It’s better now, but for years and years all they used for contact discovery was simple hashing… problem is the dataset is very small, and it was easy to generate a rainbow table of all the phone number hashes in a matter of hours. Then anyone with access to the hosts (either hackers, or the US state via AWS collaboration) had access to the entire social graph.
Yeah the way I remember it, they put a lot of effort into masking that social graph. That was a while back too, not recent.
What I’m saying though is that for the longest time they didn’t, and when they changed the technique they hardly acknowledge that it was a problem in the past and that essentially every users social graph had been compromised for years.
Signal, originally known as TextSecure, worked entirely over text messages when it first came out. It was borne from a different era and and securing communication data was the only immediate goal because at the time everything was basically viewable by anyone with enough admin rights on basically every platform. Signal helped popularize end-to-end encryption (E2EE) and dragged everyone else with them. Very few services at the time even advertised E2EE, private metadata or social graph privacy.
As they’ve improved the platform they continue to make incremental changes to enhance security. This is not a flaw, this is how progress is made.
