import java.math.*;
import java.security.*;

class GenKey
{
   // Generate some large primes in the 128 bit area.
   //
   // Possibly useful for lotteries where winning numbers
   // are "probably" large prime numbers.
   //
   // The purpose of this code is generate keys from some sort
   // of input - in this case the command line.  The intention
   // is not to generate a random prime number but a reproducible
   // number.
   //
   // Copyright 1998 by Michael Lecuyer.  You may use this in any way
   // you wish, but this version is mine.  Change it enough and you'll get
   // to place your copyright notice here instead!
   //
   public static void main(String args[])
   {
	int i;
	BigInteger biKey; // resulting key.
	BigInteger two = new BigInteger("2");
	BigInteger one = new BigInteger("1");

	// nth probable prime to pick.  Choose your own number.
	int pick = 5;

	if (args.length == 0)
	{
		System.err.println("Usage: Some phrase like 'hello fishy'");
		System.exit(1);
	}

	// Accumulate all args into a string and convert it to MD5.
	String seed = "";
	for (i = 0; i < args.length; i++)
		seed += args[i];

	MessageDigest md5 = null;
	try {
		md5 = MessageDigest.getInstance("MD5");
	} catch (NoSuchAlgorithmException e) {
		System.err.println("Can't find an MD5 message digest algorithm");
	}
	biKey = new BigInteger(md5.digest(seed.getBytes()));

	// make sure it starts out odd - there are very few even primes.
	if (biKey.and(one).compareTo(one) != 0)
		biKey = biKey.add(one);

	// Purely for entertainment purposes!
	System.out.println("Key starts with: " + dumpBytes(biKey.toByteArray()));

	// Search for n'th probable prime out of a thousand.
	for (i = 0; i < 1000; i++)
	{
		// The number 1024 was chosen at pseudorandom.  Larger numbers
		// take longer because the prime-picker is allegedly more picky.
		if (biKey.isProbablePrime(1024))
			if (--pick == 0)
			{
			System.out.println("Key: " + dumpBytes(biKey.toByteArray()));
			System.exit(0);
			}
		biKey = biKey.add(two);
	}
	System.out.println("No Key Generated.");
   }

   // Display some bytes in HEX.
   //
   static String dumpBytes(byte b[])
   {
	StringBuffer r = new StringBuffer();
	final String hex = "0123456789ABCDEF";

	for (int i = 0; i < b.length; i++)
	{
		int c = ((b[i]) >>> 4) & 0xf;
		r.append(hex.charAt(c));
		c = ((int)b[i] & 0xf);
		r.append(hex.charAt(c));
//       r.append(' '); // uncomment if you like spaces in the dump.
	}
	r.setLength(r.length() - 1);

	return r.toString();
   }

}