/*
* $HeadURL: http://juliusdavies.ca/svn/not-yet-commons-ssl/trunk/src/java/org/apache/commons/ssl/Certificates.java $
* $Revision: 121 $
* $Date: 2007-11-13 21:26:57 -0800 (Tue, 13 Nov 2007) $
*
* ====================================================================
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.commons.ssl.util;
import java.math.BigInteger;
import java.security.GeneralSecurityException;
import java.security.KeyException;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.DSAParams;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.spec.DSAPublicKeySpec;
import java.security.spec.RSAPublicKeySpec;
/**
* Utility class for deriving a public key from a given private key.
*
* @author Chad La Joie <lajoie OF georgetown.edu>
* @since November 14th, 2007
*/
public class PublicKeyDeriver {
/**
* Utility method for deriving a public key from a given private key.
*
* @param key private key for which we need a public key (DSA or RSA).
* @return the corresponding public key
* @throws GeneralSecurityException if it didn't work
*/
public static PublicKey derivePublicKey(PrivateKey key) throws GeneralSecurityException {
if (key instanceof DSAPrivateKey) {
DSAPrivateKey dsaKey = (DSAPrivateKey) key;
DSAParams keyParams = dsaKey.getParams();
BigInteger g = keyParams.getG();
BigInteger p = keyParams.getP();
BigInteger q = keyParams.getQ();
BigInteger x = dsaKey.getX();
BigInteger y = q.modPow(x, p);
DSAPublicKeySpec keySpec = new DSAPublicKeySpec(y, p, q, g);
return KeyFactory.getInstance("DSA").generatePublic(keySpec);
} else if (key instanceof RSAPrivateCrtKey) {
RSAPrivateCrtKey rsaKey = (RSAPrivateCrtKey) key;
BigInteger modulus = rsaKey.getModulus();
BigInteger exponent = rsaKey.getPublicExponent();
RSAPublicKeySpec keySpec = new RSAPublicKeySpec(modulus, exponent);
return KeyFactory.getInstance("RSA").generatePublic(keySpec);
} else {
throw new KeyException("Private key was not a DSA or RSA key");
}
}
}