[SIPForum-discussion] Authentication of the called party...

[Baniel Uri-CUB001]

Hi. I have bumped into Question #19 from
http://www.sipknowledge.com/SIP_Dev_Expert_Exam_Linked_from_most_wanted_
42.htm.
They ask there about possible cases when SIP client may get
authenticated by a server. 
 
This makes me wonder: There does not seem to be a current way to
authenticate a called party by a proxy right? (as the proxy-authenticate
header may be used only in 4xx responses but not in INVITE), so we need
to trust the registrar that it fulfilled its authentication job. But
what if we like to keep registration interval very large (e.g. for sake
of saving battery's life, keeping network quiet)? How can one make sure
the security of the phone was not compromised at the meantime?
 
-uri
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