/* 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 MÃ¶ller * * 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. */ #include #include #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; }