er.extensions.foundation
Class ERXRandomGUID

java.lang.Object
  er.extensions.foundation.ERXRandomGUID

public class ERXRandomGUID
extends java.lang.Object

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.

History

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

License

From www.JavaExchange.com, Open Software licensing

Version:

1.2.1 11/05/02

Author:

Marc A. Mnich

Field Summary

java.lang.String	valueAfterMD5
java.lang.String	valueBeforeMD5

Constructor Summary

ERXRandomGUID()
Default constructor.

ERXRandomGUID(boolean secure)
Constructor with security option.

Method Summary

static void	main(java.lang.String[] args) Demonstration and self test of class.
static java.lang.String	newGid() Returns the String representation of a new ERXRandomGUID object.
java.lang.String	toString() Convert to the standard format for GUID (Useful for SQL Server UniqueIdentifiers, etc.) Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

valueBeforeMD5

public java.lang.String valueBeforeMD5

valueAfterMD5

public java.lang.String valueAfterMD5

Constructor Detail

ERXRandomGUID

public ERXRandomGUID()

Default constructor. With no specification of security option, this constructor defaults to lower security, high performance.

ERXRandomGUID

public ERXRandomGUID(boolean secure)

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.

Parameters:

secure - true use a random number from SecureRandom, or false use a random number from Random

Method Detail

toString

public java.lang.String toString()

Convert to the standard format for GUID (Useful for SQL Server UniqueIdentifiers, etc.) Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6

Overrides:

toString in class java.lang.Object

Returns:

a String representation of this object

main

public static void main(java.lang.String[] args)

Demonstration and self test of class.

Parameters:

args - No arguments

newGid

public static java.lang.String newGid()

Returns the String representation of a new ERXRandomGUID object.

Returns:

the String representation of a new ERXRandomGUID object