Re: Simple encryption/decryption

angelochen960@gmail.com wrote:


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.

<http://en.wikipedia.org/wiki/RC4>

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 );
     }
}