Introduction to Computer Networks -- Term Project, Spring 2024 Demir Eroglu 2200678 Emir Ismail Genc 2202780 Kuzey Berk Yilmaz 2200014

This is a simple P2P chat application written in Python. It allows users to chat with each other in a secure or unsecure way.

It utilizes UDP for peer discovery and service announcement. It works by parsing every single announcement into a file called contacts.json (created automatically if it doesn't exist) and both the TCP client and the server can (and do) access this file for other operations.

The program utilizes TCP for both unsecure and secure chats (which use the pyDes library to encrypt messages with P2P exchanged keys using the Diffie-Hellman key exchange mechanism). If the user chooses "secure" chat (instead of "unsecure" where plaintext messages are exchanged), the user gets prompted for an input for generating keys. When the TCP server receives a key from the other user, it is used in the generation of a common, shared key for encrypting messages.

The program also logs and saves the chat history with every user in different text files individually. It is important to note that all of the content is saved and held in plaintext, even if the chat is encrypted.

• Python 3.x
• pyDes library

1. After downloading, navigate to the project directory.
2. Install the required Python libraries using "pip install (library name goes here)"
3. First, run the UDP Server for receiving announcements from other users and saving their info into your local contacts.json file: python UDP_Server.py
4. Then, run the UDP Client for announcing yourself over the network: python UDP_Client.py
5. In seperate terminals, run the TCP apps (Server first, client second): python TCP_Server.py python TCP_Client.py

• List Users: Lists all users who have been active within the last 15 minutes.
• Chat: Allows you to chat with another user. You will be asked to specify the username of the user you want to chat with and your chat security preference (secure/unsecure).
• History: Allows you to view the chat history with a specific user.