Questions

I have a few questions regarding the system of Signal (excpecially the background of it). I have read the Signal docs from https://signal.org/docs but couldn't find answers to these following questions: - How do Signal Users authenticate while communicating? (I don't mean the signature / verifying, but how does Signal know it the user authenticating and not someone else) - How far is Signal decentralized? Is it, not? If so, why and how? - What protocol does Signal use for messaging? HTTPS / TCP? UDP? something else?

Thank you for your help.