gnu.crypto.pad

Class TBC

Implemented Interfaces:
IPad

public final class TBC
extends BasePad

The implementation of the Trailing Bit Complement (TBC) padding algorithm.

In this mode, "...the data string is padded at the trailing end with the complement of the trailing bit of the unpadded message: if the trailing bit is 1, then 0 bits are appended, and if the trailing bit is 0, then 1 bits are appended. As few bits are added as are necessary to meet the formatting size requirement." References:
Recommendation for Block Cipher Modes of Operation Methods and Techniques, Morris Dworkin.

Version:
$Revision: 1.5 $

Field Summary

Fields inherited from class gnu.crypto.pad.BasePad

blockSize, name

Constructor Summary

TBC()
Trivial package-private constructor for use by the Factory class.

Method Summary

byte[]
pad(byte[] in, int offset, int length)
Returns the byte sequence that should be appended to the designated input.
void
setup()
int
unpad(byte[] in, int offset, int length)
Returns the number of bytes to discard from a designated input buffer.

Methods inherited from class gnu.crypto.pad.BasePad

init, name, pad, reset, selfTest, setup, unpad

Constructor Details

TBC

(package private)  TBC()
Trivial package-private constructor for use by the Factory class.

Method Details

pad

public byte[] pad(byte[] in,
                  int offset,
                  int length)
Returns the byte sequence that should be appended to the designated input.
Specified by:
pad in interface IPad
Overrides:
pad in interface BasePad
Parameters:
in - the input buffer containing the bytes to pad.
offset - the starting index of meaningful data in in.
length - the number of meaningful bytes in in.
Returns:
the possibly 0-byte long sequence to be appended to the designated input.

setup

public void setup()
Overrides:
setup in interface BasePad

unpad

public int unpad(byte[] in,
                 int offset,
                 int length)
            throws WrongPaddingException
Returns the number of bytes to discard from a designated input buffer.
Specified by:
unpad in interface IPad
Overrides:
unpad in interface BasePad
Parameters:
in - the input buffer containing the bytes to unpad.
offset - the starting index of meaningful data in in.
length - the number of meaningful bytes in in.
Returns:
the number of bytes to discard, to the left of index position offset + length in in. In other words, if the return value of a successful invocation of this method is result, then the unpadded byte sequence will be offset + length - result bytes in in, starting from index position offset.
Throws:
WrongPaddingException - if the data is not terminated with the expected padding bytes.

Copyright © 2001, 2002, 2003 Free Software Foundation, Inc. All Rights Reserved.