Re: [CFRG] [EXTERNAL] pq firmware signing question

[Michael StJohns <[e-mail]>]

On 3/18/2024 11:45 AM, John Mattsson wrote:
> Working for hardware manufacturer, I can confirm that burning trust 
> anchors into hardware is extremely common. You can burn several keys 
> but you cannot change them. 

The problem is not so much the keys being burned in, but that the first 
stage bootloader only supports a small set of algorithms. That changes 
slowly over time and I haven't seen any indication that MCUs and MPUs 
coming out in the next 5 years or so will support any PQ based firmware 
validation in the Boot ROM bootloader.

Some devices just (or in addition) use a hash to validate the customer 
provided second stage bootloader which allows you to avoid the 
limitations of the first stage bootloader, but that still begs the 
question of hardware support for PQ safe algorithms so that booting 
doesn't take 10 minutes or so.

Writing a hash of the third stage to secure flash once the signature is 
verified may be an approach, but few (if any) MPUs (e.g. processors with 
memory mapping hardware generally) have anything but a few (< 200 ) 
bytes of OTP.

Mike