From the article, I got the impression that the only way to really have secure communications is to create your own crypto. Now that you mention "air gap," I th

From the article, I got the impression that the only way to really have secure communications is to create your own crypto. Now that you mention "air gap," I think that is the key (pun intended): it would have to be a crypto device that communicates with a PC through an air gap. Not USB nor bluetooth, actually nothing digital. The device I'm thinking of would rely on certain kinds of digital-to-analog and analog-to-digital conversions.