CPChat

吴俊旻

A simple encrypted chat web application implemented on node.js , koa.js & socket.io.

How to Run?

1. Change SERVER_ADDR in client.js.

2. Change the working directory and input the following command in terminal:

   npm install
   webpack client.js public/js/bundle.js
   npm start

3. Visit SERVER_ADDR:8888 in your browser.

Key Exchange

• Assumption
  • a client always communicates with the right server (own the server's public key)
  • clients and server agree on the same hash function h
  • clients and server agree on the same way to generate a session key (using two random byte buffer)

1. The client generates random bytes (r_a) and a random integer (n), and sends E(PU_server, {PU_client, r_a, n}) (denoted by data) || E(PR_client, h(data)) (denoted by signature) to server.
2. Server generates random bytes (r_b), decrypts data and signature by PR_server and PU_client respectively and sends E(PU_client, {r_b, n-1}) (denoted by data2) || E(PR_server, h(data2)) (denoted by signature2) to the client.
3. Now that the client and server are authenticated mutually, they can use r_a & r_b the generate a session key.