aes-set-decrypt-key.c

/* aes-set-decrypt-key.c
 *
 * Inverse key setup for the aes/rijndael block cipher.
 */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2000, 2001, 2002 Rafael R. Sevilla, 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.
 */

/* Originally written by Rafael R. Sevilla <dido@pacific.net.ph> */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include "aes-internal.h"

#include "macros.h"

/* NOTE: We don't include rotated versions of the table. */
static const uint32_t mtable[0x100] =
{
  0x00000000,0x0b0d090e,0x161a121c,0x1d171b12,
  0x2c342438,0x27392d36,0x3a2e3624,0x31233f2a,
  0x58684870,0x5365417e,0x4e725a6c,0x457f5362,
  0x745c6c48,0x7f516546,0x62467e54,0x694b775a,
  0xb0d090e0,0xbbdd99ee,0xa6ca82fc,0xadc78bf2,
  0x9ce4b4d8,0x97e9bdd6,0x8afea6c4,0x81f3afca,
  0xe8b8d890,0xe3b5d19e,0xfea2ca8c,0xf5afc382,
  0xc48cfca8,0xcf81f5a6,0xd296eeb4,0xd99be7ba,
  0x7bbb3bdb,0x70b632d5,0x6da129c7,0x66ac20c9,
  0x578f1fe3,0x5c8216ed,0x41950dff,0x4a9804f1,
  0x23d373ab,0x28de7aa5,0x35c961b7,0x3ec468b9,
  0x0fe75793,0x04ea5e9d,0x19fd458f,0x12f04c81,
  0xcb6bab3b,0xc066a235,0xdd71b927,0xd67cb029,
  0xe75f8f03,0xec52860d,0xf1459d1f,0xfa489411,
  0x9303e34b,0x980eea45,0x8519f157,0x8e14f859,
  0xbf37c773,0xb43ace7d,0xa92dd56f,0xa220dc61,
  0xf66d76ad,0xfd607fa3,0xe07764b1,0xeb7a6dbf,
  0xda595295,0xd1545b9b,0xcc434089,0xc74e4987,
  0xae053edd,0xa50837d3,0xb81f2cc1,0xb31225cf,
  0x82311ae5,0x893c13eb,0x942b08f9,0x9f2601f7,
  0x46bde64d,0x4db0ef43,0x50a7f451,0x5baafd5f,
  0x6a89c275,0x6184cb7b,0x7c93d069,0x779ed967,
  0x1ed5ae3d,0x15d8a733,0x08cfbc21,0x03c2b52f,
  0x32e18a05,0x39ec830b,0x24fb9819,0x2ff69117,
  0x8dd64d76,0x86db4478,0x9bcc5f6a,0x90c15664,
  0xa1e2694e,0xaaef6040,0xb7f87b52,0xbcf5725c,
  0xd5be0506,0xdeb30c08,0xc3a4171a,0xc8a91e14,
  0xf98a213e,0xf2872830,0xef903322,0xe49d3a2c,
  0x3d06dd96,0x360bd498,0x2b1ccf8a,0x2011c684,
  0x1132f9ae,0x1a3ff0a0,0x0728ebb2,0x0c25e2bc,
  0x656e95e6,0x6e639ce8,0x737487fa,0x78798ef4,
  0x495ab1de,0x4257b8d0,0x5f40a3c2,0x544daacc,
  0xf7daec41,0xfcd7e54f,0xe1c0fe5d,0xeacdf753,
  0xdbeec879,0xd0e3c177,0xcdf4da65,0xc6f9d36b,
  0xafb2a431,0xa4bfad3f,0xb9a8b62d,0xb2a5bf23,
  0x83868009,0x888b8907,0x959c9215,0x9e919b1b,
  0x470a7ca1,0x4c0775af,0x51106ebd,0x5a1d67b3,
  0x6b3e5899,0x60335197,0x7d244a85,0x7629438b,
  0x1f6234d1,0x146f3ddf,0x097826cd,0x02752fc3,
  0x335610e9,0x385b19e7,0x254c02f5,0x2e410bfb,
  0x8c61d79a,0x876cde94,0x9a7bc586,0x9176cc88,
  0xa055f3a2,0xab58faac,0xb64fe1be,0xbd42e8b0,
  0xd4099fea,0xdf0496e4,0xc2138df6,0xc91e84f8,
  0xf83dbbd2,0xf330b2dc,0xee27a9ce,0xe52aa0c0,
  0x3cb1477a,0x37bc4e74,0x2aab5566,0x21a65c68,
  0x10856342,0x1b886a4c,0x069f715e,0x0d927850,
  0x64d90f0a,0x6fd40604,0x72c31d16,0x79ce1418,
  0x48ed2b32,0x43e0223c,0x5ef7392e,0x55fa3020,
  0x01b79aec,0x0aba93e2,0x17ad88f0,0x1ca081fe,
  0x2d83bed4,0x268eb7da,0x3b99acc8,0x3094a5c6,
  0x59dfd29c,0x52d2db92,0x4fc5c080,0x44c8c98e,
  0x75ebf6a4,0x7ee6ffaa,0x63f1e4b8,0x68fcedb6,
  0xb1670a0c,0xba6a0302,0xa77d1810,0xac70111e,
  0x9d532e34,0x965e273a,0x8b493c28,0x80443526,
  0xe90f427c,0xe2024b72,0xff155060,0xf418596e,
  0xc53b6644,0xce366f4a,0xd3217458,0xd82c7d56,
  0x7a0ca137,0x7101a839,0x6c16b32b,0x671bba25,
  0x5638850f,0x5d358c01,0x40229713,0x4b2f9e1d,
  0x2264e947,0x2969e049,0x347efb5b,0x3f73f255,
  0x0e50cd7f,0x055dc471,0x184adf63,0x1347d66d,
  0xcadc31d7,0xc1d138d9,0xdcc623cb,0xd7cb2ac5,
  0xe6e815ef,0xede51ce1,0xf0f207f3,0xfbff0efd,
  0x92b479a7,0x99b970a9,0x84ae6bbb,0x8fa362b5,
  0xbe805d9f,0xb58d5491,0xa89a4f83,0xa397468d,
};

#define MIX_COLUMN(T, key) do { \
    uint32_t _k, _nk, _t;	\
    _k = (key);			\
    _nk = T[_k & 0xff];		\
    _k >>= 8;			\
    _t = T[_k & 0xff];		\
    _nk ^= ROTL32(8, _t);	\
    _k >>= 8;			\
    _t = T[_k & 0xff];		\
    _nk ^= ROTL32(16, _t);	\
    _k >>= 8;			\
    _t = T[_k & 0xff];		\
    _nk ^= ROTL32(24, _t);	\
    (key) = _nk;		\
  } while(0)
  

#define SWAP(a, b) \
do { uint32_t t_swap = (a); (a) = (b); (b) = t_swap; } while(0)

void
aes_invert_key(struct aes_ctx *dst,
	       const struct aes_ctx *src)
{
  unsigned nrounds;
  unsigned i;

  nrounds = src->nrounds;

  /* Reverse the order of subkeys, in groups of 4. */
  /* FIXME: Instead of reordering the subkeys, change the access order
     of aes_decrypt, since it's a separate function anyway? */
  if (src == dst)
    {
      unsigned j, k;

      for (i = 0, j = nrounds * 4;
	   i < j;
	   i += 4, j -= 4)
	for (k = 0; k<4; k++)
	  SWAP(dst->keys[i+k], dst->keys[j+k]);
    }
  else
    {
      unsigned k;

      dst->nrounds = nrounds;
      for (i = 0; i <= nrounds * 4; i += 4)
	for (k = 0; k < 4; k++)
	  dst->keys[i+k] = src->keys[nrounds * 4 - i + k];
    }

  /* Transform all subkeys but the first and last. */
  for (i = 4; i < 4 * nrounds; i++)
    MIX_COLUMN (mtable, dst->keys[i]);
}

void
aes_set_decrypt_key(struct aes_ctx *ctx,
		    unsigned keysize, const uint8_t *key)
{
  /* We first create subkeys for encryption,
   * then modify the subkeys for decryption. */
  aes_set_encrypt_key(ctx, keysize, key);
  aes_invert_key(ctx, ctx);
}