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.crypto;

import org.bouncycastle.crypto.params.AsymmetricKeyParameter;

public interface KeyEncoder
{
    byte[] getEncoded(AsymmetricKeyParameter keyParameter);
}