gnu.crypto.mode

Class ICM

Implemented Interfaces:
Cloneable, IBlockCipher, IMode

public class ICM
extends BaseMode
implements Cloneable

An implementation of David McGrew Integer Counter Mode (ICM) as an IMode.

ICM 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 the case of this class, it is used as additive encryption, XOR-ing the keystream with the input text --for both encryption and decryption.

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. ICM also allows a variety of configurations based, among other things, on two parameters: the block index length and the segment index length. A constraint on those two values exists: The sum of segment index length and block index length must not half the block size of the underlying cipher. This requirement protects the ICM keystream generator from potentially failing to be pseudorandom.

For simplicity, this implementation, fixes these two values to the following:

For a 128-bit block cipher, the above values imply a maximum keystream length of 295,147,905,179,352,825,856 octets, since in ICM, each segment must not exceed the value (256 ^ block index length) * block length octets.

Finally, for this implementation of the ICM, the IV placeholder will be used to pass the value of the Offset in the keystream segment.

References:

  1. Integer Counter Mode, David A. McGrew.

Version:
$Revision: 1.6 $

Field Summary

Fields inherited from class gnu.crypto.mode.BaseMode

cipher, cipherBlockSize, iv, lock, modeBlockSize, name, state

Fields inherited from interface gnu.crypto.cipher.IBlockCipher

CIPHER_BLOCK_SIZE, KEY_MATERIAL

Fields inherited from interface gnu.crypto.mode.IMode

DECRYPTION, ENCRYPTION, IV, MODE_BLOCK_SIZE, STATE

Constructor Summary

ICM(IBlockCipher underlyingCipher, int cipherBlockSize)
Trivial package-private constructor for use by the Factory class.

Method Summary

Object
clone()
void
decryptBlock(byte[] in, int i, byte[] out, int o)
void
encryptBlock(byte[] in, int i, byte[] out, int o)
void
setup()
void
teardown()

Methods inherited from class gnu.crypto.mode.BaseMode

blockSizes, clone, currentBlockSize, decryptBlock, defaultBlockSize, defaultKeySize, encryptBlock, init, keySizes, name, reset, selfTest, setup, teardown, update

Constructor Details

ICM

(package private)  ICM(IBlockCipher underlyingCipher,
                       int cipherBlockSize)
Trivial package-private constructor for use by the Factory class.

Parameters:
underlyingCipher - the underlying cipher implementation.
cipherBlockSize - the underlying cipher block size to use.

Method Details

clone

public Object clone()
Specified by:
clone in interface IBlockCipher
Overrides:
clone in interface BaseMode


decryptBlock

public void decryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)
Specified by:
decryptBlock in interface IBlockCipher
Overrides:
decryptBlock in interface BaseMode


encryptBlock

public void encryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)
Specified by:
encryptBlock in interface IBlockCipher
Overrides:
encryptBlock in interface BaseMode


setup

public void setup()
Overrides:
setup in interface BaseMode


teardown

public void teardown()
Overrides:
teardown in interface BaseMode


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