Java Assignment Help - Solution for Diffie-Hellman Key Exchange

• 26th Jan, 2023
• 16:42 PM

Java is a widely used programming language that is suitable for implementing cryptographic algorithms such as the Diffie-Hellman key exchange method. The Java Cryptography Extension (JCE) provides a set of cryptographic algorithms including the Diffie-Hellman key agreement algorithm which makes it easy to implement secure key exchange in Java-based applications. Additionally, Java's platform independence makes it suitable for cross-platform development. It is a valuable tool for secure communication between parties.

Java Assignment Help - Java Assignment Solution

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Main {
    private static long PRIME_SIZE_LIMIT = 10000000;
    private static Random random = new Random();

    public static void main(String[] args) {
        List safePrimes = generateSafePrimes(PRIME_SIZE_LIMIT);

        long p = safePrimes.get(random.nextInt(safePrimes.size()/2) + safePrimes.size()/2);
        long q = 2*p + 1;
        long g = generateGenerator(p);

        // Alice keys
        long a = generatePrivateKey(q);
        long y_A = generatePublicKey(g, p, a);

        // Bobs keys
        long b = generatePrivateKey(q);
        long y_B = generatePublicKey(g, p, b);

        System.out.println("Alice private key: " + a);
        System.out.println("Alice public key: " + y_A);
        System.out.println("Alice will calculate the Diffie-Hellman key as follows: y_B^a " + exp(y_A, p, b));

        System.out.println("Bob private key: " + b);
        System.out.println("Bob public key: " + y_B);
        System.out.println("Bob will calculate the Diffie-Hellman key as follows: y_A^b " + exp(y_B, p, a));
    }

    private static long generatePublicKey(long g, long p, long a) {
        return exp(g, p, a);
    }

    private static long generatePrivateKey(long q) {
        return signedMod(random.nextLong(),q-3) + 1;
    }

    private static long generateGenerator(long p) {
        long h = signedMod(random.nextLong(), (p-3))+ 2;
        return (h*h) % p;
    }

    private static List generateSafePrimes(long limit) {
        List result = new ArrayList<>();
        for (long i = 2; i < limit; i++) {
            if (isPrime(i) && isPrime(2*i+1)) {
                result.add(i);
            }
        }
        return result;
    }

    private static boolean isPrime(long n) {
        for (long i = 2; i*i<=n; i++) {
            if (n%i == 0) {
                return false;
            }
        }
        return true;
    }

    private static long exp(long g, long p, long a) {
        long result = 1;
        for (long i = 0; i             result = (result*g)%p;
        }
        return result;
    }

    private static long signedMod(long a, long p) {
        if (a < 0) {
            return  a - ((a / p) - 1) * p;
        }
        return a % p;
    }
}