Semi-Secure Digital Communications for Civilians, by R.T.D.

In times of emergency, many American citizens have found both amateur radio and FRS/GMRS radios very useful to keeping in touch with friends and family as well as keeping local, state, and federal disaster response agencies up-to-date with the latest information on road conditions and disaster area damages.

All of those radio communications are made entirely in the clear as there is no need for encryption, obfuscation, or brevity codes for such work. It’s done as a public service to assist others in times of natural or man-made disasters and just part of being a good neighbor.

But just how does one communicate during times of civil unrest or on a future civilian battlefield against rogue agents of the state or an invading near-peer enemy force without making themselves a target?

The vast majority of U.S. citizens won’t have access to the encrypted radio infrastructures that the U.S. military and law enforcement use as well as the computers required to program such radio equipment to include installing digital encryption keys on each radio to ensure secure communications.

Should semi-secure communications be required, one should look to the amateur radio world for their communications needs but with a twist: Using amateur radio digital voice modes on non-amateur radio frequencies.

A Quick Primer on Digital Voice Radio Technology

So just what is a “digital voice mode”? In a nutshell, a digital voice mode on a radio takes the analog sound of any speech it hears and encodes it into a series of digital bits – ones and zeroes – and transmits that data over the airwaves where other compatible digital voice radios then convert that digital data back into analog sound. It’s very similar to how Skype or Zoom allows one to make voice calls on a computer, but uses the airwaves instead of the internet. Digital voice modes on amateur radio equipment are usually not encrypted – indeed, the C4FM Fusion and D-STAR modes don’t even have any way to encrypt the voice traffic at all while most DMR handhelds do allow for encryption keys to be set. However, most amateur radio DMR mobiles and handhelds are not able to use the highest form of AES-256 bit encryption that one would prefer and instead use lower-level forms of encryption that while not easily cracked can still be cracked by federal-level agencies given enough time and a large enough sample of suspected encrypted digital voice radio traffic.

There are several high-quality and affordable amateur radio handhelds that provide a wide array of digital voice modes, usually only a single mode per handheld. Those most prevalent digital voice modes in use today are DMR, C4FM Fusion, and D-STAR and although other modes exist such as P25 and LMR, those systems are often more expensive and more difficult to obtain than the three amateur radio digital voice modes previously mentioned and thus will not be covered in this presentation however if one has the equipment and ability they can easily be substituted for any of those main three. Just bear in mind that those systems are usually not front-panel-programmable (FPP) making them near-impossible to reprogram on-the-fly in the field without the use of a laptop and programming cable.

Also keep in mind that using encryption on amateur radio frequencies is considered a violation of the FCC rules regarding the use of those frequencies and can result in fines and legal actions (very rare), so as always your current situation would dictate your communications means and methods. I would only use it in a “balloon goes up” situation myself, but would make sure that all my radios capable of it have it pre-programmed in so it can be quickly implemented if need be. Grab radios with wired earpieces, turn them on, switch them over to pre-programmed frequencies and pre-set encryption keys and then hand them out to security/combat forces and conduct radio checks to verify everyone’s hearing each other. Should only take about 10-15 minutes.

The “Why” of using Digital Voice for Radio Communications

Why digital voice? Why not just use analog voice on cheap Baofeng radios and utilize brevity codes and OTP verification codes and pump more money into food and ammo? Why not use these special radios I found online that have a “voice scrambler” capability built-in?

Well, first off that “voice scrambler” you may choose to use is still an analog voice signal and can be pretty easily descrambled. Voice scramblers haven’t been used for secure government communications in decades for very good reasons – every adversarial agency or department on the planet knows *exactly* what it is when they hear it and they already have the equipment on-hand to quickly descramble it in real time. Farmer Jimmy next door might not know what it is but you’re not expecting to go up against your good neighbor Farmer Jimmy, now are you? He should already be part of your own area’s security team.

Citizens should switch over to digital voice modes for the very same reason why law enforcement switched over to digital voice modes many years ago – increased clarity, obfuscation, and encryption. With digital voice there is no “picket-fencing” or fading in and out of a voice signal. You either hear it or your radio doesn’t even break squelch and thus you don’t hear it at all.

Digitally-encoded voice traffic on a radio sounds the same at 10 feet as it does at 10 miles between stations. There’s also the hidden benefit of simple obfuscation when using it outside the amateur radio bands on FRS/GMRS/MURS frequencies as well. Anyone hearing a digital voice transmission on an analog radio doesn’t hear anyone talking, they just hear a bunch of indecipherable-to-the-human-ear digital noise, if their analog radio even breaks squelch at all if they’re using “privacy codes” on FRS/GMRS radios. Using brevity codes at the same time keeps transmission times down and tends to lead the typically-uninformed analog FRS/GMRS radio user thinking there’s an electric fence, strong radio antenna tower, LED/fluorescent lights, or a bad vehicle alternator “breaking in” at times especially if you keep your radio communications very brief.

The Three Main Digital Voice Modes

DMR – or Digital Mobile Radio – handheld and mobile radios can be found in a lot of the cheaper Chinese-made handhelds one can purchase easily online at various websites. While originally not designed for FPP, recent widespread adoption by the amateur radio community has resulted in many new DMR radio models specifically designed for FPP use such as the Anytone AT-D878UVII-Plus ($300) or Alinco DJ-MD5XT ($190) as well as comparable models from Wouxun and Baofeng. While these are not as cheap as the $30 Baofeng UV-5R radios most preppers tend to utilize, they do offer two things that those cheaper radios do not – digital voice and encryption. Indeed, the Anytone D878UVII-Plus is not only capable of using the DMR digital voice mode but that digital voice traffic can be completely AES-256 bit encrypted and I’d wish anyone good luck on trying to decrypt that traffic in a timely manner to make anything gained useful. Not only that but the D878UVII-Plus is capable of storing up to 32 different AES-256 encryption keys as well as 4,000 channels making timed, manual “roll-over” of not only frequencies in use but the encryption keys used on each channel fairly easy to program in and is thus nigh on impossible to be decrypted. That particular model of radio can also use digital or analog voice on pretty any frequency in the VHF (136-174Mhz) and UHF (400-480Mhz) ranges, which not only includes amateur radio but FRS/GMRS, Marine, MURS, Itinerant Business, and Railroad frequencies as well as receiving the WX (weather) and local FM radio frequencies for keeping up with changing weather conditions as well as local civilian information.

There is one caveat with DMR radios however and that is that they are very complex to understand and require pre-programing of IDs, talk groups, and encryption keys from a PC as the FPP programming is very basic usually just limited to selecting pre-programmed talk groups, channels, IDs, encryption keys, etc. But once you clear the DMR knowledge hurdle, the benefits are huge. Some DMR radios can even do APRS position beaconing should the need arise and you need to let another station know your exact GPS coordinates.

C4FM Fusion is an unencrypted digital voice mode implemented by Yeasu on a lot of their digital-voice-capable handhelds and mobiles for the amateur radio market. Pretty much all of those radios can also be “hacked” to allow transmitting outside of the amateur radio VHF & UHF frequency ranges for use on FRS/GMRS, MURS, Marine, Itinerant Business, and Railroad frequencies as well as WX weather stations.

While the digital voice traffic itself cannot be encrypted and is always sent “in the clear” and able to be decoded and listened to by just about anyone, bear in mind doing so requires not only skill and a PC but also knowing that *what* you’re hearing is actually C4FM Fusion digital voice traffic. Unless you know that the signals you’re hearing are C4FM Fusion then you won’t know what to use to “listen in” on it. Sure, an amateur radio operator might know what it sounds like but they don’t tend to be monitoring FRS/GMRS/MURS/Itinerant Business frequencies all that often and when they do it’s with scanners that may not even break squelch on such digital voice traffic. If it does break squelch they might just dismiss what they’re hearing as some sort of local neighborhood interference from someone’s noisy internet modem or Internet-over-Powerline noise because most hams just can’t believe anyone would willingly break the FCC rules and use digital voice modes on non-amateur frequencies.

Out of the three main digital voice modes, C4FM Fusion is literally the easiest to use – just set the radio to your chosen frequency and press the mode button to “turn on” the digital voice mode and that’s it. Unlike DMR or D-STAR there’s no pre-programming of any special talk groups or IDs required. An excellent C4FM Fusion radio can be found in the Yaesu FT5DR handheld radio ($460). Not only does it do digital voice and can be hacked to operate outside of the amateur radio brands but it also has extreme wideband capabilities to include air band & CB radio and it can even pickup shortwave radio stations with a simple, easy-to-make long-wire antenna connected to the radio’s antenna connector. Whenever I’m traveling across the country, an FT5DR HT is usually strapped to the driver’s A-pillar in my vehicle and set on CB radio channel 19 which it picks up easily thus keeping my Bearcat SDS-100 freed up to scan public safety frequencies as I drive. The FT5DR is an expensive handheld radio to be sure but very, very capable and much like Icom you get what you pay for when it comes to Yaesu radios.

D-STAR is a digital voice mode invented by Japanese amateur radio users in 2001 specifically for use on amateur radio bands. And by “bands” I really do mean all bands to include HF. D-STAR hams with Icon HF rigs regularly check-in on world-wide D-STAR nets. D-STAR is also capable of PC data transmission however it’s limited to 4800bps on the 2m and 70cm bands and thus really, really, really slow making it of limited benefit outside of the amateur radio hobby.

The D-STAR digital voice protocol requires pre-programming in various call groups and station IDs and can be overly-complex for new users, even those who have already mastered programming DMR handhelds. Honestly, a lot of the D-STAR repeater programming procedures are just flat-out confusing. Luckily the digital voice mode itself in simplex mode requires no programming at all other than programming in your amateur radio call sign – or your station identifier callsign if going outside the bounds of amateur radio use during emergency or battlefield conditions – and selecting a frequency and hitting the mode button to turn on Digital Voice (DV) mode. Same C4FM Fusion limits and obfuscation rules apply – no encryption available however it does require a potential eavesdropper to know that you’re using D-STAR on that frequency in order to setup a PC to listen to it and decode it in real-time. All D-STAR handhelds can be easily modded to allow for use outside of the amateur radio VHF/UHF bands and can even pickup FM radio, but that’s about it. They do not have extreme wideband receive capabilities like the Yaesu FT5DR handheld, however they are very, very easy to operate, program on-the-fly without a PC, and both the hardware and signal qualities are excellent.

And let’s also not forget that Icom HF radios with D-STAR built-in are very useful for clear, concise, and somewhat obfuscated communications between remote sites that are a long distance away from each other. The new Icom IC-705 portable HF radio is very much capable of this as are most new Icom HF radios. With D-STAR-on-HF there’s no picket-fencing, fading in and out, and the other station could be located 1000 miles away yet sound like they’re right next to you. That capability is well worth the time and monetary investment for those that require it.

Final Thoughts

So which digital voice mode should you use? That’s entirely for you to decide. Honestly, for me it’s DMR using Anytone UV878UVII-Plus handhelds that have been programmed in advance. Using the full encryption capabilities and a good radio ops SOP that rotates both the frequency and the encryption keys every 24 hours, it would be almost impossible to eavesdrop on communications between two of my handhelds no matter how long an adversary takes or what type of gear they have access to. And jumping frequencies and keys is as simple as turning a knob or pressing a button provided you’ve done your job and properly pre-programmed the radios. And with 4000 channels and 32 different AES-256 encryption keys for you to completely customize your $300 gets you encrypted handheld radio comms on par with local, state, and federal law enforcement agencies and can easily be obtained via a quick visit to any number of online store websites.

An adversary would have to actually capture one of the handhelds and given that it’s easy to wipe those radios on-the-move, with good SOPs it’s another non-issue. Just don’t forget and leave your handheld DMR radio in the barn you’re hiding out in and you should be fine.

There are also ways to use stand-alone DMR/C4FM/D-STAR digital voice radio hotspots connected to encrypted private digital voice servers located overseas in “safe” countries via the internet to keep units scattered across the planet in real-time voice communications with each other but that’s an article for a different time.

This is just a subset of general radio digital voice communications knowledge being presented to get people thinking about secure real-time communications in times of great need and I highly suggest readers to explore the subject and learn as much as they can about it.

Disclaimer:  Nothing in the foregoing article is intended as legal advice. It is presented as a purely academic exercise, for informational purposes only.