[OskarS]

Yeah, totally. It's entirely reasonable that governments can restrict SOME kind of information exchange, and since all information is just numbers, of course you could find "illegal primes"

For instance, if you encoded the entire design of a nuclear weapon (or some other highly classified military secret) inside a prime, saying "but it's just a prime!" is a very silly excuse for exchanging that information. The question is: "what kind of information should be illegal to exchange", not "which format of information should be protected".