does it? so you can say &quot;yes, we do not allow these ports&quot; or whatever... does that mean it is &quot;secure&quot;? this doesn&#x27;t check <i>iptables</i>, only the rules that you write <i>using</i> iptables (as far as I can tell)<p>the point I am getting at is that in a firewall product, what you are checking is something like &quot;only those users listed from this source may login&quot; which is &quot;easy&quot; but other more complicated things like &quot;this channel must be encrypted&quot;. what does &quot;encrypted&quot; mean? Is it just a word that you use in your specification language? if so, does it mean what you think it means? etc etc etc...<p>formally proving stuff about the behavior of a system, or a distributed system, is hard, but formally proving stuff about security, especially as it relates to information flows, side channels, etc is <i>very</i> <i>hard</i>...