[Cryptography] Amateur Radio Authentication - was: OpenPGP and trust

[Sampo Syreeni]

On 2014-03-30, Bill Frantz wrote:

> One aspect of authentication in the amateur radio context is the very 
> low bit rate used by some communication modes. JT65, which is used to 
> bounce low power (100-600 watt) signals off the moon, is operating at 
> 10-15 dB below the noise level.

But then you wouldn't operate a repeater over EME in any case. Typically 
the kinds of communications where you'd want the authentication field 
are higher rate digimodes, with enough capacity to throw in a full ECDSA 
signature some proper symmetric primitive.

The interesting thing is, many amateur modes are actually rather 
wasteful, so that if you threw in an optimized to the hilt 
authentication field using the most efficient modulation you can think 
of, it'd easily fit in the channel used without taking a whole lot of 
time compared to the utility signal.

My favourite example right now is plain Morse/CW. With its 1/3/7 dit 
commas it's nowhere near an optimal line code, not to mention that since 
it's equivalent to straight amplitude modulation at 100% depth, with 
suboptimally shaped base band pulses, it's technically as wasteful or 
more so than badly thought out DSB. If you really wanted, and was able 
to go around the -- frankly bizarre -- ban on independent sideband 
modulation, you could probably fit not only strong authentication but 
running ECC as well, into your standard narrow band CW slot, even at HST 
speeds. I haven't (yet?) tested how well something like that would work 
with a straight key and decoding by ear, but I wouldn't be surprised if 
you could sort of have even that at the same time -- and certainly could 
inject a strong authentication burst at tens of bits per second every 
here and there if you wanted to multiplex by time instead of frequency.

My point being, if you want authentication in the amateur bands, there 
are ways to fit it in where it's needed. Sure, that might mean you have 
to butcher your existing modes, but then what else is the technical side 
of ham work than that kind of tinkering? Especially in an age where hams 
unfortunately seem to lag somewhat behind the bleeding edge in bandwidth 
efficient modulation?
-- 
Sampo Syreeni, aka decoy - decoy at iki.fi, http://decoy.iki.fi/front
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