1 /*

     2  * Copyright 2004-2007 Sun Microsystems, Inc.  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.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package com.sun.crypto.provider;

    27 

    28 import javax.crypto.IllegalBlockSizeException;

    29 import javax.crypto.ShortBufferException;

    30 

    31 /**

    32  * This class represents ciphers in cipher text stealing (CTS) mode.

    33  * <br>CTS provides a way to allow block ciphers to operate on partial

    34  * blocks without padding, and all bits of the message go through

    35  * the encryption algorithm, rather than simply being XOR'd.

    36  * <br>More details can be found in RFC 2040 section 8 "Description

    37  * of RC5-CTS".

    38  *

    39  * <p>This mode is implemented independently of a particular cipher.

    40  * Ciphers to which this mode should apply (e.g., DES) must be

    41  * <i>plugged-in</i> using the constructor.

    42  *

    43  * <p>NOTE#1: CTS requires the input data to be at least one block

    44  * long. Thus, callers of this class has to buffer the input data

    45  * to make sure the input data passed to encryptFinal()/decryptFinal()

    46  * is not shorter than a block.

    47  * <p>NOTE#2: This class does not deal with buffering or padding

    48  * just like all other cipher mode implementations.

    49  *

    50  * @author Valerie Peng

    51  */

    52 

    53 final class CipherTextStealing extends CipherBlockChaining {

    54 

    55     CipherTextStealing(SymmetricCipher embeddedCipher) {

    56         super(embeddedCipher);

    57     }

    58 

    59     /**

    60      * Gets the name of this feedback mode.

    61      *

    62      * @return the string <code>CBC</code>

    63      */

    64     String getFeedback() {

    65         return "CTS";

    66     }

    67 

    68     /**

    69      * Performs the last encryption operation.

    70      *

    71      * <p>The input plain text <code>plain</code>, starting at

    72      * <code>plainOffset</code> and ending at

    73      * <code>(plainOffset + len - 1)</code>, is encrypted.

    74      * The result is stored in <code>cipher</code>, starting at

    75      * <code>cipherOffset</code>.

    76      *

    77      * <p>It is the application's responsibility to make sure that

    78      * <code>plainLen</code> is a multiple of the embedded cipher's block size,

    79      * as any excess bytes are ignored.

    80      *

    81      * @param plain the buffer with the input data to be encrypted

    82      * @param plainOffset the offset in <code>plain</code>

    83      * @param plainLen the length of the input data

    84      * @param cipher the buffer for the result

    85      * @param cipherOffset the offset in <code>cipher</code>

    86      */

    87     void encryptFinal(byte[] plain, int plainOffset, int plainLen,

    88                       byte[] cipher, int cipherOffset)

    89         throws IllegalBlockSizeException {

    90 

    91         if (plainLen < blockSize) {

    92             throw new IllegalBlockSizeException("input is too short!");

    93         } else if (plainLen == blockSize) {

    94             encrypt(plain, plainOffset, plainLen, cipher, cipherOffset);

    95         } else {

    96             // number of bytes in the last block

    97             int nLeft = plainLen % blockSize;

    98             if (nLeft == 0) {

    99                 encrypt(plain, plainOffset, plainLen, cipher, cipherOffset);

   100                 // swap the last two blocks after encryption

   101                 int lastBlkIndex = cipherOffset + plainLen - blockSize;

   102                 int nextToLastBlkIndex = lastBlkIndex - blockSize;

   103                 byte[] tmp = new byte[blockSize];

   104                 System.arraycopy(cipher, lastBlkIndex, tmp, 0, blockSize);

   105                 System.arraycopy(cipher, nextToLastBlkIndex,

   106                                  cipher, lastBlkIndex, blockSize);

   107                 System.arraycopy(tmp, 0, cipher, nextToLastBlkIndex,

   108                                  blockSize);

   109             } else {

   110                 int newPlainLen = plainLen - (blockSize + nLeft);

   111                 if (newPlainLen > 0) {

   112                     encrypt(plain, plainOffset, newPlainLen, cipher,

   113                             cipherOffset);

   114                     plainOffset += newPlainLen;

   115                     cipherOffset += newPlainLen;

   116                 }

   117 

   118                 // Do final CTS step for last two blocks (the second of which

   119                 // may or may not be incomplete).

   120                 byte[] tmp = new byte[blockSize];

   121                 // now encrypt the next-to-last block

   122                 for (int i = 0; i < blockSize; i++) {

   123                     tmp[i] = (byte) (plain[plainOffset+i] ^ r[i]);

   124                 }

   125                 byte[] tmp2 = new byte[blockSize];

   126                 embeddedCipher.encryptBlock(tmp, 0, tmp2, 0);

   127                 System.arraycopy(tmp2, 0, cipher,

   128                                  cipherOffset+blockSize, nLeft);

   129                 // encrypt the last block

   130                 for (int i=0; i<nLeft; i++) {

   131                     tmp2[i] = (byte)

   132                         (plain[plainOffset+blockSize+i] ^ tmp2[i]);

   133                 }

   134                 embeddedCipher.encryptBlock(tmp2, 0, cipher, cipherOffset);

   135             }

   136         }

   137     }

   138 

   139     /**

   140      * Performs decryption operation.

   141      *

   142      * <p>The input cipher text <code>cipher</code>, starting at

   143      * <code>cipherOffset</code> and ending at

   144      * <code>(cipherOffset + len - 1)</code>, is decrypted.

   145      * The result is stored in <code>plain</code>, starting at

   146      * <code>plainOffset</code>.

   147      *

   148      * <p>It is the application's responsibility to make sure that

   149      * <code>cipherLen</code> is a multiple of the embedded cipher's block

   150      * size, as any excess bytes are ignored.

   151      *

   152      * <p>It is also the application's responsibility to make sure that

   153      * <code>init</code> has been called before this method is called.

   154      * (This check is omitted here, to avoid double checking.)

   155      *

   156      * @param cipher the buffer with the input data to be decrypted

   157      * @param cipherOffset the offset in <code>cipherOffset</code>

   158      * @param cipherLen the length of the input data

   159      * @param plain the buffer for the result

   160      * @param plainOffset the offset in <code>plain</code>

   161      */

   162     void decryptFinal(byte[] cipher, int cipherOffset, int cipherLen,

   163                       byte[] plain, int plainOffset)

   164         throws IllegalBlockSizeException {

   165         if (cipherLen < blockSize) {

   166             throw new IllegalBlockSizeException("input is too short!");

   167         } else if (cipherLen == blockSize) {

   168             decrypt(cipher, cipherOffset, cipherLen, plain, plainOffset);

   169         } else {

   170             // number of bytes in the last block

   171             int nLeft = cipherLen % blockSize;

   172             if (nLeft == 0) {

   173                 // swap the last two blocks before decryption

   174                 int lastBlkIndex = cipherOffset + cipherLen - blockSize;

   175                 int nextToLastBlkIndex =

   176                     cipherOffset + cipherLen - 2*blockSize;

   177                 byte[] tmp = new byte[2*blockSize];

   178                 System.arraycopy(cipher, lastBlkIndex, tmp, 0, blockSize);

   179                 System.arraycopy(cipher, nextToLastBlkIndex,

   180                                  tmp, blockSize, blockSize);

   181                 int cipherLen2 = cipherLen-2*blockSize;

   182                 decrypt(cipher, cipherOffset, cipherLen2, plain, plainOffset);

   183                 decrypt(tmp, 0, 2*blockSize, plain, plainOffset+cipherLen2);

   184             } else {

   185                 int newCipherLen = cipherLen-(blockSize+nLeft);

   186                 if (newCipherLen > 0) {

   187                     decrypt(cipher, cipherOffset, newCipherLen, plain,

   188                             plainOffset);

   189                     cipherOffset += newCipherLen;

   190                     plainOffset += newCipherLen;

   191                 }

   192                 // Do final CTS step for last two blocks (the second of which

   193                 // may or may not be incomplete).

   194 

   195                 // now decrypt the next-to-last block

   196                 byte[] tmp = new byte[blockSize];

   197                 embeddedCipher.decryptBlock(cipher, cipherOffset, tmp, 0);

   198                 for (int i = 0; i < nLeft; i++) {

   199                     plain[plainOffset+blockSize+i] =

   200                         (byte) (cipher[cipherOffset+blockSize+i] ^ tmp[i]);

   201                 }

   202 

   203                 // decrypt the last block

   204                 System.arraycopy(cipher, cipherOffset+blockSize, tmp, 0,

   205                                  nLeft);

   206                 embeddedCipher.decryptBlock(tmp, 0, plain, plainOffset);

   207                 //System.arraycopy(r, 0, tmp, 0, r.length);

   208                 for (int i=0; i<blockSize; i++) {

   209                     plain[plainOffset+i] = (byte)

   210                         (plain[plainOffset+i]^r[i]);

   211                 }

   212             }

   213         }

   214     }

   215 }