aes.c

/****************************************************************************
 * crypto/aes.c
 *
 *   Copyright (C) 2011 Texas Instruments Incorporated - http://www.ti.com/
 *   Extracted from the CC3000 Host Driver Implementation.
 *
 * 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 Texas Instruments Incorporated 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.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdint.h>
#include <errno.h>

#include <nuttx/crypto/aes.h>

/****************************************************************************
 * Private Data
 ****************************************************************************/

/* Forward sbox */

static const uint8_t g_sbox[256] =
{
  /* 0    1    2      3     4     5     6     7     8    9
   *                        A     B     C     D     E    F
   */

  0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01,
                          0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, /* 0 */
  0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4,
                           0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, /* 1 */
  0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5,
                           0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, /* 2 */
  0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12,
                           0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, /* 3 */
  0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b,
                           0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, /* 4 */
  0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb,
                           0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, /* 5 */
  0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9,
                           0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, /* 6 */
  0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6,
                           0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, /* 7 */
  0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7,
                           0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, /* 8 */
  0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee,
                           0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, /* 9 */
  0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3,
                           0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, /* A */
  0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56,
                           0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, /* B */
  0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd,
                           0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, /* C */
  0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35,
                           0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, /* D */
  0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e,
                           0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, /* E */
  0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99,
                           0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16  /* F */
};

/* Inverse sbox */

static const uint8_t g_rsbox[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
};

/* Round constant */

static const uint8_t g_rcon[11] =
{
  0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36
};

static struct aes_state_s g_aes_state;

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: expand_key
 *
 * Description:
 *   Expend a 16 bytes key for AES128 implementation
 *
 * Input Parameters:
 *  key          AES128 key - 16 bytes
 *  expanded_key expanded AES128 key
 *
 * Returned Value:
 *  None
 *
 ****************************************************************************/

static void expand_key(FAR uint8_t *expanded_key, FAR const uint8_t *key)
{
  uint16_t buf1;
  uint16_t ii;

  for (ii = 0; ii < 16; ii++)
    {
      expanded_key[ii] = key[ii];
    }

  for (ii = 1; ii < 11; ii++)
    {
      buf1 = expanded_key[ii * 16 - 4];
      expanded_key[ii * 16 + 0] = g_sbox[expanded_key[ii *16 - 3]] ^
                            expanded_key[(ii - 1) * 16 + 0] ^ g_rcon[ii];

      expanded_key[ii * 16 + 1] = g_sbox[expanded_key[ii *16 - 2]] ^
                            expanded_key[(ii - 1) * 16 + 1];

      expanded_key[ii * 16 + 2] = g_sbox[expanded_key[ii *16 - 1]] ^
                            expanded_key[(ii - 1) * 16 + 2];

      expanded_key[ii * 16 + 3] = g_sbox[buf1] ^
                            expanded_key[(ii - 1) * 16 + 3];

      expanded_key[ii * 16 + 4] = expanded_key[(ii - 1) * 16 + 4] ^
                            expanded_key[ii * 16 + 0];

      expanded_key[ii * 16 + 5] = expanded_key[(ii - 1) * 16 + 5] ^
                            expanded_key[ii * 16 + 1];

      expanded_key[ii * 16 + 6] = expanded_key[(ii - 1) * 16 + 6] ^
                            expanded_key[ii * 16 + 2];

      expanded_key[ii * 16 + 7] = expanded_key[(ii - 1) * 16 + 7] ^
                            expanded_key[ii * 16 + 3];

      expanded_key[ii * 16 + 8] = expanded_key[(ii - 1) * 16 + 8] ^
                            expanded_key[ii * 16 + 4];

      expanded_key[ii * 16 + 9] = expanded_key[(ii - 1) * 16 + 9] ^
                            expanded_key[ii * 16 + 5];

      expanded_key[ii * 16 +10] = expanded_key[(ii - 1) * 16 +10] ^
                            expanded_key[ii * 16 + 6];

      expanded_key[ii * 16 +11] = expanded_key[(ii - 1) * 16 +11] ^
                            expanded_key[ii * 16 + 7];

      expanded_key[ii * 16 +12] = expanded_key[(ii - 1) * 16 +12] ^
                            expanded_key[ii * 16 + 8];

      expanded_key[ii * 16 +13] = expanded_key[(ii - 1) * 16 +13] ^
                            expanded_key[ii * 16 + 9];

      expanded_key[ii * 16 +14] = expanded_key[(ii - 1) * 16 +14] ^
                            expanded_key[ii * 16 +10];

      expanded_key[ii * 16 +15] = expanded_key[(ii - 1) * 16 +15] ^
                            expanded_key[ii * 16 +11];
    }
}

/****************************************************************************
 * Name: galois_mul2
 *
 * Description:
 *    Multiply by 2 in the galois field
 *
 * Input Parameters:
 *  value    argument to multiply
 *
 * Returned Value:
 *  Multiplied argument
 *
 ****************************************************************************/

static uint8_t galois_mul2(uint8_t value)
{
  if (value >> 7)
    {
      value = value << 1;
      return (value ^ 0x1b);
    }
  else
    {
      return value << 1;
    }
}

/****************************************************************************
 * Name: aes_encr
 *
 * Description:
 *  Internal implementation of AES128 encryption.
 *  Straight forward aes encryption implementation. First the group of
 *  operations:
 *
 *    - addRoundKey
 *    - subbytes
 *    - shiftrows
 *    - mixcolums
 *
 *  is executed 9 times, after this addroundkey to finish the 9th round,
 *  after that the 10th round without mixcolums no further subfunctions
 *  to save cycles for function calls no structuring with "for (....)"
 *  to save cycles.
 *
 * Input Parameters:
 *  expanded_key expanded AES128 key
 *  state        16 bytes of plain text and cipher text
 *
 * Returned Value:
 *  None
 *
 ****************************************************************************/

static void aes_encr(FAR uint8_t *state, FAR const uint8_t *expanded_key)
{
  uint8_t buf1;
  uint8_t buf2;
  uint8_t buf3;
  uint8_t round;

  for (round = 0; round < 9; round ++)
    {
      /* addroundkey, sbox and shiftrows */

      /* Row 0 */

      state[0]   = g_sbox[(state[0]  ^ expanded_key[(round * 16)])];
      state[4]   = g_sbox[(state[4]  ^ expanded_key[(round * 16) +  4])];
      state[8]   = g_sbox[(state[8]  ^ expanded_key[(round * 16) +  8])];
      state[12]  = g_sbox[(state[12] ^ expanded_key[(round * 16) + 12])];

      /* Row 1 */

      buf1       = state[1] ^ expanded_key[(round * 16) + 1];
      state[1]   = g_sbox[(state[5]  ^ expanded_key[(round * 16) +  5])];
      state[5]   = g_sbox[(state[9]  ^ expanded_key[(round * 16) +  9])];
      state[9]   = g_sbox[(state[13] ^ expanded_key[(round * 16) + 13])];
      state[13]  = g_sbox[buf1];

      /* Row 2 */

      buf1       = state[2] ^ expanded_key[(round * 16) + 2];
      buf2       = state[6] ^ expanded_key[(round * 16) + 6];
      state[2]   = g_sbox[(state[10] ^ expanded_key[(round * 16) + 10])];
      state[6]   = g_sbox[(state[14] ^ expanded_key[(round * 16) + 14])];
      state[10]  = g_sbox[buf1];
      state[14]  = g_sbox[buf2];

      /* Row 3 */

      buf1       = state[15] ^ expanded_key[(round * 16) + 15];
      state[15]  = g_sbox[(state[11] ^ expanded_key[(round * 16) + 11])];
      state[11]  = g_sbox[(state[7]  ^ expanded_key[(round * 16) +  7])];
      state[7]   = g_sbox[(state[3]  ^ expanded_key[(round * 16) +  3])];
      state[3]   = g_sbox[buf1];

      /* mixcolums */

      /* Col1 */

      buf1 = state[0] ^ state[1] ^ state[2] ^ state[3];
      buf2 = state[0];

      buf3 = state[0] ^ state[1];
      buf3 = galois_mul2(buf3);
      state[0] = state[0] ^ buf3 ^ buf1;

      buf3 = state[1] ^ state[2];
      buf3 = galois_mul2(buf3);
      state[1] = state[1] ^ buf3 ^ buf1;

      buf3 = state[2] ^ state[3];
      buf3 = galois_mul2(buf3);
      state[2] = state[2] ^ buf3 ^ buf1;

      buf3 = state[3] ^ buf2;
      buf3 = galois_mul2(buf3);
      state[3] = state[3] ^ buf3 ^ buf1;

      /* Col2 */

      buf1 = state[4] ^ state[5] ^ state[6] ^ state[7];
      buf2 = state[4];

      buf3 = state[4] ^ state[5];
      buf3 = galois_mul2(buf3);
      state[4] = state[4] ^ buf3 ^ buf1;

      buf3 = state[5] ^ state[6];
      buf3 = galois_mul2(buf3);
      state[5] = state[5] ^ buf3 ^ buf1;

      buf3 = state[6] ^ state[7];
      buf3 = galois_mul2(buf3);
      state[6] = state[6] ^ buf3 ^ buf1;

      buf3 = state[7] ^ buf2;
      buf3 = galois_mul2(buf3);
      state[7] = state[7] ^ buf3 ^ buf1;

      /* Col3 */

      buf1 = state[8] ^ state[9] ^ state[10] ^ state[11];
      buf2 = state[8];

      buf3 = state[8] ^ state[9];
      buf3 = galois_mul2(buf3);
      state[8] = state[8] ^ buf3 ^ buf1;

      buf3 = state[9] ^ state[10];
      buf3 = galois_mul2(buf3);
      state[9] = state[9] ^ buf3 ^ buf1;

      buf3 = state[10] ^ state[11];
      buf3 = galois_mul2(buf3);
      state[10] = state[10] ^ buf3 ^ buf1;

      buf3 = state[11] ^ buf2;
      buf3 = galois_mul2(buf3);
      state[11] = state[11] ^ buf3 ^ buf1;

      /* Col4 */

      buf1 = state[12] ^ state[13] ^ state[14] ^ state[15];
      buf2 = state[12];

      buf3 = state[12] ^ state[13];
      buf3 = galois_mul2(buf3);
      state[12] = state[12] ^ buf3 ^ buf1;

      buf3 = state[13] ^ state[14];
      buf3 = galois_mul2(buf3);
      state[13] = state[13] ^ buf3 ^ buf1;

      buf3 = state[14] ^ state[15];
      buf3 = galois_mul2(buf3);
      state[14] = state[14] ^ buf3 ^ buf1;

      buf3 = state[15] ^ buf2;
      buf3 = galois_mul2(buf3);
      state[15] = state[15] ^ buf3 ^ buf1;
    }

  /* 10th round without mixcols */

  state[0]   = g_sbox[(state[0]  ^ expanded_key[(round * 16)])];
  state[4]   = g_sbox[(state[4]  ^ expanded_key[(round * 16) +  4])];
  state[8]   = g_sbox[(state[8]  ^ expanded_key[(round * 16) +  8])];
  state[12]  = g_sbox[(state[12] ^ expanded_key[(round * 16) + 12])];

  /* Row 1 */

  buf1       = state[1] ^ expanded_key[(round * 16) + 1];
  state[1]   = g_sbox[(state[5]  ^ expanded_key[(round * 16) +  5])];
  state[5]   = g_sbox[(state[9]  ^ expanded_key[(round * 16) +  9])];
  state[9]   = g_sbox[(state[13] ^ expanded_key[(round * 16) + 13])];
  state[13]  = g_sbox[buf1];

  /* Row 2 */

  buf1       = state[2] ^ expanded_key[(round * 16) + 2];
  buf2       = state[6] ^ expanded_key[(round * 16) + 6];
  state[2]   = g_sbox[(state[10] ^ expanded_key[(round * 16) + 10])];
  state[6]   = g_sbox[(state[14] ^ expanded_key[(round * 16) + 14])];
  state[10]  = g_sbox[buf1];
  state[14]  = g_sbox[buf2];

  /* Row 3 */

  buf1       = state[15] ^ expanded_key[(round * 16) + 15];
  state[15]  = g_sbox[(state[11] ^ expanded_key[(round * 16) + 11])];
  state[11]  = g_sbox[(state[7]  ^ expanded_key[(round * 16) +  7])];
  state[7]   = g_sbox[(state[3]  ^ expanded_key[(round * 16) +  3])];
  state[3]   = g_sbox[buf1];

  /* Last addroundkey */

  state[0]  ^= expanded_key[160];
  state[1]  ^= expanded_key[161];
  state[2]  ^= expanded_key[162];
  state[3]  ^= expanded_key[163];
  state[4]  ^= expanded_key[164];
  state[5]  ^= expanded_key[165];
  state[6]  ^= expanded_key[166];
  state[7]  ^= expanded_key[167];
  state[8]  ^= expanded_key[168];
  state[9]  ^= expanded_key[169];
  state[10] ^= expanded_key[170];
  state[11] ^= expanded_key[171];
  state[12] ^= expanded_key[172];
  state[13] ^= expanded_key[173];
  state[14] ^= expanded_key[174];
  state[15] ^= expanded_key[175];
}

/****************************************************************************
 * Name: aes_decr
 *
 * Description:
 *  Internal implementation of AES128 decryption.
 *  Straight forward aes decryption implementation.  The order of substeps is
 *  the exact reverse of decryption inverse functions:
 *
 *     - addRoundKey is its own inverse
 *     - rsbox is inverse of sbox
 *     - rightshift instead of leftshift
 *     - invMixColumns = barreto + mixColumns
 *
 *  No further subfunctions to save cycles for function calls no structuring
 *  with "for (....)" to save cycles
 *
 * Input Parameters:
 *  expanded_key expanded AES128 key
 *  state        16 bytes of cipher text and plain text
 *
 * Returned Value:
 *  None
 *
 ****************************************************************************/

static void aes_decr(FAR uint8_t *state, FAR const uint8_t *expanded_key)
{
  uint8_t buf1;
  uint8_t buf2;
  uint8_t buf3;
  int8_t round;

  round = 9;

  /* Initial addroundkey */

  state[0]  ^= expanded_key[160];
  state[1]  ^= expanded_key[161];
  state[2]  ^= expanded_key[162];
  state[3]  ^= expanded_key[163];
  state[4]  ^= expanded_key[164];
  state[5]  ^= expanded_key[165];
  state[6]  ^= expanded_key[166];
  state[7]  ^= expanded_key[167];
  state[8]  ^= expanded_key[168];
  state[9]  ^= expanded_key[169];
  state[10] ^= expanded_key[170];
  state[11] ^= expanded_key[171];
  state[12] ^= expanded_key[172];
  state[13] ^= expanded_key[173];
  state[14] ^= expanded_key[174];
  state[15] ^= expanded_key[175];

  /* 10th round without mixcols */

  state[0]   = g_rsbox[state[0]]  ^ expanded_key[(round * 16)];
  state[4]   = g_rsbox[state[4]]  ^ expanded_key[(round * 16) +  4];
  state[8]   = g_rsbox[state[8]]  ^ expanded_key[(round * 16) +  8];
  state[12]  = g_rsbox[state[12]] ^ expanded_key[(round * 16) + 12];

  /* Row 1 */

  buf1       = g_rsbox[state[13]] ^ expanded_key[(round * 16) +  1];
  state[13]  = g_rsbox[state[9]]  ^ expanded_key[(round * 16) + 13];
  state[9]   = g_rsbox[state[5]]  ^ expanded_key[(round * 16) +  9];
  state[5]   = g_rsbox[state[1]]  ^ expanded_key[(round * 16) +  5];
  state[1]   = buf1;

  /* Row 2 */

  buf1       = g_rsbox[state[2]]  ^ expanded_key[(round * 16) + 10];
  buf2       = g_rsbox[state[6]]  ^ expanded_key[(round * 16) + 14];
  state[2]   = g_rsbox[state[10]] ^ expanded_key[(round * 16) +  2];
  state[6]   = g_rsbox[state[14]] ^ expanded_key[(round * 16) +  6];
  state[10]  = buf1;
  state[14]  = buf2;

  /* Row 3 */

  buf1       = g_rsbox[state[3]]  ^ expanded_key[(round * 16) + 15];
  state[3]   = g_rsbox[state[7]]  ^ expanded_key[(round * 16) +  3];
  state[7]   = g_rsbox[state[11]] ^ expanded_key[(round * 16) +  7];
  state[11]  = g_rsbox[state[15]] ^ expanded_key[(round * 16) + 11];
  state[15]  = buf1;

  for (round = 8; round >= 0; round--)
    {
      /* barreto */

      /* Col1 */

      buf1       = galois_mul2(galois_mul2(state[0] ^ state[2]));
      buf2       = galois_mul2(galois_mul2(state[1] ^ state[3]));
      state[0]  ^= buf1;
      state[1]  ^= buf2;
      state[2]  ^= buf1;
      state[3]  ^= buf2;

      /* Col2 */

      buf1       = galois_mul2(galois_mul2(state[4] ^ state[6]));
      buf2       = galois_mul2(galois_mul2(state[5] ^ state[7]));
      state[4]  ^= buf1;
      state[5]  ^= buf2;
      state[6]  ^= buf1;
      state[7]  ^= buf2;

      /* Col3 */

      buf1       = galois_mul2(galois_mul2(state[8] ^ state[10]));
      buf2       = galois_mul2(galois_mul2(state[9] ^ state[11]));
      state[8]  ^= buf1;
      state[9]  ^= buf2;
      state[10] ^= buf1;
      state[11] ^= buf2;

      /* Col4 */

      buf1       = galois_mul2(galois_mul2(state[12] ^ state[14]));
      buf2       = galois_mul2(galois_mul2(state[13] ^ state[15]));
      state[12] ^= buf1;
      state[13] ^= buf2;
      state[14] ^= buf1;
      state[15] ^= buf2;

      /* mixcolums */

      /* Col1 */

      buf1 = state[0]  ^ state[1] ^ state[2] ^ state[3];
      buf2 = state[0];

      buf3 = state[0]  ^ state[1];
      buf3 = galois_mul2(buf3);
      state[0] = state[0] ^ buf3 ^ buf1;

      buf3 = state[1]  ^ state[2];
      buf3 = galois_mul2(buf3);
      state[1] = state[1] ^ buf3 ^ buf1;

      buf3 = state[2]  ^ state[3];
      buf3 = galois_mul2(buf3);
      state[2] = state[2] ^ buf3 ^ buf1;

      buf3 = state[3]  ^ buf2;
      buf3 = galois_mul2(buf3);
      state[3] = state[3] ^ buf3 ^ buf1;

      /* Col2 */

      buf1 = state[4]  ^ state[5] ^ state[6] ^ state[7];
      buf2 = state[4];

      buf3 = state[4]  ^ state[5];
      buf3 = galois_mul2(buf3);
      state[4] = state[4] ^ buf3 ^ buf1;

      buf3 = state[5]  ^ state[6];
      buf3 = galois_mul2(buf3);
      state[5] = state[5] ^ buf3 ^ buf1;

      buf3 = state[6]  ^ state[7];
      buf3 = galois_mul2(buf3);
      state[6] = state[6] ^ buf3 ^ buf1;

      buf3 = state[7]  ^ buf2;
      buf3 = galois_mul2(buf3);
      state[7] = state[7] ^ buf3 ^ buf1;

      /* Col3 */

      buf1 = state[8]  ^ state[9] ^ state[10] ^ state[11];
      buf2 = state[8];

      buf3 = state[8]  ^ state[9];
      buf3 = galois_mul2(buf3);
      state[8] = state[8] ^ buf3 ^ buf1;

      buf3 = state[9]  ^ state[10];
      buf3 = galois_mul2(buf3);
      state[9] = state[9] ^ buf3 ^ buf1;

      buf3 = state[10] ^ state[11];
      buf3 = galois_mul2(buf3);
      state[10] = state[10] ^ buf3 ^ buf1;

      buf3 = state[11] ^ buf2;
      buf3 = galois_mul2(buf3);
      state[11] = state[11] ^ buf3 ^ buf1;

      /* Col4 */

      buf1 = state[12] ^ state[13] ^ state[14] ^ state[15];
      buf2 = state[12];

      buf3 = state[12] ^ state[13];
      buf3 = galois_mul2(buf3);
      state[12] = state[12] ^ buf3 ^ buf1;

      buf3 = state[13] ^ state[14];
      buf3 = galois_mul2(buf3);
      state[13] = state[13] ^ buf3 ^ buf1;

      buf3 = state[14] ^ state[15];
      buf3 = galois_mul2(buf3);
      state[14] = state[14] ^ buf3 ^ buf1;

      buf3 = state[15] ^ buf2;
      buf3 = galois_mul2(buf3);
      state[15] = state[15] ^ buf3 ^ buf1;

      /* addroundkey, rsbox and shiftrows */

      /* Row 0 */

      state[0]   = g_rsbox[state[0]]  ^ expanded_key[(round * 16)];
      state[4]   = g_rsbox[state[4]]  ^ expanded_key[(round * 16) +  4];
      state[8]   = g_rsbox[state[8]]  ^ expanded_key[(round * 16) +  8];
      state[12]  = g_rsbox[state[12]] ^ expanded_key[(round * 16) + 12];

      /* Row 1 */

      buf1       = g_rsbox[state[13]] ^ expanded_key[(round * 16) +  1];
      state[13]  = g_rsbox[state[9]]  ^ expanded_key[(round * 16) + 13];
      state[9]   = g_rsbox[state[5]]  ^ expanded_key[(round * 16) +  9];
      state[5]   = g_rsbox[state[1]]  ^ expanded_key[(round * 16) +  5];
      state[1]   = buf1;

      /* Row 2 */

      buf1       = g_rsbox[state[2]]  ^ expanded_key[(round * 16) + 10];
      buf2       = g_rsbox[state[6]]  ^ expanded_key[(round * 16) + 14];
      state[2]   = g_rsbox[state[10]] ^ expanded_key[(round * 16) +  2];
      state[6]   = g_rsbox[state[14]] ^ expanded_key[(round * 16) +  6];
      state[10]  = buf1;
      state[14]  = buf2;

      /* Row 3 */

      buf1       = g_rsbox[state[3]]  ^ expanded_key[(round * 16) + 15];
      state[3]   = g_rsbox[state[7]]  ^ expanded_key[(round * 16) +  3];
      state[7]   = g_rsbox[state[11]] ^ expanded_key[(round * 16) +  7];
      state[11]  = g_rsbox[state[15]] ^ expanded_key[(round * 16) + 11];
      state[15]  = buf1;
    }
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: aes_setupkey
 *
 * Description:
 *   Configure the given AES context for operation with the selected key.
 *
 * Input Parameters:
 *  state  an AES context that can be used for AES operations
 *  key    a pointer to a 16-byte buffer holding the AES-128 key
 *  len    length of the key, must be 16
 *
 * TODO: Support other key lengths of 24 (AES-192) and 32 (AES-256)
 *
 * Returned Value:
 *   0 if OK
 *   -EINVAL if len is not 16
 *
 ****************************************************************************/

int aes_setupkey(FAR struct aes_state_s *state,
                 FAR const uint8_t *key,
                 int len)
{
  if (len != 16)
    {
      return -EINVAL;
    }

  expand_key(state->expanded_key, key);
  return 0;
}

/****************************************************************************
 * Name: aes_encipher
 *
 * Description:
 *   Encipher some 16-byte blocks (without any operation mode) using the
 *   previously defined key. The function can be called multiple times with
 *   the same state parameter.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

void aes_encipher(FAR struct aes_state_s *state, FAR uint8_t *blocks,
                  int nblk)
{
  int i;
  uint32_t off = 0;

  for (i = 0; i < nblk; i++)
    {
      aes_encr(blocks + off, state->expanded_key);
      off += 16;
    }
}

/****************************************************************************
 * Name: aes_decipher
 *
 * Description:
 *   Decipher some 16-byte blocks (without any operation mode) using the
 *   previously defined key. The function can be called multiple times with
 *   the same state parameter.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

void aes_decipher(FAR struct aes_state_s *state, FAR uint8_t *blocks,
                  int nblk)
{
  int i;
  uint32_t off = 0;

  for (i = 0; i < nblk; i++)
    {
      aes_decr(blocks + off, state->expanded_key);
      off += 16;
    }
}

/****************************************************************************
 * Name: aes_encrypt
 *
 * Description:
 *   AES128 encryption:  Given AES128 key and 16 bytes plain text, cipher
 *   text of 16 bytes is computed. The AES implementation is in mode ECB
 *   (Electronic Code Book).
 *
 * Input Parameters:
 *  key   AES128 key of size 16 bytes
 *  state 16 bytes of plain text and cipher text
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

void aes_encrypt(FAR uint8_t *state, FAR const uint8_t *key)
{
  /* Expand the key into 176 bytes */

  aes_setupkey(&g_aes_state, key, 16);
  aes_encr(state, g_aes_state.expanded_key);
}

/****************************************************************************
 * Name: aes_decrypt
 *
 * Description:
 *   AES128 decryption: Given AES128 key and 16 bytes cipher text, plain
 *   text of 16 bytes is computed The AES implementation is in mode ECB
 *   (Electronic Code Book).
 *
 * Input Parameters:
 *  key   AES128 key of size 16 bytes
 *  state 16 bytes of plain text and cipher text
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

void aes_decrypt(FAR uint8_t *state, FAR const uint8_t *key)
{
  /* Expand the key into 176 bytes */

  aes_setupkey(&g_aes_state, key, 16);
  aes_decr(state, g_aes_state.expanded_key);
}