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package org.bouncycastle.crypto.agreement;
import java.math.BigInteger;
import org.bouncycastle.crypto.BasicAgreement;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.params.MQVPrivateParameters;
import org.bouncycastle.crypto.params.MQVPublicParameters;
import org.bouncycastle.math.ec.ECAlgorithms;
import org.bouncycastle.math.ec.ECConstants;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECPoint;
public class ECMQVBasicAgreement
implements BasicAgreement
{
MQVPrivateParameters privParams;
public void init(
CipherParameters key)
{
this.privParams = (MQVPrivateParameters)key;
}
public int getFieldSize()
{
return (privParams.getStaticPrivateKey().getParameters().getCurve().getFieldSize() + 7) / 8;
}
public BigInteger calculateAgreement(CipherParameters pubKey)
{
MQVPublicParameters pubParams = (MQVPublicParameters)pubKey;
ECPrivateKeyParameters staticPrivateKey = privParams.getStaticPrivateKey();
ECPoint agreement = calculateMqvAgreement(staticPrivateKey.getParameters(), staticPrivateKey,
privParams.getEphemeralPrivateKey(), privParams.getEphemeralPublicKey(),
pubParams.getStaticPublicKey(), pubParams.getEphemeralPublicKey()).normalize();
if (agreement.isInfinity())
{
throw new IllegalStateException("Infinity is not a valid agreement value for MQV");
}
return agreement.getAffineXCoord().toBigInteger();
}
// The ECMQV Primitive as described in SEC-1, 3.4
private ECPoint calculateMqvAgreement(
ECDomainParameters parameters,
ECPrivateKeyParameters d1U,
ECPrivateKeyParameters d2U,
ECPublicKeyParameters Q2U,
ECPublicKeyParameters Q1V,
ECPublicKeyParameters Q2V)
{
BigInteger n = parameters.getN();
int e = (n.bitLength() + 1) / 2;
BigInteger powE = ECConstants.ONE.shiftLeft(e);
ECCurve curve = parameters.getCurve();
ECPoint[] points = new ECPoint[]{
// The Q2U public key is optional
ECAlgorithms.importPoint(curve, Q2U == null ? parameters.getG().multiply(d2U.getD()) : Q2U.getQ()),
ECAlgorithms.importPoint(curve, Q1V.getQ()),
ECAlgorithms.importPoint(curve, Q2V.getQ())
};
curve.normalizeAll(points);
ECPoint q2u = points[0], q1v = points[1], q2v = points[2];
BigInteger x = q2u.getAffineXCoord().toBigInteger();
BigInteger xBar = x.mod(powE);
BigInteger Q2UBar = xBar.setBit(e);
BigInteger s = d1U.getD().multiply(Q2UBar).add(d2U.getD()).mod(n);
BigInteger xPrime = q2v.getAffineXCoord().toBigInteger();
BigInteger xPrimeBar = xPrime.mod(powE);
BigInteger Q2VBar = xPrimeBar.setBit(e);
BigInteger hs = parameters.getH().multiply(s).mod(n);
return ECAlgorithms.sumOfTwoMultiplies(
q1v, Q2VBar.multiply(hs).mod(n), q2v, hs);
}
}
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