cryptix.provider.mode
Class CBC

java.lang.Object
  |
  +--xjava.security.IJCE_Traceable
        |
        +--xjava.security.Cipher
              |
              +--xjava.security.Mode
                    |
                    +--cryptix.provider.mode.FeedbackMode
                          |
                          +--cryptix.provider.mode.CBC
All Implemented Interfaces:
FeedbackCipher, Parameterized, SymmetricCipher

public class CBC
extends FeedbackMode

Implements a block cipher in CBC mode. The block size is the same as that of the underlying cipher.

References:

  1. Bruce Schneier, "Section 9.3 Cipher Block Chaining 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 © 1997, 1998 Systemics Ltd on behalf of the Cryptix Development Team.
All rights reserved.

$Revision: 1.7 $

Since:
Cryptix 2.2.2
Author:
David Hopwood, Raif S. Naffah

Field Summary
protected  byte[] xorBlock
          Temporary buffer to hold input bytes when there's not enough of them to cipher.
 
Fields inherited from class cryptix.provider.mode.FeedbackMode
currentByte, ivBlock, ivStart, length
 
Fields inherited from class xjava.security.Mode
cipher
 
Fields inherited from class xjava.security.Cipher
DECRYPT, ENCRYPT, UNINITIALIZED
 
Fields inherited from class xjava.security.IJCE_Traceable
tracing
 
Constructor Summary
CBC()
          Constructs a CBC cipher, assuming that the IV will be provided via setInitializationVector.
CBC(Cipher cipher)
          Constructs a CBC cipher, assuming that the IV will be provided via setInitializationVector.
CBC(Cipher cipher, byte[] iv)
          Constructs a CBC cipher, using an initialization vector provided in the constructor.
 
Method Summary
protected  int engineBlockSize()
          SPI: Returns the length of a block, in bytes.
protected  void engineInitDecrypt(java.security.Key newkey)
          SPI: Initializes this cipher for decryption, using the specified key.
protected  void engineInitEncrypt(java.security.Key newkey)
          SPI: Initializes this cipher for encryption, using the specified key.
protected  void engineSetCipher(Cipher cipher)
          SPI: Sets the underlying cipher.
protected  int engineUpdate(byte[] in, int inOffset, int inLen, byte[] out, int outOffset)
          SPI: This is the main engine method for updating data.
 
Methods inherited from class cryptix.provider.mode.FeedbackMode
getInitializationVector, getInitializationVectorLength, setInitializationVector
 
Methods inherited from class xjava.security.Mode
engineGetParameter, engineSetParameter, getAlgorithms, getAlgorithms, getInstance, getInstance, toString
 
Methods inherited from class xjava.security.Cipher
blockSize, clone, crypt, crypt, crypt, doFinal, doFinal, doFinal, doFinal, engineCiphertextBlockSize, engineCrypt, engineInBufferSize, engineOutBufferSize, enginePlaintextBlockSize, engineSetPaddingScheme, getAlgorithm, getCiphertextBlockSize, getInputBlockSize, getInstance, getMode, getOutputBlockSize, getPadding, getPaddingScheme, getParameter, getPlaintextBlockSize, getProvider, getState, inBufferSize, inBufferSizeFinal, initDecrypt, initEncrypt, isPaddingBlockCipher, outBufferSize, outBufferSizeFinal, setParameter, update, update, update, update
 
Methods inherited from class xjava.security.IJCE_Traceable
, disableTracing, enableTracing, traceMethod, traceResult, traceResult, traceVoidMethod
 
Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

xorBlock

protected byte[] xorBlock
Temporary buffer to hold input bytes when there's not enough of them to cipher.
Constructor Detail

CBC

public CBC()
Constructs a CBC cipher, assuming that the IV will be provided via setInitializationVector.

The IV value should be random, but unlike CFB mode, it is not absolutely required to be unique.


CBC

public CBC(Cipher cipher)
Constructs a CBC 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 CBC mode.
Throws:
NullPointerException - if cipher == null
IllegalBlockSizeException - if cipher.getPlaintextBlockSize() != cipher.getCiphertextBlockSize()

CBC

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

For CBC mode the IV value should be random, but unlike CFB mode, it is not absolutely required to be unique.

Parameters:
cipher - the block cipher to use
iv - the initial value for the shift register (IV)
Throws:
NullPointerException - if cipher == null
Method Detail

engineSetCipher

protected void engineSetCipher(Cipher cipher)
Description copied from class: FeedbackMode
SPI: Sets the underlying cipher.

For example, to create an IDEA cipher in CBC mode, the cipher for "IDEA" would be passed to the mode for "CBC" using this method. It is called once, immediately after the mode object is constructed.

Subclasses that override this method (to do initialization that depends on the cipher being set) should call super.engineSetCipher(cipher) first.

Overrides:
engineSetCipher in class FeedbackMode
Following copied from class: cryptix.provider.mode.FeedbackMode
Parameters:
cipher - the underlying cipher object
Throws:
NullPointerException - if cipher == null

engineBlockSize

protected int engineBlockSize()
Description copied from class: Cipher
SPI: Returns the length of a block, in bytes. Ciphers for which plaintext and ciphertext blocks are the same size may override this method. Otherwise, both enginePlaintextBlockSize and engineCiphertextBlockSize should be overridden.

The value may change when initEncrypt or initDecrypt is called, but it should not change at other times.

Overrides:
engineBlockSize in class Cipher
Following copied from class: xjava.security.Cipher
Returns:
the length in bytes of a block for this cipher.

engineInitEncrypt

protected void engineInitEncrypt(java.security.Key newkey)
                          throws java.security.KeyException
Description copied from class: Cipher
SPI: Initializes this cipher for encryption, using the specified key.

After a call to this method, the cipher's state is set to ENCRYPT.

Overrides:
engineInitEncrypt in class Cipher
Following copied from class: xjava.security.Cipher
Parameters:
key - the key to use for encryption.
Throws:
java.security.KeyException - if the key is invalid.

engineInitDecrypt

protected void engineInitDecrypt(java.security.Key newkey)
                          throws java.security.KeyException
Description copied from class: Cipher
SPI: Initializes this cipher for decryption, using the specified key.

After a call to this method, the cipher's state is set to DECRYPT.

Overrides:
engineInitDecrypt in class Cipher
Following copied from class: xjava.security.Cipher
Parameters:
key - the key to use for decryption.
Throws:
java.security.KeyException - if the key is invalid.

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.

Overrides:
engineUpdate in class Cipher
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.