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comparison: netwerk/srtp/src/crypto/math/gf2_8.c
netwerk/srtp/src/crypto/math/gf2_8.c
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| -1:000000000000 | 0:7d28590ed6dc |
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| 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 */ | |
| 10 | |
| 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 */ | |
| 46 | |
| 47 | |
| 48 #include "datatypes.h" | |
| 49 #include "gf2_8.h" | |
| 50 | |
| 51 /* gf2_8_shift() moved to gf2_8.h as an inline function */ | |
| 52 | |
| 53 gf2_8 | |
| 54 gf2_8_multiply(gf2_8 x, gf2_8 y) { | |
| 55 gf2_8 z = 0; | |
| 56 | |
| 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; | |
| 65 | |
| 66 return z; | |
| 67 } | |
| 68 | |
| 69 | |
| 70 /* this should use the euclidean algorithm */ | |
| 71 | |
| 72 gf2_8 | |
| 73 gf2_8_compute_inverse(gf2_8 x) { | |
| 74 unsigned int i; | |
| 75 | |
| 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; | |
| 80 | |
| 81 return 0; | |
| 82 } | |
| 83 |
