aes-decrypt-internal.c

   1 /* aes-decrypt-internal.c
   2
   3    Decryption function for the aes/rijndael block cipher.
   4
   5    Copyright 2002, 2013 Niels Möller
   6
   7    This file is part of GNU Nettle.
   8
   9    GNU Nettle is free software: you can redistribute it and/or
  10    modify it under the terms of either:
  11
  12      * the GNU Lesser General Public License as published by the Free
  13        Software Foundation; either version 3 of the License, or (at your
  14        option) any later version.
  15
  16    or
  17
  18      * the GNU General Public License as published by the Free
  19        Software Foundation; either version 2 of the License, or (at your
  20        option) any later version.
  21
  22    or both in parallel, as here.
  23
  24    GNU Nettle is distributed in the hope that it will be useful,
  25    but WITHOUT ANY WARRANTY; without even the implied warranty of
  26    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  27    General Public License for more details.
  28
  29    You should have received copies of the GNU General Public License and
  30    the GNU Lesser General Public License along with this program.  If
  31    not, see http://www.gnu.org/licenses/.
  32 */
  33
  34 #if HAVE_CONFIG_H
  35 # include "config.h"
  36 #endif
  37
  38 #include <assert.h>
  39
  40 #include "aes-internal.h"
  41 #include "macros.h"
  42
  43 /* For fat builds */
  44 #if HAVE_NATIVE_aes_decrypt
  45 void
  46 _nettle_aes_decrypt_c(unsigned rounds, const uint32_t *keys,
  47     const struct aes_table *T,
  48     size_t length, uint8_t *dst,
  49     const uint8_t *src);
  50 #define _nettle_aes_decrypt _nettle_aes_decrypt_c
  51 #endif
  52
  53 void
  54 _nettle_aes_decrypt(unsigned rounds, const uint32_t *keys,
  55                     const struct aes_table *T,
  56                     size_t length, uint8_t *dst,
  57                     const uint8_t *src)
  58 {
  59   FOR_BLOCKS(length, dst, src, AES_BLOCK_SIZE)
  60     {
  61       uint32_t w0, w1, w2, w3;          /* working ciphertext */
  62       uint32_t t0, t1, t2, t3;
  63       const uint32_t *p;
  64       unsigned i;
  65
  66       /* Get clear text, using little-endian byte order.
  67        * Also XOR with the first subkey. */
  68
  69       w0 = LE_READ_UINT32(src)      ^ keys[0];
  70       w1 = LE_READ_UINT32(src + 4)  ^ keys[1];
  71       w2 = LE_READ_UINT32(src + 8)  ^ keys[2];
  72       w3 = LE_READ_UINT32(src + 12) ^ keys[3];
  73
  74       for (i = 1, p = keys - 4; i < rounds; i++, p -= 4)
  75         {
  76           t0 = AES_ROUND(T, w0, w3, w2, w1, p[0]);
  77           t1 = AES_ROUND(T, w1, w0, w3, w2, p[1]);
  78           t2 = AES_ROUND(T, w2, w1, w0, w3, p[2]);
  79           t3 = AES_ROUND(T, w3, w2, w1, w0, p[3]);
  80
  81           /* We could unroll the loop twice, to avoid these
  82              assignments. If all eight variables fit in registers,
  83              that should give a slight speedup. */
  84           w0 = t0;
  85           w1 = t1;
  86           w2 = t2;
  87           w3 = t3;
  88         }
  89
  90       /* Final round */
  91
  92       t0 = AES_FINAL_ROUND(T, w0, w3, w2, w1, p[0]);
  93       t1 = AES_FINAL_ROUND(T, w1, w0, w3, w2, p[1]);
  94       t2 = AES_FINAL_ROUND(T, w2, w1, w0, w3, p[2]);
  95       t3 = AES_FINAL_ROUND(T, w3, w2, w1, w0, p[3]);
  96
  97       LE_WRITE_UINT32(dst, t0);
  98       LE_WRITE_UINT32(dst + 4, t1);
  99       LE_WRITE_UINT32(dst + 8, t2);
 100       LE_WRITE_UINT32(dst + 12, t3);
 101     }
 102 }