MSDBRG

package gist;

import java.math.BigInteger;
import java.security.SecureRandom;

public class MSDBRG {

    private static BigInteger TWO = new BigInteger("2");
    
    public static void main(String[] args) {
        BigInteger bk = TWO.pow(256);
        BigInteger bkoutput = TWO.pow(384);
        BigInteger bk128 = TWO.pow(128);
        
        BigInteger c1 = new BigInteger("297");
        BigInteger c2 = new BigInteger("357");

        BigInteger p = bk.add(c1);
        BigInteger q = bk.add(c2);
        BigInteger n = p.multiply(q);

        BigInteger e = new BigInteger("7");
        
        BigInteger random = new BigInteger(128, new SecureRandom());
        
        BigInteger ct = random.modPow(e, n);
        
        BigInteger y = ct.mod(bkoutput);
        BigInteger x = ct.divide(bkoutput);
        
        System.out.println("output of the generator is "+ y.toString(2));
        System.out.println("internal state of the generator is "+ x.toString(2));
        
        
        //WORKING WITH THE OUTPUT ONLY Y
        
        String ys = y.toString(2);

        //taking the 128 most significant bits of the output
        BigInteger ym = new BigInteger(ys.substring(0,128),2);
        //taking the 256 less significant bits of the output
        BigInteger yl = new BigInteger(ys.substring(128),2);
        System.out.println();
        System.out.println("====================================================================");
        System.out.println("CT mod p is "+ ct.mod(p).toString(2));
        System.out.println("CT mod p is "+crandalMod(ym, yl, bk, c1).toString(2));
        System.out.println("====================================================================");
        System.out.println("CT mod p (128 lbt) "+ ct.mod(p).mod(bk128).toString(2));
        System.out.println("CT mod p (128 lbt) "+crandalMod(ym, yl, bk, c1).mod(bk128).toString(2));

    }
    
 
    
    public static BigInteger crandalMod(BigInteger ym, BigInteger yl, BigInteger bk, BigInteger c) {
        BigInteger r = yl;
        
        BigInteger r1 = ym.multiply(c); 
        r = r.subtract(r1);
        r = r.add(c);
        
        return r;
    }

}