cryptix.provider.mode

Class CFB

public class CFB extends FeedbackMode

Implements a byte-oriented stream cipher using n-bit CFB with an n-bit-sized block cipher.

The full block size of the supplied cipher is used for the Cipher Feedback Mode. The bytes supplied are processed and returned immediately.

References:

  1. Bruce Schneier, "Section 9.6 Cipher Feedback Mode," and "Section 9.11 Choosing a Cipher Mode," Applied Cryptography, 2nd edition, John Wiley & Sons, 1996

  2. sci.crypt FAQ, "Part 5: Product Ciphers," ftp://ftp.rtfm.mit.edu/pub/usenet/news.answers/cryptography-faq/part05

  3. National Bureau of Standards (now NIST), "DES Modes of Operation," NBS FIPS PUB 81, U.S. Department of Commerce, December 1980

Copyright © 1995-1997 Systemics Ltd on behalf of the Cryptix Development Team.
All rights reserved.

$Revision: 1.5 $

Since: Cryptix 2.2.2

Author: David Hopwood Raif S. Naffah

Constructor Summary
CFB()
Constructs a CFB mode object.
CFB(Cipher cipher)
Constructs a CFB cipher, assuming that the IV will be provided via setInitializationVector.
CFB(Cipher cipher, byte[] iv)
Constructs a CFB cipher, using an initialization vector provided in the constructor.
Method Summary
protected intengineBlockSize()
protected voidengineInitDecrypt(Key newkey)
protected voidengineInitEncrypt(Key newkey)
protected voidengineSetCipher(Cipher cipher)
protected intengineUpdate(byte[] in, int inOffset, int inLen, byte[] out, int outOffset)
SPI: This is the main engine method for updating data.
protected voidnext_block()
Rotates the IV left by currentByte bytes, to mimic the V2.2 behaviour.

Constructor Detail

CFB

public CFB()
Constructs a CFB mode object.

The IV is provided via setInitializationVector. This IV must be unique during the lifetime of the key. If it is not unique, at least the first block of the plaintext can be recovered.

CFB

public CFB(Cipher cipher)
Constructs a CFB cipher, assuming that the IV will be provided via setInitializationVector. See the previous constructor for more details.

Parameters: cipher the cipher object to use in CFB mode.

Throws: NullPointerException if cipher == null

CFB

public CFB(Cipher cipher, byte[] iv)
Constructs a CFB cipher, using an initialization vector provided in the constructor.

Parameters: cipher the block cipher to use iv the initial value for the shift register (IV)

Throws: NullPointerException if cipher == null

Method Detail

engineBlockSize

protected int engineBlockSize()

engineInitDecrypt

protected void engineInitDecrypt(Key newkey)

engineInitEncrypt

protected void engineInitEncrypt(Key newkey)

engineSetCipher

protected void engineSetCipher(Cipher cipher)

engineUpdate

protected int engineUpdate(byte[] in, int inOffset, int inLen, byte[] out, int outOffset)
SPI: This is the main engine method for updating data. It may be called with any size of input.

in and out may be the same array, and the input and output regions may overlap.

Parameters: in the input data. inOffset the offset into in specifying where the data starts. inLen the length of the subarray. out the output array. outOffset the offset indicating where to start writing into the out array.

Returns: the number of bytes written.

next_block

protected void next_block()
Rotates the IV left by currentByte bytes, to mimic the V2.2 behaviour. This is needed in order to implement the variant of CFB used by PGP.

See Also: CFB_PGP