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/* gcmdata.c
*
* Galois counter mode, specified by NIST,
* http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf
*
*/
/* Generation of fixed multiplication tables. */
/* nettle, low-level cryptographics library
*
* Copyright (C) 2011 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 <stdio.h>
#include <stdlib.h>
#define GHASH_POLYNOMIAL 0xE1
/* When x is shifted out over the block edge, add multiples of the
defining polynomial to eliminate each bit. */
static unsigned
reduce(unsigned x)
{
unsigned p = GHASH_POLYNOMIAL << 1;
unsigned y = 0;
for (; x; x >>= 1, p <<= 1)
if (x & 1)
y ^= p;
return y;
}
int
main(int argc UNUSED, char **argv UNUSED)
{
unsigned i;
printf("4-bit table:\n");
for (i = 0; i<16; i++)
{
unsigned x;
if (i && !(i%8))
printf("\n");
x = reduce(i << 4);
printf("W(%02x,%02x),", x >> 8, x & 0xff);
}
printf("\n\n");
printf("8-bit table:\n");
for (i = 0; i<256; i++)
{
unsigned x;
if (i && !(i%8))
printf("\n");
x = reduce(i);
printf("W(%02x,%02x),", x >> 8, x & 0xff);
}
printf("\n");
return EXIT_SUCCESS;
}
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