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SIP Security Requirements Draft: Initial Review and Future Directions

The first cut of requirements for SIP security has been drafted, serving as a foundational document for future developments. A design team is in the process of being formed to expedite the completion of this initiative. While existing protocols will inform the baseline, necessary prioritization of requirements is essential. The draft aims to balance between basic protections while addressing significant threats, such as service theft and attacks from non-call participants. Discussion is ongoing about authentication mechanisms and evolving a robust SIP security framework.

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SIP Security Requirements Draft: Initial Review and Future Directions

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  1. SIP Security Michael Thomas Mat@cisco.com

  2. Status • First Cut of Requirements Draft • draft-thomas-sip-sec-reqt-00.txt • Will be basis going forward • Design team being formed • Should complete soon • Drafts which can meet all of the requirements will not be short term exercise • Prioritization of requirements needed

  3. bis Strawman • We have enough understanding of the current requirements that some prioritization can probably be made for bis • If we are to move bis along, the baseline must be fairly uncontroversial, be based on existing protocols, and address enough threats so that it is acceptable to IESG • But… there is also a strong desire for additional mechanisms and support for different authentication backends

  4. Two Paths • Choose a limited base set of protections offered by bis with the guarantee that we will have a standards track SIP security framework • We’re relatively close to coming to consensus here • Existing hop-by-hop crypto and legacy http mechanisms • Resolve future proofing questions • Open up discussions about what ought to be in bis baseline • No consensus • Many competing agendas • Many competing authentication mechanisms

  5. My Suggestion • In order to get bis to move forward soon, we have very few options • If we don’t care about moving forward, then an endless discussion is probably appropriate • The only real question is whether an unambitious baseline will pass muster • My sense is that it solves the most serious problems that SIP deployments currently face • Other mechanisms are oriented at enabling different authentication deployment scenarios; no single answer here, so it’s difficult to pick one anyway.

  6. The bis Baseline • Two principle threats: • Various attacks from non call participants • Theft of service attacks at a remote proxy/gateway • Full Message Crypto Solves 1st Threat • IPsec, TLS, App layer • HTTP Digest provides 2nd

  7. Transport Options • IPsec + Provides keying mechanism + TCP/SCTP/UDP friendly • Credential fetching API currently lacking • TLS + Provides keying mechanism + Good credential binding mechanism • No support for UDP; SCTP still being worked on • App Layer + Most flexible since it would be SIP-custom • No keying mechanism • No off the shelf solution which fits requirements

  8. UAC->Middle/UAS • HTTP Digest currently in Bis + Widely implemented • No concept of mutual authentication • No facility for multiple challenges • Key distribution undefined • Hacked on Digest + Quick and dirty - Unproven; not widely reviewed by right people • Side effects questionable - Not clear whether benefits fits into the 80/20 rule • New SIP-secure + Should solve these kinds of problems systematically - Needs to be fully fleshed out

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