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

Bill Frantz frantz at pwpconsult.com
Sun Mar 30 11:15:21 EDT 2014

[Belatedly changing the subject to match the discussion.]

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. It uses the fact 
that a signal is coherent while noise is random to allow the 
signal to build over time to be able to separate it from the 
noise. A contact which basically only sends a little more than 
the call signs of the two stations takes several minutes, each 
station transmitting for one minute and then listening the next 
minute. (Yes, the clocks need to be synchronized.)

Classic RTTY is 45 words per minute (wpm) using Baudot code. 
PSK31 is designed so a good typest can keep up with the 
transmissions, making it good for casual conversations. For 
comparison, the model 33 Teletype at 110 bps is classified as a 
60 wpm device.

The lowest rate I know of is the recent one way signaling from a 
large collection of amateurs around the world to the Juno space 
probe at a distance of about 37,500 kilometers. There a single 
morse code dit took 30 seconds. The signal was successfully 
received. These low rates significantly limit the authentication 
codes that can be used. OTOH, they also significantly limit the 
rate at which guesses can be validated.

Cheers - Bill

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