A Mysterious Code Is Being Broadcast on Shortwave Radio. Is It Iran?

[harumph]

9. Yes. It's old school and if done properly is absolutely unbreakable.

The shared key must be truly random - but decent randomness can be obtained from the emissions of radioisotopes. A Geiger counter, an Arduino or raspberry pi and a sample of a mildly radioactive element will do. Shared key is as long as the message. Learn more here: https://en.wikipedia.org/wiki/One-time_pad#

Back in the 70's and early 80's I liked to tune into the "numbers stations" from Cuba, Colombia and other SA countries.
Very relaxing.

This smart young man explains how to get your random numbers which is the first step - then move on to the one-time pad article.
We may all need to know this someday.