🚀 go-pugleaf

tim@ais.org (Tim Tyler) writes:

>     Hmmm...  I went to the Motorola Secure Clear cordless phone
>display at a Sears store, took a deep breath, & hit the demo button
>in order to hear what the "scrambled noise" which would protect a
>conversation from eavesdropping sounded like.  
>     White-noise like that of a digital data stream? Rapid analog
>time-domain scrambling?  No, the scrambled "noise" sounded like
>inverted analog voice.  That's right, they're using the 40 or 50
>year old (3kHz baseband) speech inversion system --the same one
>which they stopped marketing for their commercial two-way radio
>gear about a decade ago-- to make Lee Trevino & other ignorant
>people's "private conversations stay private."
>     
>     For those of you not familiar with speech inversion, it simply
>flip-flops the voice spectrum so that high pitched sounds are low,
>& vice versa.  It sounds a lot like Single Side Band (SSB)
>transmissions, although an SSB receiver will not decode speech-
>inversion scrambling.  Prior to 1986, several companies -- Don
>Nobles, Capri Electronics, etc. sold inexpensive kits or scanner
>add-ons which could be used to decode speech inversion.  Several

And according to several histories of cyprtology I've seen, one of the
reasons the US & Britian *quit* using frequency inversion scramblers
for calls between Churchill and Roosevelt was that the techs working
on the system reported that with practice it became possible to understand
the inverted speech! 

Can you say "oops!"? 

I can't verify this, but similar things are well established, so I'd
not consider frequency inversion to be *at all* secure.
-- 
Leonard Erickson		      leonard@qiclab.scn.rain.com
CIS: [70465,203]			 70465.203@compuserve.com
FIDO:   1:105/51	 Leonard.Erickson@f51.n105.z1.fidonet.org
(The CIS & Fido addresses are preferred)