Estensione della classe EllipticCurve

[peppespe]

Sto cercando di estendere la classe java.security.spec.EllipticCurve nella seguente maniera:

package java.security.spec;

import java.math.BigInteger;

public class MyEllipticCurve extends EllipticCurve  {
	
	public static final BigInteger FOUR=new BigInteger("4");
	public static final BigInteger TW_FOUR=new BigInteger("27");
	
	public MyEllipticCurve(ECField field, BigInteger a, BigInteger b,
			byte[] seed) {
		super(field, a, b, seed);
		// TODO Auto-generated constructor stub
	}
	
	public MyEllipticCurve(ECField field, BigInteger a, BigInteger b) {
		super(field, a, b);
		// TODO Auto-generated constructor stub
	}
	
	public BigInteger getDelta(){
    	BigInteger first = getA().pow(3).multiply(FOUR);
    	BigInteger second = getB().pow(2).multiply(TW_FOUR); 
    	BigInteger delta = first.add(second);
    	return delta;
    }//getDelta
	
}

ma ho dei problemi per quanto riguarda la sua classe di test:

package esercizi;


import java.math.BigInteger;
import java.security.*;
import java.security.spec.ECFieldFp;
import java.security.spec.EllipticCurve;
import java.security.spec.MyEllipticCurve;

import algebra.BigIntegerMath;


public class EllipticCurveTest {
	public static void main(String[] args) {
        // TODO code application logic here
    	//lunghezza in bit del numero p del campo Z[p]
		int byteLength = 8;
		SecureRandom sr = new SecureRandom();
    	//numero di test
    	int numberBases = (int)(Math.random()*10)+1;
    	//numero da testare
    	BigInteger p=null;
    	//grandezza del numero
        byte[] ba=null;
        
        //genera un numero primo tramite test di Miller Rabin
        do {
            ba=new byte[byteLength];
            sr.nextBytes(ba);
            p=new BigInteger(1,ba);
        } while (BigIntegerMath.primeProbability(p,numberBases,sr)==0);
        
        //campo finito primo
        ECFieldFp f = new ECFieldFp(p);
        BigInteger a = BigInteger.ONE;
        BigInteger b = BigInteger.valueOf(19L);
        byte[] seed = new byte[24];
        
        //rappresenta il primo test
        MyEllipticCurve e = new MyEllipticCurve(f, a, b, seed);
        //output della curva al primo test
        System.out.println("E(Z["+p+"]) : Y^2 = X^3 + "+e.getA()+"X + "+e.getB());
        System.out.println("delta = "+e.getDelta());
        
    	
    }
}

il cui output consiste nel seguente messaggio di errore:

Exception in thread "main" java.lang.SecurityException: Prohibited package name: java.security.spec
	at java.lang.ClassLoader.preDefineClass(Unknown Source)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.access$000(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClassInternal(Unknown Source)
	at esercizi.EllipticCurveTest.main(EllipticCurveTest.java:40)