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SIP issues with S/MIME and CMS

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

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SIP issues with S/MIME and CMS

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

  2. 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 + email) • INVITE sip:rohan@cisco.com SIP/2.0 • SIP/2.0 200 OK / 404 Not Found / etc... • carries direct or indirect MIME content

  3. 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 SIP signaling media (ex: RTP audio, game, chat)

  4. 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)

  5. 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.

  6. What does SIP communitywant 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?

  7. 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 • http://www.softarmor.com/sipwg/ • http://www.softarmor.com/sipping/

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