1 /* 2 * gf2_8.h 3 * 4 * GF(256) implementation 5 * 6 * David A. McGrew 7 * Cisco Systems, Inc. 8 */ 9 10 /* 11 * 12 * Copyright (c) 2001-2006, Cisco Systems, Inc. 13 * All rights reserved. 14 * 15 * Redistribution and use in source and binary forms, with or without 16 * modification, are permitted provided that the following conditions 17 * are met: 18 * 19 * Redistributions of source code must retain the above copyright 20 * notice, this list of conditions and the following disclaimer. 21 * 22 * Redistributions in binary form must reproduce the above 23 * copyright notice, this list of conditions and the following 24 * disclaimer in the documentation and/or other materials provided 25 * with the distribution. 26 * 27 * Neither the name of the Cisco Systems, Inc. nor the names of its 28 * contributors may be used to endorse or promote products derived 29 * from this software without specific prior written permission. 30 * 31 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 32 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 33 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 34 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 35 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 36 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 37 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 38 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 39 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 40 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 41 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 42 * OF THE POSSIBILITY OF SUCH DAMAGE. 43 * 44 */ 45 46 47 #ifndef GF2_8_H 48 #define GF2_8_H 49 50 #include "datatypes.h" /* for uint8_t definition */ 51 52 typedef uint8_t gf2_8; 53 54 #define gf2_8_field_polynomial 0x1B 55 56 /* 57 * gf2_8_shift(x) returns 58 */ 59 60 /* 61 * gf2_8_shift(z) returns the result of the GF(2^8) 'multiply by x' 62 * operation, using the field representation from AES; that is, the 63 * next gf2_8 value in the cyclic representation of that field. The 64 * value z should be an uint8_t. 65 */ 66 67 #define gf2_8_shift(z) (((z) & 128) ? \ 68 (((z) << 1) ^ gf2_8_field_polynomial) : ((z) << 1)) 69 70 gf2_8 71 gf2_8_compute_inverse(gf2_8 x); 72 73 void 74 test_gf2_8(void); 75 76 gf2_8 77 gf2_8_multiply(gf2_8 x, gf2_8 y); 78 79 #endif /* GF2_8_H */ 80