/*

 * Copyright 2002-2021 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) {

        ERR_raise(ERR_LIB_EC, 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 ossl_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) {

        ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);

        goto err;

    }

    priv_key = EC_KEY_get0_private_key(ecdh);

    if (priv_key == NULL) {

        ERR_raise(ERR_LIB_EC, 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)) {

            ERR_raise(ERR_LIB_EC, ERR_R_EC_LIB);

            goto err;

        }

        if (!BN_mul(x, x, priv_key, ctx)) {

            ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);

            goto err;

        }

        priv_key = x;

    }

    if ((tmp = EC_POINT_new(group)) == NULL) {

        ERR_raise(ERR_LIB_EC, ERR_R_EC_LIB);

        goto err;

    }

    if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {

        ERR_raise(ERR_LIB_EC, 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)) {

        ERR_raise(ERR_LIB_EC, 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) {

        ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);

        goto err;

    }

    if ((buf = OPENSSL_malloc(buflen)) == NULL)

        goto err;

    memset(buf, 0, buflen - len);

    if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {

        ERR_raise(ERR_LIB_EC, 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;

}