iaik.security.cipher

Class DESKeyGenerator

java.lang.Object

javax.crypto.KeyGeneratorSpi

iaik.security.cipher.VarLengthKeyGenerator

iaik.security.cipher.DESKeyGenerator

public class DESKeyGenerator
extends VarLengthKeyGenerator

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.

Version:

File Revision 16

See Also:

KeyGenerator, KeyGeneratorSpi, SecretKey, SecretKey, DES

Constructor Summary

Constructors

Constructor and Description
DESKeyGenerator()

Method Summary

Methods

Modifier and Type	Method and Description
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.
static boolean	checkParity(byte[] key, int offset, boolean odd) Checks if the given DES key, supplied in a byte array beginning at the given offset, is parity adjusted.
protected javax.crypto.SecretKey	engineGenerateKey() Generates a DES key.
protected void	engineInit(int strength, java.security.SecureRandom random) Initializes this key generator for the given strength with the given random seed.

Methods inherited from class iaik.security.cipher.VarLengthKeyGenerator

engineInit, engineInit

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

protected void engineInit(int strength,
              java.security.SecureRandom random)

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

Overrides:

engineInit in class VarLengthKeyGenerator

Parameters:

strength - the strength of the key to be created; if -1, the default length (64) is used

random - the random seed

Throws:

java.security.InvalidParameterException - if the supplied key strength is not -1 or 56 or 64

engineGenerateKey

protected javax.crypto.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 VarLengthKeyGenerator

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

checkParity

public static boolean checkParity(byte[] key,
                  int offset,
                  boolean odd)

Checks if the given DES key, supplied in a byte array beginning at the given offset, is parity adjusted.

Parameters:

key - the byte array holding the DES key

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

odd - whether to check for odd or even parity

Returns:

true if checking for odd parity and the key is odd parity adjusted; true if checking for even parity and the key is even parity adjusted; false in any other case (note that if this method returns false when checking for odd (even) parity, this does not necessarily mean that the key is even (odd) parity adjusted