com.bouncycastle.crypto.agreement.ECDHCBasicAgreement Maven / Gradle / Ivy
package com.bouncycastle.crypto.agreement;
import java.math.BigInteger;
import com.bouncycastle.math.ec.ECPoint;
import com.bouncycastle.crypto.BasicAgreement;
import com.bouncycastle.crypto.CipherParameters;
import com.bouncycastle.crypto.params.ECPublicKeyParameters;
import com.bouncycastle.crypto.params.ECPrivateKeyParameters;
import com.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).
*
* Note: As stated P1363 compatibility mode with ECDH can be preset, and
* in this case the implementation doesn't have a ECDH compatibility 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();
}
}