Arti: reimplementing Tor in Rust

Arti is a project to produce an embeddable, production-quality implementation of the Tor anonymity protocols in the Rust programming language.

Arti is not ready for production use; see below for more information.

Links:

Why rewrite Tor in Rust?

Rust is more secure than C. Despite our efforts, it's all too simple to mess up when using a language that does not enforce memory safety. We estimate that at least half of our tracked security vulnerabilities would have been impossible in Rust, and many of the others would have been very unlikely.

Rust enables faster development than C. Because of Rust's expressiveness and strong guarantees, we've found that we can be far more efficient and confident writing code in Rust. We hope that in the long run this will improve the pace of our software development.

Arti is more flexible than our C tor implementation. Unlike our C tor, which was designed as SOCKS proxy originally, and whose integration features were later "bolted on", Arti is designed from the ground up to work as a modular, embeddable library that other applications can use.

Arti is cleaner than our C tor implementation. Although we've tried to develop C tor well, we've learned a lot since we started it back in 2002. There are lots of places in the current C codebase where complicated "spaghetti" relationships between different pieces of code make our software needlessly hard to understand and improve.

Current status

Arti is a work-in-progress. It can connect to the Tor network, bootstrap a view of the Tor directory, and make anonymized connections over the network.

We're not aware of any critical security features missing in Arti; but however, since Arti is comparatively new software, you should probably be cautious about using it in production.

Now that Arti has reached version 0.1.0, we believe it is suitable for experimental embedding within other Rust applications. We will try to keep the API as exposed by the top-level arti_client crate more or less stable over time. (We may have to break existing programs from time to time, but we will try not to do so without a very good reason. Either way, we will try to follow Rust's semantic versioning best practices.)

Trying it out today

Arti can act as a SOCKS proxy that uses the Tor network.

To try it out, run the demo program in arti as follows. It will open a SOCKS proxy on port 9150.

% cargo run --release -- proxy

Again, do not use this program yet if you seriously need anonymity, privacy, security, or stability.

If you run into any trouble building the program, please have a look at the troubleshooting guide.

Minimum supported Rust Version

Our current Minimum Supported Rust Version (MSRV) is 1.53.

When increasing this MSRV, we won't require any Rust version released in the last six months. (That is, we'll only require Rust versions released at least six months ago.)

We will not increase MSRV on PATCH releases, though our dependencies might.

We won't increase MSRV just because we can: we'll only do so when we have a reason. (We don't guarantee that you'll agree with our reasoning; only that it will exist.)

Helping out

Have a look at our contributor guidelines.

Roadmap

Thanks to a generous grant from Zcash Open Major Grants (ZOMG), we're able to devote some significant time to Arti in the years 2021-2022. Here is our rough set of plans for what we hope to deliver when.

The goal times below are complete imagination, based on broad assumptions about developer availability. Please don't take them too seriously until we can get our project manager to sign off on them.

Arti 0.0.1: Minimal Secure Client (Goal: end of October 2021??)
Target audience: developers
[x] Guard support
[x] Stream Isolation
[x] High test coverage
[x] Draft APIs for basic usage
[x] Code cleanups
and more...
Arti 0.1.0: Okay for experimental embedding (Goal: Mid March, 2022??)
Target audience: beta testers
[x] Performance: preemptive circuit construction
[x] Performance: circuit build timeout inference
[x] API support for embedding
[x] API support for status reporting
[x] Correct timeout behavior
and more...
Arti 1.0.0: Initial stable release (Goal: Mid September, 2022??)
Target audience: initial users
[ ] Stable API
[ ] Stable CLI
[ ] Stable configuration format
[ ] Automatic detection and response of more kinds of network problems
[ ] At least as secure as C Tor
[ ] Client performance similar to C Tor
[ ] More performance work
and more...
Arti 1.1.0: Anti-censorship features (Goal: End of October, 2022?)
Target audience: censored users
[ ] Bridges
[ ] Pluggable transports
and more...?
Arti 1.2.0: Onion service support (not funded, timeframe TBD)
Arti 2.0.0: Feature parity with C tor as a client (not funded, timeframe TBD)
Arti ?.?.?: Relay support

How can I report bugs?

When you find bugs, please report them on our bugtracker. If you don't already have an account there, you can either request an account or report a bug anonymously.

(The above notice, or something like it, seems to be pretty standard in Rust projects, so I'm using it here too. This instance of it is copied from the RustCrypto project's README.md file.)