1package org.bouncycastle.crypto.generators;
2
3import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
4import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator;
5import org.bouncycastle.crypto.KeyGenerationParameters;
6import org.bouncycastle.crypto.params.DSAKeyGenerationParameters;
7import org.bouncycastle.crypto.params.DSAParameters;
8import org.bouncycastle.crypto.params.DSAPrivateKeyParameters;
9import org.bouncycastle.crypto.params.DSAPublicKeyParameters;
10import org.bouncycastle.util.BigIntegers;
11
12import java.math.BigInteger;
13import java.security.SecureRandom;
14
15/**
16 * a DSA key pair generator.
17 *
18 * This generates DSA keys in line with the method described
19 * in <i>FIPS 186-3 B.1 FFC Key Pair Generation</i>.
20 */
21public class DSAKeyPairGenerator
22    implements AsymmetricCipherKeyPairGenerator
23{
24    private static final BigInteger ONE = BigInteger.valueOf(1);
25
26    private DSAKeyGenerationParameters param;
27
28    public void init(
29        KeyGenerationParameters param)
30    {
31        this.param = (DSAKeyGenerationParameters)param;
32    }
33
34    public AsymmetricCipherKeyPair generateKeyPair()
35    {
36        DSAParameters dsaParams = param.getParameters();
37
38        BigInteger x = generatePrivateKey(dsaParams.getQ(), param.getRandom());
39        BigInteger y = calculatePublicKey(dsaParams.getP(), dsaParams.getG(), x);
40
41        return new AsymmetricCipherKeyPair(
42            new DSAPublicKeyParameters(y, dsaParams),
43            new DSAPrivateKeyParameters(x, dsaParams));
44    }
45
46    private static BigInteger generatePrivateKey(BigInteger q, SecureRandom random)
47    {
48        // TODO Prefer this method? (change test cases that used fixed random)
49        // B.1.1 Key Pair Generation Using Extra Random Bits
50//        BigInteger c = new BigInteger(q.bitLength() + 64, random);
51//        return c.mod(q.subtract(ONE)).add(ONE);
52
53        // B.1.2 Key Pair Generation by Testing Candidates
54        return BigIntegers.createRandomInRange(ONE, q.subtract(ONE), random);
55    }
56
57    private static BigInteger calculatePublicKey(BigInteger p, BigInteger g, BigInteger x)
58    {
59        return g.modPow(x, p);
60    }
61}
62