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