1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/netwerk/srtp/src/crypto/math/gf2_8.c Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,83 @@
1.4 +/*
1.5 + * gf2_8.c
1.6 + *
1.7 + * GF(256) finite field implementation, with the representation used
1.8 + * in the AES cipher.
1.9 + *
1.10 + * David A. McGrew
1.11 + * Cisco Systems, Inc.
1.12 + */
1.13 +
1.14 +/*
1.15 + *
1.16 + * Copyright (c) 2001-2006, Cisco Systems, Inc.
1.17 + * All rights reserved.
1.18 + *
1.19 + * Redistribution and use in source and binary forms, with or without
1.20 + * modification, are permitted provided that the following conditions
1.21 + * are met:
1.22 + *
1.23 + * Redistributions of source code must retain the above copyright
1.24 + * notice, this list of conditions and the following disclaimer.
1.25 + *
1.26 + * Redistributions in binary form must reproduce the above
1.27 + * copyright notice, this list of conditions and the following
1.28 + * disclaimer in the documentation and/or other materials provided
1.29 + * with the distribution.
1.30 + *
1.31 + * Neither the name of the Cisco Systems, Inc. nor the names of its
1.32 + * contributors may be used to endorse or promote products derived
1.33 + * from this software without specific prior written permission.
1.34 + *
1.35 + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
1.36 + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
1.37 + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
1.38 + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
1.39 + * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
1.40 + * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
1.41 + * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
1.42 + * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
1.43 + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
1.44 + * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
1.45 + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
1.46 + * OF THE POSSIBILITY OF SUCH DAMAGE.
1.47 + *
1.48 + */
1.49 +
1.50 +
1.51 +#include "datatypes.h"
1.52 +#include "gf2_8.h"
1.53 +
1.54 +/* gf2_8_shift() moved to gf2_8.h as an inline function */
1.55 +
1.56 +gf2_8
1.57 +gf2_8_multiply(gf2_8 x, gf2_8 y) {
1.58 + gf2_8 z = 0;
1.59 +
1.60 + if (y & 1) z ^= x; x = gf2_8_shift(x);
1.61 + if (y & 2) z ^= x; x = gf2_8_shift(x);
1.62 + if (y & 4) z ^= x; x = gf2_8_shift(x);
1.63 + if (y & 8) z ^= x; x = gf2_8_shift(x);
1.64 + if (y & 16) z ^= x; x = gf2_8_shift(x);
1.65 + if (y & 32) z ^= x; x = gf2_8_shift(x);
1.66 + if (y & 64) z ^= x; x = gf2_8_shift(x);
1.67 + if (y & 128) z ^= x;
1.68 +
1.69 + return z;
1.70 +}
1.71 +
1.72 +
1.73 +/* this should use the euclidean algorithm */
1.74 +
1.75 +gf2_8
1.76 +gf2_8_compute_inverse(gf2_8 x) {
1.77 + unsigned int i;
1.78 +
1.79 + if (x == 0) return 0; /* zero is a special case */
1.80 + for (i=0; i < 256; i++)
1.81 + if (gf2_8_multiply((gf2_8) i, x) == 1)
1.82 + return (gf2_8) i;
1.83 +
1.84 + return 0;
1.85 +}
1.86 +
