I have used openssl for authentication. For which we need libssl-dev package installed on the machine

First we need to generate a key for authentication using openssl req -x509 -nodes -days 365 -newkey rsa:1024 -keyout mycert.pem -out mycert.pem

Then start the server program which is used for authentication. Command: ./app s // 's' here implies server

Then start two clients. Command: ./app c // 'c' here implies client

The first message a client sends is a Register message Usage: register

Then it should connect to a client using connect command Usage: connect

Now both clients can chat by entering messages.