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[proxmark3-svn] / common / iso14443crc.c
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1//-----------------------------------------------------------------------------
2// This code is licensed to you under the terms of the GNU GPL, version 2 or,
3// at your option, any later version. See the LICENSE.txt file for the text of
4// the license.
5//-----------------------------------------------------------------------------
6// ISO14443 CRC calculation code.
7//-----------------------------------------------------------------------------
8
9#include "../common/iso14443crc.h"
10
11static unsigned short UpdateCrc14443(unsigned char ch, unsigned short *lpwCrc)
12{
13 ch = (ch ^ (unsigned char) ((*lpwCrc) & 0x00FF));
14 ch = (ch ^ (ch << 4));
15 *lpwCrc = (*lpwCrc >> 8) ^ ((unsigned short) ch << 8) ^
16 ((unsigned short) ch << 3) ^ ((unsigned short) ch >> 4);
17 return (*lpwCrc);
18}
19
20void ComputeCrc14443(int CrcType,
21 const unsigned char *Data, int Length,
22 unsigned char *TransmitFirst,
23 unsigned char *TransmitSecond)
24{
25 unsigned char chBlock;
26 unsigned short wCrc=CrcType;
27
28 do {
29 chBlock = *Data++;
30 UpdateCrc14443(chBlock, &wCrc);
31 } while (--Length);
32
33 if (CrcType == CRC_14443_B)
34 wCrc = ~wCrc; /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
35
36 *TransmitFirst = (unsigned char) (wCrc & 0xFF);
37 *TransmitSecond = (unsigned char) ((wCrc >> 8) & 0xFF);
38 return;
39}
40
41int CheckCrc14443(int CrcType, const unsigned char *Data, int Length) {
42 unsigned char b1;
43 unsigned char b2;
44 if (Length < 3) return 0;
45 ComputeCrc14443(CrcType, Data, Length - 2, &b1, &b2);
46 if ((b1 == Data[Length - 2]) && (b2 == Data[Length - 1])) return 1;
47 return 0;
48}
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