1. VoIP Information Security Issues in Voice Over Internet Protocol
Satya Bhan, Jonathan Clark, Joshua Cuneo, Jorge Mejia

2. Road Map of Presentation
Introduction and basics
Security threats in VoIP
Encryption algorithms for VoIP
Research and development of VoIP
Conclusions

3. What is VOIP? Voice Over Internet Protocol ARPANET - 1973
Dramatic rise in popularity
Mobile
Cheap
Accessible
Full of security holes

4. How VOIP Works Resolution of IP Address Analog-digital conversion
Parsed into RTP packets
Sent via UDP protocol
Extraction of data
(8)

5. How VOIP Works H.323 Protocol Umbrella standard
Terminals, gateways, gatekeepers, and multipoint control units (MCUs)
(8)

6. How VOIP Works SIP Protocol Location stored in a location server
Proxy server resolves location
Session Description Protocol (SDP) for logistics
(8)

7. Road Map of Presentation
Introduction and basics
Security threats in VoIP
Encryption algorithms for VoIP
Research and development of VoIP
Conclusions

8. VoIP Security Myth
“Security administrators assume that because digitized voice travels in packets, they can simply plug VoIP components into their already secured networks and get a stable and secure voice network”
- Walsh, T.J.; Kuhn, D.R

9. Why are existing protections unusable?
Most firewalls, Intrusion Detection Systems (IDS), Intrusion Prevention Systems (IPS) rely on deep packet inspection
Encryption adds overheads
Max tolerable packet delay is set to 150 ms

10. Denial of Service (DOS)
Most harmful attack – effects customers, Quality of Service (QoS), profits etc.
“Latency turns traditional security measures into double-edged swords for VoIP”
Walsh, T.J.; Kuhn, D.R

11. Denial of Service – Packet Loss
User Datagram Protocol (UDP)
Fast, Lightweight
Transmission/Order not guaranteed
Small payloads – 10 to 50 bytes
1% loss – unintelligible
5% loss - catastrophic, no matter how good the codec

12. Eavesdropping Public Switch Telephone Networks (PSTN) VoIP
Physical access harder & more detectable
Proprietary protocols
VoIP
Standardized protocols
Readily available tools to monitor network
Ethereal analyzer
Voice over misconfigured Internet telephones (VOMIT)

13. Eavesdropping User software available freely for download
Using Cache-poisoning distribute hacked upgrades
Man-in-the-middle attacks
Rogue server with modified configuration files containing the IP addresses of call managers
Victims’ calls are then routed through the attacker’s call manager

14. Spoofing Identity management complicated Spoof caller’s identification
No physical device
Universal Reference Identification (URI)
Spoofing available on multiple layers (ip, mac)
Spoof caller’s identification
Attacker calls regular phone line
Flash over using 3 way calling, dial next party
First callee’s id or unknown displayed

15. Theft of Service Edwin Pena and Robert Moore VoIP fraud
Routed more than ten million calls through unsuspecting companies
Orchestrated a "brute force" attack to identify the prefixes needed to gain access to VoIP networks
Sold VoIP services cheap

16. Theft of Service Attackers gain access to VoIP networks
Security vulnerabilities in user’s software
Sniffing user accounts and passwords
Profitable attacks
Toll frauds, identity thefts etc.

17. Spam over Internet Telephony (SPIT)
“where there's a channel, there's a pitchman”
Pierce Reid, Qovia VP marketing
Mass advertisements over PSTN complex & costly

18. Spam over Internet Telephony (SPIT)
VoIP merges IT & PSTN
Easily accessible & cheap
unwanted voice messages will clog voice mail
Spam tools such as blacklists etc useless against SPIT
Session hijacking
Video conferences can be hijacked and advertisements shown instead
Similarly voice conversations disrupted by advertisements

19. Road Map of Presentation
Introduction and basics
Security threats in VoIP
Encryption algorithms for VoIP
Research and development of VoIP
Conclusions

20. PGPfone History Released in 1995
Never gained popularity due to lack of interest
Broadband was not widespread
Voice over IP was not popular
Intended more for point-to-point modem connections

21. PGPfone Motivations
Zimmermann believes in a right to privacy provided by the Constitution
Released in response to 1994 Digital Telephony law
“mandated that phone companies install remote wiretapping ports in their central office digital switches”
Says that while warrants were still necessary, a shift in policy could lead to privacy violations
NSA program to monitor without warrants

22. PGPfone Details Uses Diffie-Hellman for key generation
Keys generated from random prime numbers
Uses TripleDES, Blowfish, or CAST as ciphers
Symmetric for speed
Run in counter mode
Diffie-Hellman has vulnerability to man-in-the-middle attacks
Solved by using Short Authentication Strings

23. Secure Real-Time Transfer Protocol
Published in RFC 3711 in March 2004
Goal to create secure version of Real-Time Transfer Protocol
Ensure confidentiality and integrity of RTP packets
Provides “a framework that permits upgrading”
Allows protocol to upgrade to more secure ciphers in the future

24. Secure Real-Time Transfer Protocol
Key exchange is entirely defined in the RFC
Uses master key to generate keys
Number of keys generated by one master key is up to the user
Number of packets encrypted by one key can be set
Default cipher is Advanced Encryption Standard (AES)
Runs in counter mode by default
Keyed-Hashing for Message Authentication- Secure Hash Algorithm (HMAC-SHA1) used to ensure message authenticity

25. ZRTP Created by Phil Zimmermann
Title of RFC is “Extensions to RTP for Diffie-Hellman Key Agreement for SRTP”
Features:
Similar to PGPfone, but updated to run on top of new standards (RTP, SIP)
Backwards compatible with standard RTP
Does not rely on public key infrastructure (PKI)
Foils man-in-the-middle attacks in similar fashion to PGPfone
Adds “shared secret” for added protection

26. Zfone Also written by Phil Zimmermann Implementation of ZRTP
“Lets you turn your existing VoIP client into a secure phone”
Simply intercepts and filters RTP packets
If Zfone is not running on both sides it will simply revert to standard RTP
GUI to let you know if current call is secure
SDK to license for developers to integrate ZRTP into their applications

27. Skype Closed source and closed specification
Tom Berson's security analysis
Was allowed uninhibited access to the code and the engineers
Findings:
Skype uses only standard encryption techniques
All techniques are properly implemented
Uses a central server as public key infrastructure to authenticate messages
No backdoors or malware

28. Skype Concerns Closed does not always mean safe
Have to trust Skype when they say their software is secure
Single person, company sponsored analysis
Closed protocol makes it difficult to verify
Small Chinese company claims to have broken protocol
Will release software that connects to Skype network soon

29. Road Map of Presentation
Introduction and basics
Security threats in VoIP
Encryption algorithms for VoIP
Research and development of VoIP
Conclusions

30. Research and Development in VoIP Security
VoIP security is still a big question in the service
Many improvements are still possible
Collective effort needed by government, academia, and private companies

31. The 1st IEEE Workshop on VoIP Management and Security (2006)
Open workshop for researchers from any sector to improve state of security of VoIP
Projects to cover:
Locating SIP users
Monitoring VoIP networks
Intrusion Detection for VoIP

32. Lightweight Scheme for Locating Users: Goal/Motivation
Group of Georgia Tech Researchers (CoC)
Most important challenge in VoIP: Locate communicating parties via internet in secure and reliable way
Session Initialization Protocol (SIP) users are at risk because this technology is weak to attacks
Mainly, the Integrity of the mapping from SIP to contact address is critical

33. Is Session Initialization Protocol (SIP) Safe?
Terminal registers its contact address
Address stored in location services
During call initialization, caller finds server in DNS table
Callee’s server query location services for Address
(1)

34. Lightweight Scheme for Locating Users: Proposed Solution
Don’t use registrar services
Let SIP phone sign their own contact address bindings on behalf of their users
Verify identity through public keys
Have modified SIP infrastructure to distribute public keys

35. Solution Scheme to Interchange Public Keys
Initial Key exchange between 2 users
After the key exchange, communication follows through secure channel
This is only needed once
(1)

36. Monitoring VoIP Networks: Goal/Motivation
Researchers from NEC Japan
Goal: VoIP carriers should identify and separate legal from illegal traffic
Motivation: Stop SPAM over Internet Telephony (SPIT) from using network resources
Result: Prototype implemented to monitor traffic from Skype, SIP phones, Netmeeting

37. Monitoring VoIP Networks: Proposed Scheme/Prototype
Add time stamp to packets and measure size
Extract statistical data from the flow (I.e. payload)
Verification to check eavesdropping
Compare packet against known threats
Repeat the process and control the flow
(2)

38. Intrusion Detection and Prevention on SIP: Goal/motivation
Researchers from University of Pisa and Switzerland.
Goal: Use the same principles of network intrusion detection to provide security to VoIP networks
Motivation: Threats will move to VoIP
Results: Working prototype using Snort

39. Intrusion Detection and Prevention on SIP: Prototype
Tested successfully against a brute force generator
(3)

40. Road Map of Presentation
Introduction and basics
Security threats in VoIP
Encryption algorithms for VoIP
Research and development of VoIP
Conclusions

41. Conclusion Great effort to secure VOIP networks
Leadership efforts by companies and universities
Ideas both old and revolutionary
One solution: encryption
Speed
New, effective algorithms like ZRTP
Technology caught everybody by surprise
Encouraging future for VOIP

42. References
(1) Kong, L., Balasubramaniyan, V.B., and Ahamad, M. "A lightweight scheme for securely and reliably locating SIP users." IEEE Xplore. Georgia Tech Lib., Atlanta, GA. 12 July 2006 <
(2) Okabe, T., Kitamura, T., and Shizuno, T. "Statistical traffic identification method based on flow-level behavior for fair VoIP service." IEEE Xplore. Georgia Tech Lib., Atlanta, GA. 12 July 2006 <
(3) Niccolini, S. et al. "SIP intrusion detection and prevention: recommendations and prototype implementation." IEEE Xplore. Georgia Tech Lib., Atlanta, GA. 12 July 2006 <
(4) Zimmermann, Philip R. PGPfone Owner’s Manual. 8 July Phil’s Pretty Good Software. 13 July <ftp://ftp.pgpi.org/pub/pgp/pgpfone/manual/pgpfone10b7.pdf>.
(5) Baugher, M., et al. The Secure Real-time Protocol (SRTP). March The Internet Society. 13 July <
(6) ---, et al. ZRTP: Extensions to RTP for Diffie-Hellman Key Agreement for SRTP. 5 March The Internet Society. 13 July <
(7) Zfone Home Page. Phil Zimmermann & Associates. LLC 13 July <
(8) Kuhn, D. Richard, Thomas J. Walsh, Steffen Fries. United States. National Institute of Standards and Technology, Technology Administration, Department of Commerce. Security Considerations for Voice Over IP Systems. Gaithersburg, MD: NIST, 2005.

43. Questions?