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