common/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 {
  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
  20 void 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
  41 int 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 }