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package org.bouncycastle.crypto.ec;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.math.ec.ECMultiplier;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.math.ec.FixedPointCombMultiplier;
/**
* this does your basic ElGamal encryption algorithm using EC
*/
public class ECElGamalEncryptor
implements ECEncryptor
{
private ECPublicKeyParameters key;
private SecureRandom random;
/**
* initialise the encryptor.
*
* @param param the necessary EC key parameters.
*/
public void init(
CipherParameters param)
{
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom p = (ParametersWithRandom)param;
if (!(p.getParameters() instanceof ECPublicKeyParameters))
{
throw new IllegalArgumentException("ECPublicKeyParameters are required for encryption.");
}
this.key = (ECPublicKeyParameters)p.getParameters();
this.random = p.getRandom();
}
else
{
if (!(param instanceof ECPublicKeyParameters))
{
throw new IllegalArgumentException("ECPublicKeyParameters are required for encryption.");
}
this.key = (ECPublicKeyParameters)param;
this.random = new SecureRandom();
}
}
/**
* Process a single EC point using the basic ElGamal algorithm.
*
* @param point the EC point to process.
* @return the result of the Elgamal process.
*/
public ECPair encrypt(ECPoint point)
{
if (key == null)
{
throw new IllegalStateException("ECElGamalEncryptor not initialised");
}
ECDomainParameters ec = key.getParameters();
BigInteger k = ECUtil.generateK(ec.getN(), random);
ECMultiplier basePointMultiplier = createBasePointMultiplier();
ECPoint[] gamma_phi = new ECPoint[]{
basePointMultiplier.multiply(ec.getG(), k),
key.getQ().multiply(k).add(point)
};
ec.getCurve().normalizeAll(gamma_phi);
return new ECPair(gamma_phi[0], gamma_phi[1]);
}
protected ECMultiplier createBasePointMultiplier()
{
return new FixedPointCombMultiplier();
}
}
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