This not the point - the whole idea of restricted or secure boot is basically wrong. Can you be sure trusted keys are really safe - the answer no you can't!

The only thing a secure/restricted boot can protect you from is if you have allowed something bad on to your system, and I suspect the bad guys will find a way round this.

Its all about protecting walled $ gardens and in by book its wrong, I own the hardware and I should not be restricted period!