its already been done - and repealed because it didnt work
those who have a long a memory in the business as I have will remember this was already tried...and failed.....
back in the 90s strong encryption was classed as a 'munition' by the US and could not be exported.
So we had 2 versions of windows - one with 128 bit keys for good ol USA and one with 56-bit keys (international version) for the rest of the world.
So what did the rest of the world do:
a) bought all their software retail in New York as someone was passing through - hence we all got 'US' version regardless
b) anyone who needed real encryption bought it from Israel or Estonia - who were only too happy to supply proper software
eventually the thing was repealed after lobbying from US tech companies pointing out how much money they were losing.....