Steganography in HTTP/2

http2 felt like a major step forward from http1. Things like connection multiplexing and header compression decreased network load and improved speed for many applications without requiring them to change anything.

But the whole http/2 RFC felt like a revolution compared to simpler text like semantics of http/1.

This project implements a hidden channel communication based on http/2 features in an effort to learn more about the protocol.

Steganography

Steganography is a way of hidding a message in a communication in a way that not only the message is unreadable (by cryptografic measures) but the presence of communication itself is hidden from anyone watching.

Potential hidden channels in HTTP/2

There are many ways one can go about implementing a hidden channel in http/2, in part this is possible because the protocol is so much more complex than previous version. For a great overview you can read this paper.

For my implementation I selected PING frames

Technical notes

This project is using Ruby with http2 gem. One interesting aspect is that I used Sorbet for typechecking in most of the places.

This is a complete implementation but it should not be used in a production setup: the keys for OpenSSL are part of this repository, a lot of data is hardcoded, so it all should be treated as a proof of concept.

Usage

This project has server and client components. Each of those in turn has watcher and main processes. The idea is that server could work as usual HTTP server, client as regular HTTP client but the watcher processes allow you to view the conversation that is happening behind the scenes.

To see it action (presumably in separate tabs or in the background) you need to run the 4 following processes:

sh bin/client_watcher bin/server_watcher bin/server bin/client

The only important thing is that the client should be run after the server.