Knock: Practical and Secure Stealthy Servers , TCP STEALTH - Very interesting read -

Improved Kernel-Based Port-Knocking in Linux

Author: Julian Kirsch
Supervisor: Christian Grothoff, PhD (UCLA)
Date: 15. August 2014

https://gnunet.org/sites/default/files/ma_kirsch_2014_0.pdf
https://gnunet.org/knock

Knock: Practical and Secure Stealthy Servers

USING ANY GNU/LINUX. NOT FOR Windowz TCP/IP PROTOCOLS.