// Rc4Cipher - the RC4 encryption method
//
// Copyright (C) 1996 by Jef Poskanzer <jef@acme.com>.  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.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/

package Acme.Crypto;

import java.io.*;

/// The RC4 encryption method.
// <P>
// This may or may not be the real RC4 cipher.  It's based on
// code which showed up anonymously posted in sci.crypt.
// Here's the start of the article:
// <BLOCKQUOTE><PRE>
// Path: dog.ee.lbl.gov!overload.lbl.gov!lll-winken.llnl.gov!seismo!rsg1.er.usgs.gov!jobone!newsxfer.itd.umich.edu!europa.eng.gtefsd.com!howland.reston.ans.net!EU.net!sun4nl!hacktic!usenet
// From: nobody@vox.xs4all.nl (An0nYm0Us UsEr)
// Newsgroups: sci.crypt
// Subject: RC4 ?
// Date: 13 Sep 1994 21:30:36 GMT
// Organization: Global Anonymous Remail Services Ltd.
// Lines: 83
// Message-ID: &lt;3555ls$fsv@news.xs4all.nl&gt;
// NNTP-Posting-Host: xs1.xs4all.nl
// X-Comment: This message did not originate from the above address.
// X-Comment: It was automatically remailed by an anonymous mailservice.
// X-Comment: Info: usura@xs4all.nl, Subject: remailer-help 
// X-Comment: Please report inappropriate use to &lt;admin@vox.xs4all.nl&gt;
// 
// SUBJECT:  RC4 Source Code
// 
// I've tested this.  It is compatible with the RC4 object module
// that comes in the various RSA toolkits.  
// </PRE></BLOCKQUOTE>
// <P>
// It's surprisingly fast, for pure Java.  On a SPARC 20, wrapped
// in Acme.Crypto.EncryptedOutputStream or Acme.Crypto.EncryptedInputStream,
// it does around 13000 bytes/second.
// <P>
// <A HREF="/resources/classes/Acme/Crypto/Rc4Cipher.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.Z">Fetch the entire Acme package.</A>
// <P>
// @see EncryptedOutputStream
// @see EncryptedInputStream

public class Rc4Cipher extends StreamCipher
    {

    // Constructor, string key.
    public Rc4Cipher( String keyStr )
	{
	super( 256 );	// (typically, not all key bits are used)
	setKey( keyStr );
	}

    // Constructor, byte-array key.
    public Rc4Cipher( byte[] key )
	{
	super( 256 );	// (typically, not all key bits are used)
	setKey( key );
	}

    // Key routines.

    private byte[] state = new byte[256];
    private int x, y;

    /// Set the key.
    public void setKey( byte[] key )
	{
	int index1;
	int index2;
	int counter;
	byte temp;

	for ( counter = 0; counter < 256; ++counter )
	    state[counter] = (byte) counter;
	x = 0;
	y = 0;
	index1 = 0;
	index2 = 0;
	for ( counter = 0; counter < 256; ++counter )
	    {
	    index2 = ( key[index1] + state[counter] + index2 ) & 0xff;
	    temp = state[counter];
	    state[counter] = state[index2];
	    state[index2] = temp;
	    index1 = ( index1 + 1 ) % key.length;
	    }
	}

    /// Encrypt a byte.
    public byte encrypt( byte clearText )
	{
	return (byte) ( clearText ^ state[nextState()] );
	}

    /// Decrypt a byte.
    public byte decrypt( byte cipherText )
	{
	return (byte) ( cipherText ^ state[nextState()] );
	}

    /// Encrypt some bytes.
    public void encrypt( byte[] clearText, int clearOff, byte[] cipherText, int cipherOff, int len )
	{
	for ( int i = 0; i < len; ++i )
	    cipherText[cipherOff + i] =
		(byte) ( clearText[clearOff + i] ^ state[nextState()] );
	}

    /// Decrypt some bytes.
    public void decrypt( byte[] cipherText, int cipherOff, byte[] clearText, int clearOff, int len )
	{
	for ( int i = 0; i < len; ++i )
	    clearText[clearOff + i] =
		(byte) ( cipherText[cipherOff + i] ^ state[nextState()] );
	}

    private int nextState()
	{
	byte temp;

	x = ( x + 1 ) & 0xff;
	y = ( y + state[x] ) & 0xff;
	temp = state[x];
	state[x] = state[y];
	state[y] = temp;
	return ( state[x] + state[y] ) & 0xff;
	}

    }