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. 
package org.bouncycastle.jce.interfaces;

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


interface for Elliptic Curve Private keys.

/**
 * interface for Elliptic Curve Private keys.
 */
public interface ECPrivateKey
    extends ECKey, PrivateKey
{
    
return the private value D.

/**
     * return the private value D.
     */
    public BigInteger getD();
}