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).

• 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 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.

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)
• ~. client escape sequences
• Post quantum hybrid key exchange (mlkem)

Desirable:

• SFTP
• sntrup761
• TCP forwarding
• A std server example
• Perhaps aes256-gcm
• Perhaps ECDSA, hardware often supports it ahead of ed25519

Rust versions

At the time of writing Sunset will build with Rust 1.87.
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.