http://simonwillison.net/2004-02-25T23:40:06+00:00Simon Willison2004-02-25T23:40:06+00:002004-02-25T23:40:06+00:00https://simonwillison.net/2004/Feb/25/novel/#atom-tag

<p>An <a href="http://www.securityfocus.com/columnists/221" title="Knock, Knock, Knock">article on SecurityFocus</a> led me to this site about <a href="http://www.portknocking.org/">Port Knocking</a>. Port Knocking is an interesting security technique in which a box sits online with no ports open to connections and awaits a specific sequence of connection attempts. A user wishing to connect to the box must first attempt to initiate connections to ports in a specific, secret order. Once they do, the box starts up the required service (such as an <acronym title="Secure SHell">SSH</acronym> daemon) on a designated port and allows the user to connect properly.</p> <p>It's a pretty neat trick, and one that may well start showing up in backdoors and trojans in the future. It reminds me of a couple of other novel firewall related tricks: <a href="http://www.openlysecure.org/openbsd/how-to/invisible_firewall.html" title="Invisible Firewalling How-To">invisible firewalls</a> and <a href="http://www.linuxsecurity.com/articles/firewalls_article-4418.html" title="Running Your Firewall in runlevel 0">firewalls that are effectively turned off</a>.</p> <p>Tags: <a href="https://simonwillison.net/tags/portknocking">portknocking</a>, <a href="https://simonwillison.net/tags/security">security</a></p>