cryptix.provider.padding

Class PKCS5

public class PKCS5 extends PaddingScheme

A class for padding cipher data according to the following scheme, described in section 6.2 of RSA Data Security, Inc.'s PKCS #5 standard:

    ...
 

An IllegalBlockSizeException is thrown (by the Cipher class) if the block size is not 8 bytes.

References:

  1. PKCS#5: ... An RSA Laboratories Technical Note; Version 1.5; Revised November 1, 1993.

Copyright © 1997 Systemics Ltd on behalf of the Cryptix Development Team.
All rights reserved.

$Revision: 1.7 $

Since: Cryptix 2.2.2

Author: Raif S. Naffah David Hopwood

Constructor Summary
PKCS5()
Creates a PKCS5 object.
Method Summary
protected booleanengineIsValidBlockSize(int size)
SPI: Returns true if size is a valid block size (in bytes) for this algorithm.
protected intenginePad(byte[] in, int offset, int length)
Pads a given array of bytes.
protected intengineUnpad(byte[] in, int offset, int length)
Given the specified subarray of bytes that includes padding bytes, returns the index indicating where padding starts.

Constructor Detail

PKCS5

public PKCS5()
Creates a PKCS5 object.

Method Detail

engineIsValidBlockSize

protected boolean engineIsValidBlockSize(int size)
SPI: Returns true if size is a valid block size (in bytes) for this algorithm.

For PKCS#5 padding, the only valid size is 8 bytes.

enginePad

protected int enginePad(byte[] in, int offset, int length)
Pads a given array of bytes. The padding is written to the same buffer that is used for input (in). When this method returns, the padded block will be stored at in[offset+length..offset+7].

Parameters: in the buffer containing the incomplete block. offset the offset into the in buffer of the first byte in the group of bytes to be padded. length the number of bytes from the in buffer, starting at offset, that need to be padded.

engineUnpad

protected int engineUnpad(byte[] in, int offset, int length)
Given the specified subarray of bytes that includes padding bytes, returns the index indicating where padding starts.

For PKCS#5, the padding bytes all have value 8 - (length % 8). Hence to find the number of added bytes, it's enough to consider the last byte value of the padded message.

Parameters: in the buffer containing the bytes. offset the offset into the in buffer of the first byte in the block. length the length of the block in bytes.

Returns: the index into the in buffer indicating where the padding starts.

Throws: CryptixException if the number of padding bytes is invalid.