IETF RFC 2845 PDF

This protocol allows for transaction level authentication using shared secrets and one way hashing. It can be used to authenticate dynamic updates as coming from an approved client, or to authenticate responses as coming from an approved recursive name server.

No provision has been made here for distributing the shared secrets; it is expected that a network administrator will statically configure name servers and clients using some out of band mechanism such as sneaker-net until a secure automated mechanism for key distribution is available.