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!

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

• sunset-async - async SSH client and server library, also no_std no-alloc. This is async-executor agnostic (using Embassy for mutexes, but works on std too).

• demo 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 13kB RAM per concurrent SSH session.

• sunset-stdasync 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.

• sunset-sftp implements an SFTP server. An example of the application side is in demo/sftp/std. sunset-sftp is currently under development, treat as alpha status.

SSH Features

Working:

• Client and server
• 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)
• ecdsa256
• ~. client escape sequences
• Post quantum hybrid key exchange (mlkem)
• SFTP server

Desirable:

• SFTP client?
• sntrup761
• TCP forwarding
• A std server example
• Perhaps aes256-gcm

Rust versions

At the time of writing Sunset will build with Rust 1.95. The requirement may increase whenever useful, targetting stable.

Checks

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 compiler-generated copies will not be cleared.

Author

Matt Johnston matt@ucc.asn.au

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