The Tor Browser: netwerk/srtp/src/crypto/math/gf2

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

     1 /*

     2  * gf2_8.c

     3  *

     4  * GF(256) finite field implementation, with the representation used

     5  * in the AES cipher.

     6  *

     7  * David A. McGrew

     8  * Cisco Systems, Inc.

     9  */

    11 /*

    12  *

    13  * Copyright (c) 2001-2006, Cisco Systems, Inc.

    14  * All rights reserved.

    15  *

    16  * Redistribution and use in source and binary forms, with or without

    17  * modification, are permitted provided that the following conditions

    18  * are met:

    19  *

    20  *   Redistributions of source code must retain the above copyright

    21  *   notice, this list of conditions and the following disclaimer.

    22  *

    23  *   Redistributions in binary form must reproduce the above

    24  *   copyright notice, this list of conditions and the following

    25  *   disclaimer in the documentation and/or other materials provided

    26  *   with the distribution.

    27  *

    28  *   Neither the name of the Cisco Systems, Inc. nor the names of its

    29  *   contributors may be used to endorse or promote products derived

    30  *   from this software without specific prior written permission.

    31  *

    32  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

    33  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

    34  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS

    35  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE

    36  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,

    37  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

    38  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

    39  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

    40  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,

    41  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

    42  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED

    43  * OF THE POSSIBILITY OF SUCH DAMAGE.

    44  *

    45  */

    48 #include "datatypes.h"

    49 #include "gf2_8.h"

    51 /* gf2_8_shift() moved to gf2_8.h as an inline function */

    53 gf2_8

    54 gf2_8_multiply(gf2_8 x, gf2_8 y) {

    55   gf2_8 z = 0;

    57   if (y &   1) z ^= x; x = gf2_8_shift(x);

    58   if (y &   2) z ^= x; x = gf2_8_shift(x);

    59   if (y &   4) z ^= x; x = gf2_8_shift(x);

    60   if (y &   8) z ^= x; x = gf2_8_shift(x);

    61   if (y &  16) z ^= x; x = gf2_8_shift(x);

    62   if (y &  32) z ^= x; x = gf2_8_shift(x);

    63   if (y &  64) z ^= x; x = gf2_8_shift(x);

    64   if (y & 128) z ^= x;

    66   return z;

    67 }

    70 /* this should use the euclidean algorithm */

    72 gf2_8

    73 gf2_8_compute_inverse(gf2_8 x) {

    74   unsigned int i;

    76   if (x == 0) return 0;    /* zero is a special case */

    77   for (i=0; i < 256; i++)

    78     if (gf2_8_multiply((gf2_8) i, x) == 1)

    79       return (gf2_8) i;

    81     return 0;

    82 }

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