xjava.security

Class PaddingScheme

public abstract class PaddingScheme extends IJCE_Traceable implements Parameterized, Padding

This class is extended by classes that provide a general-purpose padding scheme, such as the ones described in PKCS #5 or in RFC 1423 (PEM).

For simplicity, an assumption is made that padding schemes always extend the plaintext to the next block boundary. That is, the input to the padding algorithm always has a length between 0 and blockSize-1, and the output always has length blockSize.

This class is not supported in JavaSoft's version of JCE.

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

$Revision: 1.8 $

Since: IJCE 1.0.1

Author: David Hopwood Raif S. Naffah

Field Summary
protected intblockSize
Constructor Summary
protected PaddingScheme(String algorithm)
Constructor for a PaddingScheme.
Method Summary
Objectclone()
Returns a clone of this cipher.
protected ObjectengineGetParameter(String param)
SPI: Gets the value of the specified algorithm parameter.
protected booleanengineIsValidBlockSize(int size)
SPI: Returns true if size is a valid block size (in bytes) for this scheme.
protected abstract intenginePad(byte[] in, int offset, int length)
SPI: Pads a single incomplete block.
protected voidengineSetBlockSize(int size)
Sets the blockSize variable for this instance.
protected voidengineSetParameter(String param, Object value)
SPI: Sets the specified algorithm parameter to the specified value.
protected abstract intengineUnpad(byte[] in, int offset, int length)
SPI: Given the specified subarray of bytes that includes padding bytes, returns the index indicating where padding starts.
StringgetAlgorithm()
Returns the standard name of the padding scheme implemented.
static String[]getAlgorithms(Provider provider)
Gets the standard names of all PaddingSchemes implemented by a provider.
static String[]getAlgorithms()
Gets the standard names of all PaddingSchemes implemented by any installed provider.
intgetBlockSize()
Returns the block size for this padding scheme.
static PaddingSchemegetInstance(String algorithm)
Generates a PaddingScheme object that implements the algorithm requested, as available in the environment.
static PaddingSchemegetInstance(String algorithm, String provider)
Generates a PaddingScheme object implementing the specified algorithm, as supplied from the specified provider, if such an algorithm is available from the provider.
ObjectgetParameter(String param)
Gets the value of the specified algorithm parameter.
intpad(byte[] in, int offset, int length)
Pads a given array of bytes.
StringpaddingScheme()
Returns the standard name of the padding scheme implemented.
intpadLength(int length)
Returns the increase in size that a padding operation would cause on input data of a given length.
voidsetParameter(String param, Object value)
Sets the specified algorithm parameter to the specified value.
StringtoString()
intunpad(byte[] in, int offset, int length)
Given the specified subarray of bytes that includes padding bytes, returns the index indicating where padding starts.

Field Detail

blockSize

protected int blockSize

Constructor Detail

PaddingScheme

protected PaddingScheme(String algorithm)
Constructor for a PaddingScheme. This constructor is only for use by subclasses; applications cannot call it directly.

See International JCE Standard Algorithm Names for a list of PaddingScheme algorithm names.

Parameters: algorithm the standard string name of the algorithm.

Throws: NullPointerException if algorithm == null

Method Detail

clone

public Object clone()
Returns a clone of this cipher.

Throws: CloneNotSupportedException if the cipher is not cloneable.

engineGetParameter

protected Object engineGetParameter(String param)
SPI: Gets the value of the specified algorithm parameter.

This method supplies a general-purpose mechanism through which it is possible to get the various parameters of this object. A uniform algorithm-specific naming scheme for each parameter is desirable but left unspecified at this time.

The default implementation always throws a NoSuchParameterException.

This method is not supported in JavaSoft's version of JCE.

Parameters: param the string name of the parameter.

Returns: the object that represents the parameter value.

Throws: NoSuchParameterException if there is no parameter with name param for this padding scheme implementation. InvalidParameterException if the parameter exists but cannot be read.

engineIsValidBlockSize

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

The default implementation always returns true.

enginePad

protected abstract int enginePad(byte[] in, int offset, int length)
SPI: Pads a single incomplete block.

The padding is written to the same buffer that is used for input (in). When this method returns, the padded block should be stored at in[offset .. offset+blockSize-1].

in will be long enough to accomodate the padding. length is guaranteed to be in the range 0 .. blockSize-1.

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

Returns: the number of padding bytes written.

engineSetBlockSize

protected void engineSetBlockSize(int size)
Sets the blockSize variable for this instance.

Subclasses that override this method (to do initialization that depends on blockSize being set) should call super.engineSetBlockSize(size) first.

Throws: IllegalBlockSizeException if size < 1 || !engineIsValidBlockSize(size)

engineSetParameter

protected void engineSetParameter(String param, Object value)
SPI: Sets the specified algorithm parameter to the specified value.

This method supplies a general-purpose mechanism through which it is possible to set the various parameters of this object. A uniform algorithm-specific naming scheme for each parameter is desirable but left unspecified at this time.

The default implementation always throws a NoSuchParameterException.

This method is not supported in JavaSoft's version of JCE.

Parameters: param the string name of the parameter. value the parameter value.

Throws: NoSuchParameterException if there is no parameter with name param for this padding scheme implementation. InvalidParameterException if the parameter exists but cannot be set. InvalidParameterTypeException if value is the wrong type for this parameter.

engineUnpad

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

length is guaranteed to be a non-negative multiple of blockSize.

Parameters: in the buffer containing the bytes. offset the offset into the in buffer of the first byte to be unpadded. length the total length in bytes of the blocks to be unpadded.

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

getAlgorithm

public final String getAlgorithm()
Returns the standard name of the padding scheme implemented.

See International JCE Standard Algorithm Names for a list of PaddingScheme algorithm names.

Returns: the standard name of the padding scheme, such as "PKCS#5".

getAlgorithms

public static String[] getAlgorithms(Provider provider)
Gets the standard names of all PaddingSchemes implemented by a provider.

getAlgorithms

public static String[] getAlgorithms()
Gets the standard names of all PaddingSchemes implemented by any installed provider. Algorithm names are not duplicated if they are supported by more than one provider. The built-in PaddingScheme "NONE" is included.

getBlockSize

public final int getBlockSize()
Returns the block size for this padding scheme.

getInstance

public static PaddingScheme getInstance(String algorithm)
Generates a PaddingScheme object that implements the algorithm requested, as available in the environment.

See International JCE Standard Algorithm Names for a list of PaddingScheme algorithm names.

Parameters: algorithm the standard name or an alias for the algorithm.

Returns: the new PaddingScheme object.

Throws: NoSuchAlgorithmException if the algorithm is not available in the environment.

getInstance

public static PaddingScheme getInstance(String algorithm, String provider)
Generates a PaddingScheme object implementing the specified algorithm, as supplied from the specified provider, if such an algorithm is available from the provider.

See International JCE Standard Algorithm Names for a list of PaddingScheme algorithm names.

Parameters: algorithm the standard name or an alias for the algorithm. provider the string name of the provider.

Returns: the new KeyGenerator object.

Throws: NoSuchAlgorithmException if the algorithm is not available from the provider. NoSuchProviderException if the provider is not available in the environment.

getParameter

public Object getParameter(String param)
Gets the value of the specified algorithm parameter.

This method supplies a general-purpose mechanism through which it is possible to get the various parameters of this object. A uniform algorithm-specific naming scheme for each parameter is desirable but left unspecified at this time.

This method is not supported in JavaSoft's version of JCE.

Parameters: param the string name of the parameter.

Returns: the object that represents the parameter value.

Throws: NullPointerException if param == null NoSuchParameterException if there is no parameter with name param for this padding scheme implementation. InvalidParameterException if the parameter exists but cannot be read.

pad

public final int pad(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 output will be stored at in[offset .. offset+length+padLength(length)-1].

The in array should be long enough to accomodate the padding.

The return value is the number of bytes written, not the total length of the padded block.

Parameters: in the buffer containing the input. offset the offset of the bytes to be padded. length the number of bytes from the in buffer, starting at offset, that need to be padded.

Returns: the number of padding bytes written to out.

Throws: ArrayIndexOutOfBoundsException if offset < 0 || length < 0 || (long)offset + length + padLength(length) > in.length

paddingScheme

public final String paddingScheme()

Deprecated: Use getAlgorithm() instead.

Returns the standard name of the padding scheme implemented.

See International JCE Standard Algorithm Names for a list of PaddingScheme algorithm names.

Returns: the standard name of the padding scheme.

padLength

public final int padLength(int length)
Returns the increase in size that a padding operation would cause on input data of a given length. This is always blockSize - (length % blockSize).

Parameters: length the length of the data to be padded.

Returns: the increase in size that a padding operation would cause on input of the specified length.

setParameter

public void setParameter(String param, Object value)
Sets the specified algorithm parameter to the specified value.

This method supplies a general-purpose mechanism through which it is possible to set the various parameters of this object. A uniform algorithm-specific naming scheme for each parameter is desirable but left unspecified at this time.

This method is not supported in JavaSoft's version of JCE.

Parameters: param the string identifier of the parameter. value the parameter value.

Throws: NullPointerException if param == null NoSuchParameterException if there is no parameter with name param for this padding scheme implementation. InvalidParameterException if the parameter exists but cannot be set. InvalidParameterTypeException if value is the wrong type for this parameter.

toString

public String toString()

unpad

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

length must be at least blockSize.

Parameters: in the buffer containing the bytes. offset the offset into the in buffer of the first byte in the block. length the total length in bytes of the blocks to be unpadded.

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

Throws: ArrayIndexOutOfBoundsException if offset < 0 || length < 0 || (long)offset + length > in.length IllegalBlockSizeException if length < blockSize