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 RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");
  27 
  28 #pragma ident   "%Z%%M% %I%     %E% SMI"
  29 
  30 #include <openssl/crypto.h>
  31 #include <openssl/bn.h>
  32 
  33 #include "xmalloc.h"
  34 #include "buffer.h"
  35 #include "bufaux.h"
  36 #include "key.h"
  37 #include "kex.h"
  38 #include "log.h"
  39 #include "packet.h"
  40 #include "dh.h"
  41 #include "ssh2.h"
  42 
  43 void
  44 kexdh_client(Kex *kex)
  45 {
  46         BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
  47         DH *dh;
  48         Key *server_host_key;
  49         u_char *server_host_key_blob = NULL, *signature = NULL;
  50         u_char *kbuf, *hash;
  51         u_int klen, kout, slen, sbloblen;
  52 
  53         /* generate and send 'e', client DH public key */
  54         dh = dh_new_group1();
  55         dh_gen_key(dh, kex->we_need * 8);
  56         packet_start(SSH2_MSG_KEXDH_INIT);
  57         packet_put_bignum2(dh->pub_key);
  58         packet_send();
  59 
  60         debug("sending SSH2_MSG_KEXDH_INIT");
  61 #ifdef DEBUG_KEXDH
  62         DHparams_print_fp(stderr, dh);
  63         fprintf(stderr, "pub= ");
  64         BN_print_fp(stderr, dh->pub_key);
  65         fprintf(stderr, "\n");
  66 #endif
  67 
  68         debug("expecting SSH2_MSG_KEXDH_REPLY");
  69         packet_read_expect(SSH2_MSG_KEXDH_REPLY);
  70 
  71         /* key, cert */
  72         server_host_key_blob = packet_get_string(&sbloblen);
  73         server_host_key = key_from_blob(server_host_key_blob, sbloblen);
  74         if (server_host_key == NULL)
  75                 fatal("cannot decode server_host_key_blob");
  76         if (server_host_key->type != kex->hostkey_type)
  77                 fatal("type mismatch for decoded server_host_key_blob");
  78         if (kex->verify_host_key == NULL)
  79                 fatal("cannot verify server_host_key");
  80         if (kex->verify_host_key(server_host_key) == -1)
  81                 fatal("server_host_key verification failed");
  82 
  83         /* DH paramter f, server public DH key */
  84         if ((dh_server_pub = BN_new()) == NULL)
  85                 fatal("dh_server_pub == NULL");
  86         packet_get_bignum2(dh_server_pub);
  87 
  88 #ifdef DEBUG_KEXDH
  89         fprintf(stderr, "dh_server_pub= ");
  90         BN_print_fp(stderr, dh_server_pub);
  91         fprintf(stderr, "\n");
  92         debug("bits %d", BN_num_bits(dh_server_pub));
  93 #endif
  94 
  95         /* signed H */
  96         signature = packet_get_string(&slen);
  97         packet_check_eom();
  98 
  99         if (!dh_pub_is_valid(dh, dh_server_pub))
 100                 packet_disconnect("bad server public DH value");
 101 
 102         klen = DH_size(dh);
 103         kbuf = xmalloc(klen);
 104         kout = DH_compute_key(kbuf, dh_server_pub, dh);
 105 #ifdef DEBUG_KEXDH
 106         dump_digest("shared secret", kbuf, kout);
 107 #endif
 108         if ((shared_secret = BN_new()) == NULL)
 109                 fatal("kexdh_client: BN_new failed");
 110         BN_bin2bn(kbuf, kout, shared_secret);
 111         memset(kbuf, 0, klen);
 112         xfree(kbuf);
 113 
 114         /* calc and verify H */
 115         hash = kex_dh_hash(
 116             kex->client_version_string,
 117             kex->server_version_string,
 118             buffer_ptr(&kex->my), buffer_len(&kex->my),
 119             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 120             server_host_key_blob, sbloblen,
 121             dh->pub_key,
 122             dh_server_pub,
 123             shared_secret
 124         );
 125         xfree(server_host_key_blob);
 126         BN_clear_free(dh_server_pub);
 127         DH_free(dh);
 128 
 129         if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
 130                 fatal("key_verify failed for server_host_key");
 131         key_free(server_host_key);
 132         xfree(signature);
 133 
 134         /* save session id */
 135         if (kex->session_id == NULL) {
 136                 kex->session_id_len = 20;
 137                 kex->session_id = xmalloc(kex->session_id_len);
 138                 memcpy(kex->session_id, hash, kex->session_id_len);
 139         }
 140 
 141         kex_derive_keys(kex, hash, shared_secret);
 142         BN_clear_free(shared_secret);
 143         kex_finish(kex);
 144 }