Encryption on Amateur Radio

The amateur radio bands are some very valuable allocations of bandwidth, free for licenced amateurs worldwide to use, subject to some rules.
One of the rules is that transmissions must not be encrypted.
In the UK, the rules state:

Messages sent from the station shall not be encrypted for the purposes of rendering the Message unintelligible to other radio spectrum users.

Other countries have similar provisions.
No doubt these rules were put in place in pre-Internet days, to prevent spies from sending reports back. Nowadays, that reasoning seems a little quaint.

In this day and age where we all use and value encryption, I often see people on Internet fora complaining about the inability to use encryption. This is a common response by people with a technical background who aren't licenced amateurs.

I'm a big advocate of encryption. Full disk encryption protects your data at rest, TLS protects it in transit, and GPG and Diffie-Hellman key exchanges can enable you to communicate securely with people you've never met (subject to out-of-band key verification, of course!)

As your actions can cause problems around the world, amateur radio relies on cooperation, and self-policing.
Once you have used the HF bands, and seen the problems that non-cooperating stations can cause, you begin to appreciate the value of cooperation, and the wisdom of requiring that all communications are understandable by all.

My views on encryption in amateur radio differ depending on whether we're talking about the HF and sub-HF bands, or VHF and upwards.


I'm never sure of what use-cases people have when they talk about encryption on amateur radio. Most of them I assume are computer-related. Here are a few of my guesses:

HF and sub-HF bands

The bands allocated for amateur use below 30MHz are very valuable. They have unique properties, in that they can be reflected around the world via ionised layers in the atmosphere.
This means that transmissions can affect people over a very large area.

The HF band allocations are also small. For example, the 40m band (one of the most useful) only covers 200kHz. If we take a voice communication as 2.7kHz wide, the whole bandwidth only allows for only 74 simultaneous communications before stations have to share frequencies. (Also, voice communications aren't allowed on the whole band)
While it's true that digital (encrypted) data could be sent over a very narrow bandwidth, the principle remains - there isn't a lot of the HF spectrum to start with, and we need to make the best possible use of it.

The lower the transmission bandwidth, the lower the bitrate. PSK31 is 31Hz wide, with a 31bps bitrate. This would make even an SSH session pretty unpleasant to use. The fading of signals, interference from other stations, and atmospheric noise would render a large percentage of the data unreadable, requiring resending, or FEC, making the effective data rate even lower.

For those of you who've never "enjoyed" Internet access at pre-broadband speeds, to get an idea of how slow those sorts of speeds are, this is what TCP/IP over AX.25 at 1200 bps over a reliable link looks like. Now imagine that where there is interference, retries, dropouts, losses.
This is what receiving emails over HF looks like.

But the big problem with encryption being used, especially on the valuable, worldwide HF bands, is that non-hams could use it, and the encryption would prevent hams from being able to identify that non-hams were using it. The limited bandwidth would then become used up by digital noise, leaving the amateur radio community unable to identify who is using it.

The reason it is called amateur radio (as opposed to professional radio) is because it cannot be used for commercial purposes. Encryption would allow businesses to use the valuable, scarce HF spectrum for commercial purposes.

VHF and above

The VHF bands and above are different. They are generally a lot larger than the HF bands.
For instance: 6m and 2m are 2 MHz wide, 70cm is 10 MHz wide, and 23cm is 60 MHz wide.

They also more easily blocked, and are not often subjected to atmospheric conditions that cause the signal to travel a long way.

This means that there:

I would possibly support the use of encryption on the higher bands, restricted to certain segments of the bands, with the proviso that whatever protocol was used, it would send the callsign in the clear at the start and end of each transmission/packet/block of data.