DH.java

package lib;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.math.BigInteger;
import java.util.Random;

public class DH {
    public static String Server(DataInputStream DIS , DataOutputStream DOS) {
        String secret = "";
        try {
        double sec = Math.abs(new Random().nextInt(10 + 1) + 5); // Secret Num , NOT FOR SHARE
        // START : p and g Agreement
        BigInteger BIp = BigInteger.probablePrime(new Random().nextInt(8 + 1) + 6, new Random()); // The prime num
        int p = (int) Math.abs(BIp.longValue()); // Prime as int
        double g = new PRM().getPrimitiveRoots(p).get(0); // g , which is primitive root modulo of p
        //log.i("P = "+p+" , G = "+g+" , "+"Secret = "+sec);
        DOS.writeUTF(p+","+g);
        // END
        // Send g^sec mod p , also known as pub_1
        //log.i("A Public Key = "+Math.pow(g, sec)%Double.valueOf(p));
        DOS.writeUTF(""+Math.pow(g, sec)%Double.valueOf(p)); // How I convert double datatype to a String , Shhhh.. don't tell anyone
        double pub_2 = Double.parseDouble(DIS.readUTF()); // The public key of the other side
        //log.i("B Public Key = "+pub_2);
        // Calculate key
        secret = ""+Math.pow(pub_2, sec) % Double.valueOf(p); // Secret
        }catch(Exception e) {

        }
        return secret;
    }
    public static String Client(DataInputStream DIS , DataOutputStream DOS) {
        String secret = "";
        try {
        double sec = Math.abs(new Random().nextInt(10 + 1) + 5); // Secret Num , NOT FOR SHARE
        // START : p and g Agreement
        String pgs = DIS.readUTF();
        String[] pg = pgs.split(","); // get p and g from server
        double p = Double.parseDouble(pg[0]);
        double g = Double.parseDouble(pg[1]);
        // END
        double pub_1 = Double.parseDouble(DIS.readUTF()); // pub_1 , the public key of the other side
        // Send g^sec mod p , also known as pub_2
        DOS.writeUTF(""+Math.pow(g, sec)%p);
        // Calculate key
        secret = ""+Math.pow(pub_1, sec) % p;
        }catch(Exception e) {

        }
        return secret;
    }
}



/*
* Primitive Root Modulo Class
*/



package lib;

import java.math.BigInteger;
import java.util.ArrayList;

public class PRM {

    ArrayList<Integer> lcf = new ArrayList<Integer>();
    ArrayList<Integer> primRoots = new ArrayList<Integer>();
    public ArrayList<Integer> getPrimitiveRoots(int n){
        if(isPrime(n)){
           n = n-1;
        }else{
            return null;
        }
        ArrayList<Integer> lowestCommonFactors = lowestCommonFactors(n);
        ArrayList<Integer> dividers = new ArrayList<Integer>();
        for (int i = 0; i < lowestCommonFactors.size(); i++) {
            dividers.add(n/lowestCommonFactors.get(i));
        }
        loop: for (int i = 2; i <= n; i++) {
            for (int j = 0; j < dividers.size(); j++) {
                BigInteger modded = performModPow(i, dividers.get(j),n+1);

                if(modded.compareTo(new BigInteger("1")) == 0){
                    continue loop;
                }
                if(j == dividers.size()-1){
                    primRoots.add(i);
                }
            }
        }
        return primRoots;
    }
    public BigInteger performModPow(int powee, int power, int mod){
        BigInteger bigPowee = new BigInteger(powee +"");
        BigInteger bigPower = new BigInteger(power+"");
        BigInteger bigMod = new BigInteger(mod+"");
        return bigPowee.modPow(bigPower,bigMod);
    }
    public ArrayList<Integer> lowestCommonFactors(int number){
        int count;
        for (int i = 2; i<=(number); i++) {
            count = 0;
            while (number % i == 0) {
                number /= i;
                count++;
            }
            if (count == 0) {
                continue;
            }
            lcf.add(i);
        }
        return lcf;
    }
    public boolean isPrime(int x){
        if(x<2){return false;}
        for (int i = 2; i <= x/2; i++) {
            if(x%i == 0){ return false; }
        }
        return true;
    }
}