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gnu.crypto.mode
Class CTR

java.lang.Object
  |
  +--gnu.crypto.mode.BaseMode
        |
        +--gnu.crypto.mode.CTR
All Implemented Interfaces:
java.lang.Cloneable, IBlockCipher, IMode

public class CTR
extends BaseMode
implements java.lang.Cloneable

The implementation of the Counter Mode.

The algorithm steps are formally described as follows:

    CTR Encryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
                    C[j] = P[j] ^ O[j]; for j = 1, 2...n.
    CTR Decryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
                    P[j] = C[j] ^ O[j]; for j = 1, 2...n.
 

where P is the plaintext, C is the ciphertext, E(K) is the underlying block cipher encryption function parametrised with the session key K, and T is the Counter.

This implementation, uses a standard incrementing function with a step of 1, and an initial value similar to that described in the NIST document.

References:

  1. Recommendation for Block Cipher Modes of Operation Methods and Techniques, Morris Dworkin.

Version:
$Revision: 1.4 $

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) CTR(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

CTR

CTR(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.

Overrides:
clone in class BaseMode
Following copied from interface: gnu.crypto.cipher.IBlockCipher
Returns:
a clone copy of this instance.

setup

public void setup()
Description copied from class: BaseMode
The initialisation phase of the concrete mode implementation.
Overrides:
setup in class BaseMode

teardown

public void teardown()
Description copied from class: BaseMode
The termination phase of the concrete mode implementation.
Overrides:
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.

Overrides:
encryptBlock in class BaseMode
Following copied from interface: gnu.crypto.cipher.IBlockCipher
Parameters:
in - the plaintext.
inOffset - index of in from which to start considering data.
out - the ciphertext.
outOffset - index of out from which to store result.
Throws:
java.lang.IllegalStateException - if the instance is not initialised.

decryptBlock

public void decryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)
Description copied from interface: IBlockCipher

Decrypts exactly one block of ciphertext.

Overrides:
decryptBlock in class BaseMode
Following copied from interface: gnu.crypto.cipher.IBlockCipher
Parameters:
in - the plaintext.
inOffset - index of in from which to start considering data.
out - the ciphertext.
outOffset - index of out from which to store result.
Throws:
java.lang.IllegalStateException - if the instance is not initialised.

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