kexdhs.c

   1 /*
   2  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26
  27 #include "xmalloc.h"
  28 #include "key.h"
  29 #include "kex.h"
  30 #include "log.h"
  31 #include "packet.h"
  32 #include "dh.h"
  33 #include "ssh2.h"
  34 #include "monitor_wrap.h"
  35
  36 void
  37 kexdh_server(Kex *kex)
  38 {
  39         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  40         DH *dh;
  41         Key *server_host_key;
  42         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  43         u_int sbloblen, klen, kout, hashlen;
  44         u_int slen;
  45
  46         /* generate server DH public key */
  47         switch (kex->kex_type) {
  48         case KEX_DH_GRP1_SHA1:
  49                 dh = dh_new_group1();
  50                 break;
  51         case KEX_DH_GRP14_SHA1:
  52                 dh = dh_new_group14();
  53                 break;
  54         default:
  55                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
  56         }
  57         dh_gen_key(dh, kex->we_need * 8);
  58
  59         debug("expecting SSH2_MSG_KEXDH_INIT");
  60         packet_read_expect(SSH2_MSG_KEXDH_INIT);
  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         /* key, cert */
  69         if ((dh_client_pub = BN_new()) == NULL)
  70                 fatal("dh_client_pub == NULL");
  71         packet_get_bignum2(dh_client_pub);
  72         packet_check_eom();
  73
  74 #ifdef DEBUG_KEXDH
  75         fprintf(stderr, "dh_client_pub= ");
  76         BN_print_fp(stderr, dh_client_pub);
  77         fprintf(stderr, "\n");
  78         debug("bits %d", BN_num_bits(dh_client_pub));
  79 #endif
  80
  81 #ifdef DEBUG_KEXDH
  82         DHparams_print_fp(stderr, dh);
  83         fprintf(stderr, "pub= ");
  84         BN_print_fp(stderr, dh->pub_key);
  85         fprintf(stderr, "\n");
  86 #endif
  87         if (!dh_pub_is_valid(dh, dh_client_pub))
  88                 packet_disconnect("bad client public DH value");
  89
  90         klen = DH_size(dh);
  91         kbuf = xmalloc(klen);
  92         kout = DH_compute_key(kbuf, dh_client_pub, dh);
  93 #ifdef DEBUG_KEXDH
  94         dump_digest("shared secret", kbuf, kout);
  95 #endif
  96         if ((shared_secret = BN_new()) == NULL)
  97                 fatal("kexdh_server: BN_new failed");
  98         BN_bin2bn(kbuf, kout, shared_secret);
  99         memset(kbuf, 0, klen);
 100         xfree(kbuf);
 101
 102         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 103
 104         /* calc H */
 105         kex_dh_hash(
 106             kex->client_version_string,
 107             kex->server_version_string,
 108             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 109             buffer_ptr(&kex->my), buffer_len(&kex->my),
 110             server_host_key_blob, sbloblen,
 111             dh_client_pub,
 112             dh->pub_key,
 113             shared_secret,
 114             &hash, &hashlen
 115         );
 116         BN_clear_free(dh_client_pub);
 117
 118         /* save session id := H */
 119         if (kex->session_id == NULL) {
 120                 kex->session_id_len = hashlen;
 121                 kex->session_id = xmalloc(kex->session_id_len);
 122                 memcpy(kex->session_id, hash, kex->session_id_len);
 123         }
 124
 125         /* sign H */
 126         PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
 127
 128         /* destroy_sensitive_data(); */
 129
 130         /* send server hostkey, DH pubkey 'f' and singed H */
 131         packet_start(SSH2_MSG_KEXDH_REPLY);
 132         packet_put_string(server_host_key_blob, sbloblen);
 133         packet_put_bignum2(dh->pub_key);        /* f */
 134         packet_put_string(signature, slen);
 135         packet_send();
 136
 137         xfree(signature);
 138         xfree(server_host_key_blob);
 139         /* have keys, free DH */
 140         DH_free(dh);
 141
 142         kex_derive_keys(kex, hash, hashlen, shared_secret);
 143         BN_clear_free(shared_secret);
 144         kex_finish(kex);
 145 }