kexdhc.c

   1 /* $OpenBSD: kexdhc.c,v 1.9 2006/08/03 03:34:42 deraadt 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 <stdio.h>
  31 #include <string.h>
  32 #include <signal.h>
  33
  34 #include "xmalloc.h"
  35 #include "buffer.h"
  36 #include "key.h"
  37 #include "cipher.h"
  38 #include "kex.h"
  39 #include "log.h"
  40 #include "packet.h"
  41 #include "dh.h"
  42 #include "ssh2.h"
  43
  44 void
  45 kexdh_client(Kex *kex)
  46 {
  47         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  48         DH *dh;
  49         Key *server_host_key;
  50         u_char *server_host_key_blob = NULL, *signature = NULL;
  51         u_char *kbuf, *hash;
  52         u_int klen, kout, slen, sbloblen, hashlen;
  53
  54         /* generate and send 'e', client DH public key */
  55         switch (kex->kex_type) {
  56         case KEX_DH_GRP1_SHA1:
  57                 dh = dh_new_group1();
  58                 break;
  59         case KEX_DH_GRP14_SHA1:
  60                 dh = dh_new_group14();
  61                 break;
  62         default:
  63                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
  64         }
  65         dh_gen_key(dh, kex->we_need * 8);
  66         packet_start(SSH2_MSG_KEXDH_INIT);
  67         packet_put_bignum2(dh->pub_key);
  68         packet_send();
  69
  70         debug("sending SSH2_MSG_KEXDH_INIT");
  71 #ifdef DEBUG_KEXDH
  72         DHparams_print_fp(stderr, dh);
  73         fprintf(stderr, "pub= ");
  74         BN_print_fp(stderr, dh->pub_key);
  75         fprintf(stderr, "\n");
  76 #endif
  77
  78         debug("expecting SSH2_MSG_KEXDH_REPLY");
  79         packet_read_expect(SSH2_MSG_KEXDH_REPLY);
  80
  81         /* key, cert */
  82         server_host_key_blob = packet_get_string(&sbloblen);
  83         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  84         if (server_host_key == NULL)
  85                 fatal("cannot decode server_host_key_blob");
  86         if (server_host_key->type != kex->hostkey_type)
  87                 fatal("type mismatch for decoded server_host_key_blob");
  88         if (kex->verify_host_key == NULL)
  89                 fatal("cannot verify server_host_key");
  90         if (kex->verify_host_key(server_host_key) == -1)
  91                 fatal("server_host_key verification failed");
  92
  93         /* DH parameter f, server public DH key */
  94         if ((dh_server_pub = BN_new()) == NULL)
  95                 fatal("dh_server_pub == NULL");
  96         packet_get_bignum2(dh_server_pub);
  97
  98 #ifdef DEBUG_KEXDH
  99         fprintf(stderr, "dh_server_pub= ");
 100         BN_print_fp(stderr, dh_server_pub);
 101         fprintf(stderr, "\n");
 102         debug("bits %d", BN_num_bits(dh_server_pub));
 103 #endif
 104
 105         /* signed H */
 106         signature = packet_get_string(&slen);
 107         packet_check_eom();
 108
 109         if (!dh_pub_is_valid(dh, dh_server_pub))
 110                 packet_disconnect("bad server public DH value");
 111
 112         klen = DH_size(dh);
 113         kbuf = xmalloc(klen);
 114         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 115 #ifdef DEBUG_KEXDH
 116         dump_digest("shared secret", kbuf, kout);
 117 #endif
 118         if ((shared_secret = BN_new()) == NULL)
 119                 fatal("kexdh_client: BN_new failed");
 120         BN_bin2bn(kbuf, kout, shared_secret);
 121         memset(kbuf, 0, klen);
 122         xfree(kbuf);
 123
 124         /* calc and verify H */
 125         kex_dh_hash(
 126             kex->client_version_string,
 127             kex->server_version_string,
 128             buffer_ptr(&kex->my), buffer_len(&kex->my),
 129             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 130             server_host_key_blob, sbloblen,
 131             dh->pub_key,
 132             dh_server_pub,
 133             shared_secret,
 134             &hash, &hashlen
 135         );
 136         xfree(server_host_key_blob);
 137         BN_clear_free(dh_server_pub);
 138         DH_free(dh);
 139
 140         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 141                 fatal("key_verify failed for server_host_key");
 142         key_free(server_host_key);
 143         xfree(signature);
 144
 145         /* save session id */
 146         if (kex->session_id == NULL) {
 147                 kex->session_id_len = hashlen;
 148                 kex->session_id = xmalloc(kex->session_id_len);
 149                 memcpy(kex->session_id, hash, kex->session_id_len);
 150         }
 151
 152         kex_derive_keys(kex, hash, hashlen, shared_secret);
 153         BN_clear_free(shared_secret);
 154         kex_finish(kex);
 155 }