Plans for PQC (Post-Quantum Cryptography)

[Mythra]

👋 I realize this is a topic that requires a lot of discussion, and may not be fit for a small issue like this. However, I didn't see any other issue on this and figured it couldn't hurt to ask.

Currently this library uses Curve25519 which while fast and secure today is not secure in a world where quantum computers exist (note: generally NIST/most organizations seem to be planning to deprecate non post-quantum safe algorithms in 2030, which is still a couple years away. However, it can take time to roll these out so it might be beneficial to talk about them now, or if anyone is concerned about "store now decrypt later" attacks). So I was hoping to kick start this topic with this issue.

Would there be any interest in reviewing contributions that provide some APIs to use something other than Curve25519 (e.g. a build time option to opt into using PQC algorithms, and not worry about migration right away. To start testing how it impacts the protocol)? Is there a larger plan to tackle it later? Is it something yall aren't considering right now?

I have many more questions about the use of Hybrids vs ML-KEM, and many other things, but don't want to blow up the discussion too much right away 😉

[zpostfacto]

Thanks for raising this — PQC is definitely a real concern and the 2030 NIST deprecation timeline is a reasonable horizon to start thinking about it.

Honestly, this library's crypto is fairly tightly coupled to how Steam does handshakes, so a meaningful change here would have to be coordinated with Steam's internal roadmap rather than driven from the open-source repo independently. That makes it hard to accept a build-time opt-in contribution, even an experimental one — it would diverge from what Steam actually ships and be difficult to keep in sync.

That said, the "store now decrypt later" concern is real and it's on our radar. When we move on this, it'll flow through here.

Closing for now since there's no actionable work we can do on the open-source side in the near term, but appreciate you kicking off the conversation.