kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.4 2006/03/25 13:17:02 djm 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 #include "monitor_wrap.h"
  38
  39 void
  40 kexgex_server(Kex *kex)
  41 {
  42         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  43         Key *server_host_key;
  44         DH *dh;
  45         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  46         u_int sbloblen, klen, kout, slen, hashlen;
  47         int min = -1, max = -1, nbits = -1, type;
  48
  49         if (kex->load_host_key == NULL)
  50                 fatal("Cannot load hostkey");
  51         server_host_key = kex->load_host_key(kex->hostkey_type);
  52         if (server_host_key == NULL)
  53                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  54
  55         type = packet_read();
  56         switch (type) {
  57         case SSH2_MSG_KEX_DH_GEX_REQUEST:
  58                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  59                 min = packet_get_int();
  60                 nbits = packet_get_int();
  61                 max = packet_get_int();
  62                 min = MAX(DH_GRP_MIN, min);
  63                 max = MIN(DH_GRP_MAX, max);
  64                 break;
  65         case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
  66                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
  67                 nbits = packet_get_int();
  68                 min = DH_GRP_MIN;
  69                 max = DH_GRP_MAX;
  70                 /* unused for old GEX */
  71                 break;
  72         default:
  73                 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
  74         }
  75         packet_check_eom();
  76
  77         if (max < min || nbits < min || max < nbits)
  78                 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
  79                     min, nbits, max);
  80
  81         /* Contact privileged parent */
  82         dh = PRIVSEP(choose_dh(min, nbits, max));
  83         if (dh == NULL)
  84                 packet_disconnect("Protocol error: no matching DH grp found");
  85
  86         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
  87         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
  88         packet_put_bignum2(dh->p);
  89         packet_put_bignum2(dh->g);
  90         packet_send();
  91
  92         /* flush */
  93         packet_write_wait();
  94
  95         /* Compute our exchange value in parallel with the client */
  96         dh_gen_key(dh, kex->we_need * 8);
  97
  98         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
  99         packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
 100
 101         /* key, cert */
 102         if ((dh_client_pub = BN_new()) == NULL)
 103                 fatal("dh_client_pub == NULL");
 104         packet_get_bignum2(dh_client_pub);
 105         packet_check_eom();
 106
 107 #ifdef DEBUG_KEXDH
 108         fprintf(stderr, "dh_client_pub= ");
 109         BN_print_fp(stderr, dh_client_pub);
 110         fprintf(stderr, "\n");
 111         debug("bits %d", BN_num_bits(dh_client_pub));
 112 #endif
 113
 114 #ifdef DEBUG_KEXDH
 115         DHparams_print_fp(stderr, dh);
 116         fprintf(stderr, "pub= ");
 117         BN_print_fp(stderr, dh->pub_key);
 118         fprintf(stderr, "\n");
 119 #endif
 120         if (!dh_pub_is_valid(dh, dh_client_pub))
 121                 packet_disconnect("bad client public DH value");
 122
 123         klen = DH_size(dh);
 124         kbuf = xmalloc(klen);
 125         kout = DH_compute_key(kbuf, dh_client_pub, dh);
 126 #ifdef DEBUG_KEXDH
 127         dump_digest("shared secret", kbuf, kout);
 128 #endif
 129         if ((shared_secret = BN_new()) == NULL)
 130                 fatal("kexgex_server: BN_new failed");
 131         BN_bin2bn(kbuf, kout, shared_secret);
 132         memset(kbuf, 0, klen);
 133         xfree(kbuf);
 134
 135         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 136
 137         if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 138                 min = max = -1;
 139
 140         /* calc H */
 141         kexgex_hash(
 142             kex->evp_md,
 143             kex->client_version_string,
 144             kex->server_version_string,
 145             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 146             buffer_ptr(&kex->my), buffer_len(&kex->my),
 147             server_host_key_blob, sbloblen,
 148             min, nbits, max,
 149             dh->p, dh->g,
 150             dh_client_pub,
 151             dh->pub_key,
 152             shared_secret,
 153             &hash, &hashlen
 154         );
 155         BN_clear_free(dh_client_pub);
 156
 157         /* save session id := H */
 158         if (kex->session_id == NULL) {
 159                 kex->session_id_len = hashlen;
 160                 kex->session_id = xmalloc(kex->session_id_len);
 161                 memcpy(kex->session_id, hash, kex->session_id_len);
 162         }
 163
 164         /* sign H */
 165         PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
 166
 167         /* destroy_sensitive_data(); */
 168
 169         /* send server hostkey, DH pubkey 'f' and singed H */
 170         debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
 171         packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
 172         packet_put_string(server_host_key_blob, sbloblen);
 173         packet_put_bignum2(dh->pub_key);        /* f */
 174         packet_put_string(signature, slen);
 175         packet_send();
 176
 177         xfree(signature);
 178         xfree(server_host_key_blob);
 179         /* have keys, free DH */
 180         DH_free(dh);
 181
 182         kex_derive_keys(kex, hash, hashlen, shared_secret);
 183         BN_clear_free(shared_secret);
 184
 185         kex_finish(kex);
 186 }