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 * 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
 */
</Content>
<PostDateTime>2002-4-12 16:31:31</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>jacky</PostUserNickName>
<rank>五级(中级)</rank>
<ranknum>user5</ranknum>
<credit>105</credit>
<ReplyID>4228279</ReplyID>
<TopicID>635830</TopicID>
<PostUserId>30398</PostUserId>
<PostUserName>kkhui</PostUserName>
<Point>0</Point>
<Content>GUID part1 --License
/*
 * RandomGUID
 * @version 1.2 01/29/02
 * @author Marc A. Mnich
 *
 * From www.JavaExchange.com, Open Software licensing
 *
 * 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
 */</Content>
<PostDateTime>2002-4-12 16:33:11</PostDateTime>
</Reply>
<Reply>
<PostUserNickName>jacky</PostUserNickName>
<rank>五级(中级)</rank>
<ranknum>user5</ranknum>
<credit>105</credit>
<ReplyID>4228303</ReplyID>
<TopicID>635830</TopicID>
<PostUserId>30398</PostUserId>
<PostUserName>kkhui</PostUserName>
<Point>0</Point>
<Content>//part2 body
public class RandomGUID extends Object {
  public String valueBeforeMD5 = "";
  public String valueAfterMD5 = "";
  private static Random myRand;
  private static SecureRandom mySecureRand;
  /*
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