rc4engine.java

这是linux下ssl vpn的实现程序

/*
 *  SSL-Explorer
 *
 *  Copyright (C) 2003-2006 3SP LTD. All Rights Reserved
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version 2 of
 *  the License, or (at your option) any later version.
 *  This program 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 for more details.
 *
 *  You should have received a copy of the GNU General Public
 *  License along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
			
package com.maverick.crypto.engines;

public class RC4Engine
{
    private final static int STATE_LENGTH = 256;

    /*
     * variables to hold the state of the RC4 engine
     * during encryption and decryption
     */

    private byte[]      engineState = null;
    private int         x = 0;
    private int         y = 0;
    private byte[]      workingKey = null;

    /**
     * initialise a RC4 cipher.
     *
     * @param forEncryption whether or not we are for encryption.
     * @param params the parameters required to set up the cipher.
     * @exception IllegalArgumentException if the params argument is
     * inappropriate.
     */
    public void init(
        boolean             forEncryption,
        byte[] key
    )
    {
            /*
             * RC4 encryption and decryption is completely
             * symmetrical, so the 'forEncryption' is
             * irrelevant.
             */
            workingKey = key;
            setKey(workingKey);
            return;
    }

    public String getAlgorithmName()
    {
        return "RC4";
    }

    public byte returnByte(byte in)
    {
        x = (x + 1) & 0xff;
        y = (engineState[x] + y) & 0xff;

        // swap
        byte tmp = engineState[x];
        engineState[x] = engineState[y];
        engineState[y] = tmp;

        // xor
        return (byte)(in ^ engineState[(engineState[x] + engineState[y]) & 0xff]);
    }

    public void processBytes(
        byte[]     in,
        int     inOff,
        int     len,
        byte[]     out,
        int     outOff
    )
    {
        if ((inOff + len) > in.length)
        {
            throw new RuntimeException("input buffer too short");
        }

        if ((outOff + len) > out.length)
        {
            throw new RuntimeException("output buffer too short");
        }

        for (int i = 0; i < len ; i++)
        {
            x = (x + 1) & 0xff;
            y = (engineState[x] + y) & 0xff;

            // swap
            byte tmp = engineState[x];
            engineState[x] = engineState[y];
            engineState[y] = tmp;

            // xor
            out[i+outOff] = (byte)(in[i + inOff]
                    ^ engineState[(engineState[x] + engineState[y]) & 0xff]);
        }
    }

    public void reset()
    {
        setKey(workingKey);
    }

    // Private implementation

    private void setKey(byte[] keyBytes)
    {
        workingKey = keyBytes;

        // System.out.println("the key length is ; "+ workingKey.length);

        x = 0;
        y = 0;

        if (engineState == null)
        {
            engineState = new byte[STATE_LENGTH];
        }

        // reset the state of the engine
        for (int i=0; i < STATE_LENGTH; i++)
        {
            engineState[i] = (byte)i;
        }

        int i1 = 0;
        int i2 = 0;

        for (int i=0; i < STATE_LENGTH; i++)
        {
            i2 = ((keyBytes[i1] & 0xff) + engineState[i] + i2) & 0xff;
            // do the byte-swap inline
            byte tmp = engineState[i];
            engineState[i] = engineState[i2];
            engineState[i2] = tmp;
            i1 = (i1+1) % keyBytes.length;
        }
    }
}