I see this line of argument very frequently - that if you are really secure, you should tell everyone how you do it, as some sort of gold standard for security. Kerchoff's principle suggests nothing of the sort - it is something of a thought experiment. When you design a system, you should ask yourself if it would still be secure if you told everyone how it worked. There is no real need to tell anyone, the obscurity adds an extra layer of defense.

Here's Steve Bellovin's thoughts on this:

'The subject of security through obscurity comes up frequently. I think a lot of the debate happens because people misunderstand the issue. It helps, I think, to go back to Kerckhoffs's second principle, translated as "The system must not require secrecy and can be stolen by the enemy without causing trouble," Kerckhoff said neither "publish everything" nor "keep everything secret"; rather, he said that the system should still be secure even if the enemy has a copy.

In other words – design your system assuming that your opponents know it in detail. (A former official at NSA's National Computer Security Center told me that the standard assumption there was that serial number 1 of any new device was delivered to the Kremlin.) After that, though, there's nothing wrong with trying to keep it secret – it's another hurdle factor the enemy has to overcome. (One obstacle the British ran into when attacking the German Enigma system was simple: they didn't know the unkeyed mapping between keyboard keys and the input to the rotor array.) But – don't rely on secrecy.'