Write a program to implement Diffie-Hellman Key Exchange algorithm. Information and Network Security (2170709) GTU

Algorithm/Steps:

1. A and B get public numbers P = 23, G = 9

2. A selected a private key a = 4 and B selected a private key b = 3

3. A and B compute public values

A:    x =(9^4 mod 23) = (6561 mod 23) = 6

B:    y = (9^3 mod 23) = (729 mod 23)  = 16

4. A and B exchange public numbers

5. A receives public key y =16 and B receives public key x = 6

6. A and B compute symmetric keys

A:  ka = y^a mod p = 65536 mod 23 = 9

B:    kb = x^b mod p = 216 mod 23 = 9

7. 9 is the shared secret.

Code:

import java.util.*;

import java.lang.*;

import java.math.BigInteger;

class Main

{

            public static void main(String args[])

            {

             Scanner sc = new Scanner(System.in);

            System.out.println("Enter the value of Xa&Xb");

            BigInteger Xa=  BigInteger.valueOf(sc.nextInt());

            BigInteger Xb=  BigInteger.valueOf(sc.nextInt());

            System.out.println("Enter a Prime no. p");

            BigInteger p =  BigInteger.valueOf(sc.nextInt());

            System.out.println("Enter Primitive Root a, such that a<p");

            BigInteger a =  BigInteger.valueOf(sc.nextInt());

            BigInteger Ya=  a.pow(Xa.intValue()).mod(p);

            BigInteger Yb=  a.pow(Xb.intValue()).mod(p);

            BigInteger Ka =  Yb.pow(Xa.intValue()).mod(p);

            BigInteger Kb=  Ya.pow(Xb.intValue()).mod(p);

            if(Ka.compareTo(Kb)==0)

             {

                        System.out.println("Transmission successful"+Ya+" "+Yb+" "+Ka+" "+Kb);}

            else{

                        System.out.println("Transmission failed"+Ya+" "+Yb+" "+Ka+" "+Kb);}

            }

}