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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.
Copyright (C) 2011 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/.
*/
#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, char **argv)
{
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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