package org.bouncycastle.crypto.agreement;
import java.math.BigInteger;
import org.bouncycastle.crypto.BasicAgreement;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.math.ec.ECPoint;
/**
* 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 int getFieldSize()
{
return (key.getParameters().getCurve().getFieldSize() + 7) / 8;
}
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();
}
}