/**********************************************************************************
* $URL: https://source.sakaiproject.org/svn/metaobj/trunk/metaobj-impl/api-impl/src/java/org/sakaiproject/metaobj/utils/id/guid/RandomGUID.java $
* $Id: RandomGUID.java 105079 2012-02-24 23:08:11Z ottenhoff@longsight.com $
***********************************************************************************
*
* Copyright (c) 2004, 2005, 2006, 2007, 2008 The Sakai Foundation
*
* Licensed under the Educational Community 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.opensource.org/licenses/ECL-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 org.sakaiproject.metaobj.utils.id.guid;
/*
* 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.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;
/*
* 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 {
protected final org.apache.commons.logging.Log logger = org.apache.commons.logging.LogFactory
.getLog(getClass());
public String valueBeforeMD5 = "";
public String valueAfterMD5 = "";
private static Random myRand;
private static SecureRandom mySecureRand;
private static String s_id;
private static final int PAD_BELOW = 0x10;
private static final int TWO_BYTES = 0xFF;
/*
* 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;
StringBuilder sbValueBeforeMD5 = new StringBuilder(128);
try {
md5 = MessageDigest.getInstance("MD5");
long time = System.currentTimeMillis();
long rand = 0;
if (secure) {
rand = mySecureRand.nextLong();
}
else {
rand = myRand.nextLong();
}
// This StringBuilder 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();
StringBuilder sb = new StringBuilder(32);
for (int j = 0; j < array.length; ++j) {
int b = array[j] & TWO_BYTES;
if (b < PAD_BELOW) {
sb.append('0');
}
sb.append(Integer.toHexString(b));
}
valueAfterMD5 = sb.toString();
}
catch (Exception e) {
logger.error("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();
StringBuilder sb = new StringBuilder(64);
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());
}
}
*/
}