From: Paul_Koning/US/3Com%3COM@smtp1.isd.3com.com
Date: Thu, 11 Apr 1996 06:11:41 +0800
To: cypherpunks@toad.com
Subject: Re: No matter where you go, there they are.
Message-ID: <9604101822.AA1919@>
MIME-Version: 1.0
Content-Type: text/plain


>Location-based System Delivers User
>Authentication Breakthrough

>By Dorothy E. Denning and Peter F. MacDoran

Nice april fools article...  

After all, position information is nothing more than a particular
phase shift (time delay) between GPS data streams received
from the set of satellites overhead.  If I report the datastreams
received -- or information about them -- then someone can
calculate where I am.  (Indeed, there are GPS applications
where the device whose position is of interest doesn't actually
decode the GPS data, it merely reports what it receives to some
central data collection site, where the arithmetic is done.)

If I want to pretend to be somewhere else, all I have to do is
some simple geometry to calculate the time delays I want to
report, and then phase-shift the GPS streams from their
received position to where they would be at the other place.

Note that relying on the PP code (military code) in the GPS
stream is no help, since I don't need to be able to interpret
the PP stream in order to pretend to be elsewhere, I merely
need to know where I am and where I want to be, to insert
the right phase shift.

 paul

!-----------------------------------------------------------------------
! Paul Koning, NI1D, C-24183
! 3Com Corporation, 1-3A, 118 Turnpike Road, Southborough MA 01772 USA
! phone: +1 508 229 1695, fax: +1 508 490 5873
! email: paul_koning@isd.3com.com  or  paul_koning@3mail.3com.com
! Pgp:   27 81 A9 73 A6 0B B3 BE 18 A3 BF DD 1A 59 51 75
!-----------------------------------------------------------------------
! "Be wary of strong drink.  It can make you shoot at tax collectors
!  -- and miss!"
!                -- Robert A. Heinlein, "The Notebooks of Lazarus Long"
!                   in "Time Enough for Love"