//==============================================================================
// tribble/security/KeyMaker.java
//------------------------------------------------------------------------------

package tribble.security;


// System imports

import java.lang.Exception;
import java.lang.String;

import java.security.Key;


// Local imports

import tribble.util.HexDump;


/*******************************************************************************
* Methods for generating an encryption/decryption key.
*
* @version	$Revision: 1.2 $ $Date: 2003/03/19 04:32:47 $
* @since	2002-04-13
* @author
*	David R. Tribble,
*	<a href="mailto:david@tribble.com">david@tribble.com</a>.
*	<br>
*	Copyright ©2002 by David R. Tribble, all rights reserved.
*	<br>
*	Permission is granted to freely use and distribute this source code
*	provided that the original copyright and authorship notices remain
*	intact.
*/

public class KeyMaker
{
// Identification

    /** Revision information. */
    static final String		REV =
        "@(#)tribble/security/KeyMaker.java $Revision: 1.2 $ $Date: 2003/03/19 04:32:47 $\n";


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Private constants

    /** LFSR bitmask. */
    private static final int	LFSR_MASK =	0x4010620A;


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Public static methods

    /***************************************************************************
    * Test driver.
    *
    * @param	args
    * Command line arguments.  A 256-bit binary key is generated from each
    * argument.
    *
    * @since	1.1, 2002-04-13
    */

    public static void main(String[] args)
    {
        // Make a 128-bit key from each password arg
        for (int i = 0;  i < args.length;  i++)
        {
            byte[]	key;

            // Make a 128-bit key from a password arg
            System.out.println("\"" + args[i] + "\"");
            key = makeKey(args[i], 256/8);
            HexDump.hexDump(System.out, key, 0, key.length);
            System.out.println();
        }
    }


    /***************************************************************************
    * Generate a binary key from a password string.
    * The password string is suitably scrambled to produce a binary key exactly
    * <tt>n</tt> bytes long.
    *
    * @param	pwd
    * A string containing a password.
    * This can be null or empty (<tt>""</tt>).
    *
    * @param	n
    * The length (in bytes) of the resulting binary key.
    *
    * @return
    * An <i>n</i>-byte encryption/decryption key value.
    *
    * @since	1.1, 2002-04-13
    */

    public static byte[] makeKey(String pwd, int n)
    {
        byte[]	key;
        int	lfsr;
        int	len;
        int	i;
        int	o;

        // Check args
        if (pwd == null  ||  pwd.length() == 0)
            pwd = "\0";

        // Set up
        len = pwd.length();
        key = new byte[n];
        lfsr = -1;

        // Scramble the bytes of the password
        i = 0;
        o = 0;
        for (int m = (n >= len ? n : len);  m >= 0;  m--)
        {
            int		ch;

            if (i >= len)
                i = 0;

            // Mix in the next char of the password
            ch = pwd.charAt(i++);

            if (o >= n)
                o = 0;
            lfsr += (ch & 0xFF);
            lfsr = (lfsr & LFSR_MASK) ^ ((lfsr << 1) | (lfsr >>> 32-1));
            key[o++] ^= (byte) lfsr;

            ch >>= 8;
            if (ch != 0x00)
            {
                if (o >= n)
                    o = 0;
                lfsr += ch;
                lfsr = (lfsr & LFSR_MASK) ^ ((lfsr << 1) | (lfsr >>> 32-1));
                key[o++] ^= (byte) lfsr;
            }
        }

        return (key);
    }


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Variables

    // (None)


// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Private constructors

    /***************************************************************************
    * Constructor.
    *
    * @since	1.1, 2002-04-13
    */

    private KeyMaker()
    {
        // Do nothing
    }
}

// End KeyMaker.java