Signal is finally bringing its secure messaging to the masses

Re:Signal is finally bringing its secure messaging to the ma... by gojomo on Friday February 14, 2020 @06:02PM (#22331315)

I don't see how account-based systems, or Wire in particular, must "effectively store[] a log of every pair of users that have spoken to each other on the platform, in a database, constantly available". As far as I can tell – and just like Signal – they just need to hold (destination-ID, blob) for all as-yet undelivered messages. And if the destination-ID isn't a phone-number, it's harder to correlated with other extant databases of (phone-number -> IMEI) or (phone-number -> person). That is, this undelivered-log has less metadata in an account-based system than a phone-number-based system.

I get that using the contact-lists, and the constant re-uploading of contact-lists, is great for Signal's bootstrapping. Anchoring IDs to phone numbers might also work as an abuse throttle.

But I don't see how it minimizes metadata. Can you clarify?

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Re:Signal is finally bringing its secure messaging to the ma... by tptacek on Friday February 14, 2020 @06:07PM (#22331362)

The contact graph isn't necessary to deliver messages, but it is necessary to make the system usable: when people open up the application, they expect to see a contact list. To make that feature work, most systems just store the contact list on the server; the aggregation of all those contact lists is the entire contact graph for the service. That's the thing Signal won't store.

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Re:Signal is finally bringing its secure messaging to the ma... by gojomo on Friday February 14, 2020 @07:02PM (#22331731)

Sure, it makes it more usable. (Though, I use Telegram & WhatsApp with many contacts just fine without sharing my contact list with them, neither once nor the repeated-uploads Signal wants.)

But Signal could still be keeping a database log of everyone who's actually ever sent a message to anyone else. (To the extent anyone's using 'sealed sender', it'd be harder – but apps like Wire could do something equivalent to 'sealed sender', too.) And that database is way more valuable to many attackers if it's keyed by the phone-numbers Signal has, compared to the aliases other systems have.

And to the extent the Signal client wants to keep re-uploading my entire contact-list, even a one-time, temporary compromise of their SGX-based system would reveal all my phone contacts.

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Re:Signal is finally bringing its secure messaging to the ma... by tptacek on Friday February 14, 2020 @07:13PM (#22331812)

The synchronized contact list feature of other messengers requires them to keep the contract graph stored. We don't have to wonder whether they're logging it; they have to be.

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