text: /* aes_decrypt.c - TinyCrypt implementation of AES decryption procedure */
  
  /*
   *  Copyright (C) 2017 by Intel Corporation, All Rights Reserved.
   *
   *  Redistribution and use in source and binary forms, with or without
   *  modification, are permitted provided that the following conditions are met:
   *
   *    - Redistributions of source code must retain the above copyright notice,
   *     this list of conditions and the following disclaimer.
   *
   *    - 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.
   *
   *    - Neither the name of Intel Corporation nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   *  AND ANY EXPRESS 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 COPYRIGHT OWNER OR 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 <aes.h>
  #include <constants.h>
  #include <utils.h>
  
  static const uint8_t inv_sbox[256] = {
      0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e,
      0x81, 0xf3, 0xd7, 0xfb, 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87,
      0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb, 0x54, 0x7b, 0x94, 0x32,
      0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
      0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49,
      0x6d, 0x8b, 0xd1, 0x25, 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16,
      0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92, 0x6c, 0x70, 0x48, 0x50,
      0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
      0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05,
      0xb8, 0xb3, 0x45, 0x06, 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02,
      0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b, 0x3a, 0x91, 0x11, 0x41,
      0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
      0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8,
      0x1c, 0x75, 0xdf, 0x6e, 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89,
      0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b, 0xfc, 0x56, 0x3e, 0x4b,
      0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
      0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59,
      0x27, 0x80, 0xec, 0x5f, 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d,
      0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef, 0xa0, 0xe0, 0x3b, 0x4d,
      0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
      0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63,
      0x55, 0x21, 0x0c, 0x7d
  };
  
  int tc_aes128_set_decrypt_key(TCAesKeySched_t s, const uint8_t *k)
  {
      return tc_aes128_set_encrypt_key(s, k);
  }
  
  #define mult8(a)(_double_byte(_double_byte(_double_byte(a))))
  #define mult9(a)(mult8(a)^(a))
  #define multb(a)(mult8(a)^_double_byte(a)^(a))
  #define multd(a)(mult8(a)^_double_byte(_double_byte(a))^(a))
  #define multe(a)(mult8(a)^_double_byte(_double_byte(a))^_double_byte(a))
  
  static inline void mult_row_column(uint8_t *out, const uint8_t *in)
  {
      out[0] = multe(in[0]) ^ multb(in[1]) ^ multd(in[2]) ^ mult9(in[3]);
      out[1] = mult9(in[0]) ^ multe(in[1]) ^ multb(in[2]) ^ multd(in[3]);
      out[2] = multd(in[0]) ^ mult9(in[1]) ^ multe(in[2]) ^ multb(in[3]);
      out[3] = multb(in[0]) ^ multd(in[1]) ^ mult9(in[2]) ^ multe(in[3]);
  }
  
  static inline void inv_mix_columns(uint8_t *s)
  {
      uint8_t t[Nb*Nk];
  
      mult_row_column(t, s);
      mult_row_column(&t[Nb], s+Nb);
      mult_row_column(&t[2*Nb], s+(2*Nb));
      mult_row_column(&t[3*Nb], s+(3*Nb));
      (void)_copy(s, sizeof(t), t, sizeof(t));
  }
  
  static inline void add_round_key(uint8_t *s, const unsigned int *k)
  {
      s[0] ^= (uint8_t)(k[0] >> 24); s[1] ^= (uint8_t)(k[0] >> 16);
      s[2] ^= (uint8_t)(k[0] >> 8); s[3] ^= (uint8_t)(k[0]);
      s[4] ^= (uint8_t)(k[1] >> 24); s[5] ^= (uint8_t)(k[1] >> 16);
      s[6] ^= (uint8_t)(k[1] >> 8); s[7] ^= (uint8_t)(k[1]);
      s[8] ^= (uint8_t)(k[2] >> 24); s[9] ^= (uint8_t)(k[2] >> 16);
      s[10] ^= (uint8_t)(k[2] >> 8); s[11] ^= (uint8_t)(k[2]);
      s[12] ^= (uint8_t)(k[3] >> 24); s[13] ^= (uint8_t)(k[3] >> 16);
      s[14] ^= (uint8_t)(k[3] >> 8); s[15] ^= (uint8_t)(k[3]);
  }
  
  static inline void inv_sub_bytes(uint8_t *s)
  {
      unsigned int i;
  
      for (i = 0; i < (Nb*Nk); ++i) {
          s[i] = inv_sbox[s[i]];
      }
  }
  
  /*
   * This inv_shift_rows also implements the matrix flip required for
   * inv_mix_columns, but performs it here to reduce the number of memory
   * operations.
   */
  static inline void inv_shift_rows(uint8_t *s)
  {
      uint8_t t[Nb*Nk];
  
      t[0]  = s[0]; t[1] = s[13]; t[2] = s[10]; t[3] = s[7];
      t[4]  = s[4]; t[5] = s[1]; t[6] = s[14]; t[7] = s[11];
      t[8]  = s[8]; t[9] = s[5]; t[10] = s[2]; t[11] = s[15];
      t[12] = s[12]; t[13] = s[9]; t[14] = s[6]; t[15] = s[3];
      (void)_copy(s, sizeof(t), t, sizeof(t));
  }
  
  int tc_aes_decrypt(uint8_t *out, const uint8_t *in, const TCAesKeySched_t s)
  {
      uint8_t state[Nk*Nb];
      unsigned int i;
  
      if (out == (uint8_t *) 0) {
          return TC_CRYPTO_FAIL;
      } else if (in == (const uint8_t *) 0) {
          return TC_CRYPTO_FAIL;
      } else if (s == (TCAesKeySched_t) 0) {
          return TC_CRYPTO_FAIL;
      }
  
      (void)_copy(state, sizeof(state), in, sizeof(state));
  
      add_round_key(state, s->words + Nb*Nr);
  
      for (i = Nr - 1; i > 0; --i) {
          inv_shift_rows(state);
          inv_sub_bytes(state);
          add_round_key(state, s->words + Nb*i);
          inv_mix_columns(state);
      }
  
      inv_shift_rows(state);
      inv_sub_bytes(state);
      add_round_key(state, s->words);
  
      (void)_copy(out, sizeof(state), state, sizeof(state));
  
      /*zeroing out the state buffer */
      _set(state, TC_ZERO_BYTE, sizeof(state));
  
  
      return TC_CRYPTO_SUCCESS;
  }
  