gnu.crypto.mode
Class CFB

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

All Implemented Interfaces:

java.lang.Cloneable, IBlockCipher, IMode

public class CFB

extends BaseMode

The cipher feedback mode. CFB mode is a stream mode that operates on s bit blocks, where 1 <= s <= b, if b is the underlying cipher's block size. Encryption is:

   I[1] = IV
   I[j] = LSB(b-s, I[j-1]) | C[j-1]   for j = 2...n
   O[j] = CIPH(K, I[j])               for j = 1,2...n
   C[j] = P[j] ^ MSB(s, O[j])         for j = 1,2...n

And decryption is:

   I[1] = IV
   I[j] = LSB(b-s, I[j-1]) | C[j-1]   for j = 2...n
   O[j] = CIPH(K, I[j])               for j = 1,2...n
   P[j] = C[j] ^ MSB(s, O[j])         for j = 1,2...n

CFB mode requires an initialization vector, which need not be kept secret.

References:

1. Bruce Schneier, Applied Cryptography: Protocols, Algorithms, and Source Code in C, Second Edition. (1996 John Wiley and Sons) ISBN 0-471-11709-9.
2. Recommendation for Block Cipher Modes of Operation Methods and Techniques, Morris Dworkin.

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)

CFB(IBlockCipher underlyingCipher, int cipherBlockSize) Package-private constructor for the factory class.

Method Summary

java.lang.Object	clone() Returns a clone of this instance.
void	decryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) Decrypts exactly one block of ciphertext.
void	encryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) 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

CFB

CFB(IBlockCipher underlyingCipher,
    int cipherBlockSize)

Package-private constructor for the factory class.

Parameters:

underlyingCipher - The cipher implementation.

cipherBlockSize - The cipher's block size.

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 inOffset,
                         byte[] out,
                         int outOffset)

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 inOffset,
                         byte[] out,
                         int outOffset)

Description copied from interface: IBlockCipher

Decrypts exactly one block of ciphertext.

Specified by:

decryptBlock in interface IBlockCipher

Specified by:

decryptBlock in class BaseMode