SIP issues with S/MIME and CMS Rohan Mahy SIP, SIPPING co-chair

Very Brief description of SIP Rendezvous protocol can “go direct” or use proxies/intermediaries register Contacts to an Address of Record discover appropriate Contacts setup sessions by exchanging offers and answers SIP-specific subscribes and notifies text-based (looks sorta like HTTP + ) –INVITE SIP/2.0 –SIP/ OK / 404 Not Found / etc... carries direct or indirect MIME content

State of SIP security Digest used for user authentication end-to-end or end-to-middle TLS used for hop-by-hop server authentication, encryption, integrity, and optional mutual auth (TLS with RSA, AES128_CBC, SHA1) optional IPsec for hop-by-hop encryption and integrity S/MIME for end-to-end encryption and integrity media (ex: RTP audio, game, chat) SIP signaling

Good reasons for Object security in SIP Verifying you are still talking to the same person you started talking with (even if they are otherwise anonymous) SIP for Instant Messaging SIP between telephone network devices 3rd-party identity assertions for folks you authenticated some other way (possibly on a per call basis)

History: SIP uses S/MIME Mar 1999: RFC-2543 (SIP) published as PS. specs PGP for end-to- end security. about 3 early implementations, none worked together (badly underspecified, lots of implicit behavior) Nov 2001: Numerous requests for Digest enhancements (including some body integrity stuff (see draft-undery-sip-auth-01.txt) Dec 2001: PGP Deprecated by SIP WG Jan 2002: IESG requests addition of S/MIME to SIP spec Feb/Jun 2002: RFC-3261 specs S/MIME for end-to-end security, provides much more motivational text, (ex: optional usage with self- signed certs), still underspecified Mar 2002: draft-peterson-sip-identity-00.txt adopted as WG item. Uses S/MIME for 3rd party assertion of identity. Oct 2002: draft-peterson-sip-smime-aes-00.txt proposes update/tighter spec of SIP S/MIME. Uses AES. Nov 2002: draft-mahy-sipping-smime-vs-digest-00.txt discusses shared-key signing issues.

What does SIP community want from S/MIME? Advice from the horse’s mouth Help with S/MIME/CMS implementations ;-) –not SIP community’s core competence to add stuff to S/MIME or CMS libraries Unification of end-to-end/end-to-middle authentication, or not… (we use Digest and S/MIME now) SIMPLE needs sessions of messages. should we use S/MIME for this? might need shared key authentication for this. Lots of stuff we want to do with 3rd party assertions: use signed “assertion” documents, or attribute certs, something else?

References RFC 3261 draft-ietf-sip-identity-00.txt draft-ietf-sip-authid-body-00.txt draft-mahy-sipping-smime-vs-digest-00.txt draft-peterson-sip-smime-aes-00.txt draft-ietf-sip-referredby-00.txt draft-ietf-sip-privacy-general-01.txt draft-undery-sip-auth-01.txt