The FireWall KNock OPerator implements an authorization scheme called
Single Packet Authorization (SPA), based on Netfilter and libpcap.

Its main application is to protect services such as OpenSSH with an
additional layer of security in order to make the exploitation of
vulnerabilities (both 0-day and unpatched code) much more difficult.

Fwknop GUI is a graphical user interface integrated with an Fwknop
client that provides the ability to send SPA packets to a remote
Fwknop server, as well as a front-end for creating and managing client
configurations for multiple Fwknop servers.

It supports exporting saved configuration data to a QR code format
readable by the Android client, as well as to the .fwknoprc format
readable by the command line client.