Secure Boot is broken on 200 models from 5 big device makers

If there is a way to make them writable via software, that would be very interesting (and dangerous).

Shooting the breeze as well...

Have some (non-modifiable, non-updatable) portion of the firmware that, on boot, calculates a checksum or hash of the important bits at the beginning of the chain of trust (efi vars, bios).

Then have it generate some sort of visualization of the hash (thinking something like gravatar/robohash) and draw it in the corner of the screen. Would need some way to prevent anything else from drawing that section of the screen until you're past that stage of boot.

That way every time you boot your computer you're gonna see, say, a smiling blue kitten with a red bow on its head. Until someone changes your platform key / key exchanges or installs a modified bios, and now suddenly you turn the computer on and it's a pink kitten with gray polka dots.

That way you don't have to actively _try_ and check the validity. It'd be very obvious and noticeable when something was different.

0. All of the BIOS code and other hardware code should be FOSS. This should be printed in the manual as well. A simple assembly language might be preferable, and if the hex codes are also printed next to it, they can also be entered manually if necessary.

1. The operating system cannot update the BIOS at all. To do so requires to set a physical switch inside of the computer which disables the write protection of the BIOS memory, and also disallows the operating system from automatically starting.

2. Require keyboards, etc to be connected to dedicated ports, not to arbitrary USB ports. (This is possible with USB but is a bit difficult; PS/2 would be better.)

3. You can program it manually (whether or not the BIOS memory is write protected) without starting the operating system (this makes the computer useful even if no operating system is installed); perhaps with an implementation of Forth. When BIOS memory is write enabled, then such a program may be used to copy data from the hard drive to the BIOS memory.

4. Like you mention, it should make it easy to audit and detect when keys have been changed. An included display might normally display other stuff (e.g. boot state, temperature measurement, etc), but a switch can be used to display a cryptographic hash. If you always fill all of the memory (even if part of it would not otherwise be used) then it can be difficult to tamper with in the case of an unknown vulnerability.

5. I had seen suggestion to add glitter and take a picture of it, to detect physical tampering. This can help in order to avoid alterations of the verifications themself. If it is desirable, you can have multiple compartments which can be sealed separately, each one with the glitter. If some of these compartments are internal, a transparent case around some of them might help in some ways (as well as to detect other problems with the computer that are not related to security).

However, even the above stuff will need to be done correctly to avoid some problems, since you will have to consider what is being tampered with. (You might also consider the use of power analysis to detect the addition of extra hardware, and the external power can then be isolated (and a surge protector added) to mitigate others attacking your system with power analysis and to sometimes mitigate problems with the power causing the computer to malfunction.)

That does make it quite difficult to pull off any kind of key rotation. I'm not sure, but I think (well known Secure Boot tool) sbctl is saying that you can sign a bootloader with multiple keys, which would permit creating a bootloader that would work with the compromised & the new root-of-trust, which at least opens some window of possibility. https://github.com/Foxboron/sbctl/blob/master/docs/sbctl.8.t...

> Would need some way to prevent anything else from drawing that section of the screen until you're past that stage of boot.

It might need to prevent drawing anything on the entire screen. Otherwise a program might be able to modify the resolution, refresh rate, etc, to try to hide the picture or to display a different one.