package org.bouncycastle.crypto.generators;
import java.math.BigInteger;
import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator;
import org.bouncycastle.crypto.KeyGenerationParameters;
import org.bouncycastle.crypto.params.ElGamalKeyGenerationParameters;
import org.bouncycastle.crypto.params.ElGamalParameters;
import org.bouncycastle.crypto.params.ElGamalPrivateKeyParameters;
import org.bouncycastle.crypto.params.ElGamalPublicKeyParameters;
/**
* a ElGamal key pair generator.
* <p>
* This generates keys consistent for use with ElGamal as described in
* page 164 of "Handbook of Applied Cryptography".
*/
public class ElGamalKeyPairGenerator
implements AsymmetricCipherKeyPairGenerator
{
private ElGamalKeyGenerationParameters param;
public void init(
KeyGenerationParameters param)
{
this.param = (ElGamalKeyGenerationParameters)param;
}
public AsymmetricCipherKeyPair generateKeyPair()
{
BigInteger p, g, x, y;
int qLength = param.getStrength() - 1;
ElGamalParameters elParams = param.getParameters();
p = elParams.getP();
g = elParams.getG();
//
// calculate the private key
//
x = new BigInteger(qLength, param.getRandom());
//
// calculate the public key.
//
y = g.modPow(x, p);
return new AsymmetricCipherKeyPair(
new ElGamalPublicKeyParameters(y, elParams),
new ElGamalPrivateKeyParameters(x, elParams));
}
}