1993-10-13 - Re: Spread-spectrum net (vulnerability of)

Header Data

From: doug@netcom.com (Doug Merritt)
To: cypherpunks@toad.com
Message Hash: 72d79e60015d5140632b136d6699fcdb7922f8ceb58197df7c2b4ec96ca4ecc1
Message ID: <9310130403.AA23351@netcom5.netcom.com>
Reply To: N/A
UTC Datetime: 1993-10-13 04:06:36 UTC
Raw Date: Tue, 12 Oct 93 21:06:36 PDT

Raw message

From: doug@netcom.com (Doug Merritt)
Date: Tue, 12 Oct 93 21:06:36 PDT
To: cypherpunks@toad.com
Subject: Re: Spread-spectrum net (vulnerability of)
Message-ID: <9310130403.AA23351@netcom5.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain

jkreznar@ininx.com (John E. Kreznar) said:
>Not even the antenna should be visible.  Remember, for spread spectrum radio
>detectable only by the intended receivers (which use the correct spread-
>spectrum code for coherent detection), the power density should be hardly
>distinguishable from the ambient noise.

This is true only for casual observers. If the FCC were after you, they
could most definitely triangulate on unusual noise sources as well as
they could a coherent signal. Power signals are a giveaway.

>One way to arrange this is to put the antenna inside of a physically
>secure perimeter, outside of which the power density is too low for
>noncoherent detection.  The perimeter can be optically opaque (e.g. a
>building), as long as it leaks enough r.f. in the direction of the
>receiver(s) for coherent detection.  Preventing noncoherent detection
>may often require _attenuation_ of an otherwise too-powerful signal,
>and the building may serve part of this function.

Good enough as far as it goes. But this implies a large drop in efficiency
of the transmitted signal. That's not a stopper...*if* you've got power
to spare. But that implies enough power for bad guys to triangulate your
noise source...ouch.

If they pin you down to within a building, you've lost.

There are other approaches...phase-sweeping...phase-conjugation...