So… I found out a way to send encrypted messages using amateur radio.
There is an app called Rattlegram that lets you convert a string of text into soundwaves that plays though your phone’s speaker. If I just use an app like Secure Space Encryptor (SSE) to encrypt a text, then copy-paste it to the Rattlegram app, then transmit that over radio, then using the same app to record the sound and reverse the process on the other end. Voila! Encrypted long(ish) range communications without a centralized server!
But I looked it up and apparantly its illegal to encrypt communications over the amateur radio bands. What are the odds of actually getting in trouble? 🤔
(To the FCC agents reading this: this is just a hypothetical, a thought experiment, I’m totally not gonna do this 😉)
The restriction is against encoding for purposes of obscuring meaning. You can use encryption for things like authentication or controlling remote equipment.
“Rattlegram” seems to be similar to the AFSK systems used for Packet Radio, APRS, etc. You might look into those methods before implementing your own.
Assuming Rattlegram encoding can fit within the audio bandwidth (which might not be the case on the narrower, longer-range ham bands) you should be able to use Rattlegram to send ordinary text messages. However, you would be allowed to use SSE to send authentication and control messages.
You could only use this approach on frequencies allocated for digital modes.