I understand that domain name registrars, for each domain they manage, register the authoritative name servers for that domain with its top-level root name server.
My question is: how do they do this? Is there a special protocol they use? How do top-level root name servers authenticate queries from registrars to change authoritative name servers for a given domain? Is that even public knowledge?
For example, say you own example.com. You want to change the authoritative name servers for it. You give your registrar the addresses of the new name servers. So far, so good. They, in turn, echo that change with the top-level root name server (the one responsible for .com). What protocol is used for the query from your registrar? How does that root name server authenticate it? How does it know it's legit?