There is no security protocol though. It will be trivial to buy an interlock which always returns 'ok to drive'.

Manufacturers are now encrypting Canbus traffic, voluntarily on current and future models.

Buying or selling tools designed to break the law is already illegal - trivial or not. If a driver gets a DUI and possess a NOOP interlock, they are getting an additional charge, and get to help am investigation into the illicit device supply chain.