pervect wrote:

:Processors and computing power are getting cheaper every year - and
:there are a lot of US weapons with military GPS around - so it's
:conceivable to me that someone could obtain one of these weapons and
:reverse-engineer the GPS system on them.

Which does them absolutely no good at all.

:If there is no sort of "auxiliary code input" to the weapon (i.e. some
:sort of activation code that has to be input) the reverse engineered
:weapons would work just as well as the US weapons, so the US would
:have to make the choice of whether it was better for everyone to have
accurate) GPS or nobody to have GPS.
:
:Without knowing for sure, I would personally expect that current
:weapons would have some sort of auxiliary code, and that this code
:would have to be entered as part of the target programming process
which is quite long according to news reports, though it's getting
:shorter).

They aren't 'auxiliary codes' at all. Military GPS data streams are
encrypted. You need keys to use them. Without keys you get nothing.
This is why copying a GPS weapon exactly does you no good.

:Assuming (as I suspect) that "auxiliary code input" to the weapon is
:required, things get more complicated. Basically the question is how
:long it would take for the enemy to figure out what the auxiliary code
:was to activate their weapons.

Longer than the key is good for. They change frequently, you see.

:Pessimistically assuming that the current military GPS system does get
:compromised, and that the code breaking process could be done in
:minutes, the US is of course free to build a better one with more
:modern (and longer) codes. Of course, retrofitting existing weapons
:to use the new GPS system might be a bit involved. OTOH, it could be
:as simple as pulling out a modular "black box", and replacing it with
:a new improved one.

Well, if you assume the enemy has magical powers (which is essentially
what you're doing above), then I suppose anything is possible. Just
by the way, even your "black box" replacement above isn't simple.
Examine the replacement of PPS-SM by SAASM, for example.

You know, if you want to keep speculating, you might want to learn a
bit of something about the GPS system before you continue. See
http://gps.losangeles.af.mil/user/pr...curity/hae.htm for a
very brief synopsis on GPS security.

--
"Millions for defense, but not one cent for tribute."
-- Charles Pinckney