Announcing Arti, a pure-Rust Tor implementation (Tor blog)

The Tor project, which provides tools for internet privacy and anonymity, has announced a rewrite of the Tor protocols in Rust, called Arti. It is not ready for prime time, yet, but based on a grant from Zcash Open Major Grants (ZOMG), significant work is ongoing; the plan is "to try bring Arti to a production-quality client implementation over the next year and a half". The C implementation is not going away anytime soon, but the idea is that Arti will eventually supplant it. The project sees a number of benefits from using Rust, including:

For years now, we've wanted to split Tor's relay cryptography across multiple CPU cores, but we've run into trouble. C's support for thread-safety is quite fragile, and it is very easy to write a program that looks safe to run across multiple threads, but which introduces subtle bugs or security holes. If one thread accesses a piece of state at the same time that another thread is changing it, then your whole program can exhibit some truly confusing and bizarre bugs.

But in Rust, this kind of bug is easy to avoid: the same type system that keeps us from writing memory unsafety prevents us from writing dangerous concurrent access patterns. Because of that, Arti's circuit cryptography has been multicore from day 1, at very little additional programming effort.