Poettering: Brave new trusted boot world

> > You should remove all the keys (even the Microsoft key ) from the uefi-bios except the one that allow your shim to work, otherwise anything that was signed with (e.g.) Microsoft key may break the protection...

> How? If anything is signed with a different cert chain (even if it's a shim signed with the Microsoft key, it will then measure the vendor cert before booting the second stage) then the PCR 7 measurement will be different and you won't be able to unseal the material.

Ok, I missed the fact that PCR7 measures the PK/KEK/db and *the "specific certificates used to validate each boot application"* [1].

But this means that the boot application have to be signed by a non public 'private key'; the same is true for the UKI.
Otherwise the user need to deploy a host-specific certificate to sign the uki.

> > From the points above it seems to me that the PCR11 signature of an UKI file, is secure only in a strongly constrained environment, i.e. where it is possible to be sure that all 'bootloader chain' is secure.

> The alternative is to seal to PCRs 0-5+11. This doesn't rely on any sort of secure boot chain but does increase fragility over firmware updates or some security-relevant configuration changes.

[1] from https://wiki.archlinux.org/title/Trusted_Platform_Module