gnu.crypto.mode
Class ICM

java.lang.Object
  gnu.crypto.mode.BaseMode
      gnu.crypto.mode.ICM

All Implemented Interfaces:

java.lang.Cloneable, IBlockCipher, IMode

public class ICM

extends BaseMode

implements java.lang.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:

• block index length: is half the underlying cipher block size, and
• segment index length: is zero.

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: 1.2 $

Field Summary

Fields inherited from class gnu.crypto.mode.BaseMode

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

Fields inherited from interface gnu.crypto.mode.IMode

DECRYPTION, ENCRYPTION, IV, MODE_BLOCK_SIZE, STATE

Fields inherited from interface gnu.crypto.cipher.IBlockCipher

CIPHER_BLOCK_SIZE, KEY_MATERIAL

Constructor Summary

(package private)

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

Method Summary

java.lang.Object	clone() Returns a clone of this instance.
void	decryptBlock(byte[] in, int i, byte[] out, int o) Decrypts exactly one block of ciphertext.
void	encryptBlock(byte[] in, int i, byte[] out, int o) Encrypts exactly one block of plaintext.
void	setup() The initialisation phase of the concrete mode implementation.
void	teardown() The termination phase of the concrete mode implementation.

Methods inherited from class gnu.crypto.mode.BaseMode

blockSizes, currentBlockSize, defaultBlockSize, defaultKeySize, init, keySizes, name, reset, selfTest, update

Methods inherited from class java.lang.Object

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

Constructor Detail

ICM

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 Detail

clone

public java.lang.Object clone()

Description copied from interface: IBlockCipher

Returns a clone of this instance.

Specified by:

clone in interface IBlockCipher

Specified by:

clone in class BaseMode

setup

public void setup()

Description copied from class: BaseMode

The initialisation phase of the concrete mode implementation.

Specified by:

setup in class BaseMode

teardown

public void teardown()

Description copied from class: BaseMode

The termination phase of the concrete mode implementation.

Specified by:

teardown in class BaseMode

encryptBlock

public void encryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)

Description copied from interface: IBlockCipher

Encrypts exactly one block of plaintext.

Specified by:

encryptBlock in interface IBlockCipher

Specified by:

encryptBlock in class BaseMode

decryptBlock

public void decryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)

Description copied from interface: IBlockCipher

Decrypts exactly one block of ciphertext.

Specified by:

decryptBlock in interface IBlockCipher

Specified by:

decryptBlock in class BaseMode