proxmark3/common/iso14443crc.c

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//-----------------------------------------------------------------------------
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// ISO14443 CRC calculation code.
//-----------------------------------------------------------------------------
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#include "iso14443crc.h"
static unsigned short UpdateCrc14443(unsigned char ch, unsigned short *lpwCrc)
{
ch = (ch ^ (unsigned char) ((*lpwCrc) & 0x00FF));
ch = (ch ^ (ch << 4));
*lpwCrc = (*lpwCrc >> 8) ^ ((unsigned short) ch << 8) ^
((unsigned short) ch << 3) ^ ((unsigned short) ch >> 4);
return (*lpwCrc);
}
void ComputeCrc14443(int CrcType,
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const unsigned char *Data, int Length,
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unsigned char *TransmitFirst,
unsigned char *TransmitSecond)
{
unsigned char chBlock;
unsigned short wCrc=CrcType;
do {
chBlock = *Data++;
UpdateCrc14443(chBlock, &wCrc);
} while (--Length);
if (CrcType == CRC_14443_B)
wCrc = ~wCrc; /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
*TransmitFirst = (unsigned char) (wCrc & 0xFF);
*TransmitSecond = (unsigned char) ((wCrc >> 8) & 0xFF);
return;
}
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int CheckCrc14443(int CrcType, const unsigned char *Data, int Length) {
unsigned char b1;
unsigned char b2;
if (Length < 3) return 0;
ComputeCrc14443(CrcType, Data, Length - 2, &b1, &b2);
if ((b1 == Data[Length - 2]) && (b2 == Data[Length - 1])) return 1;
return 0;
}