < min || BN_num_bits(p) > max)
  98                 fatal("DH_GEX group out of range: %d !< %d !< %d",
  99                     min, BN_num_bits(p), max);
 100
 101         dh = dh_new_group(g, p);
 102         dh_gen_key(dh, kex->we_need * 8);
 103
 104 #ifdef DEBUG_KEXDH
 105         DHparams_print_fp(stderr, dh);
 106         fprintf(stderr, "pub= ");
 107         BN_print_fp(stderr, dh->pub_key);
 108         fprintf(stderr, "\n");
 109 #endif
 110
 111         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 112         /* generate and send 'e', client DH public key */
 113         packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
 114         packet_put_bignum2(dh->pub_key);
 115         packet_send();
 116
 117         debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
 118         packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
 119
 120         /* key, cert */
 121         server_host_key_blob = packet_get_string(&sbloblen);
 122         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
 123         if (server_host_key == NULL)
 124                 fatal("cannot decode server_host_key_blob");
 125         if (server_host_key->type != kex->hostkey_type)
 126                 fatal("type mismatch for decoded server_host_key_blob");
 127         if (kex->verify_host_key == NULL)
 128                 fatal("cannot verify server_host_key");
 129         if (kex->verify_host_key(server_host_key) == -1)
 130                 fatal("server_host_key verification failed");
 131
 132         /* DH parameter f, server public DH key */
 133         if ((dh_server_pub = BN_new()) == NULL)
 134                 fatal("dh_server_pub == NULL");
 135         packet_get_bignum2(dh_server_pub);
 136
 137 #ifdef DEBUG_KEXDH
 138         fprintf(stderr, "dh_server_pub= ");
 139         BN_print_fp(stderr, dh_server_pub);
 140         fprintf(stderr, "\n");
 141         debug("bits %d", BN_num_bits(dh_server_pub));
 142 #endif
 143
 144         /* signed H */
 145         signature = packet_get_string(&slen);
 146         packet_check_eom();
 147
 148         if (!dh_pub_is_valid(dh, dh_server_pub))
 149                 packet_disconnect("bad server public DH value");
 150
 151         klen = DH_size(dh);
 152         kbuf = xmalloc(klen);
 153         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 154 #ifdef DEBUG_KEXDH
 155         dump_digest("shared secret", kbuf, kout);
 156 #endif
 157         if ((shared_secret = BN_new()) == NULL)
 158                 fatal("kexgex_client: BN_new failed");
 159         BN_bin2bn(kbuf, kout, shared_secret);
 160         memset(kbuf, 0, klen);
 161         xfree(kbuf);
 162
 163         if (datafellows & SSH_OLD_DHGEX)
 164                 min = max = -1;
 165
 166         /* calc and verify H */
 167         kexgex_hash(
 168             kex->evp_md,
 169             kex->client_version_string,
 170             kex->server_version_string,
 171             buffer_ptr(&kex->my), buffer_len(&kex->my),
 172             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 173             server_host_key_blob, sbloblen,
 174             min, nbits, max,
 175             dh->p, dh->g,
 176             dh->pub_key,
 177             dh_server_pub,
 178             shared_secret,
 179             &hash, &hashlen
 180         );
 181
 182         /* have keys, free DH */
 183         DH_free(dh);
 184         xfree(server_host_key_blob);
 185         BN_clear_free(dh_server_pub);
 186
 187         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 188                 fatal("key_verify failed for server_host_key");
 189         key_free(server_host_key);
 190         xfree(signature);
 191
 192         /* save session id */
 193         if (kex->session_id == NULL) {
 194                 kex->session_id_len = hashlen;
 195                 kex->session_id = xmalloc(kex->session_id_len);
 196                 memcpy(kex->session_id, hash, kex->session_id_len);
 197         }
 198         kex_derive_keys(kex, hash, hashlen, shared_secret);
 199         BN_clear_free(shared_secret);
 200
 201         kex_finish(kex);
 202 }