kexdhs.c

   1 /* $OpenBSD: kexdhs.c,v 1.12 2010/11/10 01:33:07 djm Exp $ */
   2 /*
   3  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "includes.h"
  27
  28 #include <sys/types.h>
  29
  30 #include <stdarg.h>
  31 #include <string.h>
  32 #include <signal.h>
  33
  34 #include <openssl/dh.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 #ifdef GSSAPI
  46 #include "ssh-gss.h"
  47 #endif
  48 #include "monitor_wrap.h"
  49
  50 void
  51 kexdh_server(Kex *kex)
  52 {
  53         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  54         DH *dh;
  55         Key *server_host_public, *server_host_private;
  56         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  57         u_int sbloblen, klen, hashlen, slen;
  58         int kout;
  59
  60         /* generate server DH public key */
  61         switch (kex->kex_type) {
  62         case KEX_DH_GRP1_SHA1:
  63                 dh = dh_new_group1();
  64                 break;
  65         case KEX_DH_GRP14_SHA1:
  66                 dh = dh_new_group14();
  67                 break;
  68         default:
  69                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
  70         }
  71         dh_gen_key(dh, kex->we_need * 8);
  72
  73         debug("expecting SSH2_MSG_KEXDH_INIT");
  74         packet_read_expect(SSH2_MSG_KEXDH_INIT);
  75
  76         if (kex->load_host_public_key == NULL ||
  77             kex->load_host_private_key == NULL)
  78                 fatal("Cannot load hostkey");
  79         server_host_public = kex->load_host_public_key(kex->hostkey_type);
  80         if (server_host_public == NULL)
  81                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  82         server_host_private = kex->load_host_private_key(kex->hostkey_type);
  83         if (server_host_private == NULL)
  84                 fatal("Missing private key for hostkey type %d",
  85                     kex->hostkey_type);
  86
  87         /* key, cert */
  88         if ((dh_client_pub = BN_new()) == NULL)
  89                 fatal("dh_client_pub == NULL");
  90         packet_get_bignum2(dh_client_pub);
  91         packet_check_eom();
  92
  93 #ifdef DEBUG_KEXDH
  94         fprintf(stderr, "dh_client_pub= ");
  95         BN_print_fp(stderr, dh_client_pub);
  96         fprintf(stderr, "\n");
  97         debug("bits %d", BN_num_bits(dh_client_pub));
  98 #endif
  99
 100 #ifdef DEBUG_KEXDH
 101         DHparams_print_fp(stderr, dh);
 102         fprintf(stderr, "pub= ");
 103         BN_print_fp(stderr, dh->pub_key);
 104         fprintf(stderr, "\n");
 105 #endif
 106         if (!dh_pub_is_valid(dh, dh_client_pub))
 107                 packet_disconnect("bad client public DH value");
 108
 109         klen = DH_size(dh);
 110         kbuf = xmalloc(klen);
 111         if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
 112                 fatal("DH_compute_key: failed");
 113 #ifdef DEBUG_KEXDH
 114         dump_digest("shared secret", kbuf, kout);
 115 #endif
 116         if ((shared_secret = BN_new()) == NULL)
 117                 fatal("kexdh_server: BN_new failed");
 118         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 119                 fatal("kexdh_server: BN_bin2bn failed");
 120         memset(kbuf, 0, klen);
 121         xfree(kbuf);
 122
 123         key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
 124
 125         /* calc H */
 126         kex_dh_hash(
 127             kex->client_version_string,
 128             kex->server_version_string,
 129             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 130             buffer_ptr(&kex->my), buffer_len(&kex->my),
 131             server_host_key_blob, sbloblen,
 132             dh_client_pub,
 133             dh->pub_key,
 134             shared_secret,
 135             &hash, &hashlen
 136         );
 137         BN_clear_free(dh_client_pub);
 138
 139         /* save session id := H */
 140         if (kex->session_id == NULL) {
 141                 kex->session_id_len = hashlen;
 142                 kex->session_id = xmalloc(kex->session_id_len);
 143                 memcpy(kex->session_id, hash, kex->session_id_len);
 144         }
 145
 146         /* sign H */
 147         if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash,
 148             hashlen)) < 0)
 149                 fatal("kexdh_server: key_sign failed");
 150
 151         /* destroy_sensitive_data(); */
 152
 153         /* send server hostkey, DH pubkey 'f' and singed H */
 154         packet_start(SSH2_MSG_KEXDH_REPLY);
 155         packet_put_string(server_host_key_blob, sbloblen);
 156         packet_put_bignum2(dh->pub_key);        /* f */
 157         packet_put_string(signature, slen);
 158         packet_send();
 159
 160         xfree(signature);
 161         xfree(server_host_key_blob);
 162         /* have keys, free DH */
 163         DH_free(dh);
 164
 165         kex_derive_keys(kex, hash, hashlen, shared_secret);
 166         BN_clear_free(shared_secret);
 167         kex_finish(kex);
 168 }