package org.bouncycastle.crypto;import java.math.BigInteger;/** * The basic interface that basic Diffie-Hellman implementations * conforms to. */public interface BasicAgreement{    /**     * initialise the agreement engine.     */    public void init(CipherParameters param);    /**     * given a public key from a given party calculate the next     * message in the agreement sequence.      */    public BigInteger calculateAgreement(CipherParameters pubKey);}