Imagine two people want to practice the procedure for sending and receiving messages over amateur radio that are encrypted using a one-time pad. Here’s what doing this for real would look like:
- Person A converts the message text to numeric values;
- Person A uses modular addition to add these numbers to the random numbers of a key known to both people (thereby encrypting the message);
- Person A transmits these encrypted numbers openly over the radio;
- Person B receives and records these encrypted numbers;
- Person B uses modular subtraction to subtract the encrypted numbers from the key numbers to generate the message numbers;
- Person B converts the message numbers to the message text.
Obviously, they aren’t allowed to send encrypted messages over amateur radio. But suppose they just want to practice accurately transmitting and receiving strings of numbers. Could they legally practice transmitting and receiving random numbers which do not encode any message over amateur radio? Note that from the perspective of a third party listening in, this practice would be indistinguishable from them actually exchanging encrypted messages.