fwknop: fwknop (Single Packet Authorization and Port Knocking) fwknop: fwknop: fwknop implements an authorization scheme known as Single Packet fwknop: Authorization (SPA) for Linux systems running iptables. fwknop: fwknop: fwknop: fwknop: fwknop: fwknop: Home: http://www.cipherdyne.org/fwknop/ fwknop: