cryptix.provider.key

Class DESKeyGenerator

java.lang.Object

xjava.security.KeyGenerator

cryptix.provider.key.RawKeyGenerator

cryptix.provider.key.DESKeyGenerator

All Implemented Interfaces:

java.lang.Cloneable, ExtendedKeyGenerator, Parameterized

Direct Known Subclasses:

DES_EDE3KeyGenerator, DES2XKeyGenerator, DESXKeyGenerator

public class DESKeyGenerator
extends RawKeyGenerator

A key generator for (single) DES.

DES keys have a fixed length of 8 bytes, with a parity bit as the LSB of each byte (i.e. there are 2^56 possible keys).

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

$Revision: 1.2 $

Since:

Cryptix 2.2.0a, 2.2.2

Author:

David Hopwood, Raif Naffah

Constructor Summary

Constructors

Modifier	Constructor and Description
	DESKeyGenerator()
protected	DESKeyGenerator(java.lang.String algorithm, int seedlength) Constructor for use by subclasses that need to specify a different seed length (e.g.

Method Summary

Modifier and Type	Method and Description
protected byte[]	engineGenerateKey(byte[] seed) This method allows subclasses to modify the bytes that will be used to generate a key.
protected boolean	isWeak(byte[] key) Returns true iff the first 8 bytes of key represent a weak or semi-weak single DES key.
protected boolean	isWeak(byte[] key, int offset) Returns true iff the bytes at key[offset..offset+7] represent a weak or semi-weak single DES key.
protected void	setParity(byte[] array) Sets parity bits for the given input array.

Methods inherited from class cryptix.provider.key.RawKeyGenerator

generateKey, generateKey, getDefaultKeyLength, getMaximumKeyLength, getMinimumKeyLength, initialize, initialize, isValidKeyLength, isWeakAllowed, setWeakAllowed

Methods inherited from class xjava.security.KeyGenerator

clone, engineGetParameter, engineSetParameter, getAlgorithm, getAlgorithms, getAlgorithms, getInstance, getInstance, getParameter, setParameter, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

DESKeyGenerator

public DESKeyGenerator()

DESKeyGenerator

protected DESKeyGenerator(java.lang.String algorithm,
                          int seedlength)

Constructor for use by subclasses that need to specify a different seed length (e.g. for Triple DES).

Method Detail

engineGenerateKey

protected byte[] engineGenerateKey(byte[] seed)
                            throws WeakKeyException,
                                   java.security.InvalidKeyException

Description copied from class: RawKeyGenerator

This method allows subclasses to modify the bytes that will be used to generate a key. This might be necessary in order to set parity bits, for example.

The seed array contains either randomly generated bytes, or an encoded form of the key. Subclasses should throw a WeakKeyException if isWeakAllowed() is false, and a weak key would have been generated.

The default implementation is as follows: If weak keys are not allowed, and the seed array represents a weak key (i.e. !isWeakAllowed() && isWeak(seed)), throw a WeakKeyException. Otherwise, just return the seed array. This is sufficient if the key does not have any special form (for example, parity bits that should be set correctly).

The seed array can be modified if that is convenient.

Overrides:

engineGenerateKey in class RawKeyGenerator

Parameters:

seed - the seed bytes for this key.

Returns:

the key encoding.

Throws:

WeakKeyException

java.security.InvalidKeyException

setParity

protected void setParity(byte[] array)

Sets parity bits for the given input array. The least significant bit of each byte is changed to ensure that the byte has odd parity.

isWeak

protected boolean isWeak(byte[] key)

Returns true iff the first 8 bytes of key represent a weak or semi-weak single DES key.

Overrides:

isWeak in class RawKeyGenerator

isWeak

protected boolean isWeak(byte[] key,
                         int offset)

Returns true iff the bytes at key[offset..offset+7] represent a weak or semi-weak single DES key. It can be called either before or after setting parity bits.

(This checks for the 16 weak and semi-weak keys as given by Schneier, Applied Cryptography 2nd ed., tables 12.11 and 12.12. It does not check for the possibly-weak keys in table 12.13.)