At a high level the way secure boot functionality works is by embedding the hash of the company's root cert in ROM. Then the OS image itself is signed with a key that chains up to the root cert embedded in the ROM. For example, the cert hierarchy could be something like this --

Company Root --> OS Image Root --> Consumer OS Root

So the hash burned into the ROM will be of the "Company Root". The OS image will be signed with the "Consumer OS Root".

Now let's say the Consumer OS Root private key is compromised and the company is forced to rev it. How can the company invalidate any images signed with the compromised root? It doesn't seem possible, am I missing something?

What are the usual strategies for this?

  • Firmware patch and replacement of keys, usually to be installed via driver updates delivered through the update mechanisms of the OS. Anybody concerned a malicious OS image will be used to boot on their devices would need to patch quickly before that risk can materialize. – Natanael Feb 20 at 0:37

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