arcfour.java

非常有用的操作pdf文件的java源码

/**
 * Copyright (c) 2003, www.pdfbox.org
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. Neither the name of pdfbox; nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * http://www.pdfbox.org
 *
 */
package org.pdfbox.encryption;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * This class is an implementation of the alleged RC4 algorithm.
 *
 * @author <a href="mailto:[e-mail]">Ben Litchfield</a>
 * @version $Revision: 1.8 $
 */
public class ARCFour
{
    private int[] salt;
    private int b;
    private int c;

    /**
     * Constructor.
     *
     */
    public ARCFour()
    {
        salt = new int[256];
    }

    /**
     * This will reset the key to be used.
     *
     * @param key The RC4 key used during encryption.
    */
    public void setKey( byte[] key )
    {
        b = 0;
        c = 0;

        if(key.length < 1 || key.length > 32)
        {
            throw new IllegalArgumentException("number of bytes must be between 1 and 32");
        }
        for(int i = 0; i < salt.length; i++)
        {
            salt[i] = i;
        }

        int keyIndex = 0;
        int saltIndex = 0;
        for( int i = 0; i < salt.length; i++)
        {
            saltIndex = (fixByte(key[keyIndex]) + salt[i] + saltIndex) % 256;
            swap( salt, i, saltIndex );
            keyIndex = (keyIndex + 1) % key.length;
        }

    }

    /**
     * Thie will ensure that the value for a byte >=0.
     *
     * @param aByte The byte to test against.
     *
     * @return A value >=0 and < 256
     */
    private static final int fixByte( byte aByte )
    {
        return aByte < 0 ? 256 + aByte : aByte;
    }

    /**
     * This will swap two values in an array.
     *
     * @param data The array to swap from.
     * @param firstIndex The index of the first element to swap.
     * @param secondIndex The index of the second element to swap.
     */
    private static final void swap( int[] data, int firstIndex, int secondIndex )
    {
        int tmp = data[ firstIndex ];
        data[ firstIndex ] = data[ secondIndex ];
        data[ secondIndex ] = tmp;
    }

    /**
     * This will encrypt and write the next byte.
     *
     * @param aByte The byte to encrypt.
     * @param output The stream to write to.
     *
     * @throws IOException If there is an error writing to the output stream.
     */
    public void write( byte aByte, OutputStream output ) throws IOException
    {
        b = (b + 1) % 256;
        c = (salt[b] + c) % 256;
        swap( salt, b, c );
        int saltIndex = (salt[b] + salt[c]) % 256;
        output.write(aByte ^ (byte)salt[saltIndex]);
    }

    /**
     * This will encrypt and write the data.
     *
     * @param data The data to encrypt.
     * @param output The stream to write to.
     *
     * @throws IOException If there is an error writing to the output stream.
     */
    public void write( byte[] data, OutputStream output ) throws IOException
    {
        for( int i = 0; i < data.length; i++ )
        {
            write( data[i], output );
        }
    }

    /**
     * This will encrypt and write the data.
     *
     * @param data The data to encrypt.
     * @param output The stream to write to.
     *
     * @throws IOException If there is an error writing to the output stream.
     */
    public void write( InputStream data, OutputStream output ) throws IOException
    {
        byte[] buffer = new byte[1024];
        int amountRead = 0;
        while( (amountRead = data.read( buffer )) != -1 )
        {
            write( buffer, 0, amountRead, output );
        }
    }

    /**
     * This will encrypt and write the data.
     *
     * @param data The data to encrypt.
     * @param offset The offset into the array to start reading data from.
     * @param len The number of bytes to attempt to read.
     * @param output The stream to write to.
     *
     * @throws IOException If there is an error writing to the output stream.
     */
    public void write( byte[] data, int offset, int len, OutputStream output) throws IOException
    {
        for( int i = offset; i < offset + len; i++ )
        {
            write( data[i], output );
        }
    }
}