Kerckhoffs' principle is common knowledge, but it very often violated. E. g. it is almost not possible to buy car alarm/immobiliser system with known cryptograp

Kerckhoffs' principle is common knowledge, but it very often violated. E. g. it is almost not possible to buy car alarm/immobiliser system with known cryptographic algorithms and protocols. As a result - most car security systems use weak crypto (or no crypto at all), rely on security by obscurity. And it is possible to steal car using wireless code grubbers (to sniff key when owner lock/unlock car).