Using the Diffie-Hellman Key Exchange protocol, a server and a client can securely compute a shared cryptographic key without sharing the actual secret key. Instead, they can share some shared parameters, and based on those the same secret cryptographic key can be computed by both the client and the server.

We have already discussed in detail how the Diffie-Hellman Key Exchange protocol works. In this article, we would discuss how to use the pyDHE Python module to implement the Diffie-Hellman Key Exchange protocol.

We need a server and a client. The server and the client can share shared parameters and based on the shared parameters both of them can calculate the same shared secret.

A server can be implemented in Python using the following lines of code:

import socket

HOST = "127.0.0.1"
PORT = 12345

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()

    connection, address = s.accept()

    with connection:
        print("Connected by ", address)

        data = connection.recv(2048)

And, a client can be implemented using the following lines of code:

import socket

HOST = "127.0.0.1"
PORT = 12345

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((HOST, PORT))
    s.sendall("Hello".encode())

Now, we can use the pyDHE library to calculate a shared secret between the server and the client. The server can calculate the shared secret in the following way: