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/*
 * Copyright (c) 1997, 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
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package com.sun.crypto.provider;

import java.security.InvalidKeyException;

/**
 * This class represents ciphers in output-feedback (OFB) mode.
 *
 * <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: This class does not deal with buffering or padding.
 *
 * @author Gigi Ankeny
 */
final class OutputFeedback extends FeedbackCipher {

    /*
     * output buffer
     */
    private byte[] k = null;

    /*
     * register buffer
     */
    private byte[] register = null;

    /*
     * number of bytes for each stream unit, defaults to the blocksize
     * of the embedded cipher
     */
    private int numBytes;

    // variables for save/restore calls
    private byte[] registerSave = null;

    OutputFeedback(SymmetricCipher embeddedCipher, int numBytes) {
        super(embeddedCipher);
        if (numBytes > blockSize) {
            numBytes = blockSize;
        }
        this.numBytes = numBytes;
        k = new byte[blockSize];
        register = new byte[blockSize];
    }

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

    /**
     * Initializes the cipher in the specified mode with the given key
     * and iv.
     *
     * @param decrypting flag indicating encryption or decryption
     * @param algorithm the algorithm name
     * @param key the key
     * @param iv the iv
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * initializing this cipher
     */
    void init(boolean decrypting, String algorithm, byte[] key, byte[] iv)
            throws InvalidKeyException {
        if ((key == null) || (iv == null) || (iv.length != blockSize)) {
            throw new InvalidKeyException("Internal error");
        }
        this.iv = iv;
        reset();
        // always encrypt mode for embedded cipher
        embeddedCipher.init(false, algorithm, key);
    }

    /**
     * Resets the iv to its original value.
     * This is used when doFinal is called in the Cipher class, so that the
     * cipher can be reused (with its original iv).
     */
    void reset() {
        System.arraycopy(iv, 0, register, 0, blockSize);
    }

    /**
     * Save the current content of this cipher.
     */
    void save() {
        if (registerSave == null) {
            registerSave = new byte[blockSize];
        }
        System.arraycopy(register, 0, registerSave, 0, blockSize);
    }

    /**
     * Restores the content of this cipher to the previous saved one.
     */
    void restore() {
        System.arraycopy(registerSave, 0, register, 0, blockSize);
    }

    /**
     * Performs 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 stream unit size
     * <code>numBytes</code>, 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 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 length of the encrypted data
     */
    int encrypt(byte[] plain, int plainOffset, int plainLen,
                byte[] cipher, int cipherOffset)
    {
        int i;
        int len = blockSize - numBytes;
        int loopCount = plainLen / numBytes;
        int oddBytes = plainLen % numBytes;

        if (len == 0) {
            for (; loopCount > 0;
                 plainOffset += numBytes, cipherOffset += numBytes,
                 loopCount--) {
                embeddedCipher.encryptBlock(register, 0, k, 0);
                for (i=0; i<numBytes; i++)
                    cipher[i+cipherOffset] =
                        (byte)(k[i] ^ plain[i+plainOffset]);
                System.arraycopy(k, 0, register, 0, numBytes);
            }
            if (oddBytes > 0) {
                embeddedCipher.encryptBlock(register, 0, k, 0);
                for (i=0; i<oddBytes; i++)
                    cipher[i+cipherOffset] =
                        (byte)(k[i] ^ plain[i+plainOffset]);
                System.arraycopy(k, 0, register, 0, numBytes);
            }
        } else {
            for (; loopCount > 0;
                 plainOffset += numBytes, cipherOffset += numBytes,
                 loopCount--) {
                embeddedCipher.encryptBlock(register, 0, k, 0);
                for (i=0; i<numBytes; i++)
                    cipher[i+cipherOffset] =
                        (byte)(k[i] ^ plain[i+plainOffset]);
                System.arraycopy(register, numBytes, register, 0, len);
                System.arraycopy(k, 0, register, len, numBytes);
            }
            if (oddBytes > 0) {
                embeddedCipher.encryptBlock(register, 0, k, 0);
                for (i=0; i<oddBytes; i++)
                    cipher[i+cipherOffset] =
                        (byte)(k[i] ^ plain[i+plainOffset]);
                System.arraycopy(register, numBytes, register, 0, len);
                System.arraycopy(k, 0, register, len, numBytes);
            }
        }
        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 stream unit size

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