Privacy-preserving contact discovery and obfuscation of a message's metadata (what Tor can be used for) are pretty much orthogonal issues: The first case is ab

Privacy-preserving contact discovery and obfuscation of a message's metadata (what Tor can be used for) are pretty much orthogonal issues: The first case is about finding out who of your contacts uses Signal, too. The way it's done in Signal right now is described here: https://whispersystems.org/blog/contact-discovery/ https://whispersystems.org/blog/contact-discovery/. The second problem is about whether anyone gets to see who is sending messages to whom, e.g. by tapping the wires or running the central server all messages are being routed through (for instance, Signal uses such a server). In both cases, your social network might get get exposed depending on what data is exposed exactly (IP addresses, pseudonyms, …) and what the attacker can infer from it (your name / home address?). Let me know if that helps.