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/* $OpenBSD: kexc25519.c,v 1.12 2019/01/21 09:49:37 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];
u_char zero[CURVE25519_SIZE];
int r;
crypto_scalarmult_curve25519(shared_key, key, pub);
/* Check for all-zero shared secret */
explicit_bzero(zero, CURVE25519_SIZE);
if (timingsafe_bcmp(zero, shared_key, CURVE25519_SIZE) == 0)
return SSH_ERR_KEY_INVALID_EC_VALUE;
#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;
}
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