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