JavaCard SW 6F 00 with function init() from class BigNumber (JavaCard API)

Question

I am developing an applet in JavaCard with JCDE on Eclipse.

I am testing my applet with JCWDE and APDUTOOL but I get SW1=6F and SW2=00... The thing is that I am using the class BigNumber of JavaCard API and the function init() is not working like I would like.

The code of my applet:

import javacard.framework.APDU;
import javacard.framework.APDUException;
import javacard.framework.Applet;
import javacard.framework.CardRuntimeException;
import javacard.framework.ISO7816;
import javacard.framework.ISOException;
import javacard.framework.UserException;
import javacard.framework.Util;
import javacard.security.CryptoException;
import javacardx.framework.math.BigNumber;
import javacard.security.MessageDigest;

public class SignatureGPS extends Applet {

    public static final byte CLA = (byte) 0xB0;
    public static final byte INS = (byte) 0x00;

    private BigNumber s;
    private BigNumber x; 

    private SignatureGPS() {
        try {
            s = new BigNumber((short)100);
            x = new BigNumber((short)100);
            byte[] tmp = {(byte) 0xc6, (byte) 0x85, (byte)0x8e, 0x06, (byte)0xb7, 0x04, 0x04, (byte)0xe9, (byte)0xcd, (byte)0x9e, 0x3e, (byte)0xcb, 0x66, 0x23, (byte)0x95, (byte)0xb4,
                    0x42, (byte)0x9c, 0x64, (byte)0x81, 0x39, 0x05, 0x3f, (byte)0xb5, 0x21, (byte)0xf8, 0x28, (byte)0xaf, 0x60, 0x6b, 0x4d, 0x3d, (byte)0xba, (byte)0xa1, 0x4b, 0x5e, 
                    0x77, (byte)0xef, (byte)0xe7, 0x59, 0x28, (byte)0xfe, 0x1d, (byte)0xc1, 0x27, (byte)0xa2, (byte)0xff, (byte)0xa8, (byte)0xde, 0x33, 0x48, (byte)0xb3, (byte)0xc1, 
                    (byte)0x85, 0x6a, 0x42, (byte)0x9b, (byte)0xf9, 0x7e, 0x7e, 0x31, (byte)0xc2, (byte)0xe5, (byte)0xbd, 0x66};
            x.init(tmp, (short) 0, (short) tmp.length, BigNumber.FORMAT_HEX);
            h = MessageDigest.getInstance(MessageDigest.ALG_SHA_256, false);
        }
        catch(ArithmeticException e){}
        catch(CryptoException e){CryptoException.throwIt(e.getReason());}
        catch(NullPointerException e){}
        catch(ArrayIndexOutOfBoundsException e){}
    }

    public static void install(byte bArray[], short bOffset, byte bLength) throws ISOException {
        new SignatureGPS().register();
    }

    public void process(APDU apdu) 
        throws ISOException, ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException, APDUException, {
        byte[] buffer = apdu.getBuffer();

        if (this.selectingApplet()) return;

        if (buffer[ISO7816.OFFSET_CLA] != CLA)
            ISOException.throwIt(ISO7816.SW_CLA_NOT_SUPPORTED);

        if (buffer[ISO7816.OFFSET_INS]!=0)
            ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);

        short LC = apdu.getIncomingLength();
        apdu.setIncomingAndReceive();
        s.init(buffer, (short)5, LC, BigNumber.FORMAT_HEX);
    }
}

So the problem occurs at the line s.init(buffer, (short)5, LC, BigNumber.FORMAT_HEX); but the thing that is strange is that it seems to work in the constructor (x.init(tmp, (short) 0, (short) tmp.length, BigNumber.FORMAT_HEX);)

Does anybody see what am I doing wrong?

Here is the response I get from APDUTOOL:

Java Card 2.2.2 APDU Tool, Version 1.3
Copyright 2005 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.
Opening connection to localhost on port 9025.
Connected.
powerup;
// Select the installer applet
0x00 0xA4 0x04 0x00 0x09 0xa0 0x00 0x00 0x00 0x62 0x03 0x01 0x08 0x01 0x7F;
// create SignatureGPS applet
0x80 0xB8 0x00 0x00 0xd 0xb 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x00 0x01 0x00 0x7F;Received ATR = 0x3b 0xf0 0x11 0x00 0xff 0x00 
CLA: 00, INS: a4, P1: 04, P2: 00, Lc: 09, a0, 00, 00, 00, 62, 03, 01, 08, 01, Le: 00, SW1: 90, SW2: 00

CLA: 80, INS: b8, P1: 00, P2: 00, Lc: 0d, 0b, 01, 02, 03, 04, 05, 06, 07, 08, 09, 00, 01, 00, Le: 0b, 01, 02, 03, 04, 05, 06, 07, 08, 09, 00, 01, SW1: 90, SW2: 00
// select SignatureGPS applet
0x00 0xA4 0x04 0x00 0xb 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x00 0x01 0x7F;
CLA: 00, INS: a4, P1: 04, P2: 00, Lc: 0b, 01, 02, 03, 04, 05, 06, 07, 08, 09, 00, 01, Le: 00, SW1: 90, SW2: 00
0xB0 0x00 0x00 0x00 0x02 0x03 0x04 0x7F;
CLA: b0, INS: 00, P1: 00, P2: 00, Lc: 02, 03, 04, Le: 00, SW1: 6f, SW2: 00

So in this list of APDU commands, I create my applet and select it and then I send an APDU which contains 2 datas (0x03 0x04) and with my line s.init(buffer, (short)5, LC, BigNumber.FORMAT_HEX); I expect that s gonna be initialize at 0x0304 but as you can see, I get the SW 6F00... Thank you very much for your help !

Answer 1

As you already found out in your previous question on that issue, trying to allocate s = new BigNumber((short)100); throws an ArithmethicException.

• This means that s never gets initialized in your code and, hence, is null.

• Consequently, trying to call init on a null reference in

  s.init(buffer, (short)5, LC, BigNumber.FORMAT_HEX);
  

  will result in a NullPointerException, which in turn results in the response status word 6F00.

Note that x.init(...); in your constructor will never be called due to the exception on the line

s = new BigNumber((short)100);