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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

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 *

 * 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

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 * accompanied this code).

 *

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package com.sun.crypto.provider;

import java.security.InvalidKeyException;

/**

 * This class represents ciphers in cipher block chaining (CBC) 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

 */

class CipherBlockChaining extends FeedbackCipher  {

    /*

     * random bytes that are initialized with iv

     */

    protected byte[] r;

    /*

     * output buffer

     */

    private byte[] k;

    // variables for save/restore calls

    private byte[] rSave = null;

    CipherBlockChaining(SymmetricCipher embeddedCipher) {

        super(embeddedCipher);

        k = new byte[blockSize];

        r = new byte[blockSize];

    }

    /**

     * Gets the name of this feedback mode.

     *

     * @return the string <code>CBC</code>

     */

    String getFeedback() {

        return "CBC";

    }

    /**

     * 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();

        embeddedCipher.init(decrypting, 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, r, 0, blockSize);

    }

    /**

     * Save the current content of this cipher.

     */

    void save() {

        if (rSave == null) {

            rSave = new byte[blockSize];

        }

        System.arraycopy(r, 0, rSave, 0, blockSize);

    }

    /**

     * Restores the content of this cipher to the previous saved one.

     */

    void restore() {

        System.arraycopy(rSave, 0, r, 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 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>

     */

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

                 byte[] cipher, int cipherOffset)

    {

        int i;

        int endIndex = plainOffset + plainLen;

        for (; plainOffset < endIndex;

             plainOffset+=blockSize, cipherOffset += blockSize) {

            for (i=0; i<blockSize; i++) {

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

            }

            embeddedCipher.encryptBlock(k, 0, cipher, cipherOffset);

            System.arraycopy(cipher, cipherOffset, r, 0, blockSize);

        }

    }

    /**

     * 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>

     *

     * @exception IllegalBlockSizeException if input data whose length does

     * not correspond to the embedded cipher's block size is passed to the

     * embedded cipher

     */

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

                 byte[] plain, int plainOffset)

    {

        int i;

        byte[] cipherOrig=null;

        int endIndex = cipherOffset + cipherLen;

        if (cipher==plain && (cipherOffset >= plainOffset)

            && ((cipherOffset - plainOffset) < blockSize)) {

            // Save the original ciphertext blocks, so they can be

            // stored in the feedback register "r".

            // This is necessary because in this constellation, a

            // ciphertext block (or parts of it) will be overridden by

            // the plaintext result.

        }

        for (; cipherOffset < endIndex;

             cipherOffset += blockSize, plainOffset += blockSize) {

            embeddedCipher.decryptBlock(cipher, cipherOffset, k, 0);

            for (i = 0; i < blockSize; i++) {

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

            }

            if (cipherOrig==null) {

                System.arraycopy(cipher, cipherOffset, r, 0, blockSize);

            } else {

                System.arraycopy(cipherOrig, cipherOffset, r, 0, blockSize);

            }

        }

    }

}