kexc25519s.c revision 262566 
1/* $OpenBSD: kexc25519s.c,v 1.4 2014/01/12 08:13:13 djm Exp $ */
2/*
3 * Copyright (c) 2001 Markus Friedl.  All rights reserved.
4 * Copyright (c) 2010 Damien Miller.  All rights reserved.
5 * Copyright (c) 2013 Aris Adamantiadis.  All rights reserved.
6 *
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
42void
43kexc25519_server(Kex *kex)
44{
45	Key *server_host_private, *server_host_public;
46	u_char *server_host_key_blob = NULL, *signature = NULL;
47	u_char server_key[CURVE25519_SIZE];
48	u_char *client_pubkey = NULL;
49	u_char server_pubkey[CURVE25519_SIZE];
50	u_char *hash;
51	u_int slen, sbloblen, hashlen;
52	Buffer shared_secret;
53
54	/* generate private key */
55	kexc25519_keygen(server_key, server_pubkey);
56#ifdef DEBUG_KEXECDH
57	dump_digest("server private key:", server_key, sizeof(server_key));
58#endif
59
60	if (kex->load_host_public_key == NULL ||
61	    kex->load_host_private_key == NULL)
62		fatal("Cannot load hostkey");
63	server_host_public = kex->load_host_public_key(kex->hostkey_type);
64	if (server_host_public == NULL)
65		fatal("Unsupported hostkey type %d", kex->hostkey_type);
66	server_host_private = kex->load_host_private_key(kex->hostkey_type);
67
68	debug("expecting SSH2_MSG_KEX_ECDH_INIT");
69	packet_read_expect(SSH2_MSG_KEX_ECDH_INIT);
70	client_pubkey = packet_get_string(&slen);
71	if (slen != CURVE25519_SIZE)
72		fatal("Incorrect size for server Curve25519 pubkey: %d", slen);
73	packet_check_eom();
74
75#ifdef DEBUG_KEXECDH
76	dump_digest("client public key:", client_pubkey, CURVE25519_SIZE);
77#endif
78
79	buffer_init(&shared_secret);
80	kexc25519_shared_key(server_key, client_pubkey, &shared_secret);
81
82	/* calc H */
83	key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
84	kex_c25519_hash(
85	    kex->hash_alg,
86	    kex->client_version_string,
87	    kex->server_version_string,
88	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
89	    buffer_ptr(&kex->my), buffer_len(&kex->my),
90	    server_host_key_blob, sbloblen,
91	    client_pubkey,
92	    server_pubkey,
93	    buffer_ptr(&shared_secret), buffer_len(&shared_secret),
94	    &hash, &hashlen
95	);
96
97	/* save session id := H */
98	if (kex->session_id == NULL) {
99		kex->session_id_len = hashlen;
100		kex->session_id = xmalloc(kex->session_id_len);
101		memcpy(kex->session_id, hash, kex->session_id_len);
102	}
103
104	/* sign H */
105	kex->sign(server_host_private, server_host_public, &signature, &slen,
106	    hash, hashlen);
107
108	/* destroy_sensitive_data(); */
109
110	/* send server hostkey, ECDH pubkey 'Q_S' and signed H */
111	packet_start(SSH2_MSG_KEX_ECDH_REPLY);
112	packet_put_string(server_host_key_blob, sbloblen);
113	packet_put_string(server_pubkey, sizeof(server_pubkey));
114	packet_put_string(signature, slen);
115	packet_send();
116
117	free(signature);
118	free(server_host_key_blob);
119	/* have keys, free server key */
120	free(client_pubkey);
121
122	kex_derive_keys(kex, hash, hashlen,
123	    buffer_ptr(&shared_secret), buffer_len(&shared_secret));
124	buffer_free(&shared_secret);
125	kex_finish(kex);
126}
127