Diffie-Hellman key exchange in Java

Question

I am working on a personal project in Java which involves sending sensitive data over an insecure channel. I need to know how to implement Diffie Hellman Key Exchange (DHKE) in java using its libraries. I know all the cryptographic theory about it so no need to go into details, I just need a very basic implementation so I cand have 2 programs share a secret key. I got the example from java2s.com, but it is not complete:

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;

import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHPublicKeySpec;

public class Main {
  public final static int pValue = 47;

  public final static int gValue = 71;

  public final static int XaValue = 9;

  public final static int XbValue = 14;

  public static void main(String[] args) throws Exception {
    BigInteger p = new BigInteger(Integer.toString(pValue));
    BigInteger g = new BigInteger(Integer.toString(gValue));
    BigInteger Xa = new BigInteger(Integer.toString(XaValue));
    BigInteger Xb = new BigInteger(Integer.toString(XbValue));

    int bitLength = 512; // 512 bits
    SecureRandom rnd = new SecureRandom();
    p = BigInteger.probablePrime(bitLength, rnd);
    g = BigInteger.probablePrime(bitLength, rnd);

    createSpecificKey(p, g);
  }

  public static void createSpecificKey(BigInteger p, BigInteger g) throws Exception {
    KeyPairGenerator kpg = KeyPairGenerator.getInstance("DiffieHellman");

    DHParameterSpec param = new DHParameterSpec(p, g);
    kpg.initialize(param);
    KeyPair kp = kpg.generateKeyPair();

    KeyFactory kfactory = KeyFactory.getInstance("DiffieHellman");

    DHPublicKeySpec kspec = (DHPublicKeySpec) kfactory.getKeySpec(kp.getPublic(),
        DHPublicKeySpec.class);
  }
}

How do I go on from this? Could anyone help me complete the remaining code?

Answer 1

What about the official Oracle Docs? They show a DH key exchange in code there.