cryptix.provider.elgamal

Class RawElGamalCipher

java.lang.Object

xjava.security.IJCE_Traceable

xjava.security.Cipher

cryptix.provider.elgamal.RawElGamalCipher

All Implemented Interfaces:

java.lang.Cloneable, AsymmetricCipher, Parameterized

public class RawElGamalCipher
extends Cipher
implements AsymmetricCipher, java.lang.Cloneable

The raw ElGamal encryption algorithm.

References:

1. Bruce Schneier, "Section 19.6 ElGamal," Applied Cryptography, 2nd edition, John Wiley & Sons, 1996.

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

$Revision: 1.3 $

Since:

Cryptix 2.2.2

Author:

David Hopwood

Field Summary

Fields inherited from class xjava.security.Cipher

DECRYPT, ENCRYPT, UNINITIALIZED

Constructor Summary

Constructors

Constructor and Description
RawElGamalCipher() Constructor for a RawElGamalCipher.

Method Summary

Modifier and Type	Method and Description
protected int	engineCiphertextBlockSize() SPI: Return the ciphertext block size, in bytes.
protected java.lang.Object	engineGetParameter(java.lang.String param) SPI: Return an algorithm-specific parameter.
protected void	engineInitDecrypt(java.security.Key key) SPI: Initializes the cipher for decryption, using the given private key.
protected void	engineInitEncrypt(java.security.Key key) SPI: Initializes the cipher for encryption, using the given public key.
protected int	enginePlaintextBlockSize() SPI: Return the plaintext block size, in bytes.
protected void	engineSetParameter(java.lang.String param, java.lang.Object value) SPI: Set an algorithm-specific parameter.
protected int	engineUpdate(byte[] in, int inOffset, int inLen, byte[] out, int outOffset) SPI: DOCUMENT ME
static void	main(java.lang.String[] args) Entry point for very basic self_test.
static void	self_test(java.io.PrintWriter out)

Methods inherited from class xjava.security.Cipher

blockSize, clone, crypt, crypt, crypt, doFinal, doFinal, doFinal, doFinal, engineBlockSize, engineCrypt, engineInBufferSize, engineOutBufferSize, engineSetPaddingScheme, getAlgorithm, getAlgorithms, getAlgorithms, getCiphertextBlockSize, getInputBlockSize, getInstance, getInstance, getInstance, getMode, getOutputBlockSize, getPadding, getPaddingScheme, getParameter, getPlaintextBlockSize, getProvider, getState, inBufferSize, inBufferSizeFinal, initDecrypt, initEncrypt, isPaddingBlockCipher, outBufferSize, outBufferSizeFinal, setParameter, toString, update, update, update, update

Methods inherited from class java.lang.Object

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

Constructor Detail

RawElGamalCipher

public RawElGamalCipher()

Constructor for a RawElGamalCipher.

Method Detail

engineInitEncrypt

protected void engineInitEncrypt(java.security.Key key)
                          throws java.security.KeyException

SPI: Initializes the cipher for encryption, using the given public key. The key object must implement java.security.interfaces.ElGamalPublicKey.

Specified by:

engineInitEncrypt in class Cipher

Parameters:

key - the public key

Throws:

java.security.InvalidKeyException - if !(key instanceof java.security.interfaces.ElGamalPublicKey), or the key is otherwise invalid

java.security.KeyException - if the key is invalid.

engineInitDecrypt

protected void engineInitDecrypt(java.security.Key key)
                          throws java.security.KeyException

SPI: Initializes the cipher for decryption, using the given private key. The key object must implement java.security.interfaces.ElGamalPrivateKey.

Specified by:

engineInitDecrypt in class Cipher

Parameters:

key - the private key

Throws:

java.security.InvalidKeyException - if !(key instanceof java.security.interfaces.ElGamalPrivateKey), or the key is otherwise invalid

java.security.KeyException - if the key is invalid.

enginePlaintextBlockSize

protected int enginePlaintextBlockSize()

SPI: Return the plaintext block size, in bytes. For ElGamal this is the number of bytes needed for a bit string one bit shorter than the prime, p.

If the key has not been set, this method throws CryptixException (a subclass of ProviderException).

Overrides:

enginePlaintextBlockSize in class Cipher

Returns:

the plaintext block size

engineCiphertextBlockSize

protected int engineCiphertextBlockSize()

SPI: Return the ciphertext block size, in bytes. For ElGamal this is double the number of bytes needed to represent p-1.

If the key has not been set, this method throws CryptixException (a subclass of ProviderException).

Overrides:

engineCiphertextBlockSize in class Cipher

Returns:

the ciphertext block size

engineSetParameter

protected void engineSetParameter(java.lang.String param,
                                  java.lang.Object value)

SPI: Set an algorithm-specific parameter.

ElGamal has one algorithm-specific parameter called "random", of type java.util.Random, which specifies the source of random bits used to generate the k values needed for encryption. If this parameter is not set when initKey is called, the result of new SecureRandom() will be used.

You can set the "random" parameter using the following code:

   try {
       elgamal.setParameter("random", existingSecureRandom);
   } catch (InvalidParameterException e) { /* ignore */ }
   elgamal.initEncrypt(publicKey);
 

This is not useful if the cipher will only be used for decryption.

Overrides:

engineSetParameter in class Cipher

Parameters:

param - the string identifier of the parameter.

value - the parameter value.

Throws:

java.security.InvalidParameterException - if (!(param.equals("random") && value instanceof java.util.Random))

engineGetParameter

protected java.lang.Object engineGetParameter(java.lang.String param)

SPI: Return an algorithm-specific parameter.

ElGamal has one algorithm-specific parameter called "random", as described above. It is guaranteed to be a subclass of java.util.Random. Calling this method with a param string other than "random" will return null.

Overrides:

engineGetParameter in class Cipher

Parameters:

param - the string name of the parameter.

Returns:

the object that represents the parameter value, or null if there is none.

engineUpdate

protected int engineUpdate(byte[] in,
                           int inOffset,
                           int inLen,
                           byte[] out,
                           int outOffset)

SPI: DOCUMENT ME

Specified by:

engineUpdate in class Cipher

Parameters:

in - the input data.

inOffset - the offset into in specifying where the data starts.

inLen - the length of the subarray.

out - the output array.

outOffset - the offset indicating where to start writing into the out array.

Returns:

the number of bytes written.

main

public static final void main(java.lang.String[] args)

Entry point for very basic self_test.

self_test

public static void self_test(java.io.PrintWriter out)
                      throws java.security.KeyException

Throws:

java.security.KeyException