Same way it got enforced during the Crypto Wars [1] of the 90s by the US and their allies. Up until 1996 commercial encryption was on the Munition List.
This is already common. Go try to export firmware for a fighter jet. Any software that the US govt designates as a military or weapon system is just as regulated as the fighter jet itself. And as the poster below pointed out, they have previously used this to lock down otherwise civilian software like encryption, by deciding that it falls under weapon regulations.