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.