001/* DESKeySpec -- Keys for DES.
002   Copyright (C) 2004  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package javax.crypto.spec;
040
041import java.security.InvalidKeyException;
042import java.security.spec.KeySpec;
043
044/**
045 * This class is a transparent wrapper for DES keys, which are arrays
046 * of 8 bytes.
047 *
048 * @author Casey Marshall (csm@gnu.org)
049 * @since 1.4
050 */
051public class DESKeySpec implements KeySpec
052{
053
054  // Constants.
055  // ------------------------------------------------------------------------
056
057  /**
058   * The length of a DES key, in bytes.
059   */
060  public static final int DES_KEY_LEN = 8;
061
062  /**
063   * The key bytes.
064   */
065  private byte[] key;
066
067  // Constructors.
068  // ------------------------------------------------------------------------
069
070  /**
071   * Create a new DES key spec, copying the first 8 bytes from the
072   * byte array.
073   *
074   * @param key The key bytes.
075   * @throws java.security.InvalidKeyException If there are less than 8
076   *         bytes in the array.
077   */
078  public DESKeySpec(byte[] key) throws InvalidKeyException
079  {
080    this(key, 0);
081  }
082
083  /**
084   * Create a new DES key spec, starting at <code>offset</code> in
085   * the byte array. The first 8 bytes starting at <code>offset</code>
086   * are copied.
087   *
088   * @param key    The key bytes.
089   * @param offset The offset into the byte array at which to begin.
090   * @throws java.security.InvalidKeyException If there are less than 8
091   *         bytes starting at <code>offset</code>.
092   */
093  public DESKeySpec(byte[] key, int offset) throws InvalidKeyException
094  {
095    if (key.length - offset < DES_KEY_LEN)
096      {
097        throw new InvalidKeyException("DES keys must be 8 bytes long");
098      }
099    this.key = new byte[DES_KEY_LEN];
100    System.arraycopy(key, offset, this.key, 0, DES_KEY_LEN);
101  }
102
103  // Class methods.
104  // ------------------------------------------------------------------------
105
106  /**
107   * Returns whether or not the given key is <i>parity adjusted</i>;
108   * i.e. every byte in the key has an odd number of "1" bits.
109   *
110   * @param key    The key bytes, considered between <code>[offset,
111   *               offset+7]</code>
112   * @param offset The offset into the byte array at which to begin.
113   * @return True if all bytes have an odd number of "1" bits.
114   * @throws java.security.InvalidKeyException If there are not enough
115   *         bytes in the array.
116   */
117  public static boolean isParityAdjusted(byte[] key, int offset)
118    throws InvalidKeyException
119  {
120    if (key.length - offset < DES_KEY_LEN)
121      {
122        throw new InvalidKeyException("DES keys must be 8 bytes long");
123      }
124    boolean parity = false;
125    boolean oddbits = false;
126    for (int i = 0; i < DES_KEY_LEN; i++)
127      {
128        oddbits = false;
129        for (int j = 0; j < 8; j++)
130          {
131            oddbits ^= (key[i+offset] & 1 << j) != 0;
132          }
133        parity &= oddbits;
134      }
135    return parity;
136  }
137
138  /**
139   * One-half of the weak and semiweak DES keys (the other half are the
140   * complements of these).
141   */
142  private static final byte[][] WEAK_KEYS = new byte[][] {
143    {   0,   0,   0,   0,   0,   0,   0,   0 }, // 0000 0000 0000 0000
144    {  -1,  -1,  -1,  -1,   0,   0,   0,   0 }, // ffff ffff 0000 0000
145    {   1,   1,   1,   1,   1,   1,   1,   1 }, // 0101 0101 0101 0101
146    {  31,  31,  31,  31,  14,  14,  14,  14 }, // 1f1f 1f1f 0e0e 0e0e
147    {   1,  -2,   1,  -2,   1,  -2,   1,  -2 }, // 01fe 01fe 01fe 01fe
148    {  31, -32,  31, -32, -32,  31, -32,  31 }, // 1fe0 1fe0 0e1f 0e1f
149    {   1, -32,   1, -32,   1, -15,   1, -15 }, // 01e0 01e0 01f1 01f1
150    {  31,  -2,  31,  -2,  14,  -2,  14,  -2 }, // 1ffe 1ffe 0efe 0efe
151    {   1,  31,   1,  31,   1,  14,   1,  14 }, // 011f 011f 010e 010e
152    { -32,  -2, -32,  -2, -15,  -2, -15,  -2 }, // e0fe e0fe f1fe f1fe
153  };
154
155  /**
156   * Tests if the bytes between <code>[offset, offset+7]</code>
157   * constitute a weak or semi-weak DES key.
158   *
159   * @param key    The key bytes to check.
160   * @param offset The offset in the byte array to start.
161   * @return true If the key bytes are a weak key.
162   */
163  public static boolean isWeak(byte[] key, int offset)
164    throws InvalidKeyException
165  {
166    if (key.length - offset < DES_KEY_LEN)
167      {
168        throw new InvalidKeyException("DES keys must be 8 bytes long");
169      }
170    for (int i = 0; i < WEAK_KEYS.length; i++)
171      {
172        if (equalsOrComplementEquals(key, offset, WEAK_KEYS[i]))
173          {
174            return true;
175          }
176      }
177    return false;
178  }
179
180  /**
181   * This method returns true if the first 8 bytes starting at
182   * <code>off</code> in <code>a</code> equal the first 8 bytes in
183   * <code>b</code>, or equal the <i>complement</i> of the first 8 bytes
184   * in <code>b</code>.
185   *
186   * @param a   The first byte array.
187   * @param off The index into the first byte array.
188   * @param b   The second byte array.
189   * @return <code>a == b || a == ~b</code>
190   */
191  private static boolean equalsOrComplementEquals(byte[] a, int off, byte[] b)
192  {
193    boolean result = true;
194    for (int i = 0; i < DES_KEY_LEN; i++)
195      {
196        result &= a[off+i] == b[i];
197      }
198    if (result) return true;
199    result = true;
200    for (int i = 0; i < DES_KEY_LEN; i++)
201      {
202        result &= a[off+i] == (~b[i]);
203      }
204    return result;
205  }
206
207  // Instance methods.
208  // ------------------------------------------------------------------------
209
210  /**
211   * Return the key as a byte array. This method does not copy the byte
212   * array.
213   *
214   * @return The key bytes.
215   */
216  public byte[] getKey()
217  {
218    return key;
219  }
220}