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djm@openbsd.orgf3ebaff2019-01-21 09:49:37 +00001/* $OpenBSD: kexc25519.c,v 1.12 2019/01/21 09:49:37 djm Exp $ */
Damien Miller094003f2013-11-04 22:59:27 +11002/*
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
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000038#include "sshbuf.h"
Damien Miller094003f2013-11-04 22:59:27 +110039#include "ssh2.h"
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000040#include "sshkey.h"
Damien Miller094003f2013-11-04 22:59:27 +110041#include "cipher.h"
42#include "kex.h"
43#include "log.h"
Damien Millerb3051d02014-01-10 10:58:53 +110044#include "digest.h"
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000045#include "ssherr.h"
Damien Miller094003f2013-11-04 22:59:27 +110046
47extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
48 const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
Damien Miller686c7d92014-05-15 14:37:03 +100049 __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
50 __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
51 __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));
Damien Miller094003f2013-11-04 22:59:27 +110052
53void
54kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
55{
56 static const u_char basepoint[CURVE25519_SIZE] = {9};
57
58 arc4random_buf(key, CURVE25519_SIZE);
59 crypto_scalarmult_curve25519(pub, key, basepoint);
60}
61
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000062int
Damien Miller094003f2013-11-04 22:59:27 +110063kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000064 const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
Damien Miller094003f2013-11-04 22:59:27 +110065{
66 u_char shared_key[CURVE25519_SIZE];
djm@openbsd.orgf3ebaff2019-01-21 09:49:37 +000067 u_char zero[CURVE25519_SIZE];
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000068 int r;
Damien Miller094003f2013-11-04 22:59:27 +110069
djm@openbsd.orgf3ebaff2019-01-21 09:49:37 +000070 crypto_scalarmult_curve25519(shared_key, key, pub);
71
72 /* Check for all-zero shared secret */
73 explicit_bzero(zero, CURVE25519_SIZE);
74 if (timingsafe_bcmp(zero, shared_key, CURVE25519_SIZE) == 0)
djm@openbsd.orgf9b78852015-03-26 07:00:04 +000075 return SSH_ERR_KEY_INVALID_EC_VALUE;
76
Damien Miller094003f2013-11-04 22:59:27 +110077#ifdef DEBUG_KEXECDH
78 dump_digest("shared secret", shared_key, CURVE25519_SIZE);
79#endif
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000080 sshbuf_reset(out);
81 r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE);
Damien Miller1d2c4562014-02-04 11:18:20 +110082 explicit_bzero(shared_key, CURVE25519_SIZE);
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000083 return r;
Damien Miller094003f2013-11-04 22:59:27 +110084}
85
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000086int
Damien Miller094003f2013-11-04 22:59:27 +110087kex_c25519_hash(
Damien Millerb3051d02014-01-10 10:58:53 +110088 int hash_alg,
djm@openbsd.org0a843d92018-12-27 03:25:24 +000089 const struct sshbuf *client_version,
90 const struct sshbuf *server_version,
djm@openbsd.org1a31d022016-05-02 08:49:03 +000091 const u_char *ckexinit, size_t ckexinitlen,
92 const u_char *skexinit, size_t skexinitlen,
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000093 const u_char *serverhostkeyblob, size_t sbloblen,
Damien Miller094003f2013-11-04 22:59:27 +110094 const u_char client_dh_pub[CURVE25519_SIZE],
95 const u_char server_dh_pub[CURVE25519_SIZE],
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000096 const u_char *shared_secret, size_t secretlen,
97 u_char *hash, size_t *hashlen)
Damien Miller094003f2013-11-04 22:59:27 +110098{
markus@openbsd.org57d10cb2015-01-19 20:16:15 +000099 struct sshbuf *b;
100 int r;
Damien Miller094003f2013-11-04 22:59:27 +1100101
markus@openbsd.org57d10cb2015-01-19 20:16:15 +0000102 if (*hashlen < ssh_digest_bytes(hash_alg))
103 return SSH_ERR_INVALID_ARGUMENT;
104 if ((b = sshbuf_new()) == NULL)
105 return SSH_ERR_ALLOC_FAIL;
djm@openbsd.org0a843d92018-12-27 03:25:24 +0000106 if ((r = sshbuf_put_stringb(b, client_version)) < 0 ||
107 (r = sshbuf_put_stringb(b, server_version)) < 0 ||
markus@openbsd.org57d10cb2015-01-19 20:16:15 +0000108 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
109 (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 ||
110 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
111 (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 ||
112 (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 ||
113 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
114 (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 ||
115 (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 ||
116 (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 ||
117 (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 ||
118 (r = sshbuf_put(b, shared_secret, secretlen)) < 0) {
119 sshbuf_free(b);
120 return r;
121 }
Damien Miller094003f2013-11-04 22:59:27 +1100122#ifdef DEBUG_KEX
markus@openbsd.org57d10cb2015-01-19 20:16:15 +0000123 sshbuf_dump(b, stderr);
Damien Miller094003f2013-11-04 22:59:27 +1100124#endif
markus@openbsd.org57d10cb2015-01-19 20:16:15 +0000125 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
126 sshbuf_free(b);
127 return SSH_ERR_LIBCRYPTO_ERROR;
128 }
129 sshbuf_free(b);
Damien Millerb3051d02014-01-10 10:58:53 +1100130 *hashlen = ssh_digest_bytes(hash_alg);
markus@openbsd.org57d10cb2015-01-19 20:16:15 +0000131#ifdef DEBUG_KEX
132 dump_digest("hash", hash, *hashlen);
133#endif
134 return 0;
Damien Miller094003f2013-11-04 22:59:27 +1100135}