Receiving SW 6F 00 when trying to obtain RSA public key modulus

Question

I have an issue with obtaining the RSA public key modulus with my Java Card applet implementation: The command SEND_PUB (see case statement case SEND_PUB) for sending the public 512 bits RSA key returns the status word 6F 00. What could be wrong with my implementation?

public class crypto extends Applet {


    private static final boolean NO_EXTERNAL_ACCESS = false;  
    private  static byte[] file=new byte[128];
    private  static byte[] SignedFile=new byte[20];    
    private  static RSAPublicKey p; 
    private  static RSAPublicKey publicKey; 
    private  static RSAPrivateKey privateKey; 
    private  static KeyPair keyPair;
    Signature sig;
    private final static byte ALOC= 0x07;  //vérifier le code PIN
    private final static byte INS_PIN= 0x01;  //vérifier le code PIN
    private final static byte INS_PUK= 0x02;  //vérifier le code PUK
    private final static byte UPD_PIN= 0x03;  //modifier le code PIN
    private final static byte RCV_FILE= 0x04; //recvoir le fichier
    private final static byte SIGNATURE= 0x05;  //Récupérer la clé privée
    private final static byte SEND_PUB= 0x06; //envoyer la la clé publique

    public static OwnerPIN pin,puk;

    public static void install(byte[] bArray, short bOffset, byte bLength) {

        new crypto();
    }


    protected crypto() {
        register();
         puk = new OwnerPIN(nbre_tentative, length);
         puk.update(code_puk, (short) 0, length);

         pin = new OwnerPIN(nbre_tentative, length);
         pin.update(code_pin, (short) 0, length);


        // publicKey = (RSAPublicKey) KeyBuilder.buildKey(KeyBuilder.TYPE_RSA_PUBLIC,KeyBuilder.LENGTH_RSA_512,true);
        // keyPair = new KeyPair(KeyPair.ALG_RSA, (short) publicKey.getSize()); 
        // publicKey = (RSAPublicKey) keyPair.getPublic();



    KeyPair  rsa_KeyPair = new KeyPair(KeyPair.ALG_RSA_CRT, KeyBuilder.LENGTH_RSA_512);
      rsa_KeyPair.genKeyPair();
      RSAPublicKey p = (RSAPublicKey) rsa_KeyPair.getPublic();
      //RSAPrivateKey rsa_PrivateCrtKey 0= (RSAPrivateKey) rsa_KeyPair.getPrivate();
      // cipherRSA = Cipher.getInstance(Cipher.ALG_RSA_PKCS1, false);
        }   


    public void process(APDU apdu) {
        byte[] buffer = apdu.getBuffer();
        if(selectingApplet())
            return;
        if(buffer[ISO7816.OFFSET_CLA] != CLA)
            ISOException.throwIt(ISO7816.SW_CLA_NOT_SUPPORTED);
        switch (buffer[ISO7816.OFFSET_INS]) 
        {


             case SEND_PUB :

            //this is to send the modulus
              p.getModulus(buffer, ISO7816.OFFSET_CDATA);
              apdu.setOutgoing();
              apdu.setOutgoingLength((short) 64);
              apdu.sendBytesLong(buffer, ISO7816.OFFSET_CDATA, (short) 64);

              case SIGNATURE :
                    Signature s = Signature.getInstance(Signature.ALG_RSA_SHA_PKCS1, false); 
                    s.init(privateKey, Signature.MODE_SIGN); 
                    short sigLen = s.sign(file,(short)0, (short)file.length,SignedFile, (short)0);                     
                    break;       
            default:
                    ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);
        }
    }
}  

Answer 1

You receive status word 6F 00 because you get a NullPointerException when accessing p on the line p.getModulus(...);. The reason for this is that the instance field p was never initialized (at least not with the code that you showed in your question above) and is, consequently, null.

Note that the line

RSAPublicKey p = (RSAPublicKey) rsa_KeyPair.getPublic();

does not assign the public key object to the the instance field p but to a local variable that is also named p and, thus, hides the instance field.