[Serusers] encryption on authorization

Hi there, In a REGISTER case there is a HeaderField AUTHORIZATION. The usual encryption algorithm is "MD5". Is it possible to REGISTER without any encryption? Please give a statement if I understood everything right or correct me: Digest Username => not encrypted; realm =>not encrypted; URI =>not encrypted; Nonce => encrypted => is Password? Response => encrypted => what´s that? Thanks! P.S.: I sniffered the network traffic when I registerd,established a VoIP-Connection and ended my call. Etherreal, the snifferprogramm, does understand SIP and SDP so I could easy protocol and understand what was going on.