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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: 1.4 $

Field Summary
 
Fields inherited from class gnu.crypto.pad.BasePad
blockSize, name
 
Constructor Summary
(package private) 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, reset, selfTest
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

TBC

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

See Also:
PadFactory
Method Detail

setup

public void setup()
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.

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