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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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,

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package com.sun.crypto.provider;

import java.security.InvalidKeyException;

import java.security.ProviderException;

/**

 * 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 + plainLen - 1)</code>, is encrypted.

     * The result is stored in <code>cipher</code>, starting at

     * <code>cipherOffset</code>.

     *

     * @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>

     * @exception ProviderException if <code>plainLen</code> is not

     * a multiple of the <code>numBytes</code>

     * @return the length of the encrypted data

     */

    int encrypt(byte[] plain, int plainOffset, int plainLen,

                byte[] cipher, int cipherOffset) {

        int nShift = blockSize - numBytes;

        int loopCount = plainLen / numBytes;

        for (; loopCount > 0;

             plainOffset += numBytes, cipherOffset += numBytes,

             loopCount--) {

            embeddedCipher.encryptBlock(register, 0, k, 0);

            for (int i = 0; i < numBytes; i++) {

                cipher[i + cipherOffset] =

                    (byte)(k[i] ^ plain[i + plainOffset]);

            }

            if (nShift != 0) {

                System.arraycopy(register, numBytes, register, 0, nShift);

            }

            System.arraycopy(k, 0, register, nShift, numBytes);

        }

        return plainLen;

    }

    /**

     * Performs last encryption operation.

     *

     * <p>The input plain text <code>plain</code>, starting at

     * <code>plainOffset</code> and ending at

     * <code>(plainOffset + plainLen - 1)</code>, is encrypted.

     * The result is stored in <code>cipher</code>, starting at

     * <code>cipherOffset</code>.

     *

     * @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 encryptFinal(byte[] plain, int plainOffset, int plainLen,

                     byte[] cipher, int cipherOffset) {

        int oddBytes = plainLen % numBytes;

        int len = encrypt(plain, plainOffset, (plainLen - oddBytes),

                          cipher, cipherOffset);

        plainOffset += len;

        cipherOffset += len;

        if (oddBytes != 0) {

            embeddedCipher.encryptBlock(register, 0, k, 0);

            for (int i = 0; i < oddBytes; i++) {

                cipher[i + cipherOffset] =

                    (byte)(k[i] ^ plain[ i + plainOffset]);

            }

        }

        return plainLen;

    }

    // OFB encrypt and decrypt are identical

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

                byte[] plain, int plainOffset) {

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

    }

    // OFB encrypt and decrypt are identical

    int decryptFinal(byte[] cipher, int cipherOffset, int cipherLen,

                     byte[] plain, int plainOffset) {

        // OFB encrypt and decrypt are identical

        return encryptFinal(cipher, cipherOffset, cipherLen, plain, plainOffset);

    }

}