A microcontroller with a decent CPU (a Zilog Z80 in this case) could, given enough time, run some serious AES-256 encryption. The storage is minimal but it coul

A microcontroller with a decent CPU (a Zilog Z80 in this case) could, given enough time, run some serious AES-256 encryption. The storage is minimal but it could be good enough. Of course, you could always use a paper one-time pad, and if you can get the pad distributed without interception, there's no way they can ever break that.