kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.7 2006/08/01 23:22:47 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 <sys/param.h>
  30
  31 #include <stdio.h>
  32 #include <string.h>
  33
  34 #include "xmalloc.h"
  35 #include "key.h"
  36 #include "kex.h"
  37 #include "log.h"
  38 #include "packet.h"
  39 #include "dh.h"
  40 #include "ssh2.h"
  41 #include "compat.h"
  42 #include "monitor_wrap.h"
  43
  44 void
  45 kexgex_server(Kex *kex)
  46 {
  47         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  48         Key *server_host_key;
  49         DH *dh;
  50         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  51         u_int sbloblen, klen, kout, slen, hashlen;
  52         int min = -1, max = -1, nbits = -1, type;
  53
  54         if (kex->load_host_key == NULL)
  55                 fatal("Cannot load hostkey");
  56         server_host_key = kex->load_host_key(kex->hostkey_type);
  57         if (server_host_key == NULL)
  58                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  59
  60         type = packet_read();
  61         switch (type) {
  62         case SSH2_MSG_KEX_DH_GEX_REQUEST:
  63                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  64                 min = packet_get_int();
  65                 nbits = packet_get_int();
  66                 max = packet_get_int();
  67                 min = MAX(DH_GRP_MIN, min);
  68                 max = MIN(DH_GRP_MAX, max);
  69                 break;
  70         case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
  71                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
  72                 nbits = packet_get_int();
  73                 min = DH_GRP_MIN;
  74                 max = DH_GRP_MAX;
  75                 /* unused for old GEX */
  76                 break;
  77         default:
  78                 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
  79         }
  80         packet_check_eom();
  81
  82         if (max < min || nbits < min || max < nbits)
  83                 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
  84                     min, nbits, max);
  85
  86         /* Contact privileged parent */
  87         dh = PRIVSEP(choose_dh(min, nbits, max));
  88         if (dh == NULL)
  89                 packet_disconnect("Protocol error: no matching DH grp found");
  90
  91         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
  92         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
  93         packet_put_bignum2(dh->p);
  94         packet_put_bignum2(dh->g);
  95         packet_send();
  96
  97         /* flush */
  98         packet_write_wait();
  99
 100         /* Compute our exchange value in parallel with the client */
 101         dh_gen_key(dh, kex->we_need * 8);
 102
 103         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
 104         packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
 105
 106         /* key, cert */
 107         if ((dh_client_pub = BN_new()) == NULL)
 108                 fatal("dh_client_pub == NULL");
 109         packet_get_bignum2(dh_client_pub);
 110         packet_check_eom();
 111
 112 #ifdef DEBUG_KEXDH
 113         fprintf(stderr, "dh_client_pub= ");
 114         BN_print_fp(stderr, dh_client_pub);
 115         fprintf(stderr, "\n");
 116         debug("bits %d", BN_num_bits(dh_client_pub));
 117 #endif
 118
 119 #ifdef DEBUG_KEXDH
 120         DHparams_print_fp(stderr, dh);
 121         fprintf(stderr, "pub= ");
 122         BN_print_fp(stderr, dh->pub_key);
 123         fprintf(stderr, "\n");
 124 #endif
 125         if (!dh_pub_is_valid(dh, dh_client_pub))
 126                 packet_disconnect("bad client public DH value");
 127
 128         klen = DH_size(dh);
 129         kbuf = xmalloc(klen);
 130         kout = DH_compute_key(kbuf, dh_client_pub, dh);
 131 #ifdef DEBUG_KEXDH
 132         dump_digest("shared secret", kbuf, kout);
 133 #endif
 134         if ((shared_secret = BN_new()) == NULL)
 135                 fatal("kexgex_server: BN_new failed");
 136         BN_bin2bn(kbuf, kout, shared_secret);
 137         memset(kbuf, 0, klen);
 138         xfree(kbuf);
 139
 140         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 141
 142         if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 143                 min = max = -1;
 144
 145         /* calc H */
 146         kexgex_hash(
 147             kex->evp_md,
 148             kex->client_version_string,
 149             kex->server_version_string,
 150             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 151             buffer_ptr(&kex->my), buffer_len(&kex->my),
 152             server_host_key_blob, sbloblen,
 153             min, nbits, max,
 154             dh->p, dh->g,
 155             dh_client_pub,
 156             dh->pub_key,
 157             shared_secret,
 158             &hash, &hashlen
 159         );
 160         BN_clear_free(dh_client_pub);
 161
 162         /* save session id := H */
 163         if (kex->session_id == NULL) {
 164                 kex->session_id_len = hashlen;
 165                 kex->session_id = xmalloc(kex->session_id_len);
 166                 memcpy(kex->session_id, hash, kex->session_id_len);
 167         }
 168
 169         /* sign H */
 170         PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
 171
 172         /* destroy_sensitive_data(); */
 173
 174         /* send server hostkey, DH pubkey 'f' and singed H */
 175         debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
 176         packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
 177         packet_put_string(server_host_key_blob, sbloblen);
 178         packet_put_bignum2(dh->pub_key);        /* f */
 179         packet_put_string(signature, slen);
 180         packet_send();
 181
 182         xfree(signature);
 183         xfree(server_host_key_blob);
 184         /* have keys, free DH */
 185         DH_free(dh);
 186
 187         kex_derive_keys(kex, hash, hashlen, shared_secret);
 188         BN_clear_free(shared_secret);
 189
 190         kex_finish(kex);
 191 }