[Gta04-owner] Modem off .. less technical question

Dr. H. Nikolaus Schaller hns at goldelico.com
Wed Nov 6 20:10:09 CET 2013


Am 05.11.2013 um 22:49 schrieb Peter:

> Hi all,
> 
> apologies for this possibly "naive" question.. I am a sysadmin with insufficient knowledge of mobile related hardware.
> 
> However, I am exploring how useful this project could be for security-concerned people as journalists (e.g.)
> 
> In some situations these people want to be sure that their phone does not spy on them - as well as does not make them trackable.
> 
> Here is a question: can you use software to switch off some functionality completely, e.g. stopping communication with the mobile network?

Yes, GPIO186:

http://projects.goldelico.com/p/gta04-kernel/page/Wireless/#wikititle_11

Well, how do you know that it is really off if you toggle the GPIO?

lsusb will tell if there is a USB connection and we must assume that if
there is no connection, the modem is off.

Could the modem pretend to be off? Yes, it can - but then it can't communicate
with the CPU (there is no shared memory etc.) or any other peripheral (microphone, headset).

So what could it theoretically do in this state? It could receive SMS and store
on the SIM card. It could find out that you are in the range of some base
stations. This would mean remaining registered.

And in theory it could use the internal GPS receiver to get your exact position
(but that would drain the battery with another 50 mA - and we do not have an
antenna for GPS connected to the module).

It can't use the microphone because that is a digital PCM interface.

So IMHO risk is very low that a modem without lsusb report is doing something
harmful autonomously.

BR,
Nikolaus




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