crypto/openssh/kexecdhs.c

   1 /* $OpenBSD: kexecdhs.c,v 1.10 2014/02/02 03:44:31 djm Exp $ */
   2 /*
   3  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   4  * Copyright (c) 2010 Damien Miller.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "includes.h"
  28
  29 #include <sys/types.h>
  30 #include <string.h>
  31 #include <signal.h>
  32
  33 #include "xmalloc.h"
  34 #include "buffer.h"
  35 #include "key.h"
  36 #include "cipher.h"
  37 #include "kex.h"
  38 #include "log.h"
  39 #include "packet.h"
  40 #include "ssh2.h"
  41
  42 #ifdef OPENSSL_HAS_ECC
  43
  44 #include <openssl/ecdh.h>
  45
  46 void
  47 kexecdh_server(Kex *kex)
  48 {
  49         EC_POINT *client_public;
  50         EC_KEY *server_key;
  51         const EC_GROUP *group;
  52         BIGNUM *shared_secret;
  53         Key *server_host_private, *server_host_public;
  54         u_char *server_host_key_blob = NULL, *signature = NULL;
  55         u_char *kbuf, *hash;
  56         u_int klen, slen, sbloblen, hashlen;
  57
  58         if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL)
  59                 fatal("%s: EC_KEY_new_by_curve_name failed", __func__);
  60         if (EC_KEY_generate_key(server_key) != 1)
  61                 fatal("%s: EC_KEY_generate_key failed", __func__);
  62         group = EC_KEY_get0_group(server_key);
  63
  64 #ifdef DEBUG_KEXECDH
  65         fputs("server private key:\n", stderr);
  66         key_dump_ec_key(server_key);
  67 #endif
  68
  69         if (kex->load_host_public_key == NULL ||
  70             kex->load_host_private_key == NULL)
  71                 fatal("Cannot load hostkey");
  72         server_host_public = kex->load_host_public_key(kex->hostkey_type);
  73         if (server_host_public == NULL)
  74                 fatal("Unsupported hostkey type %d", kex->hostkey_type);
  75         server_host_private = kex->load_host_private_key(kex->hostkey_type);
  76
  77         debug("expecting SSH2_MSG_KEX_ECDH_INIT");
  78         packet_read_expect(SSH2_MSG_KEX_ECDH_INIT);
  79         if ((client_public = EC_POINT_new(group)) == NULL)
  80                 fatal("%s: EC_POINT_new failed", __func__);
  81         packet_get_ecpoint(group, client_public);
  82         packet_check_eom();
  83
  84         if (key_ec_validate_public(group, client_public) != 0)
  85                 fatal("%s: invalid client public key", __func__);
  86
  87 #ifdef DEBUG_KEXECDH
  88         fputs("client public key:\n", stderr);
  89         key_dump_ec_point(group, client_public);
  90 #endif
  91
  92         /* Calculate shared_secret */
  93         klen = (EC_GROUP_get_degree(group) + 7) / 8;
  94         kbuf = xmalloc(klen);
  95         if (ECDH_compute_key(kbuf, klen, client_public,
  96             server_key, NULL) != (int)klen)
  97                 fatal("%s: ECDH_compute_key failed", __func__);
  98
  99 #ifdef DEBUG_KEXDH
 100         dump_digest("shared secret", kbuf, klen);
 101 #endif
 102         if ((shared_secret = BN_new()) == NULL)
 103                 fatal("%s: BN_new failed", __func__);
 104         if (BN_bin2bn(kbuf, klen, shared_secret) == NULL)
 105                 fatal("%s: BN_bin2bn failed", __func__);
 106         explicit_bzero(kbuf, klen);
 107         free(kbuf);
 108
 109         /* calc H */
 110         key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
 111         kex_ecdh_hash(
 112             kex->hash_alg,
 113             group,
 114             kex->client_version_string,
 115             kex->server_version_string,
 116             buffer_ptr(&kex->peer), buffer_len(&kex->peer),
 117             buffer_ptr(&kex->my), buffer_len(&kex->my),
 118             server_host_key_blob, sbloblen,
 119             client_public,
 120             EC_KEY_get0_public_key(server_key),
 121             shared_secret,
 122             &hash, &hashlen
 123         );
 124         EC_POINT_clear_free(client_public);
 125
 126         /* save session id := H */
 127         if (kex->session_id == NULL) {
 128                 kex->session_id_len = hashlen;
 129                 kex->session_id = xmalloc(kex->session_id_len);
 130                 memcpy(kex->session_id, hash, kex->session_id_len);
 131         }
 132
 133         /* sign H */
 134         kex->sign(server_host_private, server_host_public, &signature, &slen,
 135             hash, hashlen);
 136
 137         /* destroy_sensitive_data(); */
 138
 139         /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
 140         packet_start(SSH2_MSG_KEX_ECDH_REPLY);
 141         packet_put_string(server_host_key_blob, sbloblen);
 142         packet_put_ecpoint(group, EC_KEY_get0_public_key(server_key));
 143         packet_put_string(signature, slen);
 144         packet_send();
 145
 146         free(signature);
 147         free(server_host_key_blob);
 148         /* have keys, free server key */
 149         EC_KEY_free(server_key);
 150
 151         kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
 152         BN_clear_free(shared_secret);
 153         kex_finish(kex);
 154 }
 155 #else /* OPENSSL_HAS_ECC */
 156 void
 157 kexecdh_server(Kex *kex)
 158 {
 159         fatal("ECC support is not enabled");
 160 }
 161 #endif /* OPENSSL_HAS_ECC */