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/* aes-decrypt-internal.c
*
* Decryption function for the aes/rijndael block cipher.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2002, 2013 Niels Möller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include "aes-internal.h"
#include "macros.h"
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;
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; i < rounds; i++)
{
t0 = AES_ROUND(T, w0, w3, w2, w1, keys[4*i]);
t1 = AES_ROUND(T, w1, w0, w3, w2, keys[4*i + 1]);
t2 = AES_ROUND(T, w2, w1, w0, w3, keys[4*i + 2]);
t3 = AES_ROUND(T, w3, w2, w1, w0, keys[4*i + 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, keys[4*i]);
t1 = AES_FINAL_ROUND(T, w1, w0, w3, w2, keys[4*i + 1]);
t2 = AES_FINAL_ROUND(T, w2, w1, w0, w3, keys[4*i + 2]);
t3 = AES_FINAL_ROUND(T, w3, w2, w1, w0, keys[4*i + 3]);
LE_WRITE_UINT32(dst, t0);
LE_WRITE_UINT32(dst + 4, t1);
LE_WRITE_UINT32(dst + 8, t2);
LE_WRITE_UINT32(dst + 12, t3);
}
}
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