Maybe there's a different piece of legal justification elsewhere, but in this particular case it rests on the "All Writs" act. That act does not say that you ca

Maybe there's a different piece of legal justification elsewhere, but in this particular case it rests on the "All Writs" act. That act does not say that you cannot create a system that the government can't get into. It says that courts are allowed to compel you to help the government in a legal investigation. The extent to which that act allows a judge to compel Apple to assist is what is in question. IANAL, but I suspect it would be a much larger jump to try to use this statute to ban the creation of an encryption system (as opposed to helping to defeat one). If they wanted to do that they would almost certainly have to go through congress or find a different statute.