gnu.crypto.pad

Class TBC

java.lang.Object

gnu.crypto.pad.BasePad

gnu.crypto.pad.TBC

All 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: 1.1 $

Field Summary

Fields inherited from class gnu.crypto.pad.BasePad

blockSize, name

Method Summary

Modifier and Type	Method and Description
byte[]	pad(byte[] in, int offset, int length) Returns the byte sequence that should be appended to the designated input.
void	setup() If any additional checks or resource setup must be done by the subclass, then this is the hook for it.
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, reset, selfTest

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

setup

public void setup()

Description copied from class: BasePad

If any additional checks or resource setup must be done by the subclass, then this is the hook for it. This method will be called before the BasePad.init(int) method returns.

Specified by:

setup in class BasePad

pad

public byte[] pad(byte[] in,
                  int offset,
                  int length)

Description copied from interface: IPad

Returns the byte sequence that should be appended to the designated input.

Specified by:

pad in interface IPad

Specified by:

pad in class 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.

unpad

public int unpad(byte[] in,
                 int offset,
                 int length)
          throws WrongPaddingException

Description copied from interface: IPad

Returns the number of bytes to discard from a designated input buffer.

Specified by:

unpad in interface IPad

Specified by:

unpad in class 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.