mirror of
https://github.com/RfidResearchGroup/proxmark3.git
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72 lines
2.2 KiB
C
72 lines
2.2 KiB
C
//-----------------------------------------------------------------------------
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// This code is licensed to you under the terms of the GNU GPL, version 2 or,
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// at your option, any later version. See the LICENSE.txt file for the text of
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// the license.
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//-----------------------------------------------------------------------------
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// CRC16
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//-----------------------------------------------------------------------------
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#include "crc16.h"
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#define CRC16_POLY_CCITT 0x1021
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#define CRC16_POLY 0x8408
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#define CRC16_POLY_LEGIC 0xB400
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unsigned short update_crc16( unsigned short crc, unsigned char c )
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{
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unsigned short i, v, tcrc = 0;
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v = (crc ^ c) & 0xff;
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for (i = 0; i < 8; i++) {
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tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ CRC16_POLY : tcrc >> 1;
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v >>= 1;
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}
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return ((crc >> 8) ^ tcrc) & 0xffff;
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}
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uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
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if (length == 0)
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return (~remainder);
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for (int byte = 0; byte < length; ++byte) {
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remainder ^= (message[byte] << 8);
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for (uint8_t bit = 8; bit > 0; --bit) {
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if (remainder & 0x8000) {
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remainder = (remainder << 1) ^ polynomial;
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} else {
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remainder = (remainder << 1);
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}
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}
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}
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return remainder;
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}
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uint16_t crc16_ccitt(uint8_t const *message, int length) {
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return crc16(message, length, 0xffff, CRC16_POLY_CCITT);
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}
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uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
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return bit_reverse_uint16(crc16(message, length, 0x0000, CRC16_POLY_CCITT));
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}
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//ICEMAN: not working yet,
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// This CRC-16 is used in Legic Advant systems.
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uint16_t crc16_legic(uint8_t const *message, int length, uint16_t inital) {
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return crc16(message, length, inital, CRC16_POLY_LEGIC);
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}
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uint16_t bit_reverse_uint16 (uint16_t value) {
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const uint16_t mask0 = 0x5555;
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const uint16_t mask1 = 0x3333;
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const uint16_t mask2 = 0x0F0F;
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const uint16_t mask3 = 0x00FF;
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value = (((~mask0) & value) >> 1) | ((mask0 & value) << 1);
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value = (((~mask1) & value) >> 2) | ((mask1 & value) << 2);
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value = (((~mask2) & value) >> 4) | ((mask2 & value) << 4);
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value = (((~mask3) & value) >> 8) | ((mask3 & value) << 8);
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return value;
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}
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