kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.14 2010/11/10 01:33:07 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 <sys/param.h>
  30
  31 #include <stdarg.h>
  32 #include <stdio.h>
  33 #include <string.h>
  34 #include <signal.h>
  35
  36 #include <openssl/dh.h>
  37
  38 #include "xmalloc.h"
  39 #include "buffer.h"
  40 #include "key.h"
  41 #include "cipher.h"
  42 #include "kex.h"
  43 #include "log.h"
  44 #include "packet.h"
  45 #include "dh.h"
  46 #include "ssh2.h"
  47 #include "compat.h"
  48 #ifdef GSSAPI
  49 #include "ssh-gss.h"
  50 #endif
  51 #include "monitor_wrap.h"
  52
  53 void
  54 kexgex_server(Kex *kex)
  55 {
  56         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  57         Key *server_host_public, *server_host_private;
  58         DH *dh;
  59         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  60         u_int sbloblen, klen, slen, hashlen;
  61         int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1;
  62         int type, kout;
  63
  64         if (kex->load_host_public_key == NULL ||
  65             kex->load_host_private_key == NULL)
  66                 fatal("Cannot load hostkey");
  67         server_host_public = kex->load_host_public_key(kex->hostkey_type);
  68         if (server_host_public == NULL)
  69                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  70         server_host_private = kex->load_host_private_key(kex->hostkey_type);
  71         if (server_host_private == NULL)
  72                 fatal("Missing private key for hostkey type %d",
  73                     kex->hostkey_type);
  74
  75
  76         type = packet_read();
  77         switch (type) {
  78         case SSH2_MSG_KEX_DH_GEX_REQUEST:
  79                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  80                 omin = min = packet_get_int();
  81                 onbits = nbits = packet_get_int();
  82                 omax = max = packet_get_int();
  83                 min = MAX(DH_GRP_MIN, min);
  84                 max = MIN(DH_GRP_MAX, max);
  85                 nbits = MAX(DH_GRP_MIN, nbits);
  86                 nbits = MIN(DH_GRP_MAX, nbits);
  87                 break;
  88         case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
  89                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
  90                 onbits = nbits = packet_get_int();
  91                 /* unused for old GEX */
  92                 omin = min = DH_GRP_MIN;
  93                 omax = max = DH_GRP_MAX;
  94                 break;
  95         default:
  96                 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
  97         }
  98         packet_check_eom();
  99
 100         if (omax < omin || onbits < omin || omax < onbits)
 101                 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
 102                     omin, onbits, omax);
 103
 104         /* Contact privileged parent */
 105         dh = PRIVSEP(choose_dh(min, nbits, max));
 106         if (dh == NULL)
 107                 packet_disconnect("Protocol error: no matching DH grp found");
 108
 109         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
 110         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
 111         packet_put_bignum2(dh->p);
 112         packet_put_bignum2(dh->g);
 113         packet_send();
 114
 115         /* flush */
 116         packet_write_wait();
 117
 118         /* Compute our exchange value in parallel with the client */
 119         dh_gen_key(dh, kex->we_need * 8);
 120
 121         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
 122         packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
 123
 124         /* key, cert */
 125         if ((dh_client_pub = BN_new()) == NULL)
 126                 fatal("dh_client_pub == NULL");
 127         packet_get_bignum2(dh_client_pub);
 128         packet_check_eom();
 129
 130 #ifdef DEBUG_KEXDH
 131         fprintf(stderr, "dh_client_pub= ");
 132         BN_print_fp(stderr, dh_client_pub);
 133         fprintf(stderr, "\n");
 134         debug("bits %d", BN_num_bits(dh_client_pub));
 135 #endif
 136
 137 #ifdef DEBUG_KEXDH
 138         DHparams_print_fp(stderr, dh);
 139         fprintf(stderr, "pub= ");
 140         BN_print_fp(stderr, dh->pub_key);
 141         fprintf(stderr, "\n");
 142 #endif
 143         if (!dh_pub_is_valid(dh, dh_client_pub))
 144                 packet_disconnect("bad client public DH value");
 145
 146         klen = DH_size(dh);
 147         kbuf = xmalloc(klen);
 148         if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
 149                 fatal("DH_compute_key: failed");
 150 #ifdef DEBUG_KEXDH
 151         dump_digest("shared secret", kbuf, kout);
 152 #endif
 153         if ((shared_secret = BN_new()) == NULL)
 154                 fatal("kexgex_server: BN_new failed");
 155         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 156                 fatal("kexgex_server: BN_bin2bn failed");
 157         memset(kbuf, 0, klen);
 158         xfree(kbuf);
 159
 160         key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
 161
 162         if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 163                 omin = min = omax = max = -1;
 164
 165         /* calc H */
 166         kexgex_hash(
 167             kex->evp_md,
 168             kex->client_version_string,
 169             kex->server_version_string,
 170             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 171             buffer_ptr(&kex->my), buffer_len(&kex->my),
 172             server_host_key_blob, sbloblen,
 173             omin, onbits, omax,
 174             dh->p, dh->g,
 175             dh_client_pub,
 176             dh->pub_key,
 177             shared_secret,
 178             &hash, &hashlen
 179         );
 180         BN_clear_free(dh_client_pub);
 181
 182         /* save session id := H */
 183         if (kex->session_id == NULL) {
 184                 kex->session_id_len = hashlen;
 185                 kex->session_id = xmalloc(kex->session_id_len);
 186                 memcpy(kex->session_id, hash, kex->session_id_len);
 187         }
 188
 189         /* sign H */
 190         if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash,
 191             hashlen)) < 0)
 192                 fatal("kexgex_server: key_sign failed");
 193
 194         /* destroy_sensitive_data(); */
 195
 196         /* send server hostkey, DH pubkey 'f' and singed H */
 197         debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
 198         packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
 199         packet_put_string(server_host_key_blob, sbloblen);
 200         packet_put_bignum2(dh->pub_key);        /* f */
 201         packet_put_string(signature, slen);
 202         packet_send();
 203
 204         xfree(signature);
 205         xfree(server_host_key_blob);
 206         /* have keys, free DH */
 207         DH_free(dh);
 208
 209         kex_derive_keys(kex, hash, hashlen, shared_secret);
 210         BN_clear_free(shared_secret);
 211
 212         kex_finish(kex);
 213 }