Secure Voice Using AFSK Modulation

One of the things that finally prompted me to get an amateur radio license was some experiments I was doing with secure voice. There are many commercial systems that exist that require one replace their existing analog radio infrastructure, such as P25 or DMR. This can be expensive, prohibitively so for smaller organizations. And of course these systems would be useless over non-radio voice mediums such as analog telephones.

I found an open source voice codec that used a low-bitrate AFSK scheme that was designed to function using narrow-band voice FM, modified it to encrypt the voice packets, and packaged it to run on a raspberry pi and some commodity USB audio devices so anyone could use the system with minimal cost and no change to their existing radio infrastructure.

Obscured communications are illegal on amateur bands, so this page serves as documentation of how the communications are encoded and modulated so that anyone may decode and understand the transmissions. The key I use for the transmissions is also provided here. If you follow the instructions to format an SD card with the raspberry pi image, create a directory named “config” on the SD card, and copy the key file into that directory with the filename “key” (lowercase, no file extension)