gnu.crypto.prng
Class ICMGenerator

java.lang.Object
  gnu.crypto.prng.BasePRNG
      gnu.crypto.prng.ICMGenerator

All Implemented Interfaces:

java.lang.Cloneable, IRandom

public class ICMGenerator

extends BasePRNG

Counter Mode is a way to define a pseudorandom keystream generator using a block cipher. The keystream can be used for additive encryption, key derivation, or any other application requiring pseudorandom data.

In ICM, the keystream is logically broken into segments. Each segment is identified with a segment index, and the segments have equal lengths. This segmentation makes ICM especially appropriate for securing packet-based protocols.

This implementation adheres to the definition of the ICM keystream generation function that allows for any symetric key block cipher algorithm (initialisation parameter gnu.crypto.prng.icm.cipher.name taken to be an instance of String) to be used. 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 Integer) is missing or undefined in the initialisation Map, then the cipher's default block size is used.

The practical limits and constraints of such generator are:

• The number of blocks in any segment MUST NOT exceed 256 ** BLOCK_INDEX_LENGTH. The number of segments MUST NOT exceed 256 ** SEGMENT_INDEX_LENGTH. These restrictions ensure the uniqueness of each block cipher input.
• Each segment contains SEGMENT_LENGTH octets; this value MUST NOT exceed the value (256 ** BLOCK_INDEX_LENGTH) * BLOCK_LENGTH.
• The sum of SEGMENT_INDEX_LENGTH and BLOCK_INDEX_LENGTH MUST NOT exceed BLOCK_LENGTH / 2. This requirement protects the ICM keystream generator from potentially failing to be pseudorandom.

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. Integer Counter Mode, David A. McGrew.

Version:

$Revision: 1.2 $

Field Summary

static java.lang.String	BLOCK_INDEX_LENGTH Property name of ICM's block index length.
static java.lang.String	CIPHER Property name of underlying block cipher for this ICM generator.
static java.lang.String	OFFSET Property name of ICM's offset.
static java.lang.String	SEGMENT_INDEX Property name of ICM's segment index.
static java.lang.String	SEGMENT_INDEX_LENGTH Property name of ICM's segment index length.

Fields inherited from class gnu.crypto.prng.BasePRNG

buffer, initialised, name, ndx

Constructor Summary

ICMGenerator()
Trivial 0-arguments constructor.

Method Summary

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

Methods inherited from class gnu.crypto.prng.BasePRNG

init, isInitialised, name, nextByte, nextBytes

Methods inherited from class java.lang.Object

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

Field Detail

CIPHER

public static final java.lang.String CIPHER

Property name of underlying block cipher for this ICM generator.

See Also:

Constant Field Values

BLOCK_INDEX_LENGTH

public static final java.lang.String BLOCK_INDEX_LENGTH

Property name of ICM's block index length.

See Also:

Constant Field Values

SEGMENT_INDEX_LENGTH

public static final java.lang.String SEGMENT_INDEX_LENGTH

Property name of ICM's segment index length.

See Also:

Constant Field Values

OFFSET

public static final java.lang.String OFFSET

Property name of ICM's offset.

See Also:

Constant Field Values

SEGMENT_INDEX

public static final java.lang.String SEGMENT_INDEX

Property name of ICM's segment index.

See Also:

Constant Field Values

Constructor Detail

ICMGenerator

public ICMGenerator()

Trivial 0-arguments constructor.

Method Detail

clone

public java.lang.Object clone()

Description copied from interface: IRandom

Returns a clone copy of this instance.

Specified by:

clone in interface IRandom

Specified by:

clone in class BasePRNG

setup

public void setup(java.util.Map attributes)

Specified by:

setup in class BasePRNG

fillBlock

public void fillBlock()
               throws LimitReachedException

Specified by:

fillBlock in class BasePRNG

Throws:

LimitReachedException