kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.12 2009/06/21 07:37:15 dtucker 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, 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_key == NULL)
  63                 fatal("Cannot load hostkey");
  64         server_host_key = kex->load_host_key(kex->hostkey_type);
  65         if (server_host_key == NULL)
  66                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  67
  68         type = packet_read();
  69         switch (type) {
  70         case SSH2_MSG_KEX_DH_GEX_REQUEST:
  71                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  72                 omin = min = packet_get_int();
  73                 onbits = nbits = packet_get_int();
  74                 omax = max = packet_get_int();
  75                 min = MAX(DH_GRP_MIN, min);
  76                 max = MIN(DH_GRP_MAX, max);
  77                 nbits = MAX(DH_GRP_MIN, nbits);
  78                 nbits = MIN(DH_GRP_MAX, nbits);
  79                 break;
  80         case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
  81                 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
  82                 onbits = nbits = packet_get_int();
  83                 /* unused for old GEX */
  84                 omin = min = DH_GRP_MIN;
  85                 omax = max = DH_GRP_MAX;
  86                 break;
  87         default:
  88                 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
  89         }
  90         packet_check_eom();
  91
  92         if (omax < omin || onbits < omin || omax < onbits)
  93                 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
  94                     omin, onbits, omax);
  95
  96         /* Contact privileged parent */
  97         dh = PRIVSEP(choose_dh(min, nbits, max));
  98         if (dh == NULL)
  99                 packet_disconnect("Protocol error: no matching DH grp found");
 100
 101         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
 102         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
 103         packet_put_bignum2(dh->p);
 104         packet_put_bignum2(dh->g);
 105         packet_send();
 106
 107         /* flush */
 108         packet_write_wait();
 109
 110         /* Compute our exchange value in parallel with the client */
 111         dh_gen_key(dh, kex->we_need * 8);
 112
 113         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
 114         packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
 115
 116         /* key, cert */
 117         if ((dh_client_pub = BN_new()) == NULL)
 118                 fatal("dh_client_pub == NULL");
 119         packet_get_bignum2(dh_client_pub);
 120         packet_check_eom();
 121
 122 #ifdef DEBUG_KEXDH
 123         fprintf(stderr, "dh_client_pub= ");
 124         BN_print_fp(stderr, dh_client_pub);
 125         fprintf(stderr, "\n");
 126         debug("bits %d", BN_num_bits(dh_client_pub));
 127 #endif
 128
 129 #ifdef DEBUG_KEXDH
 130         DHparams_print_fp(stderr, dh);
 131         fprintf(stderr, "pub= ");
 132         BN_print_fp(stderr, dh->pub_key);
 133         fprintf(stderr, "\n");
 134 #endif
 135         if (!dh_pub_is_valid(dh, dh_client_pub))
 136                 packet_disconnect("bad client public DH value");
 137
 138         klen = DH_size(dh);
 139         kbuf = xmalloc(klen);
 140         if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
 141                 fatal("DH_compute_key: failed");
 142 #ifdef DEBUG_KEXDH
 143         dump_digest("shared secret", kbuf, kout);
 144 #endif
 145         if ((shared_secret = BN_new()) == NULL)
 146                 fatal("kexgex_server: BN_new failed");
 147         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 148                 fatal("kexgex_server: BN_bin2bn failed");
 149         memset(kbuf, 0, klen);
 150         xfree(kbuf);
 151
 152         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 153
 154         if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 155                 omin = min = omax = max = -1;
 156
 157         /* calc H */
 158         kexgex_hash(
 159             kex->evp_md,
 160             kex->client_version_string,
 161             kex->server_version_string,
 162             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 163             buffer_ptr(&kex->my), buffer_len(&kex->my),
 164             server_host_key_blob, sbloblen,
 165             omin, onbits, omax,
 166             dh->p, dh->g,
 167             dh_client_pub,
 168             dh->pub_key,
 169             shared_secret,
 170             &hash, &hashlen
 171         );
 172         BN_clear_free(dh_client_pub);
 173
 174         /* save session id := H */
 175         if (kex->session_id == NULL) {
 176                 kex->session_id_len = hashlen;
 177                 kex->session_id = xmalloc(kex->session_id_len);
 178                 memcpy(kex->session_id, hash, kex->session_id_len);
 179         }
 180
 181         /* sign H */
 182         if (PRIVSEP(key_sign(server_host_key, &signature, &slen, hash,
 183             hashlen)) < 0)
 184                 fatal("kexgex_server: key_sign failed");
 185
 186         /* destroy_sensitive_data(); */
 187
 188         /* send server hostkey, DH pubkey 'f' and singed H */
 189         debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
 190         packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
 191         packet_put_string(server_host_key_blob, sbloblen);
 192         packet_put_bignum2(dh->pub_key);        /* f */
 193         packet_put_string(signature, slen);
 194         packet_send();
 195
 196         xfree(signature);
 197         xfree(server_host_key_blob);
 198         /* have keys, free DH */
 199         DH_free(dh);
 200
 201         kex_derive_keys(kex, hash, hashlen, shared_secret);
 202         BN_clear_free(shared_secret);
 203
 204         kex_finish(kex);
 205 }