1package org.bouncycastle.crypto.generators; 2 3import java.math.BigInteger; 4import java.security.SecureRandom; 5 6import org.bouncycastle.crypto.AsymmetricCipherKeyPair; 7import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator; 8import org.bouncycastle.crypto.KeyGenerationParameters; 9import org.bouncycastle.crypto.params.DSAKeyGenerationParameters; 10import org.bouncycastle.crypto.params.DSAParameters; 11import org.bouncycastle.crypto.params.DSAPrivateKeyParameters; 12import org.bouncycastle.crypto.params.DSAPublicKeyParameters; 13import org.bouncycastle.math.ec.WNafUtil; 14import org.bouncycastle.util.BigIntegers; 15 16/** 17 * a DSA key pair generator. 18 * 19 * This generates DSA keys in line with the method described 20 * in <i>FIPS 186-3 B.1 FFC Key Pair Generation</i>. 21 */ 22public class DSAKeyPairGenerator 23 implements AsymmetricCipherKeyPairGenerator 24{ 25 private static final BigInteger ONE = BigInteger.valueOf(1); 26 27 private DSAKeyGenerationParameters param; 28 29 public void init( 30 KeyGenerationParameters param) 31 { 32 this.param = (DSAKeyGenerationParameters)param; 33 } 34 35 public AsymmetricCipherKeyPair generateKeyPair() 36 { 37 DSAParameters dsaParams = param.getParameters(); 38 39 BigInteger x = generatePrivateKey(dsaParams.getQ(), param.getRandom()); 40 BigInteger y = calculatePublicKey(dsaParams.getP(), dsaParams.getG(), x); 41 42 return new AsymmetricCipherKeyPair( 43 new DSAPublicKeyParameters(y, dsaParams), 44 new DSAPrivateKeyParameters(x, dsaParams)); 45 } 46 47 private static BigInteger generatePrivateKey(BigInteger q, SecureRandom random) 48 { 49 // B.1.2 Key Pair Generation by Testing Candidates 50 int minWeight = q.bitLength() >>> 2; 51 for (;;) 52 { 53 // TODO Prefer this method? (change test cases that used fixed random) 54 // B.1.1 Key Pair Generation Using Extra Random Bits 55// BigInteger x = new BigInteger(q.bitLength() + 64, random).mod(q.subtract(ONE)).add(ONE); 56 57 BigInteger x = BigIntegers.createRandomInRange(ONE, q.subtract(ONE), random); 58 if (WNafUtil.getNafWeight(x) >= minWeight) 59 { 60 return x; 61 } 62 } 63 } 64 65 private static BigInteger calculatePublicKey(BigInteger p, BigInteger g, BigInteger x) 66 { 67 return g.modPow(x, p); 68 } 69} 70