kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.8 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/param.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 #ifdef GSSAPI
  47 #include "ssh-gss.h"
  48 #endif
  49 #include "monitor_wrap.h"
  50
  51 void
  52 kexgex_server(Kex *kex)
  53 {
  54         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  55         Key *server_host_key;
  56         DH *dh;
  57         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  58         u_int sbloblen, klen, kout, slen, hashlen;
  59         int min = -1, max = -1, nbits = -1, type;
  60
  61         if (kex->load_host_key == NULL)
  62                 fatal("Cannot load hostkey");
  63         server_host_key = kex->load_host_key(kex->hostkey_type);
  64         if (server_host_key == NULL)
  65                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  66
  67         type = packet_read();
  68         switch (type) {
  69         case SSH2_MSG_KEX_DH_GEX_REQUEST:
  70                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  71                 min = packet_get_int();
  72                 nbits = packet_get_int();
  73                 max = packet_get_int();
  74                 min = MAX(DH_GRP_MIN, min);
  75                 max = MIN(DH_GRP_MAX, max);
  76                 break;
  77         case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
  78                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
  79                 nbits = packet_get_int();
  80                 min = DH_GRP_MIN;
  81                 max = DH_GRP_MAX;
  82                 /* unused for old GEX */
  83                 break;
  84         default:
  85                 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
  86         }
  87         packet_check_eom();
  88
  89         if (max < min || nbits < min || max < nbits)
  90                 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
  91                     min, nbits, max);
  92
  93         /* Contact privileged parent */
  94         dh = PRIVSEP(choose_dh(min, nbits, max));
  95         if (dh == NULL)
  96                 packet_disconnect("Protocol error: no matching DH grp found");
  97
  98         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
  99         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
 100         packet_put_bignum2(dh->p);
 101         packet_put_bignum2(dh->g);
 102         packet_send();
 103
 104         /* flush */
 105         packet_write_wait();
 106
 107         /* Compute our exchange value in parallel with the client */
 108         dh_gen_key(dh, kex->we_need * 8);
 109
 110         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
 111         packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
 112
 113         /* key, cert */
 114         if ((dh_client_pub = BN_new()) == NULL)
 115                 fatal("dh_client_pub == NULL");
 116         packet_get_bignum2(dh_client_pub);
 117         packet_check_eom();
 118
 119 #ifdef DEBUG_KEXDH
 120         fprintf(stderr, "dh_client_pub= ");
 121         BN_print_fp(stderr, dh_client_pub);
 122         fprintf(stderr, "\n");
 123         debug("bits %d", BN_num_bits(dh_client_pub));
 124 #endif
 125
 126 #ifdef DEBUG_KEXDH
 127         DHparams_print_fp(stderr, dh);
 128         fprintf(stderr, "pub= ");
 129         BN_print_fp(stderr, dh->pub_key);
 130         fprintf(stderr, "\n");
 131 #endif
 132         if (!dh_pub_is_valid(dh, dh_client_pub))
 133                 packet_disconnect("bad client public DH value");
 134
 135         klen = DH_size(dh);
 136         kbuf = xmalloc(klen);
 137         kout = DH_compute_key(kbuf, dh_client_pub, dh);
 138 #ifdef DEBUG_KEXDH
 139         dump_digest("shared secret", kbuf, kout);
 140 #endif
 141         if ((shared_secret = BN_new()) == NULL)
 142                 fatal("kexgex_server: BN_new failed");
 143         BN_bin2bn(kbuf, kout, shared_secret);
 144         memset(kbuf, 0, klen);
 145         xfree(kbuf);
 146
 147         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 148
 149         if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 150                 min = max = -1;
 151
 152         /* calc H */
 153         kexgex_hash(
 154             kex->evp_md,
 155             kex->client_version_string,
 156             kex->server_version_string,
 157             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 158             buffer_ptr(&kex->my), buffer_len(&kex->my),
 159             server_host_key_blob, sbloblen,
 160             min, nbits, max,
 161             dh->p, dh->g,
 162             dh_client_pub,
 163             dh->pub_key,
 164             shared_secret,
 165             &hash, &hashlen
 166         );
 167         BN_clear_free(dh_client_pub);
 168
 169         /* save session id := H */
 170         if (kex->session_id == NULL) {
 171                 kex->session_id_len = hashlen;
 172                 kex->session_id = xmalloc(kex->session_id_len);
 173                 memcpy(kex->session_id, hash, kex->session_id_len);
 174         }
 175
 176         /* sign H */
 177         PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
 178
 179         /* destroy_sensitive_data(); */
 180
 181         /* send server hostkey, DH pubkey 'f' and singed H */
 182         debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
 183         packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
 184         packet_put_string(server_host_key_blob, sbloblen);
 185         packet_put_bignum2(dh->pub_key);        /* f */
 186         packet_put_string(signature, slen);
 187         packet_send();
 188
 189         xfree(signature);
 190         xfree(server_host_key_blob);
 191         /* have keys, free DH */
 192         DH_free(dh);
 193
 194         kex_derive_keys(kex, hash, hashlen, shared_secret);
 195         BN_clear_free(shared_secret);
 196
 197         kex_finish(kex);
 198 }