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/*
* Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.
* Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* ECDH low level APIs are deprecated for public use, but still ok for
* internal use.
*/
#include "internal/deprecated.h"
#include <string.h>
#include <limits.h>
#include "internal/cryptlib.h"
#include <openssl/err.h>
#include <openssl/bn.h>
#include <openssl/objects.h>
#include <openssl/ec.h>
#include "ec_local.h"
int ossl_ecdh_compute_key(unsigned char **psec, size_t *pseclen,
const EC_POINT *pub_key, const EC_KEY *ecdh)
{
if (ecdh->group->meth->ecdh_compute_key == NULL) {
ECerr(EC_F_OSSL_ECDH_COMPUTE_KEY, EC_R_CURVE_DOES_NOT_SUPPORT_ECDH);
return 0;
}
return ecdh->group->meth->ecdh_compute_key(psec, pseclen, pub_key, ecdh);
}
/*-
* This implementation is based on the following primitives in the
* IEEE 1363 standard:
* - ECKAS-DH1
* - ECSVDP-DH
*
* It also conforms to SP800-56A r3
* See Section 5.7.1.2 "Elliptic Curve Cryptography Cofactor Diffie-Hellman
* (ECC CDH) Primitive:". The steps listed below refer to SP800-56A.
*/
int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
const EC_POINT *pub_key, const EC_KEY *ecdh)
{
BN_CTX *ctx;
EC_POINT *tmp = NULL;
BIGNUM *x = NULL;
const BIGNUM *priv_key;
const EC_GROUP *group;
int ret = 0;
size_t buflen, len;
unsigned char *buf = NULL;
if ((ctx = BN_CTX_new_ex(ecdh->libctx)) == NULL)
goto err;
BN_CTX_start(ctx);
x = BN_CTX_get(ctx);
if (x == NULL) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
goto err;
}
priv_key = EC_KEY_get0_private_key(ecdh);
if (priv_key == NULL) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_MISSING_PRIVATE_KEY);
goto err;
}
group = EC_KEY_get0_group(ecdh);
/*
* Step(1) - Compute the point tmp = cofactor * owners_private_key
* * peer_public_key.
*/
if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {
if (!EC_GROUP_get_cofactor(group, x, NULL) ||
!BN_mul(x, x, priv_key, ctx)) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
goto err;
}
priv_key = x;
}
if ((tmp = EC_POINT_new(group)) == NULL) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
goto err;
}
if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
goto err;
}
/*
* Step(2) : If point tmp is at infinity then clear intermediate values and
* exit. Note: getting affine coordinates returns 0 if point is at infinity.
* Step(3a) : Get x-coordinate of point x = tmp.x
*/
if (!EC_POINT_get_affine_coordinates(group, tmp, x, NULL, ctx)) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
goto err;
}
/*
* Step(3b) : convert x to a byte string, using the field-element-to-byte
* string conversion routine defined in Appendix C.2
*/
buflen = (EC_GROUP_get_degree(group) + 7) / 8;
len = BN_num_bytes(x);
if (len > buflen) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_INTERNAL_ERROR);
goto err;
}
if ((buf = OPENSSL_malloc(buflen)) == NULL) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
goto err;
}
memset(buf, 0, buflen - len);
if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_BN_LIB);
goto err;
}
*pout = buf;
*poutlen = buflen;
buf = NULL;
ret = 1;
err:
/* Step(4) : Destroy all intermediate calculations */
BN_clear(x);
EC_POINT_clear_free(tmp);
BN_CTX_end(ctx);
BN_CTX_free(ctx);
OPENSSL_free(buf);
return ret;
}
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