On Mon, 22 Dec 2003 03:47:23 GMT, Fred J. McCall
wrote:

pervect wrote:

:From my POV, the key point that I missed in my earlier post (the one
:you just replied to, there have been a bunch since then) is that GPS
:is spread spectrum.

Which really doesn't buy you much in the way of security. DS-SS
merely makes it easier for the receivers to do ranging functions.

You're missing the forest for the trees - or maybe you just like to
argue? :-)

I'm going to give a reference of my own:
http://arxiv.org/pdf/gr-qc/9508043

for an overview of a more theoretical and high-level approach as to
how GPS works, and to support the following statements I'm going to
make as to how GPS works.

The very basic principles of GPS are that are it is a bunch of
orbiting clocks, all of which (in the simplest model) transmit their
own proper time.

An observer on the ground, at a fixed location, knows what the proper
time on the satellite must have been when it was sent, when he
recieves the signal, because he knows (or can directly observe) the
satellites orbit.

Therfore, ultimately, an approach based on encryption is going to boil
down to encrypting something that everybody already knows or can
figure out, which is not going to be terribly secure.

Spread spectrum tecniques are really crucial to making this system
have the level of security it actually does.