Re: Simple encryption/decryption

Mark Space <>
Mon, 23 Mar 2009 11:13:22 -0700
<cjQxl.24540$> wrote:

I'm looking for a simple solution: a way to encrypt a string into a
alphanumeric string, and can be decrypted back to its original form,
using a string as the key, say 'password123', any idea how to achieve
this? Thanks.

I'm not seeing a good answer to this. In particular, the
SecretKeyFactory.getInstance( "ARCFOUR" ) method returns an error. I
don't see a simple way to use RC4 without this call succeeding. Anyone
got a solution?

Anyway, to the OP, check out the code below. It will at least get you
going. Sorry for the lack of Javadoc comments, I just had this laying
around on the hard drive. You can compare this code to the description
of RC4 at Wikipedia. It's the exact same algorithm. Note the test vectors.


package local;


COPYRIGHT 2009 Brenden Towey

This code is donated to the public domain but is unsupported and has no
warranty whatsoever. Use at your own risk.

  * @author Brenden
public class Rc4
     private byte[] state = new byte[256];
     int x, y;

     public Rc4( byte[] key )
// if( key.length<5||key.length>16 )
// {
// throw new IllegalArgumentException( "Key: "+key+
// " must be between 40 and 128 bits. (key length is "+
// key.length+".)" );
// }
         for( int i = 0; i < state.length; i++ ) {
             state[i] = (byte) i;
         for( int i = 0; i < state.length; i++ ) {
             x = (x + key[i % key.length] + state[i]) & 0xFF;
             byte swap = state[i];
             state[i] = state[x];
             state[x] = swap;
         x = 0;

     public byte[] crypt( byte[] input )
         byte[] output = new byte[input.length];
         for( int i = 0; i < input.length; i++ ) {
             x = (x + 1) % 256;
             y = (state[x] + y) & 0xFF;
             byte swap = state[x];
             state[x] = state[y];
             state[y] = swap;
             byte r = state[(state[x] + state[y]) & 0xFF];
             output[i] = (byte) (input[i] ^ r);
         return output;

     public static void main( final String... args )
         String[][] testVectors = {{"Key", "Plaintext"},
             {"Wiki", "pedia"}, {"Secret", "Attack at dawn"}
         for( String[] s : testVectors ) {
             System.out.printf( "RC4( \"%s\", \"%s\" ) == ", s[0], s[1] );
             System.out.println( hexString( new Rc4( s[0].getBytes()
).crypt( s[1].
                     getBytes() ) ) );

     private static String hexString( byte[] bytes )
         StringBuilder sb = new StringBuilder( bytes.length *2 );
         for( int i = 0; i < bytes.length; i++ ) {
             sb.append( String.format( "%02X", bytes[i] ));
         return sb.toString();
// return local.utils.ArrayUtils.toFormattedString( "%02X",
//bytes, null );

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