libjava/classpath/gnu/javax/crypto/mode/CTR.java

   1 /* CTR.java --
   2    Copyright (C) 2001, 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.java.security.util.Sequence;
  43
  44 import gnu.javax.crypto.cipher.IBlockCipher;
  45
  46 import java.math.BigInteger;
  47 import java.util.Arrays;
  48 import java.util.Iterator;
  49
  50 /**
  51  * <p>The implementation of the Counter Mode.</p>
  52  *
  53  * <p>The algorithm steps are formally described as follows:</p>
  54  *
  55  * <pre>
  56  *    CTR Encryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
  57  *                    C[j] = P[j] ^ O[j]; for j = 1, 2...n.
  58  *    CTR Decryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
  59  *                    P[j] = C[j] ^ O[j]; for j = 1, 2...n.
  60  * </pre>
  61  *
  62  * <p>where <code>P</code> is the plaintext, <code>C</code> is the ciphertext,
  63  * <code>E(K)</code> is the underlying block cipher encryption function
  64  * parametrised with the session key <code>K</code>, and <code>T</code> is the
  65  * <i>Counter</i>.</p>
  66  *
  67  * <p>This implementation, uses a standard incrementing function with a step of
  68  * 1, and an initial value similar to that described in the NIST document.</p>
  69  *
  70  * <p>References:</p>
  71  *
  72  * <ol>
  73  *    <li><a href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf">
  74  *    Recommendation for Block Cipher Modes of Operation Methods and Techniques</a>,
  75  *    Morris Dworkin.</li>
  76  * </ol>
  77  */
  78 public class CTR extends BaseMode implements Cloneable
  79 {
  80
  81   // Constants and variables
  82   // -------------------------------------------------------------------------
  83
  84   /** The current counter. */
  85   //    private BigInteger T;
  86   private int off;
  87
  88   private byte[] counter, enc;
  89
  90   // Constructor(s)
  91   // -------------------------------------------------------------------------
  92
  93   /**
  94    * <p>Trivial package-private constructor for use by the Factory class.</p>
  95    *
  96    * @param underlyingCipher the underlying cipher implementation.
  97    * @param cipherBlockSize the underlying cipher block size to use.
  98    */
  99   CTR(IBlockCipher underlyingCipher, int cipherBlockSize)
 100   {
 101     super(Registry.CTR_MODE, underlyingCipher, cipherBlockSize);
 102   }
 103
 104   /**
 105    * <p>Private constructor for cloning purposes.</p>
 106    *
 107    * @param that the instance to clone.
 108    */
 109   private CTR(CTR that)
 110   {
 111     this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize);
 112   }
 113
 114   // Class methods
 115   // -------------------------------------------------------------------------
 116
 117   // Cloneable interface implementation
 118   // -------------------------------------------------------------------------
 119
 120   public Object clone()
 121   {
 122     return new CTR(this);
 123   }
 124
 125   // Implementation of abstract methods in BaseMode
 126   // -------------------------------------------------------------------------
 127
 128   public void setup()
 129   {
 130     if (modeBlockSize > cipherBlockSize)
 131       {
 132         throw new IllegalArgumentException(
 133                                            "mode size exceeds cipher block size");
 134       }
 135     off = 0;
 136     counter = new byte[cipherBlockSize];
 137     int i = cipherBlockSize - 1;
 138     int j = iv.length - 1;
 139     while (i >= 0 && j >= 0)
 140       {
 141         counter[i--] = iv[j--];
 142       }
 143     enc = new byte[cipherBlockSize];
 144     cipher.encryptBlock(counter, 0, enc, 0);
 145     //       if (modeBlockSize != cipherBlockSize) {
 146     //          throw new IllegalArgumentException();
 147     //       }
 148
 149     //       byte[] tBytes = new byte[modeBlockSize+1];
 150     //       tBytes[0] = (byte) 0x80;
 151     //       for (int i = 0; i < modeBlockSize; i++) {
 152     //          tBytes[i+1] = (byte)(256 - modeBlockSize + i);
 153     //       }
 154
 155     //       T = new BigInteger(1, tBytes);
 156   }
 157
 158   public void teardown()
 159   {
 160     if (counter != null)
 161       {
 162         Arrays.fill(counter, (byte) 0);
 163       }
 164     if (enc != null)
 165       {
 166         Arrays.fill(enc, (byte) 0);
 167       }
 168     //       T = null;
 169   }
 170
 171   public void encryptBlock(byte[] in, int i, byte[] out, int o)
 172   {
 173     ctr(in, i, out, o);
 174   }
 175
 176   public void decryptBlock(byte[] in, int i, byte[] out, int o)
 177   {
 178     ctr(in, i, out, o);
 179   }
 180
 181   public Iterator blockSizes()
 182   {
 183     return new Sequence(1, cipherBlockSize).iterator();
 184   }
 185
 186   // own methods
 187   // -------------------------------------------------------------------------
 188
 189   private void ctr(byte[] in, int inOffset, byte[] out, int outOffset)
 190   {
 191     //       T = T.add(BigInteger.ONE);
 192     //       byte[] O = T.toByteArray();
 193     //       int ndx = O.length - modeBlockSize;
 194     //       cipher.encryptBlock(O, ndx, O, ndx);
 195     //       for (int i = 0; i < modeBlockSize; i++) {
 196     //          out[outOffset++] = (byte)(in[inOffset++] ^ O[ndx++]);
 197     //       }
 198     for (int i = 0; i < modeBlockSize; i++)
 199       {
 200         out[outOffset++] = (byte) (in[inOffset++] ^ enc[off++]);
 201         if (off == cipherBlockSize)
 202           {
 203             int j;
 204             for (j = cipherBlockSize - 1; j >= 0; j--)
 205               {
 206                 counter[j]++;
 207                 if ((counter[j] & 0xFF) != 0)
 208                   {
 209                     break;
 210                   }
 211               }
 212             if (j == 0)
 213               {
 214                 counter[cipherBlockSize - 1]++;
 215               }
 216             off = 0;
 217             cipher.encryptBlock(counter, 0, enc, 0);
 218           }
 219       }
 220   }
 221 }