[Scan-DC] spread spectrum

[Dave Emery]

On Sat, Feb 21, 2004 at 10:41:29PM -0500, sdaitch@ibb.gov wrote:
> > Is it possible to listen in on telephones that use spread 
> > spectrum on 900
> > mhz?

> It might also depend on who your neighbors are and how
> much money they have.  If they have the funds to buy some really high end gear,
> lots of technical support, and some fairly sophisticated software and hardware designed by certain folks who can't talk about it, they might be able to 
> listen to your phone calls.  
> 

	I might add that as far as I know based on what has been
circulated in the cryptography community, few if any digital cordless
phones use secure encryption with strong ciphers and long truly random
keys changed often.

	Rumor has it that most of them use essentially no encryption at
all or at best use very short keys that can be trivially guessed by
trying all combinations.

	This of course implies that it should be readily possible with
the right gear to intercept digital cordless calls (though it is clearly
not legal to do so in the USA).

	No publicly available scanner gear will work for this purpose
(though some cordless phones that claim to be digital actually transmit
analog signals in one direction or the other and can be intercepted on
analog gear, and a few others apparently radiate weak analog signals
along with the digital signal).

	But the digital signal formats and modulation are not so complex
that a sophisticated eavesdropper could not figure them out.

	And one should always remember that cheap cordless phone
receivers ARE available - namely the one that came in the box with your
cordless phone - the headset and base unit of your phone can receive
your conversations, and it may not be too much of a trick to make it
receive some other base station or headset of the same model or
manufacturer too.   Likely only some hackable firmware prevents your
phone from tuning in conversations on your neighbor's similar model.

	However - unless you have some strong evidence for your paranioa
about your neighbors, it would be much more logical and reasonable to
assume they are innocent scanner buffs interested in public safety or
other legal to listen to communications rather than spies targeting your
phone calls.   A discone makes a dandy antenna for a good grade scanner
to listen to police or fire calls on.

	And not everyone with a discone is a ham (or spy).

	On the other hand if you do have a serious reason to suspect
your neighbors you must be living a marvelously interesting life.   Most
normal people don't have phone conversations worth that kind of bother.

-- 
   Dave Emery N1PRE,  die@dieconsulting.com  DIE Consulting, Weston, Mass 02493