On 8/2/20 4:11 PM, John Pierce wrote: > isn't it more that they simply won't work with newer boots that were signed > by the new keys? and the updated BIOS's won't boot older OS versions that > weren't signed by the new keys? I don't know if the Secure Boot PKI has a publicly documented contingency plan for a compromised CA, but my understanding is that there are multiple slots for signatures: http://dreamhack.it/linux/2015/12/03/secure-boot-signed-modules-and-signed-elf-binaries.html So, I would guess that clients would receive a new trust DB that did not contain the old root CA, and new bootloaders signed by both the old root CA and the new CA. The new bootloaders would work on both new and old systems, having signatures from both. Old bootloaders would not work on new clients.