messed up the url

Rishab Aiyer Ghosh
Sun, 23 Mar 2003 23:40:03 +0000

i can speak with some authority on this topic ... despite the huge number
of sources since a5 was leaked, a search on "a3 a8 a5 gsm" (i.e. the 3
protocols used for authentication and encryption) still comes up with a
7-yr-old post of mine to cypherpunks on google...


On Sun, Mar 23, 2003 at 02:03:25PM -0800, Justin Mason wrote:
> > > Are those GSM phones?
> > the base stations you can just switch off encryption, and your mobile 
> > won't raise a ruckus.

GSM encrypts mobile-to-base, not mobile-to-mobile. so if you are sitting
in the base station, you can get the plaintext stream. you don't need to
switch off encryption.

> The bit I was wondering about, though, was triangulation of position "using
> satellites".  Is that possible with GSM?

i wish GSM broadcast a signal strong enough to be picked up by satellite! of
course, you'd probably stand an even higher chance of getting brain cancer,
but at least you wouldn't lose your call when you went into the basement (or
the metro rail). 

of course you don't need satellites for locating the position of a GSM (or
any other cellular) phone. the network needs to know which cell you are in,
so that information is available easily, without triangulation. you _could_
triangulate using GSM transmitters to locate exactly where in a cell the
phone is, but that level of precision is rarely needed since cells are
pretty small anyway.

the sort of phones you'd locate with satellite triangulation are the inmarsat/
iridium/geostar type "access-anywhere" phones.