c-socket

A comprehensive client-server application written in C that demonstrates secure, encrypted communication over both TCP (using TLS) and UDP (using DTLS) with the OpenSSL library.

🔎 About

This project was created to provide a clear and practical example of secure socket programming. Implementing TLS and DTLS from scratch can be a complex task, especially when handling different protocols and managing multiple clients. This repository breaks down the process into a well-structured, multi-threaded server that can handle both TCP and UDP connections simultaneously, along with corresponding clients to test the functionality.

The server uses pthreads to manage concurrent TCP clients and implements a custom session management system to handle connectionless DTLS clients. The codebase is organized modularly with a clean Makefile build system, making it an excellent learning resource for students, developers, or anyone interested in network security and C programming.

🛠️ Features

• Hybrid Server: A single server application listens for and handles both TCP and UDP connections on different ports.
• Secure Communication: Implements TLS v1.2+ for TCP and DTLS v1.2 for UDP to encrypt all data exchanged between the server and clients.
• Multi-Client Handling: Uses POSIX threads (pthreads) to handle multiple TCP clients concurrently without blocking.
• DTLS Session Management: Includes a robust mechanism to find or create sessions for new DTLS clients, with automatic cleanup for timed-out sessions.
• Functional & Clean Code: The project is organized into client, server, and common modules with separate header files and a functional programming style for better readability and maintenance.
• Robust Logging: Features a custom logging utility that writes timestamped events, errors, and debug messages to both the console and log files.
• Makefile Build System: A clean and efficient Makefile automates the entire compilation process.
• Example Clients: Comes with three separate clients to demonstrate:
  • Secure TCP (TLS) communication.
  • Secure UDP (DTLS) communication.
  • A basic (unencrypted) UDP broadcast.

📂 Project Structure

The source code is organized into a clean and logical directory structure.

.
├── README.md
└── src
    ├── certs/
    │   ├── cert.pem
    │   └── key.pem
    ├── client/
    │   ├── broadcast-client.c
    │   ├── tcp-client.c
    │   └── udp-client.c
    ├── common/
    │   ├── logger.c
    │   └── utils.c
    ├── include/
    │   ├── broadcast-client.h
    │   ├── logger.h
    │   ├── protocol.h
    │   ├── server.h
    │   ├── tcp-client.h
    │   └── udp-client.h
    │   └── utils.h
    ├── Makefile
    └── server/
        └── server.c

🚀 Getting Started

Follow these instructions to get the project compiled and running on your system.

Prerequisites

Before you begin, ensure you have the following installed on your Linux system:

• GCC Compiler: Or any standard C compiler.

• Make: To build the project using the Makefile.

• OpenSSL Libraries: The development package is required.

  # For Debian / Ubuntu
  sudo apt update 
  sudo apt install build-essential libssl-dev

  # For Arch Linux
  sudo pacman -Syu
  sudo pacman -S base-devel openssl

Installation & Usage

1. Clone the repository:

   git clone "https://github.com/awmiriiw/c-socket.git"
   cd c-socket/src

2. Generate Self-Signed Certificates: The project requires SSL certificates to run. You can generate a self-signed pair for testing.

   # Run this command from the src/ directory
   mkdir -p certs && openssl req -x509 -newkey rsa:4096 -nodes -keyout certs/key.pem -out certs/cert.pem -days 365

   (You can skip the informational prompts by pressing Enter.)

3. Compile the Project: Run make to compile the server and all clients. The executables will be placed in the src/bin/ directory.

   make

4. Run the Server: Open a terminal and start the server. It will listen for connections on ports 8080 (TCP) and 8081 (UDP).

   ./bin/server

5. Run the Clients: Open new terminal windows for each client.

   • Secure TCP Client:

     ./bin/tcp-client

     You can now type messages, and the server will echo them back.

   • Secure UDP Client:

     ./bin/udp-client

     This client also functions as an echo client but over DTLS.

   • UDP Broadcast Client:

     ./bin/broadcast-client

     (Note: The server does not handle this broadcast; it's a client-to-client example.)

6. Clean Up: To remove all compiled binaries, object files, and logs, run:

   make clean

📝 License

This project is open-source and available under the GNU AGPLv3 License.

Thanks for visiting! ☕