gnu.crypto.cipher

Class DES

Implemented Interfaces:
Cloneable, IBlockCipher, IBlockCipherSpi

public class DES
extends BaseCipher

The Data Encryption Standard. DES is a 64-bit block cipher with a 56-bit key, developed by IBM in the 1970's for the standardization process begun by the National Bureau of Standards (now NIST).

New applications should not use DES except for compatibility.

This version is based upon the description and sample implementation in [1].

References:

  1. Bruce Schneier, Applied Cryptography: Protocols, Algorithms, and Source Code in C, Second Edition. (1996 John Wiley and Sons) ISBN 0-471-11709-9. Pages 265--301, 623--632.
Version:
$Revision: 1.4 $

Nested Class Summary

(package private) class
DES.Context
Simple wrapper class around the session keys.

Field Summary

static int
BLOCK_SIZE
DES operates on 64 bit blocks.
static int
KEY_SIZE
DES uses 56 bits of a 64 bit parity-adjusted key.
static byte[][]
POSSIBLE_WEAK_KEYS
Possible weak keys (parity adjusted) --produce 4 instead of 16 subkeys.
static byte[][]
SEMIWEAK_KEYS
Semi-weak keys (parity adjusted): Some pairs of keys encrypt plain text to identical cipher text.
static byte[][]
WEAK_KEYS
Weak keys (parity adjusted): If all the bits in each half are either 0 or 1, then the key used for any cycle of the algorithm is the same as all other cycles.

Fields inherited from class gnu.crypto.cipher.BaseCipher

currentBlockSize, currentKey, defaultBlockSize, defaultKeySize, lock, name

Fields inherited from interface gnu.crypto.cipher.IBlockCipher

CIPHER_BLOCK_SIZE, KEY_MATERIAL

Constructor Summary

DES()
Default 0-argument constructor.

Method Summary

static void
adjustParity(byte[] kb, int offset)
Adjust the parity for a raw key array.
Iterator
blockSizes()
Returns an Iterator over the supported block sizes.
Object
clone()
void
decrypt(byte[] in, int i, byte[] out, int o, Object K, int bs)
Decrypts exactly one block of ciphertext.
void
encrypt(byte[] in, int i, byte[] out, int o, Object K, int bs)
Encrypts exactly one block of plaintext.
static boolean
isParityAdjusted(byte[] kb, int offset)
Test if a byte array, which must be at least 8 bytes long, is parity adjusted.
static boolean
isPossibleWeak(byte[] kb)
Test if the designated byte array represents a possibly weak key.
static boolean
isSemiWeak(byte[] kb)
Test if a key is a semi-weak key.
static boolean
isWeak(byte[] kb)
Test if a key is a weak key.
Iterator
keySizes()
Returns an Iterator over the supported key sizes.
Object
makeKey(byte[] kb, int bs)
Expands a user-supplied key material into a session key for a designated block size.

Methods inherited from class gnu.crypto.cipher.BaseCipher

clone, currentBlockSize, decryptBlock, defaultBlockSize, defaultKeySize, encryptBlock, init, name, reset, selfTest, testKat, testKat

Field Details

BLOCK_SIZE

public static final int BLOCK_SIZE
DES operates on 64 bit blocks.
Field Value:
8

KEY_SIZE

public static final int KEY_SIZE
DES uses 56 bits of a 64 bit parity-adjusted key.
Field Value:
8

POSSIBLE_WEAK_KEYS

public static final byte[][] POSSIBLE_WEAK_KEYS
Possible weak keys (parity adjusted) --produce 4 instead of 16 subkeys.

SEMIWEAK_KEYS

public static final byte[][] SEMIWEAK_KEYS
Semi-weak keys (parity adjusted): Some pairs of keys encrypt plain text to identical cipher text. In other words, one key in the pair can decrypt messages that were encrypted with the other key. These keys are called semi-weak keys. This occurs because instead of 16 different sub-keys being generated, these semi-weak keys produce only two different sub-keys.

WEAK_KEYS

public static final byte[][] WEAK_KEYS
Weak keys (parity adjusted): If all the bits in each half are either 0 or 1, then the key used for any cycle of the algorithm is the same as all other cycles.

Constructor Details

DES

public DES()
Default 0-argument constructor.

Method Details

adjustParity

public static void adjustParity(byte[] kb,
                                int offset)
Adjust the parity for a raw key array. This essentially means that each byte in the array will have an odd number of '1' bits (the last bit in each byte is unused.
Parameters:
kb - The key array, to be parity-adjusted.
offset - The starting index into the key bytes.

blockSizes

public Iterator blockSizes()
Returns an Iterator over the supported block sizes. Each element returned by this object is a Integer.
Specified by:
blockSizes in interface IBlockCipher
blockSizes in interface IBlockCipherSpi
Returns:
an Iterator over the supported block sizes.

clone

public Object clone()
Specified by:
clone in interface IBlockCipher
Overrides:
clone in interface BaseCipher

decrypt

public void decrypt(byte[] in,
                    int i,
                    byte[] out,
                    int o,
                    Object K,
                    int bs)
Decrypts exactly one block of ciphertext.
Specified by:
decrypt in interface IBlockCipherSpi
Parameters:
in - the ciphertext.
out - the plaintext.
bs - the block size to use.

encrypt

public void encrypt(byte[] in,
                    int i,
                    byte[] out,
                    int o,
                    Object K,
                    int bs)
Encrypts exactly one block of plaintext.
Specified by:
encrypt in interface IBlockCipherSpi
Parameters:
in - the plaintext.
out - the ciphertext.
bs - the block size to use.

isParityAdjusted

public static boolean isParityAdjusted(byte[] kb,
                                       int offset)
Test if a byte array, which must be at least 8 bytes long, is parity adjusted.
Parameters:
kb - The key bytes.
offset - The starting index into the key bytes.
Returns:
true if the first 8 bytes of kb have been parity adjusted. false otherwise.

isPossibleWeak

public static boolean isPossibleWeak(byte[] kb)
Test if the designated byte array represents a possibly weak key.
Parameters:
kb - the byte array to test.
Returns:
true if kbrepresents a possibly weak key. Returns false otherwise.

isSemiWeak

public static boolean isSemiWeak(byte[] kb)
Test if a key is a semi-weak key.
Parameters:
kb - The key to test.
Returns:
true if this key is semi-weak.

isWeak

public static boolean isWeak(byte[] kb)
Test if a key is a weak key.
Parameters:
kb - The key to test.
Returns:
true if the key is weak.

keySizes

public Iterator keySizes()
Returns an Iterator over the supported key sizes. Each element returned by this object is a Integer.
Specified by:
keySizes in interface IBlockCipher
keySizes in interface IBlockCipherSpi
Returns:
an Iterator over the supported key sizes.

makeKey

public Object makeKey(byte[] kb,
                      int bs)
            throws InvalidKeyException
Expands a user-supplied key material into a session key for a designated block size.
Specified by:
makeKey in interface IBlockCipherSpi
Parameters:
bs - the desired block size in bytes.
Returns:
an Object encapsulating the session key.

Copyright © 2001, 2002, 2003 Free Software Foundation, Inc. All Rights Reserved.