Why would you need to insert a "backdoor" in a cert in the form of a crappy key, when you could just use a real key and provide it to whatever shady organization requested the backdoor in the first place?

> what amount of time is needed in say a "civilian" gpu

Per AI, 10²¹ years

Alternatively I would presume you could do it in 1 year with 10²¹ GPUs.