package org.smartly.commons.cryptograph;
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 GUID {
public String valueBeforeMD5 = "";
public String valueAfterMD5 = "";
private static Random myRand;
private static final 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 GUID() {
this.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.
*
* @param secure True if you want each number generated is cryptographically
* strong
*/
public GUID(boolean secure) {
this.getRandomGUID(secure);
}
/**
* Method to generate the random GUID
*/
private void getRandomGUID(boolean secure) {
MessageDigest md5 = null;
final StringBuilder sbValueBeforeMD5 = new StringBuilder();
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();
final StringBuilder sb = new StringBuilder();
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
*
* @return Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
*/
@Override
public String toString() {
String raw = valueAfterMD5.toUpperCase();
StringBuilder sb = new StringBuilder();
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();
}
/**
* Convert to the standard format for GUID SESSION ID
* (Useful for SQL Server UniqueIdentifiers, etc.)
* Example: C2FEEEACCFCD11D18B0500600806D9B6
*
* @param sessionStyle True if you want a GUID in style "C2FEEEACCFCD11D18B0500600806D9B6".
* False if you want a standard GUID (see toString()).
* @return Example: C2FEEEACCFCD11D18B0500600806D9B6
*/
public String toString(boolean sessionStyle) {
String raw = valueAfterMD5.toUpperCase();
StringBuilder sb = new StringBuilder();
if (!sessionStyle) {
return this.toString();
} else {
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();
}
// ------------------------------------------------------------------------
// S T A T I C
// ------------------------------------------------------------------------
/*
* Demonstraton and self test of class
*/
public static void main(String args[]) {
for (int i = 0; i < 100; i++) {
GUID myGUID = new GUID();
System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
System.out.println("rawGUID=" + myGUID.valueAfterMD5);
System.out.println("RandomGUID=" + myGUID.toString());
}
}
public static String create() {
return create(false, false);
}
public static String create(final boolean secure) {
return create(secure, false);
}
public static String create(final boolean secure,
final boolean sessionstyle) {
GUID guid = new GUID(secure);
return guid.toString(sessionstyle);
}
}