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 incomplete but nearly ready to be used **

• 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). The examples include a Linux commandline SSH client. This uses Tokio or async-std.

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 (will be 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

License

Currently MPL2, though may possibly move to MIT-style in future (I'm undecided)

Rust versions

At present sunset requires nightly Rust, in order to use async functions in the Behaviour traits. It is intended to switch to stable Rust once that feature stabilises.

sunset-embassy requires a nightly Rust version, as required by Embassy. See the embassy/rust-toolchain.toml for a known-good version. Once async functions in traits becomes stable, Embassy should support stable Rust too.

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 matt@ucc.asn.au

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