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gnu.javax.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.

Field Summary

Fields inherited from class gnu.javax.crypto.mode.BaseMode

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

Fields inherited from interface gnu.javax.crypto.cipher.IBlockCipher

CIPHER_BLOCK_SIZE, KEY_MATERIAL

Fields inherited from interface gnu.javax.crypto.mode.IMode

DECRYPTION, ENCRYPTION, IV, MODE_BLOCK_SIZE, STATE

Method Summary

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.javax.crypto.mode.BaseMode

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

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

clone

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

decryptBlock

public void decryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)
Decrypts exactly one block of ciphertext.
Specified by:
decryptBlock in interface IBlockCipher
Overrides:
decryptBlock in interface BaseMode
Parameters:
in - the plaintext.
out - the ciphertext.
Throws:
IllegalStateException - if the instance is not initialised.

encryptBlock

public void encryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)
Encrypts exactly one block of plaintext.
Specified by:
encryptBlock in interface IBlockCipher
Overrides:
encryptBlock in interface BaseMode
Parameters:
in - the plaintext.
out - the ciphertext.
Throws:
IllegalStateException - if the instance is not initialised.

setup

public void setup()
The initialisation phase of the concrete mode implementation.
Overrides:
setup in interface BaseMode

teardown

public void teardown()
The termination phase of the concrete mode implementation.
Overrides:
teardown in interface BaseMode
ICM.java -- Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc. This file is a part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

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