Install fwknop-server by entering the following commands in the terminal:
sudo apt update sudo apt install fwknop-server
Description:
FireWall KNock OPerator server side - C version
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. . The authorization server passively listens for authorization packets via libpcap, thus preventing any connections from being processed on the traditional port. Access to a protected service is only granted after a valid encrypted and non-replayed packet is detected.
Homepage: http://www.cipherdyne.com/fwknop/
Version: 2.6.9-2
Section: universe/admin