/*******************************************************************************
    OpenAirInterface
    Copyright(c) 1999 - 2014 Eurecom

    OpenAirInterface is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.


    OpenAirInterface is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with OpenAirInterface.The full GNU General Public License is
   included in this distribution in the file called "COPYING". If not,
   see <http://www.gnu.org/licenses/>.

  Contact Information
  OpenAirInterface Admin: openair_admin@eurecom.fr
  OpenAirInterface Tech : openair_tech@eurecom.fr
  OpenAirInterface Dev  : openair4g-devel@eurecom.fr

  Address      : Eurecom, Compus SophiaTech 450, route des chappes, 06451 Biot, France.

 *******************************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>

#include "security_types.h"
#include "secu_defs.h"

#define SECU_DEBUG 1
/*!
 * @brief Derive the kNASenc from kasme and perform truncate on the generated key to
 * reduce his size to 128 bits. Definition of the derivation function can
 * be found in 3GPP TS.33401 #A.7
 * @param[in] nas_alg_type NAS algorithm distinguisher
 * @param[in] nas_enc_alg_id NAS encryption/integrity algorithm identifier.
 * Possible values are:
 *      - 0 for EIA0 algorithm (Null Integrity Protection algorithm)
 *      - 1 for 128-EIA1 SNOW 3G
 *      - 2 for 128-EIA2 AES
 * @param[in] kasme Key for MME as provided by AUC
 * @param[out] knas Pointer to reference where output of KDF will be stored.
 * NOTE: knas is dynamically allocated by the KDF function
 */
int derive_key_nas(algorithm_type_dist_t nas_alg_type, uint8_t nas_enc_alg_id,
                   const uint8_t kasme[32], uint8_t *knas)
{
  uint8_t s[7];
  uint8_t out[32];
#if defined(SECU_DEBUG)
  int i;
#endif

  /* FC */
  s[0] = FC_ALG_KEY_DER;

  /* P0 = algorithm type distinguisher */
  s[1] = (uint8_t)(nas_alg_type & 0xFF);

  /* L0 = length(P0) = 1 */
  s[2] = 0x00;
  s[3] = 0x01;

  /* P1 */
  s[4] = nas_enc_alg_id;

  /* L1 = length(P1) = 1 */
  s[5] = 0x00;
  s[6] = 0x01;

#if defined(SECU_DEBUG)
  printf("%s FC %d nas_alg_type distinguisher %d nas_enc_alg_identity %d\n",
         __FUNCTION__, FC_ALG_KEY_DER, nas_alg_type, nas_enc_alg_id);

  for (i = 0; i < 7; i ++) {
    printf("0x%02x ", s[i]);
  }

  printf("\n");
#endif

  kdf(kasme, 32, s, 7, out, 32);

  memcpy(knas, &out[31-16+1], 16);

  return 0;
}
