Kerckhoff is only directly relevant to cryptosystems, but the related notion of &quot;security by obscurity&quot; comes up again and again.<p>And it&#x27;s usually a sign that the one trying to shut down a discussion with this argument is wrong. :-)<p>Usual forum scenario: changing your SSH port to a non-standard port is security by obscurity and doesn&#x27;t do anything. Usual reply: it doesn&#x27;t cost me anything (except a few minutes of my time), but may keep a non-sophisticated attacker out – think some automated script kiddie software.