gnu.crypto.prng

Class UMacGenerator

Implemented Interfaces:
Cloneable, IRandom

public class UMacGenerator
extends BasePRNG

KDFs (Key Derivation Functions) are used to stretch user-supplied key material to specific size(s) required by high level cryptographic primitives. Described in the UMAC paper, this function basically operates an underlying symmetric key block cipher instance in output feedback mode (OFB), as a strong pseudo-random number generator.

UMacGenerator requires an index parameter (initialisation parameter gnu.crypto.prng.umac.kdf.index taken to be an instance of java.lang.Integer with a value between 0 and 255). Using the same key, but different indices, generates different pseudorandom outputs.

This implementation generalises the definition of the UmacGenerator algorithm to allow for other than the AES symetric key block cipher algorithm (initialisation parameter gnu.crypto.prng.umac.cipher.name taken to be an instance of java.lang.String). If such a parameter is not defined/included in the initialisation Map, then the "Rijndael" algorithm is used. Furthermore, if the initialisation parameter gnu.crypto.cipher.block.size (taken to be a instance of java.lang.Integer) is missing or undefined in the initialisation Map , then the cipher's default block size is used.

NOTE: Rijndael is used as the default symmetric key block cipher algorithm because, with its default block and key sizes, it is the AES. Yet being Rijndael, the algorithm offers more versatile block and key sizes which may prove to be useful for generating "longer" key streams.

References:

  1. UMAC: Message Authentication Code using Universal Hashing.
    T. Krovetz, J. Black, S. Halevi, A. Hevia, H. Krawczyk, and P. Rogaway.

Version:
$Revision: 1.5 $

Field Summary

static String
CIPHER
The name of the underlying symmetric key block cipher algorithm.
static String
INDEX
Property name of the KDF index value to use in this instance.

Fields inherited from class gnu.crypto.prng.BasePRNG

buffer, initialised, name, ndx

Constructor Summary

UMacGenerator()
Trivial 0-arguments constructor.

Method Summary

Object
clone()
Returns a clone copy of this instance.
void
fillBlock()
void
setup(Map attributes)

Methods inherited from class gnu.crypto.prng.BasePRNG

clone, fillBlock, init, isInitialised, name, nextByte, nextBytes, setup

Field Details

CIPHER

public static final String CIPHER
The name of the underlying symmetric key block cipher algorithm.


INDEX

public static final String INDEX
Property name of the KDF index value to use in this instance. The value is taken to be an Integer less than 256.

Constructor Details

UMacGenerator

public UMacGenerator()
Trivial 0-arguments constructor.

Method Details

clone

public Object clone()
Returns a clone copy of this instance.
Specified by:
clone in interface IRandom
Overrides:
clone in interface BasePRNG

Returns:
a clone copy of this instance.


fillBlock

public void fillBlock()
            throws LimitReachedException
Overrides:
fillBlock in interface BasePRNG


setup

public void setup(Map attributes)
Overrides:
setup in interface BasePRNG


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