/*

 * 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 javax.crypto.ShortBufferException;

/**

 * This class implements padding as specified in the PKCS#5 standard.

 *

 * @author Gigi Ankeny

 *

 *

 * @see Padding

 */

final class PKCS5Padding implements Padding {

    private int blockSize;

    PKCS5Padding(int blockSize) {

        this.blockSize = blockSize;

    }

    /**

     * Adds the given number of padding bytes to the data input.

     * The value of the padding bytes is determined

     * by the specific padding mechanism that implements this

     * interface.

     *

     * @param in the input buffer with the data to pad

     * @param off the offset in <code>in</code> where the padding bytes

     * are appended

     * @param len the number of padding bytes to add

     *

     * @exception ShortBufferException if <code>in</code> is too small to hold

     * the padding bytes

     */

    public void padWithLen(byte[] in, int off, int len)

        throws ShortBufferException

    {

        if (in == null)

            return;

        if ((off + len) > in.length) {

            throw new ShortBufferException("Buffer too small to hold padding");

        }

        byte paddingOctet = (byte) (len & 0xff);

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

            in[i + off] = paddingOctet;

        }

        return;

    }

    /**

     * Returns the index where the padding starts.

     *

     * <p>Given a buffer with padded data, this method returns the

     * index where the padding starts.

     *

     * @param in the buffer with the padded data

     * @param off the offset in <code>in</code> where the padded data starts

     * @param len the length of the padded data

     *

     * @return the index where the padding starts, or -1 if the input is

     * not properly padded

     */

    public int unpad(byte[] in, int off, int len) {

        if ((in == null) ||

            (len == 0)) { // this can happen if input is really a padded buffer

            return 0;

        }

        byte lastByte = in[off + len - 1];

        int padValue = (int)lastByte & 0x0ff;

        if ((padValue < 0x01)

            || (padValue > blockSize)) {

            return -1;

        }

        int start = off + len - ((int)lastByte & 0x0ff);

        if (start < off) {

            return -1;

        }

        for (int i = 0; i < ((int)lastByte & 0x0ff); i++) {

            if (in[start+i] != lastByte) {

                return -1;

            }

        }

        return start;

    }

    /**

     * Determines how long the padding will be for a given input length.

     *

     * @param len the length of the data to pad

     *

     * @return the length of the padding

     */

    public int padLength(int len) {

        int paddingOctet = blockSize - (len % blockSize);

        return paddingOctet;

    }

}