The Signal protocol does not require a phone number or any other PII. This is what has been "proven secure". The Signal app is a messaging platform built on th

The Signal protocol does not require a phone number or any other PII. This is what has been "proven secure". The Signal app is a messaging platform built on this protocol by the same developers. That is what requires a phone number. Anyone can build their own messenger using the Signal protocol and use whatever means of authentication they want. I think there is also a useful distinction between "anonymity" and "privacy". The protocol is capable of facilitating both. The Signal app itself primarily focused on just the latter. Signal knows who you are, at least in so far as they know a hash of your phone number. You are not totally anonymous to them. But they do not know what you are saying. Your interactions on their platform are private.