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; /** * P1363 7.2.1 ECSVDP-DH * * ECSVDP-DH is Elliptic Curve Secret Value Derivation Primitive, * Diffie-Hellman version. It is based on the work of [DH76], [Mil86], * and [Kob87]. 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 assumes that the input keys are valid (see also * Section 7.2.2). */ public class ECDHBasicAgreement implements BasicAgreement { private ECPrivateKeyParameters key; public void init( CipherParameters key) { this.key = (ECPrivateKeyParameters)key; } public BigInteger calculateAgreement( CipherParameters pubKey) { ECPublicKeyParameters pub = (ECPublicKeyParameters)pubKey; ECPoint P = pub.getQ().multiply(key.getD()); // if ( p.isInfinity() ) throw new RuntimeException("d*Q == infinity"); return P.getX().toBigInteger(); } }