/* Copyright (c) 2014, Google Inc.

 *

 * Permission to use, copy, modify, and/or distribute this software for any

 * purpose with or without fee is hereby granted, provided that the above

 * copyright notice and this permission notice appear in all copies.

 *

 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY

 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION

 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN

 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/hkdf.h>

#include <assert.h>

#include <string.h>

#include <openssl/err.h>

#include <openssl/hmac.h>

#include "../../internal.h"

int HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest,

         const uint8_t *secret, size_t secret_len, const uint8_t *salt,

         size_t salt_len, const uint8_t *info, size_t info_len) {

  // https://tools.ietf.org/html/rfc5869#section-2

  uint8_t prk[EVP_MAX_MD_SIZE];

  size_t prk_len;

  if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt,

                    salt_len) ||

      !HKDF_expand(out_key, out_len, digest, prk, prk_len, info, info_len)) {

    return 0;

  }

  return 1;

}

int HKDF_extract(uint8_t *out_key, size_t *out_len, const EVP_MD *digest,

                 const uint8_t *secret, size_t secret_len, const uint8_t *salt,

                 size_t salt_len) {

  // https://tools.ietf.org/html/rfc5869#section-2.2

  // If salt is not given, HashLength zeros are used. However, HMAC does that

  // internally already so we can ignore it.

  unsigned len;

  if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) == NULL) {

    OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);

    return 0;

  }

  *out_len = len;

  assert(*out_len == EVP_MD_size(digest));

  return 1;

}

int HKDF_expand(uint8_t *out_key, size_t out_len, const EVP_MD *digest,

                const uint8_t *prk, size_t prk_len, const uint8_t *info,

                size_t info_len) {

  // https://tools.ietf.org/html/rfc5869#section-2.3

  const size_t digest_len = EVP_MD_size(digest);

  uint8_t previous[EVP_MAX_MD_SIZE];

  size_t n, done = 0;

  unsigned i;

  int ret = 0;

  HMAC_CTX hmac;

  // Expand key material to desired length.

  n = (out_len + digest_len - 1) / digest_len;

  if (out_len + digest_len < out_len || n > 255) {

    OPENSSL_PUT_ERROR(HKDF, HKDF_R_OUTPUT_TOO_LARGE);

    return 0;

  }

  HMAC_CTX_init(&hmac);

  if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) {

    goto out;

  }

  for (i = 0; i < n; i++) {

    uint8_t ctr = i + 1;

    size_t todo;

    if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) ||

                   !HMAC_Update(&hmac, previous, digest_len))) {

      goto out;

    }

    if (!HMAC_Update(&hmac, info, info_len) ||

        !HMAC_Update(&hmac, &ctr, 1) ||

        !HMAC_Final(&hmac, previous, NULL)) {

      goto out;

    }

    todo = digest_len;

    if (todo > out_len - done) {

      todo = out_len - done;

    }

    OPENSSL_memcpy(out_key + done, previous, todo);

    done += todo;

  }

  ret = 1;

out:

  HMAC_CTX_cleanup(&hmac);

  if (ret != 1) {

    OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB);

  }

  return ret;

}