[66813] in Cypherpunks
Re: GPS [MARGINAL, at best]
daemon@ATHENA.MIT.EDU (P. J. Ponder)
Sun Sep 29 21:33:30 1996
Date: Sun, 29 Sep 1996 21:20:52 -0400 (EDT)
From: "P. J. Ponder" <ponder@freenet.tlh.fl.us>
To: cypherpunks@toad.com
There was an article in _Scientific American_ February 1996 about GPS. I=
=20
couldn't find the magazine, but they had this squib on the www.sciam.com=20
website:
=91The Global Positioning System=92
Thomas A. Herring
Two dozen satellites hovering thousands of miles up can locate your=20
position on the earth's surface to within a few centimeters.=20
Originally constructed for military applications, this network of=20
space beacons today finds civilian applications--such as landing=20
airplanes in fog--that demand accuracy beyond what its designers had=20
thought would be technically possible.
According to the website, there was also a letter in the June 1996 issue=20
responding to Herring=92s article. Here it is:
MILITARY ADVANTAGE=20
I was pleased when I first saw your February article "The Global=20
Positioning System," by Thomas A. Herring. As developers and operators=20
of GPS, we in the Department of Defense and our partners in industry=20
are justifiably proud of the technology. GPS represents the best of=20
American scientific and technical ingenuity as well as being an=20
excellent example of cooperation between the military and civilian=20
sectors. But after reading the entire article, I was disappointed by=20
its unbalanced discussion of the national security aspects of GPS.=20
Yes, the Defense Department does operate GPS with unpopular security=20
features. But these features were not designed to inconvenience the=20
peaceful users of the system, as Herring implies. Rather they were=20
designed to provide U.S. and allied forces with a crucial military=20
edge. Furthermore, the Defense Department is well aware that the=20
security aspects of GPS are an additional burden for many users. And=20
while we believe such measures are still needed at this time to help=20
preserve our military advantage, we have set a goal of discontinuing=20
regular use of the feature known as Selective Availability, the=20
component that degrades GPS accuracy, within a decade.=20
Both time and resources are needed to replace the advantages Selective=20
Availability provides. In light of the revolutionary contributions of=20
GPS to both military and commercial enterprise, Herring could have=20
portrayed the technology in a more evenhanded manner.=20
PAUL G. KAMINSKI=20
Under Secretary=20
Department of Defense=20
-- end of quoted material --
The article, as I recall, was about ways in which civilian users have=20
found, or are finding, ways around the built-in inaccuarcy of the GPS.
I don't recall whether crypto was mentioned in the article. My=20
recollection of it was that they had been diddling with the timers or the=
=20
clock signal or something, as opposed to encrypting anything. But then=20
again it has been a while, and my memory of it isn't too clear.
I seem to remember another crypto scheme discussed here at length about=20
GPS, based on a paper by Dr. Dorothy [?] Denning, which involved having=20
the intended recipient's coordinates - which were somehow involved in the=
=20
encryption. =20
The coordinates are in 3-D. Spheres centered on three of the GPS
satellites intersect within a very small space.=20
--=20
public service announcement:
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