I honestly don't remember which OS they used, but not this wasn't something built into any existing OS already. The point was that the code that displayed the p

I honestly don't remember which OS they used, but not this wasn't something built into any existing OS already. The point was that the code that displayed the password prompt was outside of the kernel and kernel control entirely. The UI wasn't the important part, it was that the OS never got access to the password in the first place. I imagine if you had a password prompt LED on your device that could only be lit up by the separate chip that does password prompts, that would help create an off screen UI.