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 1.8.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.pqc.jcajce.interfaces;

import java.security.PrivateKey;

public interface NHPrivateKey
    extends NHKey, PrivateKey
{
    short[] getSecretData();
}