But the issues with backdoors are not technological they are political. If we really could trust the government not to use the backdoor on anything other than a single iphone 5c then it would mathematically and technologically work fine. Just like nuclear power can technically be made safe and everyone wants that, but politics always gets in the way and shortcuts get taken that reduce safety. Sure it’s possible to build a safe nuclear power plant, but it’s not possible to build a goverment that can safely handle nuclear power. Similar with backdoors; no technical reason they can’t work, but no political will to make them work.