xjava.security

Class PaddingScheme

Implemented Interfaces:
Padding, Parameterized
Known Direct Subclasses:
OneAndZeroes, PKCS5, PKCS7

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 $

Authors:
David Hopwood
Raif S. Naffah

Since:
IJCE 1.0.1

Field Summary

protected int
blockSize

Fields inherited from class xjava.security.IJCE_Traceable

tracing

Constructor Summary

PaddingScheme(String algorithm)
Constructor for a PaddingScheme.

Method Summary

Object
clone()
Returns a clone of this cipher.
protected Object
engineGetParameter(String param)
SPI: Gets the value of the specified algorithm parameter.
protected boolean
engineIsValidBlockSize(int size)
SPI: Returns true if size is a valid block size (in bytes) for this scheme.
protected int
enginePad(byte[] in, int offset, int length)
SPI: Pads a single incomplete block.
protected void
engineSetBlockSize(int size)
Sets the blockSize variable for this instance.
protected void
engineSetParameter(String param, Object value)
SPI: Sets the specified algorithm parameter to the specified value.
protected 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.
String
getAlgorithm()
Returns the standard name of the padding scheme implemented.
static String[]
getAlgorithms()
Gets the standard names of all PaddingSchemes implemented by any installed provider.
static String[]
getAlgorithms(Provider provider)
Gets the standard names of all PaddingSchemes implemented by a provider.
int
getBlockSize()
Returns the block size for this padding scheme.
static PaddingScheme
getInstance(String algorithm)
Generates a PaddingScheme object that implements the algorithm requested, as available in the environment.
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.
Object
getParameter(String param)
Gets the value of the specified algorithm parameter.
int
pad(byte[] in, int offset, int length)
Pads a given array of bytes.
int
padLength(int length)
Returns the increase in size that a padding operation would cause on input data of a given length.
String
paddingScheme()
Deprecated. Use getAlgorithm() instead.
void
setParameter(String param, Object value)
Sets the specified algorithm parameter to the specified value.
String
toString()
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.

Methods inherited from class xjava.security.IJCE_Traceable

disableTracing, enableTracing, traceMethod, traceResult, traceResult, traceVoidMethod

Field Details

blockSize

protected int blockSize

Constructor Details

PaddingScheme

protected PaddingScheme(String algorithm)

Parameters:
algorithm - the standard string name of the algorithm.

Method Details

clone

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


engineGetParameter

protected Object engineGetParameter(String param)
            throws NoSuchParameterException,
                   InvalidParameterException
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.


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 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.


engineSetParameter

protected void engineSetParameter(String param,
                                  Object value)
            throws NoSuchParameterException,
                   InvalidParameterException,
                   InvalidParameterTypeException
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.
InvalidParameterTypeException - if value is the wrong type for this parameter.


engineUnpad

protected 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, such as "PKCS#5".


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.


getAlgorithms

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


getBlockSize

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


getInstance

public static PaddingScheme getInstance(String algorithm)
            throws NoSuchAlgorithmException
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.


getInstance

public static PaddingScheme getInstance(String algorithm,
                                        String provider)
            throws NoSuchAlgorithmException,
                   NoSuchProviderException
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.


getParameter

public Object getParameter(String param)
            throws NoSuchParameterException,
                   InvalidParameterException
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.

Specified by:
getParameter in interface Parameterized

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.


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.


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).
Specified by:
padLength in interface Padding

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.


paddingScheme

public final String paddingScheme()

Deprecated. Use getAlgorithm() instead.

Specified by:
paddingScheme in interface Padding

Returns:
the standard name of the padding scheme.


setParameter

public void setParameter(String param,
                         Object value)
            throws NoSuchParameterException,
                   InvalidParameterException,
                   InvalidParameterTypeException
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.

Specified by:
setParameter in interface Parameterized

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

Throws:
NoSuchParameterException - if there is no parameter with name param for this padding scheme implementation.
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.