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SIP Security & the Future of VoIP

This paper discusses the threats to SIP security, the existing problems with the protocol, attempted solutions, and a comparison with Skype. It also explores possible solutions and the need for a combination of approaches to secure SIP.

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SIP Security & the Future of VoIP

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  1. SIP Security & the Future of VoIP • Nate Klingenstein • APAN 26 Queenstown • August 5, 2008 http://people.internet2.edu/ ~ndk/apanSIP.pdf

  2. Securing SIP • The threats • The existing protocol’s problems • Attempted solutions • Skype for comparison • Next steps

  3. The Threat Model • A lot like any other network application’s problems • Denial-of-Service (DoS) attacks • Eavesdropping / Man in the Middle • Spoofing, replay, spam (SPIT) • Poor authentication, authorization • Demonstrated attacks

  4. Are these threats hypothetical? • Security must always be pragmatic and proportional • http://www.loria.fr/~nassar/readme.html • http://www.voipsa.org/Resources/tools.php • Human faces and voice recognition do provide limited authentication & protection

  5. Enterprise Middleware • Many universities and companies manage information about their members • Directories, databases • Applications use these data for better security, auditing, user services • Large benefits for enterprise webapps

  6. Specific Problems • Authentication: HTTP digest, basic • Realm-specific • Traffic unencrypted • Trust between realms and proxies poor • Disconnected from identity management infrastructure

  7. Possible Solutions • Look a lot like the solutions for other old protocols: • Hack security into an old protocol • Firewall everything • Accept that SIP is too difficult to secure

  8. Security Attempts • Many tries with varying success • New RFC’s, internet-drafts • Integration with RADIUS, TLS authentication • Integration with directories • Improved deployment practices

  9. Inter-Realm SIP SIP Proxy Bob on a desktop With a SIP VC-UA Alice on a desktop With a SIP VC-UA SIP Proxy INVITE If Bob is valid, Forward INVITE Realm CGU.EDU Can I trust you? Realm: Microsoft.com Sure, I belong to the same club Invite from Bob 180 Ringing 180 Ringing 180 Ringing 200 OK SURA/ViDe 4th Annual Workshop

  10. SAML + SIP • Attempt to fix three major problems • Authentication methods • Realm trust • Connection to infrastructure • internet-drafts were written to make a SAML MIME on the invite, but failed

  11. Firewall Everything • Private networks • VPN • IDS/IPS • TLS/IPSec • Dedicated hardware devices • STUN & TURN

  12. Issues with Firewall Everything • Cross-realm trust not addressed • Possibly multiple interfaces and/or devices with private network • One more step towards Internet quarantine...

  13. Securing SIP • A combination of approaches is necessary • Network-level protection • Federated trust • Middleware integration • Phones and other hardware make modification more difficult

  14. VoIP Higher Ed Security Survey Which VoIP Securitymechanisms do[n’t] you use? • Use of IPS between VoIP network and data IP network. • Use of IDS between VoIP network and data IP network. • Use NAC (network access control) such as 802.1X and RADIUS to authenticate hard phones. • Softphones require the use of the separate VoIP network (physical LAN, VLAN, subnet address, etc.) from the data IP network. • Softphones are allowed with IPSEC transport mode. • Softphones are allowed with IPSEC VPNs. • Use NAC (network access control) such as 802.1X and RADIUS to authenticate hard phones. • Allow NAT traversal via STUN or TURN Internet proxies. • Provide separate dedicated bandwidth for VoIP traffic to the Internet.

  15. VoIP Higher Ed Security Survey

  16. The Skype Model • Proprietary, decentralized protocol • RC4 encryption • Firewall and NAT detection, agility • Central login server, hashed • SIP used by SkypeOut/SkypeIn with PSTN interconnections; gateways to SIP phones

  17. Can SIP Learn from Skype? • TLS/IPSec offer good encryption • Authentication over TLS (digest/PKI/SAML) is good • Bandwidth, centralization not big problems • The world has no central login server • Cross-domain trust not solved

  18. Conclusions • SIP needs a lot of attention to be secure • Existing ideas can address some shortcomings • Some efforts stopped • No central work combining all efforts • Some attacks don’t have cost-effective solutions

  19. Questions? • http://www.internet2.edu/sip.edu/ • ndk@internet2.edu

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