Good Encryption Equipment is Physically and Electrically Isolated
I am a consumer of encrypted communications, mainly text and occasionally verbal. Our commercial encryption-decryption equipment is deliberately separated physically from the communications equipment, the only interconnection between the units are through opto-isolators, and the encryption-decryption equipment is powered from separate batteries (when portable) and separate power units when mains powered.
More importantly, the encryption-decryption equipment can only be programmed locally (i.e. physically, hands-on) using a key - which makes the programming more challenging.
Working for a provider of military equipment, we ensure that there is isolation in the data chain (again opto) and that the power supplies are from using ferrite filters and many individual power regulators powering different circuits in the encoder.
The military, and others have a preference for remote programming for encryption equipment, which might be understandable. If you analyse the the GPS military transmissions you will see that there is way more non-GPS traffic than enhanced location data. Daily and per-operation encryption codes are transmitted embedded in the GPS signal for air and ground assets - worldwide.
There is one area where clear voice transmissions occur - in passing drone~bomber infra-red signalling codes. The drone operator passes data to the bomb carrier, who dials the 4-digit code into the guided munition. Another example is where ground-based troops 'mark' or 'paint' a target with hand-carried equipment and pass the same 4-digit code to the bomb dispatcher.
This number is of interest to us since we make infra-red repeaters that capture the paint signature which can then be re-transmitted against another target - or empty terrain.
Interestingly most civilian encryption devices are integral in portable equipment including Fraunhofer as well as Secusmart (turns the BlackBerry Z10 into a self-contained secure communications device) support the German government made establishing universal and easy-to-use encryption part of its Digital Agenda. Rohde & Schwarz SIT GmbH ships 'bug-proof' cell handsets.
The much vaunted US <b<P25 universal radio system</b> has easy-to-use encryption and is equally susceptible to people who have an interest in gaining access to clear voice.
Easy-to-use encryption is adverse to good encryption techniques, excluding simple plug-in units.