CRC Polynomial

[Mjohn.1]

Hi,

How to calculate the ISO14443-a CRC value(16 bit). Please help me how to get the CRC.

ISO14443-A >>> CR95HFDLL_SENDRECEIVE, 300028

<< 8015 6A1E4DB17E00004B3592000000000000 9BC3 080000

0x9BC3 ISO14443-a CRC value

Kind Regards,

Merin

[alister · Accepted solution]

A Google search threw these...

A CRC function and links to others: https://stackoverflow.com/questions/40869293/iso-iec-14443a-crc-calcuation

Some details on CR95HF and clues where to get more: https://community.st.com/s/question/0D50X00009XkW7G/iso-14443a-cr95hf-and-the-crc-bit

Another CRC implementation: https://www.microchip.com/forums/m896426.aspx

Datasheets, tools and software: https://www.st.com/en/nfc/st25-nfc-rfid-tags-readers.html

[Mjohn.1]

The resolved program to calculate the ISO14443-a CRC value(16 bit) as follow.

data_byte = 0x12;

CHECKSUM_CALCULATE(0x12 ^ 0x6363);

unsigned int CHECKSUM_DATA;

void CHECKSUM_CALCULATE(unsigned int C_DATA)

{

unsigned int n;

 for(n=1;n<=8;n++)

 {

 if((C_DATA & 0x01)==0x01)

 {

 C_DATA = C_DATA >> 1;

 C_DATA = C_DATA ^ 0x8408;

 }

 else

 {

 C_DATA = C_DATA >> 1;

 }

 }

 CHECKSUM_DATA = C_DATA;

}

ISO14443A Polynomial is 0x8408, initial value is 0x6363, CRC output is 0x626d

online 16bit crc calculator : https://hub.zhovner.com/tools/nfc/

Kind Regards,

Merin

[Brian TIDAL]

Hi,

just for my curiosity, why do you need to compute the CRC? The CR95HF does the job for you and provides a CRC error bit in the response flags of the SendReceive command.

Rgds

BT

[Tesla DeLorean]

The CRC here is 0xC39B in small endian form. If you run the data+crc thru the right shifting algorithm the data will divide cleanly resulting in a zero remainder.

C:\MSVC\CRC>iso14443a

626D == 0x626D

626D

test_one=C39B << Note High/Low bytes swapped

test_two=0000

PASS

// ISO14443A CRC Example   sourcer32@gmail.com
 
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
 
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned long uint32_t;
 
uint16_t crc_iso14443a(uint16_t crc, uint8_t data)
{
  int i;
  crc = crc ^ data;
  for(i=0; i<8; i++)
    if (crc & 1)
      crc = (crc >> 1) ^ 0x8408;
    else
      crc >>= 1;
  return(crc);
}
 
uint16_t crc_iso14443a_quick(uint16_t crc, uint8_t data)
{
  static const uint16_t crctbl[] = { // 0x8408 Nibble Table, sourcer32@gmail.com
    0x0000,0x1081,0x2102,0x3183,0x4204,0x5285,0x6306,0x7387,
    0x8408,0x9489,0xA50A,0xB58B,0xC60C,0xD68D,0xE70E,0xF78F };
 
  crc = crc ^ data;
 
  crc = (crc >> 4) ^ crctbl[crc & 0xF]; // Two rounds of 4-bits
  crc = (crc >> 4) ^ crctbl[crc & 0xF];
 
  return(crc);
}
 
uint16_t crc_iso14443a_quick_block(uint16_t crc, int size, uint8_t *buffer)
{
  while(size--)
    crc = crc_iso14443a_quick(crc, *buffer++);
 
  return(crc);
}
 
void test_one(void)
{
  // ISO14443-A >>> CR95HFDLL_SENDRECEIVE, 300028
  // << 8015 6A1E4DB17E00004B3592000000000000 9BC3 080000
 
  uint8_t data[] = {
    0x6A,0x1E,0x4D,0xB1,0x7E,0x00,0x00,0x4B,
    0x35,0x92,0x00,0x00,0x00,0x00,0x00,0x00 };
 
  uint16_t crc;
 
  crc = crc_iso14443a_quick_block(0x6363, sizeof(data), data);
 
  printf("test_one=%04X\n", crc );
}
 
void test_two(void)
{
  // ISO14443-A >>> CR95HFDLL_SENDRECEIVE, 300028
  // << 8015 6A1E4DB17E00004B3592000000000000 9BC3 080000
 
  uint8_t data[] = {
    0x6A,0x1E,0x4D,0xB1,0x7E,0x00,0x00,0x4B,
    0x35,0x92,0x00,0x00,0x00,0x00,0x00,0x00,
    0x9B,0xC3 };
 
  uint16_t crc;
 
  crc = crc_iso14443a_quick_block(0x6363, sizeof(data), data);
 
  printf("test_two=%04X\n", crc);
  if (crc == 0) puts("PASS"); else puts("!!FAIL!!");
}
 
int main(int argc, char **argv)
{
  printf("%04X == 0x626D\n", crc_iso14443a(0x6363, 0x12) );
 
  printf("%04X\n", crc_iso14443a_quick(0x6363, 0x12) );
 
  test_one();
  test_two();
 
  return(1);
}