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/*
 * $HeadURL: http://juliusdavies.ca/svn/not-yet-commons-ssl/tags/commons-ssl-0.3.9/src/java/org/apache/commons/ssl/X509CertificateChainBuilder.java $
 * $Revision: 121 $
 * $Date: 2007-11-14 05:26:57 +0000 (Wed, 14 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
 * .
 *
 */

package org.apache.commons.ssl;

import java.io.FileInputStream;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SignatureException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;

/**
 * Utility for building X509 certificate chains.
 *
 * @author Credit Union Central of British Columbia
 * @author www.cucbc.com
 * @author [email protected]
 * @since 16-Nov-2005
 */
public class X509CertificateChainBuilder {
    /**
     * Builds the ordered certificate chain upwards from the startingPoint.
     * Uses the supplied X509Certificate[] array to search for the parent,
     * grandparent, and higher ancestor certificates.  Stops at self-signed
     * certificates, or when no ancestor can be found.
     * 
     * Thanks to Joe Whitney for helping me put together a Big-O( m * n )
     * implementation where m = the length of the final certificate chain.
     * For a while I was using a Big-O( n ^ 2 ) implementation!
     *
     * @param startingPoint the X509Certificate for which we want to find
     *                      ancestors
     * @param certificates  A pool of certificates in which we expect to find
     *                      the startingPoint's ancestors.
     * @return Array of X509Certificates, starting with the "startingPoint" and
     *         ending with highest level ancestor we could find in the supplied
     *         collection.
     * @throws java.security.NoSuchAlgorithmException
     *          on unsupported signature
     *          algorithms.
     * @throws java.security.InvalidKeyException
     *          on incorrect key.
     * @throws java.security.NoSuchProviderException
     *          if there's no default provider.
     * @throws java.security.cert.CertificateException
     *          on encoding errors.
     */
    public static X509Certificate[] buildPath(X509Certificate startingPoint,
                                              Certificate[] certificates)
        throws NoSuchAlgorithmException, InvalidKeyException,
        NoSuchProviderException, CertificateException {
        // Use a LinkedList, because we do lots of random it.remove() operations.
        return buildPath(startingPoint,
            new LinkedList(Arrays.asList(certificates)));
    }

    /**
     * Builds the ordered certificate chain upwards from the startingPoint.
     * Uses the supplied collection to search for the parent, grandparent,
     * and higher ancestor certificates.  Stops at self-signed certificates,
     * or when no ancestor can be found.
     * 
     * Thanks to Joe Whitney for helping me put together a Big-O( m * n )
     * implementation where m = the length of the final certificate chain.
     * For a while I was using a Big-O( n ^ 2 ) implementation!
     *
     * @param startingPoint the X509Certificate for which we want to find
     *                      ancestors
     * @param certificates  A pool of certificates in which we expect to find
     *                      the startingPoint's ancestors.
     * @return Array of X509Certificates, starting with the "startingPoint" and
     *         ending with highest level ancestor we could find in the supplied
     *         collection.
     * @throws java.security.NoSuchAlgorithmException
     *          on unsupported signature
     *          algorithms.
     * @throws java.security.InvalidKeyException
     *          on incorrect key.
     * @throws java.security.NoSuchProviderException
     *          if there's no default provider.
     * @throws java.security.cert.CertificateException
     *          on encoding errors.
     */
    public static X509Certificate[] buildPath(X509Certificate startingPoint,
                                              Collection certificates)
        throws NoSuchAlgorithmException, InvalidKeyException,
        NoSuchProviderException, CertificateException {
        LinkedList path = new LinkedList();
        path.add(startingPoint);
        boolean nodeAdded = true;
        // Keep looping until an iteration happens where we don't add any nodes
        // to our path.
        while (nodeAdded) {
            // We'll start out by assuming nothing gets added.  If something
            // gets added, then nodeAdded will be changed to "true".
            nodeAdded = false;
            X509Certificate top = (X509Certificate) path.getLast();
            try {
                top.verify(top.getPublicKey());
                // We're self-signed, so we're done!
                break;
            }
            catch (SignatureException se) {
                // Not self-signed.  Let's see if we're signed by anyone in the
                // collection.
                Iterator it = certificates.iterator();
                while (it.hasNext()) {
                    X509Certificate x509 = (X509Certificate) it.next();
                    try {
                        top.verify(x509.getPublicKey());
                        // No exception thrown, so we're signed by this guy!
                        path.add(x509);
                        nodeAdded = true;
                        it.remove(); // Not interested in this guy anymore!
                        break;
                    }
                    catch (SignatureException se2) {
                        // Not signed by this guy, let's try the next guy.
                    }
                }
            }
        }

        X509Certificate[] results = new X509Certificate[path.size()];
        path.toArray(results);
        return results;
    }

    public static void main(String[] args) throws Exception {
        if (args.length < 2) {
            System.out.println("Usage: [special-one] [file-with-certs]");
            System.exit(1);
        }
        FileInputStream f1 = new FileInputStream(args[0]);
        FileInputStream f2 = new FileInputStream(args[1]);
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        X509Certificate theOne = (X509Certificate) cf.generateCertificate(f1);
        Collection c = cf.generateCertificates(f2);

        X509Certificate[] path = buildPath(theOne, c);
        for (int i = 0; i < path.length; i++) {
            System.out.println(Certificates.getCN(path[i]));
        }
    }
}