iaik.security.cipher
Class DESKeyGenerator

java.lang.Object
  |
  +--javax.crypto.KeyGeneratorSpi
        |
        +--iaik.security.cipher.DESKeyGenerator

public class DESKeyGenerator

extends KeyGeneratorSpi

This class provides the functionality of a DES key generator. A key generator is used for creating secret keys for symmetric algorithms.

An application uses

KeyGenerator des_key_gen = 
 KeyGenerator.getInstance("DES");

for creating a KeyGenerator object for the DES algorithm. For actually generating the requested secret DES key from the KeyGenerator object just created, an application calls the generateKey method after having initialized the generator with some random seed or relied on the default system-provided source of randomness:

 SecretKey des_key = des_key_gen.generateKey();
 

Due to the way, the DES algorithm generates sub-keys for the several DES rounds, some initial keys may be classified as weak or semi-weak keys reducing the security of the DES cipher (see "Applied Cryptography", Bruce Schneier, ISBN 0-471-59756-2). This KeyGenerator class ensures to generate a strong DES key by repeating the key generation process as long as comparison with all the known weak and semi-weak DES keys will show that the just created key is not a strong one.

See Also:

KeyGenerator, KeyGeneratorSpi, SecretKey, SecretKey, DES

Constructor Summary

DESKeyGenerator()

Method Summary

static void	adjustParity(byte[] key, int offset) Adjusts the parity-bits of a DES key, supplied in a byte array beginning at the given offset.
SecretKey	engineGenerateKey() Generates a DES key.
void	engineInit(AlgorithmParameterSpec params, SecureRandom random) Because this DES key generator needs no parameter this initialization method only throws a InvalidAlgorithmParameterException.
void	engineInit(int strength, SecureRandom random) Initializes this DES key generator for the given strength with the given random seed.
void	engineInit(SecureRandom random) Initializes this DES key generator with the given random seed.

Methods inherited from class java.lang.Object

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

Constructor Detail

DESKeyGenerator

public DESKeyGenerator()

Method Detail

engineInit

public void engineInit(AlgorithmParameterSpec params,
                       SecureRandom random)
                throws InvalidAlgorithmParameterException

Because this DES key generator needs no parameter this initialization method only throws a InvalidAlgorithmParameterException.

Overrides:

engineInit in class KeyGeneratorSpi

Throws:

InvalidAlgorithmParameterException - since this DES key generator needs no parameters

engineInit

public void engineInit(SecureRandom random)

Initializes this DES key generator with the given random seed.

Overrides:

engineInit in class KeyGeneratorSpi

Parameters:

random - the random seed for this DES key generator

engineInit

public void engineInit(int strength,
                       SecureRandom random)

Initializes this DES key generator for the given strength with the given random seed.

Since a DES key has a defined length of 56 bits (respectively 64 bits when including parity bits), the given strength value would be ignored.

Overrides:

engineInit in class KeyGeneratorSpi

Parameters:

strength - the strength of the key to be created; ignored

random - the random seed

engineGenerateKey

public SecretKey engineGenerateKey()

Generates a DES key.

For ensuring to create a strong DES key, the key generation process is repeated as long as comparison with all the known weak and semi-weak DES keys will show that the just created key is not a strong DES key.

Overrides:

engineGenerateKey in class KeyGeneratorSpi

Returns:

the new created parity adjusted DES key

See Also:

SecretKey

adjustParity

public static void adjustParity(byte[] key,
                                int offset)

Adjusts the parity-bits of a DES key, supplied in a byte array beginning at the given offset.

Parameters:

key - the byte array holding the DES key

offset - the offset indicating where the key starts within the given byte array