Letmein: Authenticating port knocker - Written in Rust — Letmein is a simple port knocker with a simple and secure authentication mechanism. It can be used to harden against pre-authentication attacks on services like SSH, VPN, IMAP and many more.
fwknop: Single Packet Authorization > Port Knocking — fwknop stands for the "FireWall KNock OPerator", and implements an authorization scheme called Single Packet Authorization (SPA). This method of authorization is based around a default-drop packet filter