pervect wrote:
: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? :-)
Or maybe I know more about botany than you do?
: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.
I would suggest a pair of alternative documents for more than just a
brief relativistic discussion: "NAVSTAR GPS User Equipment
Introduction" for an overview of the system and ICD-GPS-200C for a
description of what the signals actually look like and how they're
used (what you really want to look at are ICD-GPS-203, ICD-GPS-224,
and ICD-GPS-225, but those aren't really open to discussion here).
:The very basic principles of GPS are that are it is a bunch of
rbiting clocks, all of which (in the simplest model) transmit their
wn proper time.
Right so far.
: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.
Well, not quite. There's a bit more to it than that.
: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.
Except you don't know all of what you need to know, so you really
don't know what the clear text is supposed to be.
:Spread spectrum tecniques are really crucial to making this system
:have the level of security it actually does.
Ok, view it that way if you like. I'm really not going to talk about
it other than what I've already said.
--
"Millions for defense, but not one cent for tribute."
-- Charles Pinckney