Matrix is looking good, but again not P2P only federated. This is why we are trying to do fully P2P end-to-end encryption like with https://hackernoon.com/so-you-want-to-build-a-p2p-twitter-wi... .
Notably, things we don’t have stored include anything about a user’s contacts (such as the contacts themselves, a hash of the contacts, any other derivative contact information), anything about a user’s groups (such as how many groups a user is in, which groups a user is in, the membership lists of a user’s groups), or any records of who a user has been communicating with.
All message contents are end to end encrypted, so we don’t have that information either.
I installed Signal a few days ago for the first time and there was definitely a prompt, with an easy way to skip it, before it did the find my friends thing.
The wording also seemed to indicate that only the hashes of the numbers would be uploaded but not sure if thats actually true.
Signal periodically sends truncated cryptographically hashed phone numbers for contact discovery. Names are never transmitted, and the information is not stored on the servers. The server responds with the contacts that are Signal users and then immediately discards this information. Your phone now knows which of your contacts is a Signal user and notifies you if your contact just started using Signal.
https://support.signal.org/hc/en-us/articles/115005045728-Do...