Chat App Backend

A secure, real-time chat application backend built with Go, featuring WebSocket connections and end-to-end encryption using AES and Diffie-Hellman key exchange.

🚀 Features

• Real-time Communication: WebSocket-based messaging for instant communication
• End-to-End Encryption: Secure message encryption using AES-256 in CTR mode
• Diffie-Hellman Key Exchange: Secure key establishment between clients
• Lightweight Architecture: Simple and efficient Go-based server
• Cross-Origin Support: CORS-enabled for web client integration

🔐 Security Features

AES Encryption

• Algorithm: AES-256 in Counter (CTR) mode
• Key Size: 256-bit keys derived from Diffie-Hellman shared secrets
• IV Generation: Cryptographically secure random IV for each message

Diffie-Hellman Key Exchange

• Prime: 2048-bit safe prime for secure key exchange
• Generator: 2 (standard DH generator)
• Key Derivation: SHA-256 hash of shared secret for AES key

🛠️ Installation

Prerequisites

• Go 1.24.4 or higher
• Git

Setup

1. Clone the repository:

git clone <repository-url>
cd chat-app-backend

2. Install dependencies:

go mod download

3. Run the server:

go run main.go

The server will start on http://localhost:8080

📡 API Endpoints

WebSocket Connection

• Endpoint: /ws
• Protocol: WebSocket
• Description: Establishes a WebSocket connection for real-time messaging

Example Connection (JavaScript)

const ws = new WebSocket('ws://localhost:8080/ws');

ws.onopen = function() {
    console.log('Connected to chat server');
};

ws.onmessage = function(event) {
    console.log('Received:', event.data);
};

ws.send('Hello, World!');

🔧 Usage

Basic WebSocket Communication

The server currently implements a simple echo functionality. When a client sends a message, the server responds with "Echo " + the original message.

Encryption Implementation

The crypto package provides utilities for implementing end-to-end encryption:

// Generate DH key pair
private, public, err := crypto.GenerateKeyPair()

// Compute shared secret (after receiving peer's public key)
sharedSecret := crypto.SharedSecretKey(private, peerPublic)

// Derive AES key
aesKey := crypto.DerivesAesKey(sharedSecret)

// Encrypt message
ciphertext, err := crypto.Encrypt([]byte("Hello, World!"), aesKey)

// Decrypt message
plaintext, err := crypto.Decrypt(ciphertext, aesKey)

🚧 Roadmap

• Complete authentication system
• Implement message persistence
• Add user management
• Room/channel support
• Message history
• File sharing capabilities
• Rate limiting
• Comprehensive logging

🤝 Contributing

I created this project as it would be a good oppurtunity for me to learn about the Diffie–Hellman key exchange algorithm so feel free to wonder around this repo and make pull requests. Let's learn together

📝 License

This project is licensed under the MIT License - see the LICENSE file for details.

📞 Support

For questions and support, please open an issue in the GitHub repository.

---

Built with ❤️ using Go and modern cryptographic practices.