package org.bouncycastle.crypto.generators; import java.math.BigInteger; import java.security.SecureRandom; import org.bouncycastle.crypto.AsymmetricCipherKeyPair; import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator; import org.bouncycastle.crypto.KeyGenerationParameters; import org.bouncycastle.crypto.params.DSAKeyGenerationParameters; import org.bouncycastle.crypto.params.DSAParameters; import org.bouncycastle.crypto.params.DSAPrivateKeyParameters; import org.bouncycastle.crypto.params.DSAPublicKeyParameters; import org.bouncycastle.math.ec.WNafUtil; import org.bouncycastle.util.BigIntegers; /** * a DSA key pair generator. * * This generates DSA keys in line with the method described * in <i>FIPS 186-3 B.1 FFC Key Pair Generation</i>. */ public class DSAKeyPairGenerator implements AsymmetricCipherKeyPairGenerator { private static final BigInteger ONE = BigInteger.valueOf(1); private DSAKeyGenerationParameters param; public void init( KeyGenerationParameters param) { this.param = (DSAKeyGenerationParameters)param; } public AsymmetricCipherKeyPair generateKeyPair() { DSAParameters dsaParams = param.getParameters(); BigInteger x = generatePrivateKey(dsaParams.getQ(), param.getRandom()); BigInteger y = calculatePublicKey(dsaParams.getP(), dsaParams.getG(), x); return new AsymmetricCipherKeyPair( new DSAPublicKeyParameters(y, dsaParams), new DSAPrivateKeyParameters(x, dsaParams)); } private static BigInteger generatePrivateKey(BigInteger q, SecureRandom random) { // B.1.2 Key Pair Generation by Testing Candidates int minWeight = q.bitLength() >>> 2; for (;;) { // TODO Prefer this method? (change test cases that used fixed random) // B.1.1 Key Pair Generation Using Extra Random Bits // BigInteger x = new BigInteger(q.bitLength() + 64, random).mod(q.subtract(ONE)).add(ONE); BigInteger x = BigIntegers.createRandomInRange(ONE, q.subtract(ONE), random); if (WNafUtil.getNafWeight(x) >= minWeight) { return x; } } } private static BigInteger calculatePublicKey(BigInteger p, BigInteger g, BigInteger x) { return g.modPow(x, p); } }