forked from Mirrors/freeswitch
b3d890ef25
git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@1086 d0543943-73ff-0310-b7d9-9358b9ac24b2
84 lines
2.5 KiB
C
84 lines
2.5 KiB
C
/*
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* gf2_8.c
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*
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* GF(256) finite field implementation, with the representation used
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* in the AES cipher.
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*
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* David A. McGrew
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* Cisco Systems, Inc.
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*/
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/*
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*
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* Copyright (c) 2001-2005, Cisco Systems, Inc.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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*
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* Neither the name of the Cisco Systems, Inc. nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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#include "datatypes.h"
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#include "gf2_8.h"
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/* gf2_8_shift() moved to gf2_8.h as an inline function */
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inline gf2_8
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gf2_8_multiply(gf2_8 x, gf2_8 y) {
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gf2_8 z = 0;
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if (y & 1) z ^= x; x = gf2_8_shift(x);
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if (y & 2) z ^= x; x = gf2_8_shift(x);
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if (y & 4) z ^= x; x = gf2_8_shift(x);
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if (y & 8) z ^= x; x = gf2_8_shift(x);
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if (y & 16) z ^= x; x = gf2_8_shift(x);
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if (y & 32) z ^= x; x = gf2_8_shift(x);
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if (y & 64) z ^= x; x = gf2_8_shift(x);
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if (y & 128) z ^= x;
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return z;
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}
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/* this should use the euclidean algorithm */
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gf2_8
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gf2_8_compute_inverse(gf2_8 x) {
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unsigned int i;
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if (x == 0) return 0; /* zero is a special case */
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for (i=0; i < 256; i++)
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if (gf2_8_multiply((gf2_8) i, x) == 1)
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return (gf2_8) i;
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return 0;
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}
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