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/*
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* Copyright (c) 1997, 2007, 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 java.security.InvalidKeyException;
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/**
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* This class represents ciphers in output-feedback (OFB) mode.
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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: This class does not deal with buffering or padding.
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*
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* @author Gigi Ankeny
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*/
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final class OutputFeedback extends FeedbackCipher {
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/*
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* output buffer
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*/
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private byte[] k = null;
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/*
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* register buffer
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*/
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private byte[] register = null;
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/*
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* number of bytes for each stream unit, defaults to the blocksize
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* of the embedded cipher
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*/
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private int numBytes;
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// variables for save/restore calls
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private byte[] registerSave = null;
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OutputFeedback(SymmetricCipher embeddedCipher, int numBytes) {
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super(embeddedCipher);
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if (numBytes > blockSize) {
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numBytes = blockSize;
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}
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this.numBytes = numBytes;
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k = new byte[blockSize];
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register = new byte[blockSize];
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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>OFB</code>
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*/
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String getFeedback() {
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return "OFB";
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}
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/**
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* Initializes the cipher in the specified mode with the given key
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* and iv.
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*
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* @param decrypting flag indicating encryption or decryption
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* @param algorithm the algorithm name
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* @param key the key
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* @param iv the iv
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*
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* @exception InvalidKeyException if the given key is inappropriate for
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* initializing this cipher
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*/
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void init(boolean decrypting, String algorithm, byte[] key, byte[] iv)
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throws InvalidKeyException {
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if ((key == null) || (iv == null) || (iv.length != blockSize)) {
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throw new InvalidKeyException("Internal error");
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}
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this.iv = iv;
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reset();
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// always encrypt mode for embedded cipher
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embeddedCipher.init(false, algorithm, key);
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}
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/**
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* Resets the iv to its original value.
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* This is used when doFinal is called in the Cipher class, so that the
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* cipher can be reused (with its original iv).
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*/
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void reset() {
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System.arraycopy(iv, 0, register, 0, blockSize);
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}
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/**
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* Save the current content of this cipher.
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*/
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void save() {
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if (registerSave == null) {
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registerSave = new byte[blockSize];
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}
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System.arraycopy(register, 0, registerSave, 0, blockSize);
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}
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/**
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* Restores the content of this cipher to the previous saved one.
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*/
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void restore() {
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System.arraycopy(registerSave, 0, register, 0, blockSize);
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}
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/**
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* Performs 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 stream unit size
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* <code>numBytes</code>, 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 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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*/
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void encrypt(byte[] plain, int plainOffset, int plainLen,
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byte[] cipher, int cipherOffset)
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{
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int i;
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int len = blockSize - numBytes;
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int loopCount = plainLen / numBytes;
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int oddBytes = plainLen % numBytes;
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if (len == 0) {
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for (; loopCount > 0;
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plainOffset += numBytes, cipherOffset += numBytes,
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loopCount--) {
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embeddedCipher.encryptBlock(register, 0, k, 0);
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for (i=0; i<numBytes; i++)
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cipher[i+cipherOffset] =
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(byte)(k[i] ^ plain[i+plainOffset]);
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System.arraycopy(k, 0, register, 0, numBytes);
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}
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if (oddBytes > 0) {
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embeddedCipher.encryptBlock(register, 0, k, 0);
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for (i=0; i<oddBytes; i++)
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cipher[i+cipherOffset] =
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(byte)(k[i] ^ plain[i+plainOffset]);
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System.arraycopy(k, 0, register, 0, numBytes);
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}
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} else {
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for (; loopCount > 0;
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plainOffset += numBytes, cipherOffset += numBytes,
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loopCount--) {
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embeddedCipher.encryptBlock(register, 0, k, 0);
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for (i=0; i<numBytes; i++)
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cipher[i+cipherOffset] =
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(byte)(k[i] ^ plain[i+plainOffset]);
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System.arraycopy(register, numBytes, register, 0, len);
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System.arraycopy(k, 0, register, len, numBytes);
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}
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if (oddBytes > 0) {
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embeddedCipher.encryptBlock(register, 0, k, 0);
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for (i=0; i<oddBytes; i++)
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cipher[i+cipherOffset] =
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(byte)(k[i] ^ plain[i+plainOffset]);
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System.arraycopy(register, numBytes, register, 0, len);
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System.arraycopy(k, 0, register, len, numBytes);
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}
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}
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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 stream unit size
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* <code>numBytes</code>, 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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*/
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void decrypt(byte[] cipher, int cipherOffset, int cipherLen,
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byte[] plain, int plainOffset)
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{
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// OFB encrypt and decrypt are identical
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encrypt(cipher, cipherOffset, cipherLen, plain, plainOffset);
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}
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}
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