cryptix.provider.mode

Class FeedbackMode

abstract class FeedbackMode extends Mode implements FeedbackCipher, SymmetricCipher

FeedbackMode is used to provide the functionality of an encryption mode, such as CBC, CFB, or OFB, that works as a feedback cipher, where the size of the IV and feedback buffer are equal to the cipher's block size.

It is internal to Cryptix, and not intended to be used directly by applications.

Copyright © 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

Field Summary
protected intcurrentByte
Index into the ivBlock.
protected byte[]ivBlock
Value of the current feedback register/queue/buffer.
protected byte[]ivStart
Value of the IV at initialisation phase as supplied by user.
protected intlength
Size of the feedback register/queue/buffer.
Constructor Summary
protected FeedbackMode(boolean implBuffering, boolean implPadding, String provider)
Constructor for a Mode.
Method Summary
protected voidengineSetCipher(Cipher cipher)
SPI: Sets the underlying cipher.
byte[]getInitializationVector()
Gets a copy of the starting initialization vector.
intgetInitializationVectorLength()
Returns the size of the initialization vector expected by setInitializationVector.
voidsetInitializationVector(byte[] iv)
Sets the initialization vector.

Field Detail

currentByte

protected int currentByte
Index into the ivBlock.

ivBlock

protected byte[] ivBlock
Value of the current feedback register/queue/buffer.

ivStart

protected byte[] ivStart
Value of the IV at initialisation phase as supplied by user.

length

protected int length
Size of the feedback register/queue/buffer.

Constructor Detail

FeedbackMode

protected FeedbackMode(boolean implBuffering, boolean implPadding, String provider)
Constructor for a Mode. This constructor is only for use by subclasses, which should pass the correct arguments to convey their behaviour to the superclass. Applications typically do not use Mode classes directly; they should call one of the Cipher.getInstance factory methods instead.

Parameters: implBuffering if true, this argument indicates that data will be passed from update/crypt to engineUpdate/engineCrypt without modification. implPadding if true, this argument indicates that the implementation can perform padding, and that the engineCrypt method will be called when padding is required. provider the name of the provider of the underlying cryptographic engine.

Throws: NullPointerException if provider == null

Method Detail

engineSetCipher

protected void engineSetCipher(Cipher cipher)
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.

Parameters: cipher the underlying cipher object

Throws: NullPointerException if cipher == null

getInitializationVector

public byte[] getInitializationVector()
Gets a copy of the starting initialization vector. It will return null if the initialization vector has not been set.

Returns: a copy of the initialization vector for this cipher object.

getInitializationVectorLength

public int getInitializationVectorLength()
Returns the size of the initialization vector expected by setInitializationVector. For this class, that is the block size of the underlying cipher.

Returns: the required size of the argument to setInitializationVector.

setInitializationVector

public void setInitializationVector(byte[] iv)
Sets the initialization vector.

Note: in JavaSoft's version of JCE, this method may only be called when the cipher is in the UNINITIALIZED state. In IJCE that is relaxed to also allow it to be called after initEncrypt/initDecrypt, but before the first call to update or crypt, provided that the IV is not set twice.

Parameters: iv the initialization vector.

Throws: InvalidParameterException if the initialization vector is of the wrong length or has already been set.