alt Hacker NewsI have seen some manufacturers enroll multiple manufacturer keys, probably with this notion, but this isn’t useful against almost any threat model.
If keys are recovered using some form of low level hardware attack, as was almost surely the case here, the attacker can usually recover the unused key sets too.
If the chip manufacturing provisioning supply chain is leaky the new keys will probably be disclosed anyway, and if the key custody chain is broken (ie, keys are shared with OEMs or third parties) they will definitely be disclosed anyway.
Wouldn't the other reason to have multiple manufacturer keys, be to guard against them losing the private key for one in a way that means they can't sign anything any more?