Java Card Application Development
by Darryl Barnes


Example 1:

public class Loyalty extends javacard.framework.Applet
{
public void static install(APDU _apdu)
{
}
public boolean select()
{
}
public void process(APDU _apdu)
{
}
public void deselect()
{
}
}

Example 2:
public static void install(APDU _apdu)
{
        Loyalty loyalty = new Loyalty();
        // initialize user PIN
        loyalty.pin = new OwnerPIN((byte)5, PIN_LENGTH);
        loyalty.pin.updateAndUnblock(baPINValue, (short)0, PIN_LENGTH);
        // register the applet
        loyalty.register();
}


Example 3:

public void process(APDU _apdu)
{
// get reference to apdu buffer
      byte[] baBuffer = _apdu.getBuffer();
// verify class
      if(baBuffer[ISO.OFFSET_CLA] != CLA_LOYALTY)
            ISOException.throwIt(ISO.SW_CLA_NOT_SUPPORTED);
    // branch to each instruction
      switch(baBuffer[ISO.OFFSET_INS])
      {
          case INS_VALIDATE_PIN:
              this.validatePIN(_apdu);
              break;
          case INS_DEBIT:
              this.debit(_apdu);
              break;
          case INS_CREDIT:
              this.credit(_apdu);
              break;
          case INS_GETBALANCE:
              this.getBalance(_apdu);
              break;
        }
}


Example 4:
protected void validatePIN(APDU _apdu)
{
        // get reference to apdu buffer

        baBuffer = _apdu.getBuffer();
        // get data from terminal
        byte bLc = (byte)_apdu.setIncomingAndReceive();
        // check length being sent
        if(bLc != PIN_LENGTH)
            ISOException.throwIt(ISO.SW_WRONG_LENGTH);
        // validate PIN
        if(pin.check(baBuffer, ISO.OFFSET_CDATA, PIN_LENGTH))
            zIsAuthorized = true;
        else
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
}
protected void debit(APDU _apdu)
{
        // check if PIN is validated
        if(!zIsAuthorized)
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // get data from terminal
        byte bLc = (byte)_apdu.setIncomingAndReceive();
        // get amount from apdu buffer
        short sAmount = Util.getShort(baBuffer, ISO.OFFSET_P1);
        // don't allow negative balance
        if((sPoints - sAmount) < 0)
            sPoints = 0;
      else // debit account
            sPoints = (short)(sPoints - sAmount);
}
protected void credit(APDU _apdu)
{
        // check if PIN is validated
        if(!zIsAuthorized)
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // get data from terminal
        byte bLc = (byte)_apdu.setIncomingAndReceive();
        // get amount from apdu buffer
        short sAmount = Util.getShort(baBuffer, ISO.OFFSET_P1);
        // increment balance
        sPoints = (short)(sPoints + sAmount);
}
protected void getBalance(APDU _apdu)
{
        // check access permissions
        if(!zIsAuthorized)
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // put balance value into apdu buffer
        Util.setShort(baBuffer, ISO.OFFSET_CDATA, sPoints);
        // send balance
        _apdu.setOutgoingAndSend(ISO.OFFSET_CDATA, (short)2);
}


Listing One
package article;
import javacard.framework.*;
public class Loyalty extends Applet
{
    // these attributes are made static because they 
    // are referenced in the static install method
    protected static short sPoints = 0;
    protected static byte[] baBuffer;
    // CLA & INS definitions
    public static final byte CLA_LOYALTY = (byte)0xAA;
    public static final byte INS_VALIDATE_PIN = 0x10;
    public static final byte INS_GETBALANCE = 0x20;
    public static final byte INS_DEBIT = 0x30;
    public static final byte INS_CREDIT = 0x40;

    // PIN attributes
    public static final byte PIN_LENGTH = 8;
    protected OwnerPIN pin;
    protected static byte[] baPINValue = {0x0A, 0x0B, 0x0A, 0x0B, 
                                            0x0A, 0x0B, 0x0A, 0x0B};
    protected transient boolean zIsAuthorized = false;
    
    public static void install(APDU _apdu)
    {
        Loyalty loyalty = new Loyalty();
        
        // initialize user PIN
        loyalty.pin = new OwnerPIN((byte)5, PIN_LENGTH);
        loyalty.pin.updateAndUnblock(baPINValue, (short)0, PIN_LENGTH);
        
        // register the applet
        loyalty.register();
    }
    public void process(APDU _apdu)
    {
        // get reference to apdu buffer
        byte[] baBuffer = _apdu.getBuffer();
        // verify class
        if(baBuffer[ISO.OFFSET_CLA] != CLA_LOYALTY)
            ISOException.throwIt(ISO.SW_CLA_NOT_SUPPORTED);
        // branch to each instruction
        switch(baBuffer[ISO.OFFSET_INS])
        {
            case INS_VALIDATE_PIN:
                this.validatePIN(_apdu);
                break;
            case INS_DEBIT:
                this.debit(_apdu);
                break;
            case INS_CREDIT:
                this.credit(_apdu);
                break;
            case INS_GETBALANCE:
                this.getBalance(_apdu);
                break;
        }
    }
    protected void validatePIN(APDU _apdu)
    {
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // get data from terminal
        byte bLc = (byte)_apdu.setIncomingAndReceive();
        // check length being sent
        if(bLc != PIN_LENGTH)
            ISOException.throwIt(ISO.SW_WRONG_LENGTH);
        // validate PIN
        if(pin.check(baBuffer, ISO.OFFSET_CDATA, PIN_LENGTH))
            zIsAuthorized = true;
        else
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
    }
    protected void debit(APDU _apdu)
    {
        // check if PIN is validated
        if(!zIsAuthorized)
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // get data from terminal
        byte bLc = (byte)_apdu.setIncomingAndReceive();
        // get amount from apdu buffer
        short sAmount = Util.getShort(baBuffer, ISO.OFFSET_P1);
        // don't allow negative balance
        if((sPoints - sAmount) < 0)
            sPoints = 0;
        else // debit account
            sPoints = (short)(sPoints - sAmount);
    }
    protected void credit(APDU _apdu)
    {
        // check if PIN is validated
        if(!zIsAuthorized)
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // get data from terminal
        byte bLc = (byte)_apdu.setIncomingAndReceive();
        // get amount from apdu buffer
        short sAmount = Util.getShort(baBuffer, ISO.OFFSET_P1);
        // increment balance
        sPoints = (short)(sPoints + sAmount);
    }
    protected void getBalance(APDU _apdu)
    {
        // check access permissions
        if(!zIsAuthorized)
            ISOException.throwIt(ISO.SW_SECURITY_STATUS_NOT_SATISFIED);
        // get reference to apdu buffer
        baBuffer = _apdu.getBuffer();
        // put balance value into apdu buffer
        Util.setShort(baBuffer, ISO.OFFSET_CDATA, sPoints);
        // send balance
        _apdu.setOutgoingAndSend(ISO.OFFSET_CDATA, (short)2);
    }
}


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