kexdhc.c

   1 /* $OpenBSD: kexdhc.c,v 1.6 2006/05/18 21:27:25 miod 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 "xmalloc.h"
  29 #include "key.h"
  30 #include "kex.h"
  31 #include "log.h"
  32 #include "packet.h"
  33 #include "dh.h"
  34 #include "ssh2.h"
  35
  36 void
  37 kexdh_client(Kex *kex)
  38 {
  39         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  40         DH *dh;
  41         Key *server_host_key;
  42         u_char *server_host_key_blob = NULL, *signature = NULL;
  43         u_char *kbuf, *hash;
  44         u_int klen, kout, slen, sbloblen, hashlen;
  45
  46         /* generate and send 'e', client 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         packet_start(SSH2_MSG_KEXDH_INIT);
  59         packet_put_bignum2(dh->pub_key);
  60         packet_send();
  61
  62         debug("sending SSH2_MSG_KEXDH_INIT");
  63 #ifdef DEBUG_KEXDH
  64         DHparams_print_fp(stderr, dh);
  65         fprintf(stderr, "pub= ");
  66         BN_print_fp(stderr, dh->pub_key);
  67         fprintf(stderr, "\n");
  68 #endif
  69
  70         debug("expecting SSH2_MSG_KEXDH_REPLY");
  71         packet_read_expect(SSH2_MSG_KEXDH_REPLY);
  72
  73         /* key, cert */
  74         server_host_key_blob = packet_get_string(&sbloblen);
  75         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  76         if (server_host_key == NULL)
  77                 fatal("cannot decode server_host_key_blob");
  78         if (server_host_key->type != kex->hostkey_type)
  79                 fatal("type mismatch for decoded server_host_key_blob");
  80         if (kex->verify_host_key == NULL)
  81                 fatal("cannot verify server_host_key");
  82         if (kex->verify_host_key(server_host_key) == -1)
  83                 fatal("server_host_key verification failed");
  84
  85         /* DH parameter f, server public DH key */
  86         if ((dh_server_pub = BN_new()) == NULL)
  87                 fatal("dh_server_pub == NULL");
  88         packet_get_bignum2(dh_server_pub);
  89
  90 #ifdef DEBUG_KEXDH
  91         fprintf(stderr, "dh_server_pub= ");
  92         BN_print_fp(stderr, dh_server_pub);
  93         fprintf(stderr, "\n");
  94         debug("bits %d", BN_num_bits(dh_server_pub));
  95 #endif
  96
  97         /* signed H */
  98         signature = packet_get_string(&slen);
  99         packet_check_eom();
 100
 101         if (!dh_pub_is_valid(dh, dh_server_pub))
 102                 packet_disconnect("bad server public DH value");
 103
 104         klen = DH_size(dh);
 105         kbuf = xmalloc(klen);
 106         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 107 #ifdef DEBUG_KEXDH
 108         dump_digest("shared secret", kbuf, kout);
 109 #endif
 110         if ((shared_secret = BN_new()) == NULL)
 111                 fatal("kexdh_client: BN_new failed");
 112         BN_bin2bn(kbuf, kout, shared_secret);
 113         memset(kbuf, 0, klen);
 114         xfree(kbuf);
 115
 116         /* calc and verify H */
 117         kex_dh_hash(
 118             kex->client_version_string,
 119             kex->server_version_string,
 120             buffer_ptr(&kex->my), buffer_len(&kex->my),
 121             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 122             server_host_key_blob, sbloblen,
 123             dh->pub_key,
 124             dh_server_pub,
 125             shared_secret,
 126             &hash, &hashlen
 127         );
 128         xfree(server_host_key_blob);
 129         BN_clear_free(dh_server_pub);
 130         DH_free(dh);
 131
 132         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 133                 fatal("key_verify failed for server_host_key");
 134         key_free(server_host_key);
 135         xfree(signature);
 136
 137         /* save session id */
 138         if (kex->session_id == NULL) {
 139                 kex->session_id_len = hashlen;
 140                 kex->session_id = xmalloc(kex->session_id_len);
 141                 memcpy(kex->session_id, hash, kex->session_id_len);
 142         }
 143
 144         kex_derive_keys(kex, hash, hashlen, shared_secret);
 145         BN_clear_free(shared_secret);
 146         kex_finish(kex);
 147 }