bcprov/src/main/java/org/bouncycastle/crypto/generators/ElGamalKeyPairGenerator.java


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44

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.DHParameters;
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()
    {
        DHKeyGeneratorHelper helper = DHKeyGeneratorHelper.INSTANCE;
        ElGamalParameters egp = param.getParameters();
        DHParameters dhp = new DHParameters(egp.getP(), egp.getG(), null, egp.getL());  

        BigInteger x = helper.calculatePrivate(dhp, param.getRandom()); 
        BigInteger y = helper.calculatePublic(dhp, x);

        return new AsymmetricCipherKeyPair(
            new ElGamalPublicKeyParameters(y, egp),
            new ElGamalPrivateKeyParameters(x, egp));
    }
}