kexc25519.c revision 262566 
1/* $OpenBSD: kexc25519.c,v 1.4 2014/01/12 08:13:13 djm Exp $ */
2/*
3 * Copyright (c) 2001, 2013 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 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28#include "includes.h"
29
30#include <sys/types.h>
31
32#include <signal.h>
33#include <string.h>
34
35#include <openssl/bn.h>
36#include <openssl/evp.h>
37
38#include "buffer.h"
39#include "ssh2.h"
40#include "key.h"
41#include "cipher.h"
42#include "kex.h"
43#include "log.h"
44#include "digest.h"
45
46extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
47    const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
48	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
49	__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
50	__attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));
51
52void
53kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
54{
55	static const u_char basepoint[CURVE25519_SIZE] = {9};
56
57	arc4random_buf(key, CURVE25519_SIZE);
58	crypto_scalarmult_curve25519(pub, key, basepoint);
59}
60
61void
62kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
63    const u_char pub[CURVE25519_SIZE], Buffer *out)
64{
65	u_char shared_key[CURVE25519_SIZE];
66
67	crypto_scalarmult_curve25519(shared_key, key, pub);
68#ifdef DEBUG_KEXECDH
69	dump_digest("shared secret", shared_key, CURVE25519_SIZE);
70#endif
71	buffer_clear(out);
72	buffer_put_bignum2_from_string(out, shared_key, CURVE25519_SIZE);
73	memset(shared_key, 0, CURVE25519_SIZE);	/* XXX explicit_bzero() */
74}
75
76void
77kex_c25519_hash(
78    int hash_alg,
79    char *client_version_string,
80    char *server_version_string,
81    char *ckexinit, int ckexinitlen,
82    char *skexinit, int skexinitlen,
83    u_char *serverhostkeyblob, int sbloblen,
84    const u_char client_dh_pub[CURVE25519_SIZE],
85    const u_char server_dh_pub[CURVE25519_SIZE],
86    const u_char *shared_secret, u_int secretlen,
87    u_char **hash, u_int *hashlen)
88{
89	Buffer b;
90	static u_char digest[SSH_DIGEST_MAX_LENGTH];
91
92	buffer_init(&b);
93	buffer_put_cstring(&b, client_version_string);
94	buffer_put_cstring(&b, server_version_string);
95
96	/* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
97	buffer_put_int(&b, ckexinitlen+1);
98	buffer_put_char(&b, SSH2_MSG_KEXINIT);
99	buffer_append(&b, ckexinit, ckexinitlen);
100	buffer_put_int(&b, skexinitlen+1);
101	buffer_put_char(&b, SSH2_MSG_KEXINIT);
102	buffer_append(&b, skexinit, skexinitlen);
103
104	buffer_put_string(&b, serverhostkeyblob, sbloblen);
105	buffer_put_string(&b, client_dh_pub, CURVE25519_SIZE);
106	buffer_put_string(&b, server_dh_pub, CURVE25519_SIZE);
107	buffer_append(&b, shared_secret, secretlen);
108
109#ifdef DEBUG_KEX
110	buffer_dump(&b);
111#endif
112	if (ssh_digest_buffer(hash_alg, &b, digest, sizeof(digest)) != 0)
113		fatal("%s: digest_buffer failed", __func__);
114
115	buffer_free(&b);
116
117#ifdef DEBUG_KEX
118	dump_digest("hash", digest, ssh_digest_bytes(hash_alg));
119#endif
120	*hash = digest;
121	*hashlen = ssh_digest_bytes(hash_alg);
122}
123