001 /*
002 * $HeadURL: http://juliusdavies.ca/svn/not-yet-commons-ssl/trunk/src/java/org/apache/commons/ssl/Certificates.java $
003 * $Revision: 121 $
004 * $Date: 2007-11-13 21:26:57 -0800 (Tue, 13 Nov 2007) $
005 *
006 * ====================================================================
007 * Licensed to the Apache Software Foundation (ASF) under one
008 * or more contributor license agreements. See the NOTICE file
009 * distributed with this work for additional information
010 * regarding copyright ownership. The ASF licenses this file
011 * to you under the Apache License, Version 2.0 (the
012 * "License"); you may not use this file except in compliance
013 * with the License. You may obtain a copy of the License at
014 *
015 * http://www.apache.org/licenses/LICENSE-2.0
016 *
017 * Unless required by applicable law or agreed to in writing,
018 * software distributed under the License is distributed on an
019 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
020 * KIND, either express or implied. See the License for the
021 * specific language governing permissions and limitations
022 * under the License.
023 * ====================================================================
024 *
025 * This software consists of voluntary contributions made by many
026 * individuals on behalf of the Apache Software Foundation. For more
027 * information on the Apache Software Foundation, please see
028 * <http://www.apache.org/>.
029 *
030 */
031 package org.apache.commons.ssl.util;
032
033 import java.math.BigInteger;
034 import java.security.GeneralSecurityException;
035 import java.security.KeyException;
036 import java.security.KeyFactory;
037 import java.security.PrivateKey;
038 import java.security.PublicKey;
039 import java.security.interfaces.DSAParams;
040 import java.security.interfaces.DSAPrivateKey;
041 import java.security.interfaces.RSAPrivateCrtKey;
042 import java.security.spec.DSAPublicKeySpec;
043 import java.security.spec.RSAPublicKeySpec;
044
045 /**
046 * Utility class for deriving a public key from a given private key.
047 *
048 * @author Chad La Joie <lajoie OF georgetown.edu>
049 * @since November 14th, 2007
050 */
051 public class PublicKeyDeriver {
052
053 /**
054 * Utility method for deriving a public key from a given private key.
055 *
056 * @param key private key for which we need a public key (DSA or RSA).
057 * @return the corresponding public key
058 * @throws GeneralSecurityException if it didn't work
059 */
060 public static PublicKey derivePublicKey(PrivateKey key) throws GeneralSecurityException {
061 if (key instanceof DSAPrivateKey) {
062 DSAPrivateKey dsaKey = (DSAPrivateKey) key;
063 DSAParams keyParams = dsaKey.getParams();
064 BigInteger g = keyParams.getG();
065 BigInteger p = keyParams.getP();
066 BigInteger q = keyParams.getQ();
067 BigInteger x = dsaKey.getX();
068 BigInteger y = q.modPow(x, p);
069 DSAPublicKeySpec keySpec = new DSAPublicKeySpec(y, p, q, g);
070 return KeyFactory.getInstance("DSA").generatePublic(keySpec);
071 } else if (key instanceof RSAPrivateCrtKey) {
072 RSAPrivateCrtKey rsaKey = (RSAPrivateCrtKey) key;
073 BigInteger modulus = rsaKey.getModulus();
074 BigInteger exponent = rsaKey.getPublicExponent();
075 RSAPublicKeySpec keySpec = new RSAPublicKeySpec(modulus, exponent);
076 return KeyFactory.getInstance("RSA").generatePublic(keySpec);
077 } else {
078 throw new KeyException("Private key was not a DSA or RSA key");
079 }
080 }
081 }
082