/* aes-decrypt-internal.c

   Decryption function for the aes/rijndael block cipher.

   Copyright 2002, 2013 Niels Möller

   This file is part of GNU Nettle.

   GNU Nettle is free software: you can redistribute it and/or

   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free

       Software Foundation; either version 3 of the License, or (at your

       option) any later version.

   or

     * the GNU General Public License as published by the Free

       Software Foundation; either version 2 of the License, or (at your

       option) any later version.

   or both in parallel, as here.

   GNU Nettle 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 copies of the GNU General Public License and

   the GNU Lesser General Public License along with this program.  If

   not, see http://www.gnu.org/licenses/.

*/

#if HAVE_CONFIG_H

# include "config.h"

#endif

#include <assert.h>

#include "aes-internal.h"

#include "macros.h"

/* For fat builds */

#if HAVE_NATIVE_aes_decrypt

void

_nettle_aes_decrypt_c(unsigned rounds, const uint32_t *keys,

    const struct aes_table *T,

    size_t length, uint8_t *dst,

    const uint8_t *src);

#define _nettle_aes_decrypt _nettle_aes_decrypt_c

#endif

void

_nettle_aes_decrypt(unsigned rounds, const uint32_t *keys,

        const struct aes_table *T,

        size_t length, uint8_t *dst,

        const uint8_t *src)

{

  FOR_BLOCKS(length, dst, src, AES_BLOCK_SIZE)

    {

      uint32_t w0, w1, w2, w3;    /* working ciphertext */

      uint32_t t0, t1, t2, t3;

      const uint32_t *p;

      unsigned i;

      /* Get clear text, using little-endian byte order.

       * Also XOR with the first subkey. */

      w0 = LE_READ_UINT32(src)      ^ keys[0];

      w1 = LE_READ_UINT32(src + 4)  ^ keys[1];

      w2 = LE_READ_UINT32(src + 8)  ^ keys[2];

      w3 = LE_READ_UINT32(src + 12) ^ keys[3];

      for (i = 1, p = keys - 4; i < rounds; i++, p -= 4)

  {

    t0 = AES_ROUND(T, w0, w3, w2, w1, p[0]);

    t1 = AES_ROUND(T, w1, w0, w3, w2, p[1]);

    t2 = AES_ROUND(T, w2, w1, w0, w3, p[2]);

    t3 = AES_ROUND(T, w3, w2, w1, w0, p[3]);

    /* We could unroll the loop twice, to avoid these

       assignments. If all eight variables fit in registers,

       that should give a slight speedup. */

    w0 = t0;

    w1 = t1;

    w2 = t2;

    w3 = t3;

  }

      /* Final round */

      t0 = AES_FINAL_ROUND(T, w0, w3, w2, w1, p[0]);

      t1 = AES_FINAL_ROUND(T, w1, w0, w3, w2, p[1]);

      t2 = AES_FINAL_ROUND(T, w2, w1, w0, w3, p[2]);

      t3 = AES_FINAL_ROUND(T, w3, w2, w1, w0, p[3]);

      LE_WRITE_UINT32(dst, t0);

      LE_WRITE_UINT32(dst + 4, t1);

      LE_WRITE_UINT32(dst + 8, t2);

      LE_WRITE_UINT32(dst + 12, t3);

    }

}