rc4.java

abou加密的RC4的java source code

//
//  RC4.java
//
//  Created by Thomas Dixon on 02/10/06.
//  Copyright 2006, Thomas Dixon
//  Released under the GNU LGPL
//

import java.security.InvalidKeyException;

public class RC4 {

/**** Constants ****/
private static final int
    STATE_ARRAY_SIZE = 256,
    BLOCK_SIZE       = 1; // Stream cipher
    
/**** Instance vars ****/
private static byte[] sArray = new byte[STATE_ARRAY_SIZE]; // State array aka "sbox"

private static int x,y; // i, j

    // User Initialization
    public static void engineInit(byte[] key)
    throws InvalidKeyException {
        if (key == null )
            throw new InvalidKeyException("Null key");
        
        if (key.length < 1 || key.length > 256)
            throw new InvalidKeyException("Invalid key length (req. 1-256 bytes "+
                                          key.length+")");
        
        rc4Init(key);
    }
    
    // Encipher with RC4 algorithm
    public static byte[] engineCrypt(byte[] in, int inOffset) {
        int outOffset = 0;
        byte[] out = new byte[in.length];
            
        byte t; // tmp
        for (int i = 0; i < in.length; i++) {
            x = (x + 1) & 0xff;
            y = (sArray[x] + y) & 0xff;
            // swap
            t = sArray[x];
            sArray[x] = sArray[y];
            sArray[y] = t;
            // xor input by keystream
            out[outOffset++] = (byte)(in[inOffset++] ^ sArray[(sArray[x] + sArray[y]) & 0xff]);
        }
            return out;
    }
	
    // Cipher initialization
    public static void rc4Init(byte[] key) {
        // fill state array
        for (int i = 0; i < STATE_ARRAY_SIZE; i++)
            sArray[i] = (byte)i;
        
        x = 0;
        byte t; // tmp
        for (int i = 0; i < STATE_ARRAY_SIZE; i++) {
            x = ((key[i % key.length] & 0xff) + sArray[i] + x) & 0xff;
            // swap
            t = sArray[i];
            sArray[i] = sArray[x];
            sArray[x] = t;
        }
        x = y = 0;
    }
}