kexdhc.c

   1 /* $OpenBSD: kexdhc.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 <openssl/dh.h>
  31
  32 #include <stdarg.h>
  33 #include <stdio.h>
  34 #include <string.h>
  35 #include <signal.h>
  36
  37 #include "xmalloc.h"
  38 #include "buffer.h"
  39 #include "key.h"
  40 #include "cipher.h"
  41 #include "kex.h"
  42 #include "log.h"
  43 #include "packet.h"
  44 #include "dh.h"
  45 #include "ssh2.h"
  46
  47 void
  48 kexdh_client(Kex *kex)
  49 {
  50         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  51         DH *dh;
  52         Key *server_host_key;
  53         u_char *server_host_key_blob = NULL, *signature = NULL;
  54         u_char *kbuf, *hash;
  55         u_int klen, slen, sbloblen, hashlen;
  56         int kout;
  57
  58         /* generate and send 'e', client DH public key */
  59         switch (kex->kex_type) {
  60         case KEX_DH_GRP1_SHA1:
  61                 dh = dh_new_group1();
  62                 break;
  63         case KEX_DH_GRP14_SHA1:
  64                 dh = dh_new_group14();
  65                 break;
  66         default:
  67                 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
  68         }
  69         dh_gen_key(dh, kex->we_need * 8);
  70         packet_start(SSH2_MSG_KEXDH_INIT);
  71         packet_put_bignum2(dh->pub_key);
  72         packet_send();
  73
  74         debug("sending SSH2_MSG_KEXDH_INIT");
  75 #ifdef DEBUG_KEXDH
  76         DHparams_print_fp(stderr, dh);
  77         fprintf(stderr, "pub= ");
  78         BN_print_fp(stderr, dh->pub_key);
  79         fprintf(stderr, "\n");
  80 #endif
  81
  82         debug("expecting SSH2_MSG_KEXDH_REPLY");
  83         packet_read_expect(SSH2_MSG_KEXDH_REPLY);
  84
  85         /* key, cert */
  86         server_host_key_blob = packet_get_string(&sbloblen);
  87         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  88         if (server_host_key == NULL)
  89                 fatal("cannot decode server_host_key_blob");
  90         if (server_host_key->type != kex->hostkey_type)
  91                 fatal("type mismatch for decoded server_host_key_blob");
  92         if (kex->verify_host_key == NULL)
  93                 fatal("cannot verify server_host_key");
  94         if (kex->verify_host_key(server_host_key) == -1)
  95                 fatal("server_host_key verification failed");
  96
  97         /* DH parameter f, server public DH key */
  98         if ((dh_server_pub = BN_new()) == NULL)
  99                 fatal("dh_server_pub == NULL");
 100         packet_get_bignum2(dh_server_pub);
 101
 102 #ifdef DEBUG_KEXDH
 103         fprintf(stderr, "dh_server_pub= ");
 104         BN_print_fp(stderr, dh_server_pub);
 105         fprintf(stderr, "\n");
 106         debug("bits %d", BN_num_bits(dh_server_pub));
 107 #endif
 108
 109         /* signed H */
 110         signature = packet_get_string(&slen);
 111         packet_check_eom();
 112
 113         if (!dh_pub_is_valid(dh, dh_server_pub))
 114                 packet_disconnect("bad server public DH value");
 115
 116         klen = DH_size(dh);
 117         kbuf = xmalloc(klen);
 118         if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0)
 119                 fatal("DH_compute_key: failed");
 120 #ifdef DEBUG_KEXDH
 121         dump_digest("shared secret", kbuf, kout);
 122 #endif
 123         if ((shared_secret = BN_new()) == NULL)
 124                 fatal("kexdh_client: BN_new failed");
 125         if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
 126                 fatal("kexdh_client: BN_bin2bn failed");
 127         memset(kbuf, 0, klen);
 128         xfree(kbuf);
 129
 130         /* calc and verify H */
 131         kex_dh_hash(
 132             kex->client_version_string,
 133             kex->server_version_string,
 134             buffer_ptr(&kex->my), buffer_len(&kex->my),
 135             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 136             server_host_key_blob, sbloblen,
 137             dh->pub_key,
 138             dh_server_pub,
 139             shared_secret,
 140             &hash, &hashlen
 141         );
 142         xfree(server_host_key_blob);
 143         BN_clear_free(dh_server_pub);
 144         DH_free(dh);
 145
 146         if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
 147                 fatal("key_verify failed for server_host_key");
 148         key_free(server_host_key);
 149         xfree(signature);
 150
 151         /* save session id */
 152         if (kex->session_id == NULL) {
 153                 kex->session_id_len = hashlen;
 154                 kex->session_id = xmalloc(kex->session_id_len);
 155                 memcpy(kex->session_id, hash, kex->session_id_len);
 156         }
 157
 158         kex_derive_keys(kex, hash, hashlen, shared_secret);
 159         BN_clear_free(shared_secret);
 160         kex_finish(kex);
 161 }