RandomGUID[源代码，转]

/*
* RandomGUID
* @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.*;
import java.util.*;
import java.security.*;

/*
* 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.
*
* 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.
*
* 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.
*
* 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.
*
* ----> Security of RandomGUID: <-----
* 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.
*
* 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.
*
* Using the secure random option, this class compies with the statistical
* random number generator tests specified in FIPS 140-2, Security
* Requirements for Cryptographic Modules, secition 4.9.1.
*
* 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.
*
* 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.
*
*
* - Marc
*/

public class RandomGUID extends Object {

    public String valueBeforeMD5 = "";
    public String valueAfterMD5 = "";
    private static Random myRand;
    private static SecureRandom mySecureRand;

    private static String s_id;

    /*
     * 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 {
        mySecureRand = new SecureRandom();
        long secureInitializer = mySecureRand.nextLong();
        myRand = new Random(secureInitializer);
        try {
            s_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 = mySecureRand.nextLong();
            } else {
                rand = myRand.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(s_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();
    }

    /*
     * Demonstraton and self test of class
     */
    public static void main(String args[]) {
        for (int i=0; i< 100; i++) {
    RandomGUID myGUID = new RandomGUID();
    System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
    System.out.println("rawGUID=" + myGUID.valueAfterMD5);
    System.out.println("RandomGUID=" + myGUID.toString());
        }
    }
}