Sentinel Server

Privacy and security-focused messaging application featuring end-to-end encryption.
Built with WebSockets, Drogon HTTP web framework, and SQL database for secure communication.

Features • Installation • Building • Usage • E2E Encryption • Testing • Architecture • Contributing

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About

Sentinel is a proof-of-concept, privacy and security-focused messaging application co-created as a demonstration of secure communication protocols. It features end-to-end encryption and utilizes WebSockets, the Drogon HTTP web framework, and an SQL database to provide a secure and efficient communication platform. After completing the text-based user interface and proof of concept, the project was open-sourced for the community to learn from and build upon.

Features

• End-To-End Encryption: All messages are encrypted between clients for maximum privacy
• WebSocket Support: Real-time, bidirectional communication for instant messaging
• Drogon Framework: High-performance C++ HTTP application framework
• SQL Database: Reliable data persistence with database integration
• Text-Based UI: Clean, minimal interface for terminal-based communication
• Privacy-Focused: Built with security and user privacy as primary concerns

Installation

Prerequisites

• C++ compiler with C++17 support
• CMake (3.10 or higher)
• vcpkg package manager (recommended)
• Drogon framework

Clone the Repository

git clone --recursive https://github.com/theczechr/Sentinel-server.git
cd Sentinel-server

Install Dependencies

Using vcpkg (Windows)

vcpkg install drogon:x64-windows openssl

Using vcpkg (Linux/macOS)

vcpkg install drogon openssl

Building

Using CMake

mkdir build
cd build
cmake ..
make

Windows (Visual Studio)

1. Open the project in Visual Studio
2. Configure CMake with vcpkg toolchain
3. Build the solution

E2E Encryption

The server is designed as a dumb relay. It does not decrypt messages. Clients are responsible for encrypting/decrypting.

• Register: /register?username=<u>&pub_key_fprint=<f>&recovery_phrase=<r>[&public_key=<base64>]
• Publish/rotate key: /publishPubKey?pub_key_fprint=<f>&public_key=<base64>&signed_payload=<base64>&signature=<base64>
  • Server validates that pub_key_fprint equals SHA-256(public_key) in lowercase hex and verifies the Ed25519 signature over signed_payload.
  • signed_payload format: pub_key_fprint|timestamp (as UTF-8), Base64-encoded; max age 5 minutes.
  • Rate limit: 5 publish attempts per minute per ip|pub_key_fprint.
• Discover peer key: /getPubKey?pub_key_fprint=<peer_fingerprint> returns the peer’s public key string (empty if unknown).
• Send messages: Encrypt on the client, then send the opaque ciphertext to /sendtxt?room_name=<room>. The server relays without inspecting or logging message contents.
• Message size limit: Text frames larger than 64KB are dropped by the server.
• Public key persistence: Published keys are stored on disk in a simple file-backed store (keys.db). Replace with a production database for real deployments.

Testing

Build tests alongside the project:

mkdir build && cd build
cmake ..
make SentinelTests
./tests/SentinelTests  # or run per-test binaries if split

License

This project is open source and available under the MIT License.

Acknowledgments

• Built with Drogon - A C++14/17-based HTTP application framework
• Inspired by the need for privacy-focused communication tools

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Made with ❤️ for secure communication