http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.7. 
package org.bouncycastle.jce.interfaces;

import java.math.BigInteger;
import java.security.PrivateKey;

public interface ElGamalPrivateKey
    extends ElGamalKey, PrivateKey
{
    public BigInteger getX();
}