Appnr

FireWall KNock OPerator server side

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
libcap, 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.