First off. Thank you for an interesting discussion.
N1b I think what de0u means and elaborated yesterday is that cellular networks are fundamentally tracking networks. Since you want your users to utilize mobile data for Signal messages, they will be trackable via triangulation any time they use it. Law enforcement, if motivated enough, could simply wait for the users to turn off Airplane mode, track them down and arrest them. They could also force mobile carriers to hand over logs and figure out where your users regularly and where they sleep.
I am aware of this "problem". Im not 100% ut to date on the technical progress in the field when it comes to triangulation/location pinpointing. But I'm under the assumption that its is not even close to as precice as GPS. The towers can give you a signal strength and general direct of the cellphone. These are not precise but by combining data from more than one tower they can narrow the location down to (I'm guessing now) within a circle of 300 meters I diameter.
BUT. The only thing the have is a sim card that transmittws from that location.
If the user is unknown, the contents of the communication is unknown and the recipient is unknown, then this data is totally worthless.
There's simply no way around it: If the users' threat model involves hiding from three letter agencies or other well-resourced law enforcement, they should not use mobile data and operate their phone only in Airplane mode (with occasional WiFi when using signal). Using a mobile router that allows shuffling IMEIs around and buy a new SIM card regularly like Hb1hf suggested (if I understood them correctly) will make the users harder to target, but still: As soon as a SIM card connects to a network, it will be trackable
I agree, but lets take an example. You and me start an underground news agency that reports on crimes of a repressive regime. The regimes "3 letter angencies" would have to:
- Find out who we are
- Find out what sim cards we are using
- Find out when we are communicating
- Find out the contents of our communication
- Find out our current location
Solving 5 if you 1-4 is known is fairly simple. But solving 1-4 is nearly impossible.
Another similar scenario would arize if you switch nr 4 and 5 so that the agency hope to
find out the contents of our communication after they have arrested us. This task would range from nearly impossible to haes depending of how repressive the government is (using torture, etc) since our phones are encrypted and have not a panic wipe function, a timer wipw function and do not store any communication data even if they are unlocked/cracked.
As stated earlier, i agree that finding the current location of a device (nr 5 in original list) can be fairly easy.
1-4 I would grade as nearly impossible undless resources of extreme proportions are used (and event if so, a mall chance of success)
Please feel free to elaborate/comment further.