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/* $OpenBSD: kexdh.c,v 1.32 2019/01/21 10:40:11 djm Exp $ */
/*
* 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 <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include "sshkey.h"
#include "kex.h"
#include "sshbuf.h"
#include "digest.h"
#include "ssherr.h"
#include "dh.h"
int
kex_dh_keygen(struct kex *kex)
{
switch (kex->kex_type) {
case KEX_DH_GRP1_SHA1:
kex->dh = dh_new_group1();
break;
case KEX_DH_GRP14_SHA1:
case KEX_DH_GRP14_SHA256:
kex->dh = dh_new_group14();
break;
case KEX_DH_GRP16_SHA512:
kex->dh = dh_new_group16();
break;
case KEX_DH_GRP18_SHA512:
kex->dh = dh_new_group18();
break;
default:
return SSH_ERR_INVALID_ARGUMENT;
}
if (kex->dh == NULL)
return SSH_ERR_ALLOC_FAIL;
return (dh_gen_key(kex->dh, kex->we_need * 8));
}
int
kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
{
BIGNUM *shared_secret = NULL;
u_char *kbuf = NULL;
size_t klen = 0;
int kout, r;
#ifdef DEBUG_KEXDH
fprintf(stderr, "dh_pub= ");
BN_print_fp(stderr, dh_pub);
fprintf(stderr, "\n");
debug("bits %d", BN_num_bits(dh_pub));
DHparams_print_fp(stderr, kex->dh);
fprintf(stderr, "\n");
#endif
if (!dh_pub_is_valid(kex->dh, dh_pub)) {
r = SSH_ERR_MESSAGE_INCOMPLETE;
goto out;
}
klen = DH_size(kex->dh);
if ((kbuf = malloc(klen)) == NULL ||
(shared_secret = BN_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
r = SSH_ERR_LIBCRYPTO_ERROR;
goto out;
}
#ifdef DEBUG_KEXDH
dump_digest("shared secret", kbuf, kout);
#endif
r = sshbuf_put_bignum2(out, shared_secret);
out:
freezero(kbuf, klen);
BN_clear_free(shared_secret);
return r;
}
int
kex_dh_keypair(struct kex *kex)
{
const BIGNUM *pub_key;
struct sshbuf *buf = NULL;
int r;
if ((r = kex_dh_keygen(kex)) != 0)
return r;
DH_get0_key(kex->dh, &pub_key, NULL);
if ((buf = sshbuf_new()) == NULL)
return SSH_ERR_ALLOC_FAIL;
if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
(r = sshbuf_get_u32(buf, NULL)) != 0)
goto out;
#ifdef DEBUG_KEXDH
DHparams_print_fp(stderr, kex->dh);
fprintf(stderr, "pub= ");
BN_print_fp(stderr, pub_key);
fprintf(stderr, "\n");
#endif
kex->client_pub = buf;
buf = NULL;
out:
sshbuf_free(buf);
return r;
}
int
kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
{
const BIGNUM *pub_key;
struct sshbuf *server_blob = NULL;
int r;
*server_blobp = NULL;
*shared_secretp = NULL;
if ((r = kex_dh_keygen(kex)) != 0)
goto out;
DH_get0_key(kex->dh, &pub_key, NULL);
if ((server_blob = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
(r = sshbuf_get_u32(server_blob, NULL)) != 0)
goto out;
if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
goto out;
*server_blobp = server_blob;
server_blob = NULL;
out:
DH_free(kex->dh);
kex->dh = NULL;
sshbuf_free(server_blob);
return r;
}
int
kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
struct sshbuf **shared_secretp)
{
struct sshbuf *buf = NULL;
BIGNUM *dh_pub = NULL;
int r;
*shared_secretp = NULL;
if ((buf = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
(r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
goto out;
sshbuf_reset(buf);
if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
goto out;
*shared_secretp = buf;
buf = NULL;
out:
DH_free(kex->dh);
kex->dh = NULL;
sshbuf_free(buf);
return r;
}
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