randomguid.java

一个很好的开源项目管理系统源代码

/*
 * Copyright 2002-2004 the original author or authors. Licensed 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.
 */
package net.java.workeffort.infrastructure;

/*
 * RandomGUID from http://www.javaexchange.com/aboutRandomGUID.html
 * @version 1.2.1 11/05/02 @author Marc A. Mnich From www.JavaExchange.com, Open
 *          Software licensing 11/05/02 -- Performance enhancement from Mike
 *          Dubman. Moved InetAddr.getLocal to static block. Mike has measured a
 *          10 fold improvement in run time. 01/29/02 -- Bug fix: Improper
 *          seeding of nonsecure Random object caused duplicate GUIDs to be
 *          produced. Random object is now only created once per JVM. 01/19/02 --
 *          Modified random seeding and added new constructor to allow secure
 *          random feature. 01/14/02 -- Added random function seeding with JVM
 *          run time
 */

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

/**
 * Globally unique identifier generator.
 * <p>
 * In the multitude of java GUID generators, I found none that guaranteed
 * randomness. GUIDs are guaranteed to be globally unique by using ethernet
 * MACs, IP addresses, time elements, and sequential numbers. GUIDs are not
 * expected to be random and most often are easy/possible to guess given a
 * sample from a given generator. SQL Server, for example generates GUID that
 * are unique but sequencial within a given instance.
 * <p>
 * GUIDs can be used as security devices to hide things such as files within a
 * filesystem where listings are unavailable (e.g. files that are served up from
 * a Web server with indexing turned off). This may be desireable in cases where
 * standard authentication is not appropriate. In this scenario, the RandomGuids
 * are used as directories. Another example is the use of GUIDs for primary keys
 * in a database where you want to ensure that the keys are secret. Random GUIDs
 * can then be used in a URL to prevent hackers (or users) from accessing
 * records by guessing or simply by incrementing sequential numbers.
 * <p>
 * There are many other possiblities of using GUIDs in the realm of security and
 * encryption where the element of randomness is important. This class was
 * written for these purposes but can also be used as a general purpose GUID
 * generator as well.
 * <p>
 * RandomGuid generates truly random GUIDs by using the system's IP address
 * (name/IP), system time in milliseconds (as an integer), and a very large
 * random number joined together in a single String that is passed through an
 * MD5 hash. The IP address and system time make the MD5 seed globally unique
 * and the random number guarantees that the generated GUIDs will have no
 * discernable pattern and cannot be guessed given any number of previously
 * generated GUIDs. It is generally not possible to access the seed information
 * (IP, time, random number) from the resulting GUIDs as the MD5 hash algorithm
 * provides one way encryption.
 * <p>
 * <b>Security of RandomGuid </b>: RandomGuid can be called one of two ways --
 * with the basic java Random number generator or a cryptographically strong
 * random generator (SecureRandom). The choice is offered because the secure
 * random generator takes about 3.5 times longer to generate its random numbers
 * and this performance hit may not be worth the added security especially
 * considering the basic generator is seeded with a cryptographically strong
 * random seed.
 * <p>
 * Seeding the basic generator in this way effectively decouples the random
 * numbers from the time component making it virtually impossible to predict the
 * random number component even if one had absolute knowledge of the System
 * time. Thanks to Ashutosh Narhari for the suggestion of using the static
 * method to prime the basic random generator.
 * <p>
 * Using the secure random option, this class complies with the statistical
 * random number generator tests specified in FIPS 140-2, Security Requirements
 * for Cryptographic Modules, secition 4.9.1.
 * <p>
 * I converted all the pieces of the seed to a String before handing it over to
 * the MD5 hash so that you could print it out to make sure it contains the data
 * you expect to see and to give a nice warm fuzzy. If you need better
 * performance, you may want to stick to byte[] arrays.
 * <p>
 * I believe that it is important that the algorithm for generating random GUIDs
 * be open for inspection and modification. This class is free for all uses.
 * @version 1.2.1 11/05/02
 * @author Marc A. Mnich
 */
public class RandomGuid extends Object {

    private static Random random;

    private static SecureRandom secureRandom;

    private static String id;

    private String valueBeforeMD5 = "";

    private String valueAfterMD5 = "";

    /*
     * Static block to take care of one time secureRandom seed. It takes a few
     * seconds to initialize SecureRandom. You might want to consider removing
     * this static block or replacing it with a "time since first loaded" seed
     * to reduce this time. This block will run only once per JVM instance.
     */
    static {
        secureRandom = new SecureRandom();
        long secureInitializer = secureRandom.nextLong();
        random = new Random(secureInitializer);
        try {
            id = InetAddress.getLocalHost().toString();
        }
        catch (UnknownHostException e) {
            e.printStackTrace();
        }

    }

    /**
     * Default constructor. With no specification of security option, this
     * constructor defaults to lower security, high performance.
     */
    public RandomGuid() {
        getRandomGuid(false);
    }

    /**
     * Constructor with security option. Setting secure true enables each random
     * number generated to be cryptographically strong. Secure false defaults to
     * the standard Random function seeded with a single cryptographically
     * strong random number.
     */
    public RandomGuid(boolean secure) {
        getRandomGuid(secure);
    }

    /**
     * Method to generate the random GUID
     */
    private void getRandomGuid(boolean secure) {
        MessageDigest md5 = null;
        StringBuffer sbValueBeforeMD5 = new StringBuffer();

        try {
            md5 = MessageDigest.getInstance("MD5");
        }
        catch (NoSuchAlgorithmException e) {
            System.out.println("Error: " + e);
        }

        try {
            long time = System.currentTimeMillis();
            long rand = 0;

            if (secure) {
                rand = secureRandom.nextLong();
            }
            else {
                rand = random.nextLong();
            }

            // This StringBuffer can be a long as you need; the MD5
            // hash will always return 128 bits. You can change
            // the seed to include anything you want here.
            // You could even stream a file through the MD5 making
            // the odds of guessing it at least as great as that
            // of guessing the contents of the file!
            sbValueBeforeMD5.append(id);
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(time));
            sbValueBeforeMD5.append(":");
            sbValueBeforeMD5.append(Long.toString(rand));

            valueBeforeMD5 = sbValueBeforeMD5.toString();
            md5.update(valueBeforeMD5.getBytes());

            byte[] array = md5.digest();
            StringBuffer sb = new StringBuffer();
            for (int j = 0; j < array.length; ++j) {
                int b = array[j] & 0xFF;
                if (b < 0x10)
                    sb.append('0');
                sb.append(Integer.toHexString(b));
            }
            valueAfterMD5 = sb.toString();
        }
        catch (Exception e) {
            System.out.println("Error:" + e);
        }
    }

    /**
     * Convert to the standard format for GUID. (Useful for SQL Server
     * UniqueIdentifiers, etc.) Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
     */
    public String toString() {
        String raw = valueAfterMD5.toUpperCase();
        StringBuffer sb = new StringBuffer();
        sb.append(raw.substring(0, 8));
        sb.append("-");
        sb.append(raw.substring(8, 12));
        sb.append("-");
        sb.append(raw.substring(12, 16));
        sb.append("-");
        sb.append(raw.substring(16, 20));
        sb.append("-");
        sb.append(raw.substring(20));
        return sb.toString();
    }
}