Onioncat

Abstract

1. Introduction

OnionCat creates a transparent IPv6 layer on top of Tor's hidden services or I2P's tunnels. It transmits any kind of IP-based data transparently through the Tor/I2P network on a location hidden basis. You can think of it as a peer-to-peer VPN between hidden services.

OnionCat is a stand-alone application which runs in userland and is a connector between Tor/I2P and the local OS. Any protocol which is based on IP can be transmitted. Of course, UDP and TCP (and probably ICMP) are the most important ones but all other protocols can also be forwarded through it.

OnionCat opens a TUN device and assigns an IPv6 address to it. All packets forwarded to the TUN device by the kernel are forwarded by OnionCat to other OnionCats listening on Tor's hidden service ports or I2P's server tunnels. The IPv6 address depends on the _onion\_id_ or the i2p_id, respectively. The _onion\_id_ is the hostname of the locally configured hidden service (see

2. Objective

Official repository of OnionCat, the VPN adapter for Tor and I2P.

This project demonstrates how C can be applied to a real-world Cybersecurity & Ethical Hacking problem.

4. Technology Stack

5. System Requirements

General requirements for this technology stack — check the README for exact versions.

• Arduino IDE / PlatformIO or a C compiler (gcc)
• Target board where applicable
• Git (to clone the repository)

6. Installation & Setup

git clone https://github.com/rahra/onioncat.git
cd onioncat

Full setup instructions are in the project README.

7. Future Enhancements

Suggested extensions you can add to make this your own project.

• Add logging and alert notifications (email / Telegram)
• Write a threat model document for the tool
• Package it with Docker for safe lab testing

8. Viva / Review Questions

Common questions examiners ask for projects in this domain.

1. Which threat or attack does this project defend against?
2. What detection or protection technique is used and what are its limits?
3. How are false positives and false negatives handled?
4. Which cryptographic algorithms or security standards are involved?
5. What legal and ethical rules apply when testing a tool like this?

9. Source Code & License

This project is developed by rahra and published on GitHub under the GNU General Public License v3.0. Please follow the license terms and credit the original author when you use or modify this code.