/* $OpenBSD: ech_key.c,v 1.13 2022/06/30 11:14:47 tb Exp $ */

/* ====================================================================

 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.

 *

 * The Elliptic Curve Public-Key Crypto Library (ECC Code) included

 * herein is developed by SUN MICROSYSTEMS, INC., and is contributed

 * to the OpenSSL project.

 *

 * The ECC Code is licensed pursuant to the OpenSSL open source

 * license provided below.

 *

 * The ECDH software is originally written by Douglas Stebila of

 * Sun Microsystems Laboratories.

 *

 */

/* ====================================================================

 * Copyright (c) 1998-2003 The OpenSSL Project.  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.

 *

 * 3. All advertising materials mentioning features or use of this

 *    software must display the following acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"

 *

 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to

 *    endorse or promote products derived from this software without

 *    prior written permission. For written permission, please contact

 *    openssl-core@OpenSSL.org.

 *

 * 5. Products derived from this software may not be called "OpenSSL"

 *    nor may "OpenSSL" appear in their names without prior written

 *    permission of the OpenSSL Project.

 *

 * 6. Redistributions of any form whatsoever must retain the following

 *    acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"

 *

 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY

 * EXPRESSED 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 OpenSSL PROJECT OR

 * ITS CONTRIBUTORS 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.

 * ====================================================================

 *

 * This product includes cryptographic software written by Eric Young

 * (eay@cryptsoft.com).  This product includes software written by Tim

 * Hudson (tjh@cryptsoft.com).

 *

 */

#include <limits.h>

#include <string.h>

#include <openssl/opensslconf.h>

#include <openssl/bn.h>

#include <openssl/err.h>

#include <openssl/objects.h>

#include <openssl/sha.h>

#include "bn_lcl.h"

#include "ech_locl.h"

#include "ec_lcl.h"

static int ecdh_compute_key(void *out, size_t len, const EC_POINT *pub_key,

    EC_KEY *ecdh,

    void *(*KDF)(const void *in, size_t inlen, void *out, size_t *outlen));

/*

 * This implementation is based on the following primitives in the IEEE 1363

 * standard:

 *  - ECKAS-DH1

 *  - ECSVDP-DH

 * Finally an optional KDF is applied.

 */

static int

ecdh_compute_key(void *out, size_t outlen, const EC_POINT *pub_key,

    EC_KEY *ecdh,

    void *(*KDF)(const void *in, size_t inlen, void *out, size_t *outlen))

{

  BN_CTX *ctx;

  EC_POINT *tmp = NULL;

  BIGNUM *x = NULL, *y = NULL;

  const BIGNUM *priv_key;

  const EC_GROUP* group;

  int ret = -1;

  size_t buflen, len;

  unsigned char *buf = NULL;

  if (outlen > INT_MAX) {

    /* Sort of, anyway. */

    ECDHerror(ERR_R_MALLOC_FAILURE);

    return -1;

  }

  if ((ctx = BN_CTX_new()) == NULL)

    goto err;

  BN_CTX_start(ctx);

  if ((x = BN_CTX_get(ctx)) == NULL)

    goto err;

  if ((y = BN_CTX_get(ctx)) == NULL)

    goto err;

  priv_key = EC_KEY_get0_private_key(ecdh);

  if (priv_key == NULL) {

    ECDHerror(ECDH_R_NO_PRIVATE_VALUE);

    goto err;

  }

  group = EC_KEY_get0_group(ecdh);

  if (!EC_POINT_is_on_curve(group, pub_key, ctx))

    goto err;

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

    ECDHerror(ERR_R_MALLOC_FAILURE);

    goto err;

  }

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

    ECDHerror(ECDH_R_POINT_ARITHMETIC_FAILURE);

    goto err;

  }

  if (!EC_POINT_get_affine_coordinates(group, tmp, x, y, ctx)) {

    ECDHerror(ECDH_R_POINT_ARITHMETIC_FAILURE);

    goto err;

  }

  buflen = ECDH_size(ecdh);

  len = BN_num_bytes(x);

  if (len > buflen) {

    ECDHerror(ERR_R_INTERNAL_ERROR);

    goto err;

  }

  if (KDF == NULL && outlen < buflen) {

    /* The resulting key would be truncated. */

    ECDHerror(ECDH_R_KEY_TRUNCATION);

    goto err;

  }

  if ((buf = malloc(buflen)) == NULL) {

    ECDHerror(ERR_R_MALLOC_FAILURE);

    goto err;

  }

  memset(buf, 0, buflen - len);

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

    ECDHerror(ERR_R_BN_LIB);

    goto err;

  }

  if (KDF != NULL) {

    if (KDF(buf, buflen, out, &outlen) == NULL) {

      ECDHerror(ECDH_R_KDF_FAILED);

      goto err;

    }

    ret = outlen;

  } else {

    /* No KDF, just copy out the key and zero the rest. */

    if (outlen > buflen) {

      memset((void *)((uintptr_t)out + buflen), 0, outlen - buflen);

      outlen = buflen;

    }

    memcpy(out, buf, outlen);

    ret = outlen;

  }

err:

  EC_POINT_free(tmp);

  if (ctx)

    BN_CTX_end(ctx);

  BN_CTX_free(ctx);

  free(buf);

  return (ret);

}

static ECDH_METHOD openssl_ecdh_meth = {

  .name = "OpenSSL ECDH method",

  .compute_key = ecdh_compute_key

};

const ECDH_METHOD *

ECDH_OpenSSL(void)

{

  return &openssl_ecdh_meth;

}

/* replace w/ ecdh_compute_key() when ECDH_METHOD gets removed */

int

ossl_ecdh_compute_key(void *out, size_t outlen, const EC_POINT *pub_key,

    EC_KEY *eckey,

    void *(*KDF)(const void *in, size_t inlen, void *out, size_t *outlen))

{

  ECDH_DATA *ecdh;

  if ((ecdh = ecdh_check(eckey)) == NULL)

    return 0;

  return ecdh->meth->compute_key(out, outlen, pub_key, eckey, KDF);

}

int

ECDH_compute_key(void *out, size_t outlen, const EC_POINT *pub_key,

    EC_KEY *eckey,

    void *(*KDF)(const void *in, size_t inlen, void *out, size_t *outlen))

{

  if (eckey->meth->compute_key != NULL)

    return eckey->meth->compute_key(out, outlen, pub_key, eckey, KDF);

  ECerror(EC_R_NOT_IMPLEMENTED);

  return 0;

}