220 lines
9.4 KiB
Java
220 lines
9.4 KiB
Java
/*
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* Copyright (c) 2004, 2013, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package com.sun.crypto.provider;
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import javax.crypto.IllegalBlockSizeException;
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import javax.crypto.ShortBufferException;
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/**
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* This class represents ciphers in cipher text stealing (CTS) mode.
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* <br>CTS provides a way to allow block ciphers to operate on partial
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* blocks without padding, and all bits of the message go through
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* the encryption algorithm, rather than simply being XOR'd.
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* <br>More details can be found in RFC 2040 section 8 "Description
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* of RC5-CTS".
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*
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* <p>This mode is implemented independently of a particular cipher.
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* Ciphers to which this mode should apply (e.g., DES) must be
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* <i>plugged-in</i> using the constructor.
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*
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* <p>NOTE#1: CTS requires the input data to be at least one block
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* long. Thus, callers of this class has to buffer the input data
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* to make sure the input data passed to encryptFinal()/decryptFinal()
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* is not shorter than a block.
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* <p>NOTE#2: This class does not deal with buffering or padding
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* just like all other cipher mode implementations.
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*
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* @author Valerie Peng
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*/
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final class CipherTextStealing extends CipherBlockChaining {
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CipherTextStealing(SymmetricCipher embeddedCipher) {
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super(embeddedCipher);
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}
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/**
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* Gets the name of this feedback mode.
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*
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* @return the string <code>CBC</code>
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*/
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String getFeedback() {
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return "CTS";
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}
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/**
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* Performs the last encryption operation.
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*
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* <p>The input plain text <code>plain</code>, starting at
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* <code>plainOffset</code> and ending at
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* <code>(plainOffset + len - 1)</code>, is encrypted.
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* The result is stored in <code>cipher</code>, starting at
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* <code>cipherOffset</code>.
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*
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* <p>It is the application's responsibility to make sure that
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* <code>plainLen</code> is a multiple of the embedded cipher's block size,
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* as any excess bytes are ignored.
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*
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* @param plain the buffer with the input data to be encrypted
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* @param plainOffset the offset in <code>plain</code>
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* @param plainLen the length of the input data
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* @param cipher the buffer for the result
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* @param cipherOffset the offset in <code>cipher</code>
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* @return the number of bytes placed into <code>cipher</code>
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*/
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int encryptFinal(byte[] plain, int plainOffset, int plainLen,
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byte[] cipher, int cipherOffset)
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throws IllegalBlockSizeException {
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if (plainLen < blockSize) {
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throw new IllegalBlockSizeException("input is too short!");
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} else if (plainLen == blockSize) {
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encrypt(plain, plainOffset, plainLen, cipher, cipherOffset);
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} else {
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// number of bytes in the last block
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int nLeft = plainLen % blockSize;
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if (nLeft == 0) {
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encrypt(plain, plainOffset, plainLen, cipher, cipherOffset);
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// swap the last two blocks after encryption
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int lastBlkIndex = cipherOffset + plainLen - blockSize;
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int nextToLastBlkIndex = lastBlkIndex - blockSize;
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byte[] tmp = new byte[blockSize];
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System.arraycopy(cipher, lastBlkIndex, tmp, 0, blockSize);
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System.arraycopy(cipher, nextToLastBlkIndex,
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cipher, lastBlkIndex, blockSize);
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System.arraycopy(tmp, 0, cipher, nextToLastBlkIndex,
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blockSize);
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} else {
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int newPlainLen = plainLen - (blockSize + nLeft);
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if (newPlainLen > 0) {
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encrypt(plain, plainOffset, newPlainLen, cipher,
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cipherOffset);
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plainOffset += newPlainLen;
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cipherOffset += newPlainLen;
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}
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// Do final CTS step for last two blocks (the second of which
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// may or may not be incomplete).
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byte[] tmp = new byte[blockSize];
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// now encrypt the next-to-last block
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for (int i = 0; i < blockSize; i++) {
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tmp[i] = (byte) (plain[plainOffset+i] ^ r[i]);
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}
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byte[] tmp2 = new byte[blockSize];
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embeddedCipher.encryptBlock(tmp, 0, tmp2, 0);
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System.arraycopy(tmp2, 0, cipher,
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cipherOffset+blockSize, nLeft);
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// encrypt the last block
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for (int i=0; i<nLeft; i++) {
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tmp2[i] = (byte)
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(plain[plainOffset+blockSize+i] ^ tmp2[i]);
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}
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embeddedCipher.encryptBlock(tmp2, 0, cipher, cipherOffset);
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}
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}
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return plainLen;
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}
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/**
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* Performs decryption operation.
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*
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* <p>The input cipher text <code>cipher</code>, starting at
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* <code>cipherOffset</code> and ending at
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* <code>(cipherOffset + len - 1)</code>, is decrypted.
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* The result is stored in <code>plain</code>, starting at
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* <code>plainOffset</code>.
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*
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* <p>It is the application's responsibility to make sure that
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* <code>cipherLen</code> is a multiple of the embedded cipher's block
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* size, as any excess bytes are ignored.
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*
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* <p>It is also the application's responsibility to make sure that
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* <code>init</code> has been called before this method is called.
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* (This check is omitted here, to avoid double checking.)
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*
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* @param cipher the buffer with the input data to be decrypted
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* @param cipherOffset the offset in <code>cipherOffset</code>
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* @param cipherLen the length of the input data
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* @param plain the buffer for the result
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* @param plainOffset the offset in <code>plain</code>
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* @return the number of bytes placed into <code>plain</code>
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*/
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int decryptFinal(byte[] cipher, int cipherOffset, int cipherLen,
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byte[] plain, int plainOffset)
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throws IllegalBlockSizeException {
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if (cipherLen < blockSize) {
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throw new IllegalBlockSizeException("input is too short!");
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} else if (cipherLen == blockSize) {
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decrypt(cipher, cipherOffset, cipherLen, plain, plainOffset);
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} else {
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// number of bytes in the last block
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int nLeft = cipherLen % blockSize;
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if (nLeft == 0) {
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// swap the last two blocks before decryption
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int lastBlkIndex = cipherOffset + cipherLen - blockSize;
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int nextToLastBlkIndex =
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cipherOffset + cipherLen - 2*blockSize;
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byte[] tmp = new byte[2*blockSize];
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System.arraycopy(cipher, lastBlkIndex, tmp, 0, blockSize);
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System.arraycopy(cipher, nextToLastBlkIndex,
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tmp, blockSize, blockSize);
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int cipherLen2 = cipherLen-2*blockSize;
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decrypt(cipher, cipherOffset, cipherLen2, plain, plainOffset);
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decrypt(tmp, 0, 2*blockSize, plain, plainOffset+cipherLen2);
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} else {
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int newCipherLen = cipherLen-(blockSize+nLeft);
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if (newCipherLen > 0) {
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decrypt(cipher, cipherOffset, newCipherLen, plain,
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plainOffset);
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cipherOffset += newCipherLen;
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plainOffset += newCipherLen;
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}
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// Do final CTS step for last two blocks (the second of which
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// may or may not be incomplete).
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// now decrypt the next-to-last block
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byte[] tmp = new byte[blockSize];
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embeddedCipher.decryptBlock(cipher, cipherOffset, tmp, 0);
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for (int i = 0; i < nLeft; i++) {
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plain[plainOffset+blockSize+i] =
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(byte) (cipher[cipherOffset+blockSize+i] ^ tmp[i]);
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}
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// decrypt the last block
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System.arraycopy(cipher, cipherOffset+blockSize, tmp, 0,
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nLeft);
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embeddedCipher.decryptBlock(tmp, 0, plain, plainOffset);
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//System.arraycopy(r, 0, tmp, 0, r.length);
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for (int i=0; i<blockSize; i++) {
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plain[plainOffset+i] = (byte)
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(plain[plainOffset+i]^r[i]);
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}
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}
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}
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return cipherLen;
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}
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}
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