How to SECURE SSH - Port Knocking on Ubuntu |Knock-Knock | Linux Containers
References
https://help.ubuntu.com/community/Por...
Note:
Simple portknocking daemons (such as knockd) are vulnerable because a sniffer may recover the port sequence that was used. A better solution is Cryptknock (http://cryptknock.sourceforge.net/)
https://osgroup-techies.blogspot.com/...