O is for... One Time....


The One-Time-Pad. I have used then a few times. Good fun! Great for training-days with
new students, or when playing intercept/decode games. I designed and built some tiny
1watt hf transmitters for training-days. The scenario is as follows.

A bunch of cadets or T/A are over for a training weekend. One of their tasks is to
use a radio-set/pad captured from the enemy. To log/decode any messages received
then to direction-find the transmitter and capture it and any operator.

The radio set I use is an old plessey manpack. It's an ssb tranciever on 6 channels.
pretty much any receiver will do as long as it has a BFO to produce an audible tone
from the tinyTX. This and a one-time-pad "fall into the trainee's hands"

The tinyTX has been planted somewhere on a 120 acre area. (usually in an overgrown field)
The microcontroller inside the tinyTX waits for the programmed time period, then begins to
send messages in CW on the hour. With a new message every hour. Points and beer is issued
for logging/decrypting/DF-ing and speed.

The initial delay is important, as the TinyTX is often planted some time before the exercise
is due to begin

My trainees are, after a brief lesson in morse-code. one-time-pads, modular-maths, and
direction finding with loop or rod aerials left to get on with it. It's really great fun!

Rather than the cumbersome modular maths in your head. I tend to use a couple of thin
strips of paper each with the alphabet printed on twice. One above the other to encode.
and turn top one upside-down to decode. I can decode like this very quickly.


(copyright (c) S.Bluck 2009-2015)