org.springframework.webflow.util.RandomGuid Maven / Gradle / Ivy
/*
* Copyright 2004-2007 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 org.springframework.webflow.util;
/*
* 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.
*
* 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 complies 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.
*
* @version 1.2.1 11/05/02
* @author Marc A. Mnich
*/
public class RandomGuid {
private static Random random;
private static SecureRandom secureRandom;
private static String id;
private String guid;
/*
* 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) {
throw new RuntimeException(e);
}
}
/**
* 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) {
throw new RuntimeException(e);
}
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));
String 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));
}
guid = sb.toString();
}
/**
* Convert to the standard format for GUID (Useful for SQL Server UniqueIdentifiers, etc). Example:
* "C2FEEEAC-CFCD-11D1-8B05-00600806D9B6".
*/
public String toString() {
String raw = guid.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();
}
}