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    1   /*
    2    * Copyright (c) 2002, 2007, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package com.sun.crypto.provider;
   27   
   28   import java.security.InvalidKeyException;
   29   
   30   /**
   31    * This class represents ciphers in counter (CTR) mode.
   32    *
   33    * <p>This mode is implemented independently of a particular cipher.
   34    * Ciphers to which this mode should apply (e.g., DES) must be
   35    * <i>plugged-in</i> using the constructor.
   36    *
   37    * <p>NOTE: This class does not deal with buffering or padding.
   38    *
   39    * @author Andreas Sterbenz
   40    * @since 1.4.2
   41    */
   42   final class CounterMode extends FeedbackCipher {
   43   
   44       // current counter value
   45       private final byte[] counter;
   46   
   47       // encrypted bytes of the previous counter value
   48       private final byte[] encryptedCounter;
   49   
   50       // number of bytes in encryptedCounter already used up
   51       private int used;
   52   
   53       // variables for save/restore calls
   54       private byte[] counterSave = null;
   55       private byte[] encryptedCounterSave = null;
   56       private int usedSave = 0;
   57   
   58       CounterMode(SymmetricCipher embeddedCipher) {
   59           super(embeddedCipher);
   60           counter = new byte[blockSize];
   61           encryptedCounter = new byte[blockSize];
   62       }
   63   
   64       /**
   65        * Gets the name of the feedback mechanism
   66        *
   67        * @return the name of the feedback mechanism
   68        */
   69       String getFeedback() {
   70           return "CTR";
   71       }
   72   
   73       /**
   74        * Resets the iv to its original value.
   75        * This is used when doFinal is called in the Cipher class, so that the
   76        * cipher can be reused (with its original iv).
   77        */
   78       void reset() {
   79           System.arraycopy(iv, 0, counter, 0, blockSize);
   80           used = blockSize;
   81       }
   82   
   83       /**
   84        * Save the current content of this cipher.
   85        */
   86       void save() {
   87           if (counterSave == null) {
   88               counterSave = new byte[blockSize];
   89               encryptedCounterSave = new byte[blockSize];
   90           }
   91           System.arraycopy(counter, 0, counterSave, 0, blockSize);
   92           System.arraycopy(encryptedCounter, 0, encryptedCounterSave, 0,
   93               blockSize);
   94           usedSave = used;
   95       }
   96   
   97       /**
   98        * Restores the content of this cipher to the previous saved one.
   99        */
  100       void restore() {
  101           System.arraycopy(counterSave, 0, counter, 0, blockSize);
  102           System.arraycopy(encryptedCounterSave, 0, encryptedCounter, 0,
  103               blockSize);
  104           used = usedSave;
  105       }
  106   
  107       /**
  108        * Initializes the cipher in the specified mode with the given key
  109        * and iv.
  110        *
  111        * @param decrypting flag indicating encryption or decryption
  112        * @param algorithm the algorithm name
  113        * @param key the key
  114        * @param iv the iv
  115        *
  116        * @exception InvalidKeyException if the given key is inappropriate for
  117        * initializing this cipher
  118        */
  119       void init(boolean decrypting, String algorithm, byte[] key, byte[] iv)
  120               throws InvalidKeyException {
  121           if ((key == null) || (iv == null) || (iv.length != blockSize)) {
  122               throw new InvalidKeyException("Internal error");
  123           }
  124           this.iv = iv;
  125           reset();
  126           // always encrypt mode for embedded cipher
  127           embeddedCipher.init(false, algorithm, key);
  128       }
  129   
  130       /**
  131        * Performs encryption operation.
  132        *
  133        * <p>The input plain text <code>plain</code>, starting at
  134        * <code>plainOffset</code> and ending at
  135        * <code>(plainOffset + len - 1)</code>, is encrypted.
  136        * The result is stored in <code>cipher</code>, starting at
  137        * <code>cipherOffset</code>.
  138        *
  139        * <p>It is the application's responsibility to make sure that
  140        * <code>plainLen</code> is a multiple of the embedded cipher's block size,
  141        * as any excess bytes are ignored.
  142        *
  143        * <p>It is also the application's responsibility to make sure that
  144        * <code>init</code> has been called before this method is called.
  145        * (This check is omitted here, to avoid double checking.)
  146        *
  147        * @param in the buffer with the input data to be encrypted
  148        * @param inOffset the offset in <code>plain</code>
  149        * @param len the length of the input data
  150        * @param out the buffer for the result
  151        * @param outOff the offset in <code>cipher</code>
  152        */
  153       void encrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
  154           crypt(in, inOff, len, out, outOff);
  155       }
  156   
  157       /**
  158        * Performs decryption operation.
  159        *
  160        * <p>The input cipher text <code>cipher</code>, starting at
  161        * <code>cipherOffset</code> and ending at
  162        * <code>(cipherOffset + len - 1)</code>, is decrypted.
  163        * The result is stored in <code>plain</code>, starting at
  164        * <code>plainOffset</code>.
  165        *
  166        * <p>It is the application's responsibility to make sure that
  167        * <code>cipherLen</code> is a multiple of the embedded cipher's block
  168        * size, as any excess bytes are ignored.
  169        *
  170        * <p>It is also the application's responsibility to make sure that
  171        * <code>init</code> has been called before this method is called.
  172        * (This check is omitted here, to avoid double checking.)
  173        *
  174        * @param in the buffer with the input data to be decrypted
  175        * @param inOff the offset in <code>cipherOffset</code>
  176        * @param len the length of the input data
  177        * @param out the buffer for the result
  178        * @param outOff the offset in <code>plain</code>
  179        */
  180       void decrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
  181           crypt(in, inOff, len, out, outOff);
  182       }
  183   
  184       /**
  185        * Increment the counter value.
  186        */
  187       private static void increment(byte[] b) {
  188           int n = b.length - 1;
  189           while ((n >= 0) && (++b[n] == 0)) {
  190               n--;
  191           }
  192       }
  193   
  194       /**
  195        * Do the actual encryption/decryption operation.
  196        * Essentially we XOR the input plaintext/ciphertext stream with a
  197        * keystream generated by encrypting the counter values. Counter values
  198        * are encrypted on demand.
  199        */
  200       private void crypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
  201           while (len-- > 0) {
  202               if (used >= blockSize) {
  203                   embeddedCipher.encryptBlock(counter, 0, encryptedCounter, 0);
  204                   increment(counter);
  205                   used = 0;
  206               }
  207               out[outOff++] = (byte)(in[inOff++] ^ encryptedCounter[used++]);
  208           }
  209       }
  210   }

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