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* accompanied this code).
*
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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 1024 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 = 1024;
// The size in bits of the random exponent (private value)
private int exponentSize = 0;
// The source of randomness
private SecureRandom random = null;
/**
* 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
*/
protected void engineInit(int keysize, SecureRandom random) {
if ((keysize < 512) || (keysize > 1024) || (keysize % 64 != 0)) {
throw new InvalidParameterException("Keysize must be multiple "
+ "of 64, and can only range "
+ "from 512 to 1024 "
+ "(inclusive)");
}
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 params 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
*/
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();
if ((primeSize<512) || (primeSize>1024) || (primeSize%64 != 0)) {
throw new InvalidAlgorithmParameterException
("Modulus size must be multiple of 64, and can only range "
+ "from 512 to 1024 (inclusive)");
}
exponentSize = dhParamSpec.getExponentSize();
if (exponentSize <= 0) {
throw new InvalidAlgorithmParameterException
("Exponent size must be greater than zero");
}
// Require exponentSize < primeSize
if (exponentSize >= primeSize) {
throw new InvalidAlgorithmParameterException
("Exponent size must be less than modulus size");
}
}
/**
* Generates the parameters.
*
* @return the new AlgorithmParameters object
*/
protected AlgorithmParameters engineGenerateParameters() {
AlgorithmParameters algParams = null;
if (this.exponentSize == 0) {
this.exponentSize = this.primeSize - 1;
}
if (this.random == null)
this.random = SunJCE.RANDOM;
try {
AlgorithmParameterGenerator paramGen;
DSAParameterSpec dsaParamSpec;
paramGen = AlgorithmParameterGenerator.getInstance("DSA");
paramGen.init(this.primeSize, random);
algParams = paramGen.generateParameters();
dsaParamSpec = (DSAParameterSpec)
algParams.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());
}
algParams = AlgorithmParameters.getInstance("DH", "SunJCE");
algParams.init(dhParamSpec);
} catch (InvalidParameterSpecException e) {
// this should never happen
throw new RuntimeException(e.getMessage());
} catch (NoSuchAlgorithmException e) {
// this should never happen, because we provide it
throw new RuntimeException(e.getMessage());
} catch (NoSuchProviderException e) {
// this should never happen, because we provide it
throw new RuntimeException(e.getMessage());
}
return algParams;
}
}