summaryrefslogtreecommitdiff
path: root/kexc25519.c
blob: 712dd523df8599291d0ba1e73a78e80e824e9897 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
/* $OpenBSD: kexc25519.c,v 1.11 2018/12/27 03:25:25 djm Exp $ */
/*
 * Copyright (c) 2001, 2013 Markus Friedl.  All rights reserved.
 * Copyright (c) 2010 Damien Miller.  All rights reserved.
 * Copyright (c) 2013 Aris Adamantiadis.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>

#include <signal.h>
#include <string.h>

#include <openssl/bn.h>
#include <openssl/evp.h>

#include "sshbuf.h"
#include "ssh2.h"
#include "sshkey.h"
#include "cipher.h"
#include "kex.h"
#include "log.h"
#include "digest.h"
#include "ssherr.h"

extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
    const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
	__attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
	__attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
	__attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));

void
kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
{
	static const u_char basepoint[CURVE25519_SIZE] = {9};

	arc4random_buf(key, CURVE25519_SIZE);
	crypto_scalarmult_curve25519(pub, key, basepoint);
}

int
kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
    const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
{
	u_char shared_key[CURVE25519_SIZE];
	int r;

	/* Check for all-zero public key */
	explicit_bzero(shared_key, CURVE25519_SIZE);
	if (timingsafe_bcmp(pub, shared_key, CURVE25519_SIZE) == 0)
		return SSH_ERR_KEY_INVALID_EC_VALUE;

	crypto_scalarmult_curve25519(shared_key, key, pub);
#ifdef DEBUG_KEXECDH
	dump_digest("shared secret", shared_key, CURVE25519_SIZE);
#endif
	sshbuf_reset(out);
	r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE);
	explicit_bzero(shared_key, CURVE25519_SIZE);
	return r;
}

int
kex_c25519_hash(
    int hash_alg,
    const struct sshbuf *client_version,
    const struct sshbuf *server_version,
    const u_char *ckexinit, size_t ckexinitlen,
    const u_char *skexinit, size_t skexinitlen,
    const u_char *serverhostkeyblob, size_t sbloblen,
    const u_char client_dh_pub[CURVE25519_SIZE],
    const u_char server_dh_pub[CURVE25519_SIZE],
    const u_char *shared_secret, size_t secretlen,
    u_char *hash, size_t *hashlen)
{
	struct sshbuf *b;
	int r;

	if (*hashlen < ssh_digest_bytes(hash_alg))
		return SSH_ERR_INVALID_ARGUMENT;
	if ((b = sshbuf_new()) == NULL)
		return SSH_ERR_ALLOC_FAIL;
	if ((r = sshbuf_put_stringb(b, client_version)) < 0 ||
	    (r = sshbuf_put_stringb(b, server_version)) < 0 ||
	    /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
	    (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 ||
	    (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
	    (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 ||
	    (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 ||
	    (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
	    (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 ||
	    (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 ||
	    (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 ||
	    (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 ||
	    (r = sshbuf_put(b, shared_secret, secretlen)) < 0) {
		sshbuf_free(b);
		return r;
	}
#ifdef DEBUG_KEX
	sshbuf_dump(b, stderr);
#endif
	if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
		sshbuf_free(b);
		return SSH_ERR_LIBCRYPTO_ERROR;
	}
	sshbuf_free(b);
	*hashlen = ssh_digest_bytes(hash_alg);
#ifdef DEBUG_KEX
	dump_digest("hash", hash, *hashlen);
#endif
	return 0;
}