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gnu.crypto.mode
Class CTR

java.lang.Object
  extended by gnu.crypto.mode.BaseMode
      extended by gnu.crypto.mode.CTR
All Implemented Interfaces:
IBlockCipher, IMode, Cloneable

public class CTR
extends BaseMode
implements 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: 1.7 $

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
CTR(IBlockCipher underlyingCipher, int cipherBlockSize)
          Trivial package-private constructor for use by the Factory class.
 
Method Summary
 Iterator blockSizes()
          Returns an Iterator over the supported block sizes.
 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
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 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
Returns:
a clone copy of this instance.

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
Parameters:
in - the plaintext.
i - index of in from which to start considering data.
out - the ciphertext.
o - index of out from which to store result.

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
Parameters:
in - the plaintext.
i - index of in from which to start considering data.
out - the ciphertext.
o - index of out from which to store result.

blockSizes

public Iterator blockSizes()
Description copied from class: BaseMode

Returns an Iterator over the supported block sizes. Each element returned by this object is an Integer.

The default behaviour is to return an iterator with just one value, which is that currently configured for the underlying block cipher. Concrete implementations may override this behaviour to signal their ability to support other values.

Specified by:
blockSizes in interface IBlockCipher
Overrides:
blockSizes in class BaseMode
Returns:
an Iterator over the supported block sizes.

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