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The associated paper [1] summarises the information revealed by Signal succinctly: The Signal messenger is primarily focused on user privacy, and thus exposes

The associated paper [1] summarises the information revealed by Signal succinctly: The Signal messenger is primarily focused on user privacy, and thus exposes almost no information about users through the contact discovery service. The only information available about registered users is their ability to receive voice and video calls. It is also possible to retrieve the encrypted profile picture of registered users through a separate API call,if they have set any. However, user name and avatar can only be decrypted if the user has consented to this explicitly for the user requesting the information and has exchanged at least one message with them. So Signal comes out excellently from this, yet is mentioned in the title. However, the paper does find that Telegram reveals to the world, in real time, exactly how many Telegram users have a particular phone number in their address book... Can we change the title from the (click baiting) university press release to one which more accurately reflects the content of the paper? [1] https://encrypto.de/papers/HWSDS21.pdf https://encrypto.de/papers/HWSDS21.pdf

drummer 6y ago
Yeah definitely agree; they probably inluded Signal for the clickbait.
ignoramous 6y ago
From TFA, here's the damning telegram bit: For Telegram, the researchers found that its contact discovery service exposes sensitive information even about owners of phone numbers who are not registered with the service. For Signal, TFA makes it clear that correlation defeats Signal's privacy measures: Interestingly, 40% of Signal users, which can be assumed to be more privacy concerned in general, are also using WhatsApp, and every other of those Signal users has a public profile picture on WhatsApp. Tracking such data over time enables attackers to build accurate behavior models. When the data is matched across social networks and public data sources, third parties can also build detailed profiles, for example to scam users. ... More privacy-concerned messengers like Signal transfer only short cryptographic hash values of phone numbers or rely on trusted hardware. However, the research team shows that with new and optimized attack strategies, the low entropy of phone numbers enables attackers to deduce corresponding phone numbers from cryptographic hashes within milliseconds. It is hard to say how Signal can improve upon these attacks other than to not use phone numbers at all.
- TimSchumann 6y ago
  > It is hard to say how Signal can improve upon these attacks other than to not use phone numbers at all. I think it would be wonderful if you could use signal without a phone number. I wonder if there is a technical reason they don’t implement this, as it sure seems like it would only have benefits for users privacy and security.
  - raspyberr 6y ago
    If you follow in the forums (https://whispersystems.discoursehosting.net/ https://whispersystems.discoursehosting.net/) it is slowly happening. Signal will eventually not require phone numbers.
    - jkepler 6y ago
      That would be great, as I would like to unify my Signal correspondence but its currently split between two phone numbers.
  - Vinnl 6y ago
    They're working on it: https://mobile.twitter.com/moxie/status/1281353119369097217 https://mobile.twitter.com/moxie/status/1281353119369097217 As I understand it, the challenge is to do it in a privacy-friendly way, since your contact list of phone numbers is on your phone, but this has to live on Signal's servers.
    - em-bee 6y ago
      why does it have to live on the signal servers? the signal client could store its contacts locally just as well.
      - thekyle 6y ago
        Because then if you lose your phone you lose both your contacts and messages. Right now you only lose your messages.
DyslexicAtheist 6y ago
I think Signal's necessity of tying the user to the phone number is where it could be improved. Signal could take a lesson from Wireapp which allows setting up a pseudonym so when connecting to another user I do not automatically have to share my phone number with them. ... e.g. if I want to make my phone number not be a problem, then I need a burner (or get burned). which is another step for the user. Depends on the threat-model if this is an issue I suppose. Telegram so far never had an independent audit of its crypto or maybe I'm wrong?
- bigiain 6y ago
  I'm pretty sure Moxie knew the upsides and downsides to using telephone numbers - and explicitly chose the alternative that maximised network effects over the one that maximised privacy. I suspect now there's (probably?) a large enough Signal network too self-sustain, and they can (and are) condsider allowing non-phone-number users to exists on their platform. I'm not sure they made the compromises and decisions the way I would have preferred them, but their e2e secure messenger platform is way more ubiquitous than mine (which I never wrote), so in spite of that, I reckon they've done more to "make the world a better place" than I have... (I do still get mad everytime Signal tells me "Some random or friend who's phone number you saved sometime in the last decade or so is now using Signal!" I'm 99% certain none of those people knew I was going to see that message when they installed/configured their "super private e2e encrypted messenger app!!!")
mahemm 6y ago
This is the exact sort of thing that allows people to think that things like Telegram are acceptable equivalents to Signal instead of disastrously poor imitators. It's a shame the discourse around secure messengers has become so polluted.
- jk700 6y ago
  In the paper they were still able to cover 100% of US numbers for Signal and discover all of its users, but less than 0.02% for Telegram and discover only 908 of its users due to simple rate limits, how is Signal better at this exactly? On top of that the paper purposely chose unrealistic threat models and assumptions about privacy, as if letting other people know your phone number is somehow acceptable for privacy in the first place (it isn't and never was).
  - ThePowerOfFuet 6y ago
    Rate limits are trivial to skirt with rented botnets. Some "Free VPN" apps allow inbound traffic from paying clients to be redirected out to the internet.
- Dahoon 6y ago
  How is user discovery of Telegram at 0.02% worse than Signal at 100%? It isn't like they could possible get it any higher and Telegram's couldn't get much lower. People who know what they are talking about have been critical of Signals use of phone numbers since the start but Signal have always brushed it off as irrelevant.
dang 6y ago
Ok, we've changed the URL to that from https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/einzelansicht_271872.en.jsp https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen..., and the title accordingly. Thanks!

drummer 6y ago

Yeah definitely agree; they probably inluded Signal for the clickbait.

ignoramous 6y ago

From TFA, here's the damning telegram bit: For Telegram, the researchers found that its contact discovery service exposes sensitive information even about owners of phone numbers who are not registered with the service. For Signal, TFA makes it clear that correlation defeats Signal's privacy measures: Interestingly, 40% of Signal users, which can be assumed to be more privacy concerned in general, are also using WhatsApp, and every other of those Signal users has a public profile picture on WhatsApp. Tracking such data over time enables attackers to build accurate behavior models. When the data is matched across social networks and public data sources, third parties can also build detailed profiles, for example to scam users. ... More privacy-concerned messengers like Signal transfer only short cryptographic hash values of phone numbers or rely on trusted hardware. However, the research team shows that with new and optimized attack strategies, the low entropy of phone numbers enables attackers to deduce corresponding phone numbers from cryptographic hashes within milliseconds. It is hard to say how Signal can improve upon these attacks other than to not use phone numbers at all.

TimSchumann 6y ago
> It is hard to say how Signal can improve upon these attacks other than to not use phone numbers at all. I think it would be wonderful if you could use signal without a phone number. I wonder if there is a technical reason they don’t implement this, as it sure seems like it would only have benefits for users privacy and security.
- raspyberr 6y ago
  If you follow in the forums (https://whispersystems.discoursehosting.net/ https://whispersystems.discoursehosting.net/) it is slowly happening. Signal will eventually not require phone numbers.
  - jkepler 6y ago
    That would be great, as I would like to unify my Signal correspondence but its currently split between two phone numbers.
- Vinnl 6y ago
  They're working on it: https://mobile.twitter.com/moxie/status/1281353119369097217 https://mobile.twitter.com/moxie/status/1281353119369097217 As I understand it, the challenge is to do it in a privacy-friendly way, since your contact list of phone numbers is on your phone, but this has to live on Signal's servers.
  - em-bee 6y ago
    why does it have to live on the signal servers? the signal client could store its contacts locally just as well.
    - thekyle 6y ago
      Because then if you lose your phone you lose both your contacts and messages. Right now you only lose your messages.

DyslexicAtheist 6y ago

I think Signal's necessity of tying the user to the phone number is where it could be improved. Signal could take a lesson from Wireapp which allows setting up a pseudonym so when connecting to another user I do not automatically have to share my phone number with them. ... e.g. if I want to make my phone number not be a problem, then I need a burner (or get burned). which is another step for the user. Depends on the threat-model if this is an issue I suppose. Telegram so far never had an independent audit of its crypto or maybe I'm wrong?

bigiain 6y ago
I'm pretty sure Moxie knew the upsides and downsides to using telephone numbers - and explicitly chose the alternative that maximised network effects over the one that maximised privacy. I suspect now there's (probably?) a large enough Signal network too self-sustain, and they can (and are) condsider allowing non-phone-number users to exists on their platform. I'm not sure they made the compromises and decisions the way I would have preferred them, but their e2e secure messenger platform is way more ubiquitous than mine (which I never wrote), so in spite of that, I reckon they've done more to "make the world a better place" than I have... (I do still get mad everytime Signal tells me "Some random or friend who's phone number you saved sometime in the last decade or so is now using Signal!" I'm 99% certain none of those people knew I was going to see that message when they installed/configured their "super private e2e encrypted messenger app!!!")

mahemm 6y ago

This is the exact sort of thing that allows people to think that things like Telegram are acceptable equivalents to Signal instead of disastrously poor imitators. It's a shame the discourse around secure messengers has become so polluted.

jk700 6y ago
In the paper they were still able to cover 100% of US numbers for Signal and discover all of its users, but less than 0.02% for Telegram and discover only 908 of its users due to simple rate limits, how is Signal better at this exactly? On top of that the paper purposely chose unrealistic threat models and assumptions about privacy, as if letting other people know your phone number is somehow acceptable for privacy in the first place (it isn't and never was).
- ThePowerOfFuet 6y ago
  Rate limits are trivial to skirt with rented botnets. Some "Free VPN" apps allow inbound traffic from paying clients to be redirected out to the internet.
Dahoon 6y ago
How is user discovery of Telegram at 0.02% worse than Signal at 100%? It isn't like they could possible get it any higher and Telegram's couldn't get much lower. People who know what they are talking about have been critical of Signals use of phone numbers since the start but Signal have always brushed it off as irrelevant.

dang 6y ago

Ok, we've changed the URL to that from https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/einzelansicht_271872.en.jsp https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen..., and the title accordingly. Thanks!