Auguste Kerckhoffs

A 19th century Flemish cryptographer best known for enunciating Kerckhoffs' law, the principle that the security of a cryptosystem must depend only on the key, not on the secrecy of any other part of the system.

In war, the enemy will have spies and will capture and analyse your equipment. For computer security systems, a determined attacker will run your software under control of a debugger or probe your hardware in various ways until he finds out in detail how it works. If a product is not secure against an opponent who has done such things, then it is utterly worthless.

In short, security by obscurity does not work.