kexdhs.c

   1 /* $OpenBSD: kexdhs.c,v 1.6 2006/07/22 20:48:23 stevesk 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 <string.h>
  29
  30 #include "xmalloc.h"
  31 #include "key.h"
  32 #include "kex.h"
  33 #include "log.h"
  34 #include "packet.h"
  35 #include "dh.h"
  36 #include "ssh2.h"
  37 #include "monitor_wrap.h"
  38
  39 void
  40 kexdh_server(Kex *kex)
  41 {
  42         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  43         DH *dh;
  44         Key *server_host_key;
  45         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  46         u_int sbloblen, klen, kout, hashlen;
  47         u_int slen;
  48
  49         /* generate server DH public key */
  50         switch (kex->kex_type) {
  51         case KEX_DH_GRP1_SHA1:
  52                 dh = dh_new_group1();
  53                 break;
  54         case KEX_DH_GRP14_SHA1:
  55                 dh = dh_new_group14();
  56                 break;
  57         default:
  58                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
  59         }
  60         dh_gen_key(dh, kex->we_need * 8);
  61
  62         debug("expecting SSH2_MSG_KEXDH_INIT");
  63         packet_read_expect(SSH2_MSG_KEXDH_INIT);
  64
  65         if (kex->load_host_key == NULL)
  66                 fatal("Cannot load hostkey");
  67         server_host_key = kex->load_host_key(kex->hostkey_type);
  68         if (server_host_key == NULL)
  69                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  70
  71         /* key, cert */
  72         if ((dh_client_pub = BN_new()) == NULL)
  73                 fatal("dh_client_pub == NULL");
  74         packet_get_bignum2(dh_client_pub);
  75         packet_check_eom();
  76
  77 #ifdef DEBUG_KEXDH
  78         fprintf(stderr, "dh_client_pub= ");
  79         BN_print_fp(stderr, dh_client_pub);
  80         fprintf(stderr, "\n");
  81         debug("bits %d", BN_num_bits(dh_client_pub));
  82 #endif
  83
  84 #ifdef DEBUG_KEXDH
  85         DHparams_print_fp(stderr, dh);
  86         fprintf(stderr, "pub= ");
  87         BN_print_fp(stderr, dh->pub_key);
  88         fprintf(stderr, "\n");
  89 #endif
  90         if (!dh_pub_is_valid(dh, dh_client_pub))
  91                 packet_disconnect("bad client public DH value");
  92
  93         klen = DH_size(dh);
  94         kbuf = xmalloc(klen);
  95         kout = DH_compute_key(kbuf, dh_client_pub, dh);
  96 #ifdef DEBUG_KEXDH
  97         dump_digest("shared secret", kbuf, kout);
  98 #endif
  99         if ((shared_secret = BN_new()) == NULL)
 100                 fatal("kexdh_server: BN_new failed");
 101         BN_bin2bn(kbuf, kout, shared_secret);
 102         memset(kbuf, 0, klen);
 103         xfree(kbuf);
 104
 105         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 106
 107         /* calc H */
 108         kex_dh_hash(
 109             kex->client_version_string,
 110             kex->server_version_string,
 111             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 112             buffer_ptr(&kex->my), buffer_len(&kex->my),
 113             server_host_key_blob, sbloblen,
 114             dh_client_pub,
 115             dh->pub_key,
 116             shared_secret,
 117             &hash, &hashlen
 118         );
 119         BN_clear_free(dh_client_pub);
 120
 121         /* save session id := H */
 122         if (kex->session_id == NULL) {
 123                 kex->session_id_len = hashlen;
 124                 kex->session_id = xmalloc(kex->session_id_len);
 125                 memcpy(kex->session_id, hash, kex->session_id_len);
 126         }
 127
 128         /* sign H */
 129         PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
 130
 131         /* destroy_sensitive_data(); */
 132
 133         /* send server hostkey, DH pubkey 'f' and singed H */
 134         packet_start(SSH2_MSG_KEXDH_REPLY);
 135         packet_put_string(server_host_key_blob, sbloblen);
 136         packet_put_bignum2(dh->pub_key);        /* f */
 137         packet_put_string(signature, slen);
 138         packet_send();
 139
 140         xfree(signature);
 141         xfree(server_host_key_blob);
 142         /* have keys, free DH */
 143         DH_free(dh);
 144
 145         kex_derive_keys(kex, hash, hashlen, shared_secret);
 146         BN_clear_free(shared_secret);
 147         kex_finish(kex);
 148 }