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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.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
// BEGIN android-added
import org.bouncycastle.math.ec.ECCurve;
// END android-added
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)
{
// BEGIN android-changed
ECPoint peerPoint = ((ECPublicKeyParameters) pubKey).getQ();
ECCurve myCurve = key.getParameters().getCurve();
if (peerPoint.isInfinity()) {
throw new IllegalStateException("Infinity is not a valid public key for ECDH");
}
try {
myCurve.validatePoint(peerPoint.getXCoord().toBigInteger(),
peerPoint.getYCoord().toBigInteger());
} catch (IllegalArgumentException ex) {
throw new IllegalStateException("The peer public key must be on the curve for ECDH");
}
// Explicitly construct a public key using the private key's curve.
ECPoint pubPoint = myCurve.createPoint(peerPoint.getXCoord().toBigInteger(),
peerPoint.getYCoord().toBigInteger());
ECPublicKeyParameters pub = (ECPublicKeyParameters)pubKey;
if (!pub.getParameters().equals(key.getParameters()))
{
throw new IllegalStateException("ECDH public key has wrong domain parameters");
}
ECPoint P = pubPoint.multiply(key.getD()).normalize();
// END android-changed
if (P.isInfinity())
{
throw new IllegalStateException("Infinity is not a valid agreement value for ECDH");
}
return P.getAffineXCoord().toBigInteger();
}
}
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