A simple software fix could limit location data sharing • Hacker News Board

Re: A simple software fix could limit location data sharing

#11

Post by barathr » Sat, Aug 14, 2021, 8:02 PM UTC

neolog wrote: post #8

Can either of you recommend resources or tools for learning how to design good protocols?

If you're interested in security protocols, I'd recommend Bruce Schneier's book Cryptography Engineering (and Ross Anderson's Security Engineering). If general networking protocols, there are many options -- Kurose, Peterson and Davie, Tanenbaum, etc.

Re: A simple software fix could limit location data sharing

#12

Post by barathr » Sat, Aug 14, 2021, 8:05 PM UTC

NotSwift wrote: post #9

barathr wrote: post #4

I'm co-author of this research (with my colleague Paul) -- happy to answer any questions.

First of all, congratulations, when you get Bruce Schneier to endorse your work, you have probably done something interesting. But still the article is not very clear on technical details. Of course on initial contacts your phone has to provide information about your service provider (they will somehow have to pay for your communications) and it has also has to have some form of identification about your phone (so th…

Thanks! So the paper that the other commenter linked is a good deep dive. The basic answer to your question is that we have multiple variants but the simplest is that phones using PGPP would have the same IMSI; once you do that, you hide who's who but create a new problem of how to make sure users are valid paying subscribers. We solve that new problem by developing a new oblivious authentication protocol that can verify someone is a valid user (i.e. someone who has authentication tokens that are not linked to them but are issued by the network).

Re: A simple software fix could limit location data sharing

#13

Post by red0point » Sat, Aug 14, 2021, 8:26 PM UTC

I skimmed through the paper, what isn’t clear to me is how the original Registration Procedure is modified exactly. How is the Authentication Procedure done by the AUF when it doesn’t know the shared key K between the USIM and the network?

Can you elaborate a bit on that? Is every USIM using the same shared key?

Thanks!

Re: A simple software fix could limit location data sharing

#14

Post by red0point » Sat, Aug 14, 2021, 9:10 PM UTC

red0point wrote: post #13

I skimmed through the paper, what isn’t clear to me is how the original Registration Procedure is modified exactly. How is the Authentication Procedure done by the AUF when it doesn’t know the shared key K between the USIM and the network? Can you elaborate a bit on that? Is every USIM using the same shared key? Thanks!

Additional question for my understanding - this needs an app running in the background to send the signed token at every other time interval, correct?

Re: A simple software fix could limit location data sharing

#15

Post by barathr » Sat, Aug 14, 2021, 10:44 PM UTC

red0point wrote: post #14

red0point wrote: post #13

I skimmed through the paper, what isn’t clear to me is how the original Registration Procedure is modified exactly. How is the Authentication Procedure done by the AUF when it doesn’t know the shared key K between the USIM and the network? Can you elaborate a bit on that? Is every USIM using the same shared key? Thanks!

Additional question for my understanding - this needs an app running in the background to send the signed token at every other time interval, correct?

That's right. (The token is used for oblivious authentication, so it's not identifying.) The attach procedure works as usual, it's just that the IMSI/SUPI is no longer individually identifying (which then necessitates the oblivious authentication protocol).

Re: A simple software fix could limit location data sharing

#16

Post by prschmitt » Sat, Aug 14, 2021, 11:06 PM UTC

red0point wrote: post #13

I skimmed through the paper, what isn’t clear to me is how the original Registration Procedure is modified exactly. How is the Authentication Procedure done by the AUF when it doesn’t know the shared key K between the USIM and the network? Can you elaborate a bit on that? Is every USIM using the same shared key? Thanks!

The regular attach procedure is unchanged. In the simplest version we give every SIM the identical IMSI and key.

However, their use is to only gain IP connectivity - the equivalent of an allow list on the backend db (AUSF) which gives you IP connectivity. At that point you do billing and auth at the PGPP-GW using oblivious auth tokens.

Re: A simple software fix could limit location data sharing

#17

Post by 2Gkashmiri » Sun, Aug 15, 2021, 4:46 AM UTC

Why doesn't android have an os level permission manager, so if I decide to not give location to maps, the os would simply say no signal and continue to work. Same for sms access or contacts or phone. I saw one ROM do this, realme it was I think but apps apparently see this and they complain so no point.

BTW, why does truecaller on android 10 show an overlay after a call when settings page specifically disables it ?

Re: A simple software fix could limit location data sharing

#18

Post by red0point » Sun, Aug 15, 2021, 6:41 AM UTC

prschmitt wrote: post #16

red0point wrote: post #13

I skimmed through the paper, what isn’t clear to me is how the original Registration Procedure is modified exactly. How is the Authentication Procedure done by the AUF when it doesn’t know the shared key K between the USIM and the network? Can you elaborate a bit on that? Is every USIM using the same shared key? Thanks!

The regular attach procedure is unchanged. In the simplest version we give every SIM the identical IMSI and key. However, their use is to only gain IP connectivity - the equivalent of an allow list on the backend db (AUSF) which gives you IP connectivity. At that point you do billing and auth at the PGPP-GW using oblivious auth tokens.

Thanks! You mention that this is the simplest version, is there one where you use distinct keys?

Also, regarding the IMEI - let‘s assume the UE nullified it, how would you distinguish between a legitimately nullified UE and a stolen UE that had its IMEI nullified?