de.flexiprovider.core.random
Class BBSRandom

java.lang.Object
  |
  +--java.security.SecureRandomSpi
        |
        +--de.flexiprovider.api.SecureRandom
              |
              +--de.flexiprovider.core.random.BBSRandom

All Implemented Interfaces:

java.io.Serializable

public final class BBSRandom

extends SecureRandom

This is an implementation of a pseudorandom number based on a paper written by L. Blum, M. Blum and M. Shub in 1982. The BBS (or X²-mod-N) generator is proved to be as secure as the factorization of the Modulus (which is a 1024 bit number).

The implementation follows the JCA conventions and subclasses the proper engine class (SecureRandom). This class is normaly not instantiated directly. You should use the factory-method provided by the JCA framework (i.e. call java.security.SecureRandom.getInstance(...)). The generator works in three steps:

1. The generator uses an internal 200 bit seed, so it is inefficient to do something like a "brute force" attack (i.e. enumerate all possible seeds). The seed can be set using the setSeed(byte[] bytes) member function. If it is not set explicitly, then it is generated by a seed generator.
2. In order to generate the parameters used during the generation, the internal seed is expanded using a Linear Congruential Generator (LCG). This generator is not secure in a cryptographical manner, but as no output of the (LCG) is visible to the outside world, this is no problem. The parameters are the seed X and the modulus N which is the product of two different prime numbers P,Q of equal bit length. N is at least a 1024 bit number. The parameters are generated after the instantiation and after each call to setSeed(byte[]). The generation takes place within the nextBytes(byte[] bytes) member function.
3. Using these parameters, the generator iteratively determines a new X by raising X to the power of 2 modulo N. During each iteration the log₂(|N|)-least-significant bits of the binary representation of X are collected and form the output of the generator.

Timings:

	Seed generation	Parameter generation	Byte generation
			10000 bytes	20000 bytes
PII-233, with JIT	10.036 s	8.042 s	5.708 s	11.405 s

Author:

Marcus Lippert, Martin Döring

See Also:

"java.security.SecureRandom", "java.security.SecureRandomSpi", "de.flexiprovider.common.util.SeedGenerator", Serialized Form

Constructor Summary

BBSRandom()
Default constructor of BBSRandom, to be called by SecureRandom's getInstance(...) method according to a factory pattern.

Method Summary

byte[]	generateSeed(int numBytes) Returns the requested number of seed bytes.
void	nextBytes(byte[] bytes) Generates a user-specified number of random bytes.
void	setSeed(byte[] newSeed) Modifies the seed of this random object in the following way: If this method is called before the object is seeded, i.e it is the first call of this method and no bytes have been generated by this object yet, the seed is set in a way that entirely depends on the given parameter and therefore is reproducible. If this method is called to an object already seeded, the new seed depends on both the current inner state and the given parameter.

Methods inherited from class de.flexiprovider.api.SecureRandom

engineGenerateSeed, engineNextBytes, engineSetSeed, nextInt, nextInt

Methods inherited from class java.lang.Object

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

Constructor Detail

BBSRandom

public BBSRandom()

Default constructor of BBSRandom, to be called by SecureRandom's getInstance(...) method according to a factory pattern.

Method Detail

generateSeed

public byte[] generateSeed(int numBytes)

Returns the requested number of seed bytes.

Overrides:

generateSeed in class SecureRandom

Parameters:

numBytes - number of random bytes to generate

Returns:

a byte array containig the pseudo-random bytes

nextBytes

public void nextBytes(byte[] bytes)

Generates a user-specified number of random bytes.

Overrides:

nextBytes in class SecureRandom

Parameters:

bytes - byte array the generated bytes will be stored in

setSeed

public void setSeed(byte[] newSeed)

Modifies the seed of this random object in the following way:

• If this method is called before the object is seeded, i.e it is the first call of this method and no bytes have been generated by this object yet, the seed is set in a way that entirely depends on the given parameter and therefore is reproducible.
• If this method is called to an object already seeded, the new seed depends on both the current inner state and the given parameter.

Overrides:

setSeed in class SecureRandom

Parameters:

newSeed - the byte array containing a new seed