openssh/kexecdh.c

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2022-06-16 16:57:06 +08:00
/* $OpenBSD: kexecdh.c,v 1.10 2019/01/21 10:40:11 djm Exp $ */
/*
* Copyright (c) 2010 Damien Miller. All rights reserved.
* Copyright (c) 2019 Markus Friedl. 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"
#if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <openssl/ecdh.h>
#include "sshkey.h"
#include "kex.h"
#include "sshbuf.h"
#include "digest.h"
#include "ssherr.h"
static int
kex_ecdh_dec_key_group(struct kex *, const struct sshbuf *, EC_KEY *key,
const EC_GROUP *, struct sshbuf **);
int
kex_ecdh_keypair(struct kex *kex)
{
EC_KEY *client_key = NULL;
const EC_GROUP *group;
const EC_POINT *public_key;
struct sshbuf *buf = NULL;
int r;
if ((client_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if (EC_KEY_generate_key(client_key) != 1) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
group = EC_KEY_get0_group(client_key);
public_key = EC_KEY_get0_public_key(client_key);
if ((buf = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_put_ec(buf, public_key, group)) != 0 ||
(r = sshbuf_get_u32(buf, NULL)) != 0)
goto out;
#ifdef DEBUG_KEXECDH
fputs("client private key:\n", stderr);
sshkey_dump_ec_key(client_key);
#endif
kex->ec_client_key = client_key;
kex->ec_group = group;
client_key = NULL; /* owned by the kex */
kex->client_pub = buf;
buf = NULL;
out:
EC_KEY_free(client_key);
sshbuf_free(buf);
return r;
}
int
kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,
struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
{
const EC_GROUP *group;
const EC_POINT *pub_key;
EC_KEY *server_key = NULL;
struct sshbuf *server_blob = NULL;
int r;
*server_blobp = NULL;
*shared_secretp = NULL;
if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if (EC_KEY_generate_key(server_key) != 1) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
group = EC_KEY_get0_group(server_key);
#ifdef DEBUG_KEXECDH
fputs("server private key:\n", stderr);
sshkey_dump_ec_key(server_key);
#endif
pub_key = EC_KEY_get0_public_key(server_key);
if ((server_blob = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_put_ec(server_blob, pub_key, group)) != 0 ||
(r = sshbuf_get_u32(server_blob, NULL)) != 0)
goto out;
if ((r = kex_ecdh_dec_key_group(kex, client_blob, server_key, group,
shared_secretp)) != 0)
goto out;
*server_blobp = server_blob;
server_blob = NULL;
out:
EC_KEY_free(server_key);
sshbuf_free(server_blob);
return r;
}
static int
kex_ecdh_dec_key_group(struct kex *kex, const struct sshbuf *ec_blob,
EC_KEY *key, const EC_GROUP *group, struct sshbuf **shared_secretp)
{
struct sshbuf *buf = NULL;
BIGNUM *shared_secret = NULL;
EC_POINT *dh_pub = NULL;
u_char *kbuf = NULL;
size_t klen = 0;
int r;
*shared_secretp = NULL;
if ((buf = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_put_stringb(buf, ec_blob)) != 0)
goto out;
if ((dh_pub = EC_POINT_new(group)) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_get_ec(buf, dh_pub, group)) != 0) {
goto out;
}
sshbuf_reset(buf);
#ifdef DEBUG_KEXECDH
fputs("public key:\n", stderr);
sshkey_dump_ec_point(group, dh_pub);
#endif
if (sshkey_ec_validate_public(group, dh_pub) != 0) {
r = SSH_ERR_MESSAGE_INCOMPLETE;
goto out;
}
klen = (EC_GROUP_get_degree(group) + 7) / 8;
if ((kbuf = malloc(klen)) == NULL ||
(shared_secret = BN_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if (ECDH_compute_key(kbuf, klen, dh_pub, key, NULL) != (int)klen ||
BN_bin2bn(kbuf, klen, shared_secret) == NULL) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
#ifdef DEBUG_KEXECDH
dump_digest("shared secret", kbuf, klen);
#endif
if ((r = sshbuf_put_bignum2(buf, shared_secret)) != 0)
goto out;
*shared_secretp = buf;
buf = NULL;
out:
EC_POINT_clear_free(dh_pub);
BN_clear_free(shared_secret);
freezero(kbuf, klen);
sshbuf_free(buf);
return r;
}
int
kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,
struct sshbuf **shared_secretp)
{
int r;
r = kex_ecdh_dec_key_group(kex, server_blob, kex->ec_client_key,
kex->ec_group, shared_secretp);
EC_KEY_free(kex->ec_client_key);
kex->ec_client_key = NULL;
return r;
}
#else
#include "ssherr.h"
struct kex;
struct sshbuf;
struct sshkey;
int
kex_ecdh_keypair(struct kex *kex)
{
return SSH_ERR_SIGN_ALG_UNSUPPORTED;
}
int
kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,
struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
{
return SSH_ERR_SIGN_ALG_UNSUPPORTED;
}
int
kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,
struct sshbuf **shared_secretp)
{
return SSH_ERR_SIGN_ALG_UNSUPPORTED;
}
#endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */