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	/*
	* Copyright (c) 2004, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.crypto.provider;

	import javax.crypto.IllegalBlockSizeException;
	import javax.crypto.ShortBufferException;

	/**
	* This class represents ciphers in cipher text stealing (CTS) mode.
	* <br>CTS provides a way to allow block ciphers to operate on partial
	* blocks without padding, and all bits of the message go through
	* the encryption algorithm, rather than simply being XOR'd.
	* <br>More details can be found in RFC 2040 section 8 "Description
	* of RC5-CTS".
	*
	* <p>This mode is implemented independently of a particular cipher.
	* Ciphers to which this mode should apply (e.g., DES) must be
	* <i>plugged-in</i> using the constructor.
	*
	* <p>NOTE#1: CTS requires the input data to be at least one block
	* long. Thus, callers of this class has to buffer the input data
	* to make sure the input data passed to encryptFinal()/decryptFinal()
	* is not shorter than a block.
	* <p>NOTE#2: This class does not deal with buffering or padding
	* just like all other cipher mode implementations.
	*
	* @author Valerie Peng
	*/

	final class CipherTextStealing extends CipherBlockChaining {

	CipherTextStealing(SymmetricCipher embeddedCipher) {
	super(embeddedCipher);
	}

	/**
	* Gets the name of this feedback mode.
	*
	* @return the string <code>CBC</code>
	*/
	String getFeedback() {
	return "CTS";
	}

	/**
	* Performs the last encryption operation.
	*
	* <p>The input plain text <code>plain</code>, starting at
	* <code>plainOffset</code> and ending at
	* <code>(plainOffset + len - 1)</code>, is encrypted.
	* The result is stored in <code>cipher</code>, starting at
	* <code>cipherOffset</code>.
	*
	* <p>It is the application's responsibility to make sure that
	* <code>plainLen</code> is a multiple of the embedded cipher's block size,
	* as any excess bytes are ignored.
	*
	* @param plain the buffer with the input data to be encrypted
	* @param plainOffset the offset in <code>plain</code>
	* @param plainLen the length of the input data
	* @param cipher the buffer for the result
	* @param cipherOffset the offset in <code>cipher</code>
	* @return the number of bytes placed into <code>cipher</code>
	*/
	int encryptFinal(byte[] plain, int plainOffset, int plainLen,
	byte[] cipher, int cipherOffset)
	throws IllegalBlockSizeException {

	if (plainLen < blockSize) {
	throw new IllegalBlockSizeException("input is too short!");
	} else if (plainLen == blockSize) {
	encrypt(plain, plainOffset, plainLen, cipher, cipherOffset);
	} else {
	// number of bytes in the last block
	int nLeft = plainLen % blockSize;
	if (nLeft == 0) {
	encrypt(plain, plainOffset, plainLen, cipher, cipherOffset);
	// swap the last two blocks after encryption
	int lastBlkIndex = cipherOffset + plainLen - blockSize;
	int nextToLastBlkIndex = lastBlkIndex - blockSize;
	byte[] tmp = new byte[blockSize];
	System.arraycopy(cipher, lastBlkIndex, tmp, 0, blockSize);
	System.arraycopy(cipher, nextToLastBlkIndex,
	cipher, lastBlkIndex, blockSize);
	System.arraycopy(tmp, 0, cipher, nextToLastBlkIndex,
	blockSize);
	} else {
	int newPlainLen = plainLen - (blockSize + nLeft);
	if (newPlainLen > 0) {
	encrypt(plain, plainOffset, newPlainLen, cipher,
	cipherOffset);
	plainOffset += newPlainLen;
	cipherOffset += newPlainLen;
	}

	// Do final CTS step for last two blocks (the second of which
	// may or may not be incomplete).
	byte[] tmp = new byte[blockSize];
	// now encrypt the next-to-last block
	for (int i = 0; i < blockSize; i++) {
	tmp[i] = (byte) (plain[plainOffset+i] ^ r[i]);
	}
	byte[] tmp2 = new byte[blockSize];
	embeddedCipher.encryptBlock(tmp, 0, tmp2, 0);
	System.arraycopy(tmp2, 0, cipher,
	cipherOffset+blockSize, nLeft);
	// encrypt the last block
	for (int i=0; i<nLeft; i++) {
	tmp2[i] = (byte)
	(plain[plainOffset+blockSize+i] ^ tmp2[i]);
	}
	embeddedCipher.encryptBlock(tmp2, 0, cipher, cipherOffset);
	}
	}
	return plainLen;
	}

	/**
	* Performs decryption operation.
	*
	* <p>The input cipher text <code>cipher</code>, starting at
	* <code>cipherOffset</code> and ending at
	* <code>(cipherOffset + len - 1)</code>, is decrypted.
	* The result is stored in <code>plain</code>, starting at
	* <code>plainOffset</code>.
	*
	* <p>It is the application's responsibility to make sure that
	* <code>cipherLen</code> is a multiple of the embedded cipher's block
	* size, as any excess bytes are ignored.
	*
	* <p>It is also the application's responsibility to make sure that
	* <code>init</code> has been called before this method is called.
	* (This check is omitted here, to avoid double checking.)
	*
	* @param cipher the buffer with the input data to be decrypted
	* @param cipherOffset the offset in <code>cipherOffset</code>
	* @param cipherLen the length of the input data
	* @param plain the buffer for the result
	* @param plainOffset the offset in <code>plain</code>
	* @return the number of bytes placed into <code>plain</code>
	*/
	int decryptFinal(byte[] cipher, int cipherOffset, int cipherLen,
	byte[] plain, int plainOffset)
	throws IllegalBlockSizeException {
	if (cipherLen < blockSize) {
	throw new IllegalBlockSizeException("input is too short!");
	} else if (cipherLen == blockSize) {
	decrypt(cipher, cipherOffset, cipherLen, plain, plainOffset);
	} else {
	// number of bytes in the last block
	int nLeft = cipherLen % blockSize;
	if (nLeft == 0) {
	// swap the last two blocks before decryption
	int lastBlkIndex = cipherOffset + cipherLen - blockSize;
	int nextToLastBlkIndex =
	cipherOffset + cipherLen - 2*blockSize;
	byte[] tmp = new byte[2*blockSize];
	System.arraycopy(cipher, lastBlkIndex, tmp, 0, blockSize);
	System.arraycopy(cipher, nextToLastBlkIndex,
	tmp, blockSize, blockSize);
	int cipherLen2 = cipherLen-2*blockSize;
	decrypt(cipher, cipherOffset, cipherLen2, plain, plainOffset);
	decrypt(tmp, 0, 2*blockSize, plain, plainOffset+cipherLen2);
	} else {
	int newCipherLen = cipherLen-(blockSize+nLeft);
	if (newCipherLen > 0) {
	decrypt(cipher, cipherOffset, newCipherLen, plain,
	plainOffset);
	cipherOffset += newCipherLen;
	plainOffset += newCipherLen;
	}
	// Do final CTS step for last two blocks (the second of which
	// may or may not be incomplete).

	// now decrypt the next-to-last block
	byte[] tmp = new byte[blockSize];
	embeddedCipher.decryptBlock(cipher, cipherOffset, tmp, 0);
	for (int i = 0; i < nLeft; i++) {
	plain[plainOffset+blockSize+i] =
	(byte) (cipher[cipherOffset+blockSize+i] ^ tmp[i]);
	}

	// decrypt the last block
	System.arraycopy(cipher, cipherOffset+blockSize, tmp, 0,
	nLeft);
	embeddedCipher.decryptBlock(tmp, 0, plain, plainOffset);
	//System.arraycopy(r, 0, tmp, 0, r.length);
	for (int i=0; i<blockSize; i++) {
	plain[plainOffset+i] = (byte)
	(plain[plainOffset+i]^r[i]);
	}
	}
	}
	return cipherLen;
	}
	}

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