Implement CRC algorithm

[aahmadzadeh]

How can i implement bellow CRC algorithm in java card (without using of Int data type)?
My problem is "ushort" data type, and also i think here byte is unsigned value.

Code: Select all

ushort __crcBDefault = 0x6363;

private ushort UpdateCrc(byte b, ushort crc)
{
      byte ch = (byte)(b ^ (byte)(crc & 0x00ff));
      ch = (byte)(ch ^ (ch << 4));
      return (ushort)((crc >> 8) ^ (ch << 8) ^ (ch << 3) ^ (ch >> 4));
}

public ushort ComputeCrc(byte[] bytes)
{
   var res = __crcBDefault;
   foreach (var b in bytes)
      res = UpdateCrc(b, res);
   return res;
}

sample input: 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66
current output: 0xCA 0XDD

thank you

[Tolice]

The "ushort" data type ?It is not a standard data type, Is it yourself defined?

[aahmadzadeh]

The "ushort" data type ?It is not a standard data type, Is it yourself defined?

ushort is a data type in C#
ushort = unsigned short

[Tolice]

So, I don't understand the C#.

[mabel]

Why don't you use CRC implementation of java card API?

It's not necessary to implement it yourself.

[aahmadzadeh]

Why don't you use CRC implementation of java card API?

It's not necessary to implement it yourself.

Because i need special type of CRC which dose not implemented in JavaCard

[UNKNwYSHSA]

Code:

Code: Select all

package testCRC;

import javacard.framework.*;

public class testCRC extends Applet
{

   public static void install(byte[] bArray, short bOffset, byte bLength) 
   {
      new testCRC().register(bArray, (short) (bOffset + 1), bArray[bOffset]);
   }
   
   short __crcBDefault = 0x6363;

   private short UpdateCrc(byte b, short crc)
   {
      byte ch = (byte)(b ^ (byte)(crc & 0x00FF));
      ch = (byte)(ch ^ ((ch << 4) & 0xF0));
      return (short)(((crc >> 8) & 0x00FF) ^ ((ch << 8) & 0xFF00) ^ ((ch << 3) & 0x07F8) ^ ((ch >> 4) & 0x000F));
   }

   public short ComputeCrc(byte[] bytes, short offset, short length)
   {
      short res = __crcBDefault;
      for (short i = 0; i < length; ++i) {
         byte b = bytes[(short) (offset + i)];
        res = UpdateCrc(b, res);
      }

      return res;
   }

   public void process(APDU apdu)
   {
      if (selectingApplet())
      {
         return;
      }

      byte[] buf = apdu.getBuffer();
      switch (buf[ISO7816.OFFSET_INS])
      {
      case (byte)0x00:
         break;
      case (byte)0x01:
         short dataLen = apdu.setIncomingAndReceive();
         short crc = ComputeCrc(buf, ISO7816.OFFSET_CDATA, dataLen);
         Util.setShort(buf, (short) 0, crc);
         apdu.setOutgoingAndSend((short) 0, (short) 2);
         break;
      default:
         ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
      }
   }

}

Test:

Code: Select all

>> /select 112233445500
>> 00 A4 04 00 06 11 22 33 44 55 00 00
<< 90 00

>> /send 000100001011223344556677889900112233445566
>> 00 01 00 00 10 11 22 33 44 55 66 77 88 99 00 11 22 33 44 55 66
<< DD CA 90 00

Notice:
Make sure that the shift operation of type java short is same as type unsigned short.