> If x has me on the list and I have x on the list, how can our two Signal apps discover that? Without telling the Signal server, and without telling random thi

> If x has me on the list and I have x on the list, how can our two Signal apps discover that? Without telling the Signal server, and without telling random third parties? Take a look at the protocol documented in https://news.ycombinator.com/item?id=11289223 https://news.ycombinator.com/item?id=11289223 It's secure against an honest server and a malicious person, and against a dishonest server; it's insecure against a colluding server and person.