Sip security
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SIP Security. Henning Schulzrinne Columbia University. Priority security requirements. REGISTER protection authentication and integrity confidentiality (harder) DOS prevention for non-authenticated requests

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SIP Security

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Sip security

SIP Security

Henning Schulzrinne

Columbia University


Priority security requirements

Priority security requirements

  • REGISTER protection

    • authentication and integrity

    • confidentiality (harder)

  • DOS prevention for non-authenticated requests

    • authenticated requests already prevent DOS and amplification, but not realistic for INVITE

  • End-to-end authentication

    • for random clients (very hard)

    • for repeat visitors

  • End-to-end message confidentiality

52nd IETF SLC


Re using existing technology

Re-using existing technology

  • Options include:

    • Enhanced C/R (digest) authentication

    • IP DOS prevention

    • S/MIME

    • Shared secret via common infrastructure

    • Transport-layer security

  • Pointless to argue about which we don’t need – all have different strengths and weaknesses

  • Does not preclude new mechanisms

52nd IETF SLC


Enhanced digest

Enhanced digest

  • Protect selectable subset of headers

  • Minimal extension to Digest

  • Ease of implementation – trivial addition to existing Digest

  • No infrastructure

  • No privacy

  • REGISTER

52nd IETF SLC


Ip reachability security

IP-reachability security

  • DOSA prevention: Simply ensure that INVITE comes from valid IP address

  • Inherent in Digest, but not likely to be common for INVITE

  • Require guessing of large random number

  • Must be stateless in server

  • Options:

    • NULL authentication

    • Special Digest qop value

  • Does not prevent use as reflector

52nd IETF SLC


S mime

S/MIME

  • Existing solution, existing code

  • Treat SIP message like email attachment:

  • Content-Type: message/sip ???

  • Requires client certs?

    • What if ssh-style security is sufficient (same host as last time, but can’t prevent MiM for first attempt)

52nd IETF SLC


Shared secret

Shared secret

  • Avoid SIP-PGP mistakes:

    • canonical form

    • header ordering

    • special headers

  • SIP part is easy once infrastructure is assumed (CMS?)

52nd IETF SLC


Automating future trust

Automating future trust

  • Authentication not very helpful for random callers as long as identities are cheap – yes, it’s indeed [email protected]

  • Want to ensure subsequent call is from same person

  • D-H works except for active MiM – ssh has the same problem!

52nd IETF SLC


Transport layer security

Transport-layer security

  • TLS works for server authentication

    • Is this indeed sip.example.com?

  • Works well iff

    • number of peers small (some evidence in DNS measurements – Zipf distribution)

    • setup delay for new peers reasonable (need measurements!)

52nd IETF SLC


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