package org.bouncycastle.crypto.agreement;import java.math.BigInteger;import org.bouncycastle.math.ec.ECPoint;import org.bouncycastle.crypto.BasicAgreement;import org.bouncycastle.crypto.CipherParameters;import org.bouncycastle.crypto.params.ECPublicKeyParameters;import org.bouncycastle.crypto.params.ECPrivateKeyParameters;import org.bouncycastle.crypto.params.ECDomainParameters;/** * P1363 7.2.2 ECSVDP-DHC * * ECSVDP-DHC is Elliptic Curve Secret Value Derivation Primitive, * Diffie-Hellman version with cofactor multiplication. It is based on * the work of [DH76], [Mil86], [Kob87], [LMQ98] and [Kal98a]. This * primitive derives a shared secret value from one party's private key * and another party's public key, where both have the same set of EC * domain parameters. If two parties correctly execute this primitive, * they will produce the same output. This primitive can be invoked by a * scheme to derive a shared secret key; specifically, it may be used * with the schemes ECKAS-DH1 and DL/ECKAS-DH2. It does not assume the * validity of the input public key (see also Section 7.2.1). * <p> * Note: As stated P1363 compatability mode with ECDH can be preset, and * in this case the implementation doesn't have a ECDH compatability mode * (if you want that just use ECDHBasicAgreement and note they both implement * BasicAgreement!). */public class ECDHCBasicAgreement    implements BasicAgreement{    ECPrivateKeyParameters key;    public void init(        CipherParameters key)    {        this.key = (ECPrivateKeyParameters)key;    }    public BigInteger calculateAgreement(        CipherParameters pubKey)    {        ECPublicKeyParameters   pub = (ECPublicKeyParameters)pubKey;        ECDomainParameters      params = pub.getParameters();        ECPoint P = pub.getQ().multiply(params.getH().multiply(key.getD()));        // if (p.isInfinity()) throw new RuntimeException("Invalid public key");        return P.getX().toBigInteger();    }}