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