tools/mfc/card_reader/iso14443crc.c

   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 "iso14443crc.h"
  10
  11 static unsigned short UpdateCrc14443(unsigned char ch, unsigned short *lpwCrc) {
  12     ch = (ch ^ (unsigned char)((*lpwCrc) & 0x00FF));
  13     ch = (ch ^ (ch << 4));
  14     *lpwCrc = (*lpwCrc >> 8) ^ ((unsigned short) ch << 8) ^
  15               ((unsigned short) ch << 3) ^ ((unsigned short) ch >> 4);
  16     return (*lpwCrc);
  17 }
  18
  19 void ComputeCrc14443(int CrcType,
  20                      const unsigned char *Data, int Length,
  21                      unsigned char *TransmitFirst,
  22                      unsigned char *TransmitSecond) {
  23     unsigned short wCrc = CrcType;
  24
  25     do {
  26         unsigned char chBlock = *Data++;
  27         UpdateCrc14443(chBlock, &wCrc);
  28     } while (--Length);
  29
  30     if (CrcType == CRC_14443_B)
  31         wCrc = ~wCrc;                /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
  32
  33     *TransmitFirst = (unsigned char)(wCrc & 0xFF);
  34     *TransmitSecond = (unsigned char)((wCrc >> 8) & 0xFF);
  35     return;
  36 }
  37
  38 int CheckCrc14443(int CrcType, const unsigned char *Data, int Length) {
  39     unsigned char b1;
  40     unsigned char b2;
  41     if (Length < 3) return 0;
  42     ComputeCrc14443(CrcType, Data, Length - 2, &b1, &b2);
  43     if ((b1 == Data[Length - 2]) && (b2 == Data[Length - 1])) return 1;
  44     return 0;
  45 }