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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.AlgorithmParameterSpec;
import java.security.spec.InvalidParameterSpecException;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHGenParameterSpec;
import sun.security.provider.ParameterCache;
/**
* This class represents the key pair generator for Diffie-Hellman key pairs.
*
* <p>This key pair generator may be initialized in two different ways:
*
* <ul>
* <li>By providing the size in bits of the prime modulus -
* This will be used to create a prime modulus and base generator, which will
* then be used to create the Diffie-Hellman key pair. The default size of the
* prime modulus is 1024 bits.
* <li>By providing a prime modulus and base generator
* </ul>
*
* @author Jan Luehe
*
*
* @see java.security.KeyPairGenerator
*/
public final class DHKeyPairGenerator extends KeyPairGeneratorSpi {
// parameters to use or null if not specified
private DHParameterSpec params;
// The size in bits of the prime modulus
private int pSize;
// The size in bits of the random exponent (private value)
private int lSize;
// The source of randomness
private SecureRandom random;
public DHKeyPairGenerator() {
super();
initialize(1024, null);
}
/**
* Initializes this key pair 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
*/
public void initialize(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.pSize = keysize;
this.lSize = 0;
this.random = random;
this.params = null;
}
/**
* Initializes this key pair generator for the specified parameter
* set and source of randomness.
*
* <p>The given parameter set contains the prime modulus, the base
* generator, and optionally the requested size in bits of the random
* exponent (private value).
*
* @param params the parameter set used to generate the key pair
* @param random the source of randomness
*
* @exception InvalidAlgorithmParameterException if the given parameters
* are inappropriate for this key pair generator
*/
public void initialize(AlgorithmParameterSpec algParams,
SecureRandom random) throws InvalidAlgorithmParameterException {
if (!(algParams instanceof DHParameterSpec)){
throw new InvalidAlgorithmParameterException
("Inappropriate parameter type");
}
params = (DHParameterSpec)algParams;
pSize = params.getP().bitLength();
if ((pSize < 512) || (pSize > 1024) ||
(pSize % 64 != 0)) {
throw new InvalidAlgorithmParameterException
("Prime size must be multiple of 64, and can only range "
+ "from 512 to 1024 (inclusive)");
}
// exponent size is optional, could be 0
lSize = params.getL();
// Require exponentSize < primeSize
if ((lSize != 0) && (lSize > pSize)) {
throw new InvalidAlgorithmParameterException
("Exponent size must not be larger than modulus size");
}
this.random = random;
}
/**
* Generates a key pair.
*
* @return the new key pair
*/
public KeyPair generateKeyPair() {
if (random == null) {
random = SunJCE.RANDOM;
}
if (params == null) {
try {
params = ParameterCache.getDHParameterSpec(pSize, random);
} catch (GeneralSecurityException e) {
// should never happen
throw new ProviderException(e);
}
}
BigInteger p = params.getP();
BigInteger g = params.getG();
if (lSize <= 0) {
// use an exponent size of (pSize / 2) but at least 384 bits
lSize = Math.max(384, pSize >> 1);
// if lSize is larger than pSize, limit by pSize
lSize = Math.min(lSize, pSize);
}
BigInteger x;
BigInteger pMinus2 = p.subtract(BigInteger.valueOf(2));
//
// Handbook of Applied Cryptography: Menezes, et.al.
// Repeat if the following does not hold:
// 1 <= x <= p-2
//
do {
// generate random x up to 2^lSize bits long
x = new BigInteger(lSize, random);
} while ((x.compareTo(BigInteger.ONE) < 0) ||
((x.compareTo(pMinus2) > 0)));
// calculate public value y
BigInteger y = g.modPow(x, p);
DHPublicKey pubKey = new DHPublicKey(y, p, g, lSize);
DHPrivateKey privKey = new DHPrivateKey(x, p, g, lSize);
return new KeyPair(pubKey, privKey);
}
}