/*

 * Written by Stephen Henson for the OpenSSL project.

 */

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

 * Copyright (c) 2013 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.

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

 */

#include <string.h>

#include <openssl/ec.h>

#include <openssl/evp.h>

#include "ech_locl.h"

/*

 * Key derivation function from X9.63/SECG.

 */

/* Way more than we will ever need */

#define ECDH_KDF_MAX  (1 << 30)

int

ecdh_KDF_X9_63(unsigned char *out, size_t outlen, const unsigned char *Z,

    size_t Zlen, const unsigned char *sinfo, size_t sinfolen, const EVP_MD *md)

{

  EVP_MD_CTX *mctx = NULL;

  unsigned int i;

  size_t mdlen;

  unsigned char ctr[4];

  int rv = 0;

  if (sinfolen > ECDH_KDF_MAX || outlen > ECDH_KDF_MAX ||

      Zlen > ECDH_KDF_MAX)

    return 0;

  mctx = EVP_MD_CTX_new();

  if (mctx == NULL)

    return 0;

  mdlen = EVP_MD_size(md);

  for (i = 1;; i++) {

    unsigned char mtmp[EVP_MAX_MD_SIZE];

    if (!EVP_DigestInit_ex(mctx, md, NULL))

      goto err;

    ctr[3] = i & 0xFF;

    ctr[2] = (i >> 8) & 0xFF;

    ctr[1] = (i >> 16) & 0xFF;

    ctr[0] = (i >> 24) & 0xFF;

    if (!EVP_DigestUpdate(mctx, Z, Zlen))

      goto err;

    if (!EVP_DigestUpdate(mctx, ctr, sizeof(ctr)))

      goto err;

    if (!EVP_DigestUpdate(mctx, sinfo, sinfolen))

      goto err;

    if (outlen >= mdlen) {

      if (!EVP_DigestFinal(mctx, out, NULL))

        goto err;

      outlen -= mdlen;

      if (outlen == 0)

        break;

      out += mdlen;

    } else {

      if (!EVP_DigestFinal(mctx, mtmp, NULL))

        goto err;

      memcpy(out, mtmp, outlen);

      explicit_bzero(mtmp, mdlen);

      break;

    }

  }

  rv = 1;

 err:

  EVP_MD_CTX_free(mctx);

  return rv;

}