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package com.sun.crypto.provider;
import java.math.BigInteger;
import java.security.*;
import java.security.spec.*;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHGenParameterSpec;
/*
* This class generates parameters for the Diffie-Hellman algorithm.
* The parameters are a prime, a base, and optionally the length in bits of
* the private value.
*
* <p>The Diffie-Hellman parameter generation accepts the size in bits of the
* prime modulus and the size in bits of the random exponent as input.
* The size of the prime modulus defaults to 2048 bits.
*
* @author Jan Luehe
*
*
* @see java.security.AlgorithmParameters
* @see java.security.spec.AlgorithmParameterSpec
* @see DHParameters
*/
public final class DHParameterGenerator extends AlgorithmParameterGeneratorSpi {
// The size in bits of the prime modulus
private int primeSize = 2048;
// The size in bits of the random exponent (private value)
private int exponentSize = 0;
// The source of randomness
private SecureRandom random = null;
private static void checkKeySize(int keysize)
throws InvalidParameterException {
boolean supported = ((keysize == 2048) || (keysize == 3072) ||
((keysize >= 512) && (keysize <= 1024) && ((keysize & 0x3F) == 0)));
if (!supported) {
throw new InvalidParameterException(
"DH key size must be multiple of 64 and range " +
"from 512 to 1024 (inclusive), or 2048, 3072. " +
"The specific key size " + keysize + " is not supported");
}
}
/**
* Initializes this parameter generator for a certain keysize
* and source of randomness.
* The keysize is specified as the size in bits of the prime modulus.
*
* @param keysize the keysize (size of prime modulus) in bits
* @param random the source of randomness
*/
@Override
protected void engineInit(int keysize, SecureRandom random) {
checkKeySize(keysize);
this.primeSize = keysize;
this.random = random;
}
/**
* Initializes this parameter generator with a set of parameter
* generation values, which specify the size of the prime modulus and
* the size of the random exponent, both in bits.
*
* @param genParamSpec the set of parameter generation values
* @param random the source of randomness
*
* @exception InvalidAlgorithmParameterException if the given parameter
* generation values are inappropriate for this parameter generator
*/
@Override
protected void engineInit(AlgorithmParameterSpec genParamSpec,
SecureRandom random) throws InvalidAlgorithmParameterException {
if (!(genParamSpec instanceof DHGenParameterSpec)) {
throw new InvalidAlgorithmParameterException
("Inappropriate parameter type");
}
DHGenParameterSpec dhParamSpec = (DHGenParameterSpec)genParamSpec;
primeSize = dhParamSpec.getPrimeSize();
exponentSize = dhParamSpec.getExponentSize();
if ((exponentSize <= 0) || (exponentSize >= primeSize)) {
throw new InvalidAlgorithmParameterException(
"Exponent size (" + exponentSize +
") must be positive and less than modulus size (" +
primeSize + ")");
}
try {
checkKeySize(primeSize);
} catch (InvalidParameterException ipe) {
throw new InvalidAlgorithmParameterException(ipe.getMessage());
}
this.random = random;
}
/**
* Generates the parameters.
*
* @return the new AlgorithmParameters object
*/
@Override
protected AlgorithmParameters engineGenerateParameters() {
if (random == null) {
random = SunJCE.getRandom();
}
BigInteger paramP = null;
BigInteger paramG = null;
try {
AlgorithmParameterGenerator dsaParamGen =
AlgorithmParameterGenerator.getInstance("DSA");
dsaParamGen.init(primeSize, random);
AlgorithmParameters dsaParams = dsaParamGen.generateParameters();
DSAParameterSpec dsaParamSpec =
dsaParams.getParameterSpec(DSAParameterSpec.class);
DHParameterSpec dhParamSpec;
if (this.exponentSize > 0) {
dhParamSpec = new DHParameterSpec(dsaParamSpec.getP(),
dsaParamSpec.getG(),
this.exponentSize);
} else {
dhParamSpec = new DHParameterSpec(dsaParamSpec.getP(),
dsaParamSpec.getG());
}
AlgorithmParameters algParams =
AlgorithmParameters.getInstance("DH", SunJCE.getInstance());
algParams.init(dhParamSpec);
return algParams;
} catch (Exception ex) {
throw new ProviderException("Unexpected exception", ex);
}
}
}