mkj / sunset

SSH for Rust, no_std and elsewhere

Sunset SSH

A SSH client and server implementation. It is intended to be very flexible to embed pretty much anywhere, I'm collecting possible use cases in discussions. Don't hesitate to suggest something!

This software is in an early stage. It is suitable for some applications but will certainly have API changes

• sunset (this toplevel) is the core SSH implementation. It provides a non-async API, runs with no_std and no alloc.

• sunset-embassy - async SSH client and server library, also no_std. This uses Embassy crate but is async executor agnostic.

• embassy/demos has demos with Embassy executor for wifi on a Raspberry Pi Pico W or a Linux tap device on std running locally.

  At present the Pico W build is around 150kB binary size (plus ~200KB cyw43 wifi firmware), using about 15kB RAM per concurrent SSH session (max stack size not confirmed).

• sunset-async adds functionality to use Sunset as a normal SSH client or server async library in normal Rust (not no_std). This uses Tokio or async-std.

  The examples include a Linux commandline SSH client sunsetc. It works as a day-to-day SSH client.

SSH Features

Working:

• Shell or command connection
• Password and public key authentication
• ed25519 signatures
• curve25519 key exchange
• chacha20-poly1305, aes256-ctr ciphers
• hmac-sha256 integrity
• rsa (std-only unless someone writes a no_std crate)
• ~. client escape sequences

Desirable:

• TCP forwarding
• dh-group14 (probably std-only, need to investigate crates)
• Perhaps aes256-gcm
• Perhaps ECDSA, hardware often supports it ahead of ed25519
• SFTP

Rust versions

At present Sunset will build with latest stable (1.75 at time of writing).

Safety

Sunset uses forbid(unsafe), apart from sunset-async which requires unsafe for Unix interactions.

Release builds should not panic, instead returning Error::bug(). debug_assert! is used in some places for invariants during testing or fuzzing.

Some attempts are made to clear sensitive memory after use, but stack copies will not be cleared.

Author

Matt Johnston [e-mail]

It's built on top of lots of other work, particularly Embassy, the rust-crypto crates, Virtue, smoltcp, and Salty.