🚀 go-pugleaf

>>Expensive and easy to defeat -- probably...
>
>Most any non-digital scrambler, no matter how tricky, is probably going to
>fall under this heading.  There is lots and *lots* of redundancy in the
>human voice, and it's very hard to hide it completely.

Not necessarily true: the (west) german police uses a system that digitizes
speech, cuts the data in short blocks, permutes the order of these blocks
according to a digitally computed key, converts it back to analog and sends
it. A key tone is added to synchronize the receiver so that it can undue
the process. The system is not easy to defeat and has the virtue of using
no more bandwidth than the original signal. This point is important to be
able to use it over existing gear (radios, phone lines, etc.).

While a full digital system is possible in the same bandwidth, the complexity
is much higher and more likely to break down under marginal signal
conditions, interference, and routine day-to-day use.

  --  Andreas
-- 
   --  Andreas Nowatzyk  (DC5ZV)

   Carnegie-Mellon University	     agn@unh.cs.cmu.edu
   Computer Science Department       (412) 268-3617