/*

 * Copyright (c) 1997, 2007, 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>

     */

    void 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);

            }

        }

    }

    /**

     * 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

     * <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 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>

     */

    void decrypt(byte[] cipher, int cipherOffset, int cipherLen,

                        byte[] plain, int plainOffset)

    {

        // OFB encrypt and decrypt are identical

        encrypt(cipher, cipherOffset, cipherLen, plain, plainOffset);

    }

}