org.bouncycastle.crypto.modes
Class OFBBlockCipher

java.lang.Object
  org.bouncycastle.crypto.modes.OFBBlockCipher

All Implemented Interfaces:

BlockCipher

public class OFBBlockCipher
extends java.lang.Object
implements BlockCipher

implements a Output-FeedBack (OFB) mode on top of a simple cipher.

Field Summary

private int	blockSize
private BlockCipher	cipher
private byte[]	IV
private byte[]	ofbOutV
private byte[]	ofbV

Constructor Summary

OFBBlockCipher(BlockCipher cipher, int blockSize)
Basic constructor.

Method Summary

java.lang.String	getAlgorithmName() return the algorithm name and mode.
int	getBlockSize() return the block size we are operating at (in bytes).
BlockCipher	getUnderlyingCipher() return the underlying block cipher that we are wrapping.
void	init(boolean encrypting, CipherParameters params) Initialise the cipher and, possibly, the initialisation vector (IV).
int	processBlock(byte[] in, int inOff, byte[] out, int outOff) Process one block of input from the array in and write it to the out array.
void	reset() reset the feedback vector back to the IV and reset the underlying cipher.

Methods inherited from class java.lang.Object

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

Field Detail

IV

private byte[] IV

ofbV

private byte[] ofbV

ofbOutV

private byte[] ofbOutV

blockSize

private final int blockSize

cipher

private final BlockCipher cipher

Constructor Detail

OFBBlockCipher

public OFBBlockCipher(BlockCipher cipher,
                      int blockSize)

Basic constructor.

Parameters:

cipher - the block cipher to be used as the basis of the feedback mode.

blockSize - the block size in bits (note: a multiple of 8)

Method Detail

getUnderlyingCipher

public BlockCipher getUnderlyingCipher()

return the underlying block cipher that we are wrapping.

Returns:

the underlying block cipher that we are wrapping.

init

public void init(boolean encrypting,
                 CipherParameters params)
          throws java.lang.IllegalArgumentException

Initialise the cipher and, possibly, the initialisation vector (IV). If an IV isn't passed as part of the parameter, the IV will be all zeros. An IV which is too short is handled in FIPS compliant fashion.

Specified by:

init in interface BlockCipher

Parameters:

encrypting - if true the cipher is initialised for encryption, if false for decryption.

params - the key and other data required by the cipher.

Throws:

java.lang.IllegalArgumentException - if the params argument is inappropriate.

getAlgorithmName

public java.lang.String getAlgorithmName()

return the algorithm name and mode.

Specified by:

getAlgorithmName in interface BlockCipher

Returns:

the name of the underlying algorithm followed by "/OFB" and the block size in bits

getBlockSize

public int getBlockSize()

return the block size we are operating at (in bytes).

Specified by:

getBlockSize in interface BlockCipher

Returns:

the block size we are operating at (in bytes).

processBlock

public int processBlock(byte[] in,
                        int inOff,
                        byte[] out,
                        int outOff)
                 throws DataLengthException,
                        java.lang.IllegalStateException

Process one block of input from the array in and write it to the out array.

Specified by:

processBlock in interface BlockCipher

Parameters:

in - the array containing the input data.

inOff - offset into the in array the data starts at.

out - the array the output data will be copied into.

outOff - the offset into the out array the output will start at.

Returns:

the number of bytes processed and produced.

Throws:

DataLengthException - if there isn't enough data in in, or space in out.

java.lang.IllegalStateException - if the cipher isn't initialised.

reset

public void reset()

reset the feedback vector back to the IV and reset the underlying cipher.

Specified by:

reset in interface BlockCipher