git.zerfleddert.de Git - proxmark3-svn/blob - common/iso14443_crc.c

   1 //-----------------------------------------------------------------------------
   2 // Routines to compute the CRCs (two different flavours, just for confusion)
   3 // required for ISO 14443, swiped directly from the spec.
   4 //-----------------------------------------------------------------------------
   5
   6 #define CRC_14443_A     0x6363  /* ITU-V.41 */
   7 #define CRC_14443_B     0xFFFF  /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
   8
   9 static unsigned short UpdateCrc14443(unsigned char ch, unsigned short *lpwCrc)
  10 {
  11     ch = (ch ^ (unsigned char) ((*lpwCrc) & 0x00FF));
  12     ch = (ch ^ (ch << 4));
  13     *lpwCrc =   (*lpwCrc >> 8) ^ ((unsigned short) ch << 8) ^
  14                 ((unsigned short) ch << 3) ^ ((unsigned short) ch >> 4);
  15     return (*lpwCrc);
  16 }
  17
  18 static void ComputeCrc14443(int CrcType, BYTE *Data, int Length,
  19            BYTE *TransmitFirst, BYTE *TransmitSecond)
  20 {
  21     unsigned char chBlock;
  22     unsigned short wCrc=CrcType;
  23
  24         do {
  25         chBlock = *Data++;
  26         UpdateCrc14443(chBlock, &wCrc);
  27     } while (--Length);
  28
  29     if (CrcType == CRC_14443_B)
  30         wCrc = ~wCrc;                /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
  31
  32     *TransmitFirst = (BYTE) (wCrc & 0xFF);
  33     *TransmitSecond = (BYTE) ((wCrc >> 8) & 0xFF);
  34     return;
  35 }