kexdhs.c

   1 /* $OpenBSD: kexdhs.c,v 1.8 2006/10/31 16:33:12 markus 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 <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 #ifdef GSSAPI
  44 #include "ssh-gss.h"
  45 #endif
  46 #include "monitor_wrap.h"
  47
  48 void
  49 kexdh_server(Kex *kex)
  50 {
  51         BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
  52         DH *dh;
  53         Key *server_host_key;
  54         u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
  55         u_int sbloblen, klen, hashlen, slen;
  56         int kout;
  57
  58         /* generate server 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
  71         debug("expecting SSH2_MSG_KEXDH_INIT");
  72         packet_read_expect(SSH2_MSG_KEXDH_INIT);
  73
  74         if (kex->load_host_key == NULL)
  75                 fatal("Cannot load hostkey");
  76         server_host_key = kex->load_host_key(kex->hostkey_type);
  77         if (server_host_key == NULL)
  78                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  79
  80         /* key, cert */
  81         if ((dh_client_pub = BN_new()) == NULL)
  82                 fatal("dh_client_pub == NULL");
  83         packet_get_bignum2(dh_client_pub);
  84         packet_check_eom();
  85
  86 #ifdef DEBUG_KEXDH
  87         fprintf(stderr, "dh_client_pub= ");
  88         BN_print_fp(stderr, dh_client_pub);
  89         fprintf(stderr, "\n");
  90         debug("bits %d", BN_num_bits(dh_client_pub));
  91 #endif
  92
  93 #ifdef DEBUG_KEXDH
  94         DHparams_print_fp(stderr, dh);
  95         fprintf(stderr, "pub= ");
  96         BN_print_fp(stderr, dh->pub_key);
  97         fprintf(stderr, "\n");
  98 #endif
  99         if (!dh_pub_is_valid(dh, dh_client_pub))
 100                 packet_disconnect("bad client public DH value");
 101
 102         klen = DH_size(dh);
 103         kbuf = xmalloc(klen);
 104         if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
 105                 fatal("DH_compute_key: failed");
 106 #ifdef DEBUG_KEXDH
 107         dump_digest("shared secret", kbuf, kout);
 108 #endif
 109         if ((shared_secret = BN_new()) == NULL)
 110                 fatal("kexdh_server: BN_new failed");
 111         BN_bin2bn(kbuf, kout, shared_secret);
 112         memset(kbuf, 0, klen);
 113         xfree(kbuf);
 114
 115         key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
 116
 117         /* calc H */
 118         kex_dh_hash(
 119             kex->client_version_string,
 120             kex->server_version_string,
 121             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 122             buffer_ptr(&kex->my), buffer_len(&kex->my),
 123             server_host_key_blob, sbloblen,
 124             dh_client_pub,
 125             dh->pub_key,
 126             shared_secret,
 127             &hash, &hashlen
 128         );
 129         BN_clear_free(dh_client_pub);
 130
 131         /* save session id := H */
 132         if (kex->session_id == NULL) {
 133                 kex->session_id_len = hashlen;
 134                 kex->session_id = xmalloc(kex->session_id_len);
 135                 memcpy(kex->session_id, hash, kex->session_id_len);
 136         }
 137
 138         /* sign H */
 139         PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
 140
 141         /* destroy_sensitive_data(); */
 142
 143         /* send server hostkey, DH pubkey 'f' and singed H */
 144         packet_start(SSH2_MSG_KEXDH_REPLY);
 145         packet_put_string(server_host_key_blob, sbloblen);
 146         packet_put_bignum2(dh->pub_key);        /* f */
 147         packet_put_string(signature, slen);
 148         packet_send();
 149
 150         xfree(signature);
 151         xfree(server_host_key_blob);
 152         /* have keys, free DH */
 153         DH_free(dh);
 154
 155         kex_derive_keys(kex, hash, hashlen, shared_secret);
 156         BN_clear_free(shared_secret);
 157         kex_finish(kex);
 158 }