💬 Secure LAN Chat App

A secure, real-time LAN chat application built using Python — featuring encrypted communication, private and global chat tabs, and a modern GUI for both server and client.
This project is developed as part of a Computer Networks (CN) B.Tech project, enabling seamless communication between users connected to the same local network.

---

🚀 Overview

The Secure LAN Chat App provides a simple yet powerful platform for real-time messaging within a LAN (Local Area Network).
It operates on a client-server architecture — where the server manages connections, encryption, and message routing, while clients offer an easy-to-use graphical interface for chatting securely.

Messages are end-to-end encrypted using Fernet (AES-based symmetric encryption) to ensure complete privacy even within the local network.

---

✨ Features

• 🔒 End-to-End Encryption using cryptography.Fernet
• 🌐 Global Chat Tab – for all users on the LAN
• 💬 Private Chat Tabs – automatically open when you click a user
• 👥 Dynamic Online User List
• 🧱 Cross-Platform GUI (Tkinter)
• 🧵 Multi-threaded Communication
• 🧠 Server-Side Authentication
• ⚡ Lightweight and Portable

---

🗂️ Folder Structure

Secure-LAN-Chat/
│
├── server/
│   ├── server_core.py
│   └── server_gui.py
│
├── client/
│   ├── client_core.py
│   └── client_gui.py
│
└── README.md

---

⚙️ Installation & Setup

---

🪟 For Windows

1. Install Python 3.13.1

   • Download from https://www.python.org/downloads/
   • During installation, check ✅ “Add Python to PATH”

2. Install Required Package

   pip install cryptography

3. Start the Server

   cd server
   python server_gui.py

   • Enter a password (default: admin123)
   • Click Start Server

4. Start the Client

   cd client
   python client_gui.py

   • Enter:

     • Server IP: local IP of the server (e.g. 127.0.0.1)
     • Port: 5555
     • Password: same as server password
     • Username: your display name

   • Click Connect

---

🍏 For macOS / Linux

1. Install Python 3

   brew install python3         # macOS (Homebrew)
   sudo apt install python3-pip # Linux (Debian/Ubuntu)

2. Install Required Package

   pip3 install cryptography

3. Run the Server

   cd server
   python3 server_gui.py

4. Run the Client

   cd client
   python3 client_gui.py

---

🧩 How It Works

🔐 Encryption

• The server generates a unique Fernet key at startup.
• This key is securely shared with connected clients.
• All messages are encrypted before sending and decrypted upon receipt, ensuring full confidentiality.

🌐 Global Chat

• Every user connected to the LAN can chat in the Global tab.
• The server broadcasts these messages to all connected clients.
• System messages notify users when someone joins or leaves.

💬 Private Chat

• Double-click a username in the Online Users list to open a private chat tab.
• Messages are routed securely between the two selected clients only.
• The server handles delivery while preserving end-to-end encryption.

🧠 User Management

• Server maintains:

  • A dictionary mapping connections ↔ usernames
  • Real-time user list updates on connect/disconnect

🧵 Multithreading

• The server uses one thread per client to handle concurrent communication.
• The client runs a background thread for receiving messages without blocking the UI.

---

🖼️ GUI Overview

🖥️ Server Window

• Password field
• Start/Stop buttons
• Connection logs
• Real-time status messages

💻 Client Window

• Global Chat tab (always pinned)
• List of online users
• Private chat tabs (open dynamically)
• Timestamped chat bubbles
• Clean, responsive layout

---

🧪 Example Usage

1. Start the Server

   python server_gui.py

   Output:

   🟢 Server started on 0.0.0.0:5555
   Waiting for clients...
   

2. Start Clients on LAN Devices

   python client_gui.py

   Console:

   🟢 Connected to server 192.168.1.10:5555
   ✅ Authentication successful!
   

3. Chat Example

   [Global] Raghav: Hey everyone!
   [Private → Nikhita]: Ready for the CN lab test?
   

---

🛠️ Tech Stack

Component	Technology
Language	Python 3
GUI	Tkinter
Networking	Socket, Threading
Security	cryptography (Fernet encryption)
Architecture	Client-Server over TCP

---

🧱 requirements.txt

If you’d like, create a file named requirements.txt with this single line:

cryptography

Then install all dependencies easily using:

pip install -r requirements.txt

---

💡 Future Enhancements

• 📁 File Transfer between clients
• 💾 Chat History / Message Logging
• 🔔 Notification pop-ups for new messages
• 🌙 Dark Mode
• 🧑‍💼 Admin Control Panel
• 📡 Multi-room (Group) Chat

---