Source for gnu.javax.crypto.mode.CBC

   1: /* CBC.java --
   2:    Copyright (C) 2002, 2006 Free Software Foundation, Inc.
   3: 
   4: This file is a part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2 of the License, or (at
   9: your option) any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; if not, write to the Free Software
  18: Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  19: USA
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version.  */
  37: 
  38: 
  39: package gnu.javax.crypto.mode;
  40: 
  41: import gnu.java.security.Registry;
  42: import gnu.javax.crypto.cipher.IBlockCipher;
  43: 
  44: /**
  45:  * The Cipher Block Chaining mode. This mode introduces feedback into the cipher
  46:  * by XORing the previous ciphertext block with the plaintext block before
  47:  * encipherment. That is, encrypting looks like this:
  48:  *
  49:  * <pre>
  50:  *  C<sub>i</sub> = E<sub>K</sub>(P<sub>i</sub>&circ; C<sub>i-1</sub>)
  51:  * </pre>
  52:  * <p>
  53:  * Similarly, decrypting is:
  54:  * <pre>
  55:  *  P<sub>i</sub> = C<sub>i-1</sub> &circ; D<sub>K</sub>(C<sub>i</sub>)
  56:  * </pre>
  57:  */
  58: public class CBC
  59:     extends BaseMode
  60:     implements Cloneable
  61: {
  62:   /** The last (de|en)crypted block */
  63:   private byte[] lastBlock;
  64:   /** An intermediate buffer. */
  65:   private byte[] scratch;
  66: 
  67:   /**
  68:    * Package-private constructor for the factory class.
  69:    *
  70:    * @param underlyingCipher The cipher implementation.
  71:    * @param cipherBlockSize The cipher's block size.
  72:    */
  73:   CBC(IBlockCipher underlyingCipher, int cipherBlockSize)
  74:   {
  75:     super(Registry.CBC_MODE, underlyingCipher, cipherBlockSize);
  76:   }
  77: 
  78:   /** Our constructor for cloning. */
  79:   private CBC(CBC that)
  80:   {
  81:     this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize);
  82:   }
  83: 
  84:   public Object clone()
  85:   {
  86:     return new CBC(this);
  87:   }
  88: 
  89:   public void setup()
  90:   {
  91:     if (modeBlockSize != cipherBlockSize)
  92:       throw new IllegalArgumentException();
  93:     scratch = new byte[cipherBlockSize];
  94:     lastBlock = new byte[cipherBlockSize];
  95:     // lastBlock gets initialized to the initialization vector.
  96:     for (int i = 0; i < lastBlock.length && i < iv.length; i++)
  97:       lastBlock[i] = iv[i];
  98:   }
  99: 
 100:   public void teardown()
 101:   {
 102:     lastBlock = null;
 103:     scratch = null;
 104:   }
 105: 
 106:   public void encryptBlock(byte[] in, int i, byte[] out, int o)
 107:   {
 108:     for (int k = 0; k < scratch.length; k++)
 109:       scratch[k] = (byte)(lastBlock[k] ^ in[k + i]);
 110:     cipher.encryptBlock(scratch, 0, out, o);
 111:     System.arraycopy(out, o, lastBlock, 0, cipherBlockSize);
 112:   }
 113: 
 114:   public void decryptBlock(byte[] in, int i, byte[] out, int o)
 115:   {
 116:     byte[] buf = new byte[cipherBlockSize];
 117:     System.arraycopy(in, i, buf, 0, cipherBlockSize);
 118:     cipher.decryptBlock(in, i, scratch, 0);
 119:     for (int k = 0; k < scratch.length; k++)
 120:       out[o + k] = (byte)(lastBlock[k] ^ scratch[k]);
 121:     System.arraycopy(buf, 0, lastBlock, 0, cipherBlockSize);
 122:   }
 123: }