kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.13 2010/02/26 20:29:54 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 "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_public, *server_host_private;
  56         DH *dh;
  57         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  58         u_int sbloblen, klen, slen, hashlen;
  59         int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1;
  60         int type, kout;
  61
  62         if (kex->load_host_public_key == NULL ||
  63             kex->load_host_private_key == NULL)
  64                 fatal("Cannot load hostkey");
  65         server_host_public = kex->load_host_public_key(kex->hostkey_type);
  66         if (server_host_public == NULL)
  67                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  68         server_host_private = kex->load_host_private_key(kex->hostkey_type);
  69         if (server_host_private == NULL)
  70                 fatal("Missing private key for hostkey type %d",
  71                     kex->hostkey_type);
  72
  73
  74         type = packet_read();
  75         switch (type) {
  76         case SSH2_MSG_KEX_DH_GEX_REQUEST:
  77                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  78                 omin = min = packet_get_int();
  79                 onbits = nbits = packet_get_int();
  80                 omax = max = packet_get_int();
  81                 min = MAX(DH_GRP_MIN, min);
  82                 max = MIN(DH_GRP_MAX, max);
  83                 nbits = MAX(DH_GRP_MIN, nbits);
  84                 nbits = MIN(DH_GRP_MAX, nbits);
  85                 break;
  86         case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
  87                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
  88                 onbits = nbits = packet_get_int();
  89                 /* unused for old GEX */
  90                 omin = min = DH_GRP_MIN;
  91                 omax = max = DH_GRP_MAX;
  92                 break;
  93         default:
  94                 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
  95         }
  96         packet_check_eom();
  97
  98         if (omax < omin || onbits < omin || omax < onbits)
  99                 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
 100                     omin, onbits, omax);
 101
 102         /* Contact privileged parent */
 103         dh = PRIVSEP(choose_dh(min, nbits, max));
 104         if (dh == NULL)
 105                 packet_disconnect("Protocol error: no matching DH grp found");
 106
 107         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
 108         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
 109         packet_put_bignum2(dh->p);
 110         packet_put_bignum2(dh->g);
 111         packet_send();
 112
 113         /* flush */
 114         packet_write_wait();
 115
 116         /* Compute our exchange value in parallel with the client */
 117         dh_gen_key(dh, kex->we_need * 8);
 118
 119         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
 120         packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
 121
 122         /* key, cert */
 123         if ((dh_client_pub = BN_new()) == NULL)
 124                 fatal("dh_client_pub == NULL");
 125         packet_get_bignum2(dh_client_pub);
 126         packet_check_eom();
 127
 128 #ifdef DEBUG_KEXDH
 129         fprintf(stderr, "dh_client_pub= ");
 130         BN_print_fp(stderr, dh_client_pub);
 131         fprintf(stderr, "\n");
 132         debug("bits %d", BN_num_bits(dh_client_pub));
 133 #endif
 134
 135 #ifdef DEBUG_KEXDH
 136         DHparams_print_fp(stderr, dh);
 137         fprintf(stderr, "pub= ");
 138         BN_print_fp(stderr, dh->pub_key);
 139         fprintf(stderr, "\n");
 140 #endif
 141         if (!dh_pub_is_valid(dh, dh_client_pub))
 142                 packet_disconnect("bad client public DH value");
 143
 144         klen = DH_size(dh);
 145         kbuf = xmalloc(klen);
 146         if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
 147                 fatal("DH_compute_key: failed");
 148 #ifdef DEBUG_KEXDH
 149         dump_digest("shared secret", kbuf, kout);
 150 #endif
 151         if ((shared_secret = BN_new()) == NULL)
 152                 fatal("kexgex_server: BN_new failed");
 153         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 154                 fatal("kexgex_server: BN_bin2bn failed");
 155         memset(kbuf, 0, klen);
 156         xfree(kbuf);
 157
 158         key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
 159
 160         if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 161                 omin = min = omax = max = -1;
 162
 163         /* calc H */
 164         kexgex_hash(
 165             kex->evp_md,
 166             kex->client_version_string,
 167             kex->server_version_string,
 168             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 169             buffer_ptr(&kex->my), buffer_len(&kex->my),
 170             server_host_key_blob, sbloblen,
 171             omin, onbits, omax,
 172             dh->p, dh->g,
 173             dh_client_pub,
 174             dh->pub_key,
 175             shared_secret,
 176             &hash, &hashlen
 177         );
 178         BN_clear_free(dh_client_pub);
 179
 180         /* save session id := H */
 181         if (kex->session_id == NULL) {
 182                 kex->session_id_len = hashlen;
 183                 kex->session_id = xmalloc(kex->session_id_len);
 184                 memcpy(kex->session_id, hash, kex->session_id_len);
 185         }
 186
 187         /* sign H */
 188         if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash,
 189             hashlen)) < 0)
 190                 fatal("kexgex_server: key_sign failed");
 191
 192         /* destroy_sensitive_data(); */
 193
 194         /* send server hostkey, DH pubkey 'f' and singed H */
 195         debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
 196         packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
 197         packet_put_string(server_host_key_blob, sbloblen);
 198         packet_put_bignum2(dh->pub_key);        /* f */
 199         packet_put_string(signature, slen);
 200         packet_send();
 201
 202         xfree(signature);
 203         xfree(server_host_key_blob);
 204         /* have keys, free DH */
 205         DH_free(dh);
 206
 207         kex_derive_keys(kex, hash, hashlen, shared_secret);
 208         BN_clear_free(shared_secret);
 209
 210         kex_finish(kex);
 211 }