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Ｐage <date> 1January 2008 - 1
Lawful Interception of VoIP in Highly Decentralised SystemsLawful Interception of VoIP in Highly Decentralised Systems
Jan Seedorf(jan.seedorf_at_nw.neclab.eu)
NEC Laboratories EuropeHeidelberg, Germany
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 2
Intention of the talk
• Give a technical overview on VoIP signalling without central components (P2PSIP) and current standardisation of P2PSIP in IETF
• Identify the implications on Lawful Interception of such a serverless / highly decentralised signalling approach
• Discuss possible solutions with respect to future standardisation
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 3
Outline
• Introduction: Lawful Interception of VoIP
• VoIP Signalling without Servers: P2P-SIP• Technical Implications of P2P Paradigm for Lawful
Interception of VoIP
• Possible Solutions and Standardisation Efforts
• Conclusion
Ｐage <date> 4January 2008 - 4
IntroductionLawful Interception of VoIP
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 5
Lawful Interception
• Lawful Interception• authorised wiretapping of communications carried out by law
enforcement organisations
• Some Terminology• LEA: Law Enforcement Agency• IRI: Intercept Related Information• CC: Content of Communication
• Standardisation• Handover Interfaces standardised by ETSI/TC LI
H1 – administrative informationH2 – Delivery of IRIH3 – Delivery of CC
• For more info see presentations on Lawful Interception from 1st & 2nd
ETSI security workshop
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 6
ETSI Reference Model for Lawful Interception
N W O/A P /S vP’sadm in istra tion
func tion
IR I m e dia tionfunc tion
C C m e dia tionfunc tion
N etw orkIn ternalFun ctions
IIF
IN I
inte rce pt re la tedinfo rma tion (IR I)
content o fc o m m u nica tion (C C )
LI handov er in terfa ce HI
H I1
H I2
H I3
LE M F
LEAdo m a inN W O /AP/Sv P ’s do m ain
ETSI TR 102 528
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 7
Challenges for Lawful Interception of VoIP
• Different Types of VoIP Service Architectures• Service Provider, Access Provider and Network Operator can
be different entities• Signalling (IRI) and media (CC) can take different routes
With a session border controller, signalling and media are fullycontrolled by the VoIP service providerWith a regular SIP proxy media packets do not necessarily traverse the server of the VoIP service providerStandard IETF SIP allows signalling to go directly between terminals once the SIP-Invite has reached the callee
• ConsequencesIRI and CC may be delivered by different entitiesNode (and entity) for intercepting the CC have to be determined in real-time from the IRI
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 8
ETSI Reference Model for LI in IP networks
LI Administration Function (AF)
Lawful Interception Mediation Function
(MF)
HI1
HI2
HI3
INI2
INI3
HI
INI1a
CCCI
LEA CSP DOMAIN
CCTI
Intercept Related Information Internal
Interception Function (IRI-IIF)
Content of Communication
Internal Interception Function (CC-IIF)
LEA Administration
Function
Law Enforcement Monitoring
Facility (LEMF)
Content of Communication Trigger Function
(CCTF)
INI1b INI1c
ETSI TR 102 528
Ｐage <date> 9January 2008 - 9
VoIP Signalling without Servers:P2P-SIP
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 10
P2P-SIP: how does it work technically?
• What is P2P-SIP?• Using a peer-to-peer network as a substrate for SIP user
registration and location lookup
• SIP registrations are not stored on a server but instead distributed in a P2P network at participating nodes• A scenario where we do not have any trust at all in the
registrar, becausearbitrary clients/terminals are storing registrationsResponsibility among nodes for registrations changes frequently
=> no pre-established trust between SIP-registrar and LEA possible
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 11
P2P-SIP: Basic Overview
Location Service
SIP Proxy
SIP Proxy
DNS Server
SIP Registrar
Central Components in SIP Signalling
27
2426
215
210212
89 88
65
55
31
Lookup Locationfor Bob’s SIP URI
P2P node(can be the user‘s SIP phone)
Hash of the SIP-URI = keyID
Content stored: Current location (IP-address) for
SIP-URI
Join DHT Join DHT
DHT
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 12
P2P-SIP: Registration and Location
5. Forward INVITE
?27
2426
215
210212
89 88
65
55
(1) Bob‘s node joins the DHT
(2) Alice‘s node joins the DHT
(3) Bob registers his URI with the DHT
(4) Alice wants to call Bob(5) DHT delivers the node
(+IP-address) responsible for Bob‘s URI to Alice (node 215)
(6) Alice contacts node 215 to get Bob‘s IP-address (without using the overlay)
(7) Alice and Bob negotiate parameters and set up their session directly(without using the overlay)
231
33
h(SIP:[email protected])= 206
206 Lookup(206)
Hash of the node‘s IP-address = nodeID
Content stored: Current location (IP-address) for
SIP-URI
Store(206)67
200
159
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 13
P2PSIP: IETF Standardisation
• P2PSIP is an official IETF working group:• “The Peer-to-Peer (P2P) Session Initiation Protocol working
group (P2PSIP WG) is chartered to develop protocols and mechanisms for the use of the Session Initiation Protocol (SIP) in settings where the service of establishing and managing sessions is principally handled by a collection of intelligent endpoints, rather than centralized servers as in SIP as currently deployed.” (http://www.ietf.org/html.charters/p2psip-charter.html)
• More info: http://www.p2psip.org/
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 14
P2PSIP: IETF work (only 2007)• V. Pascual Avila, M. Matuszewski, E. Shim, H. Zheng, P2PSIP Clients (November 2007) draft-pascual-p2psip-clients-00 (txt) • L Ch. Li, Y. Wang, Different types of nodes in P2PSIP (November 2007) draft-li-p2psip-node-types-00 (txt) • S. Baset, H. Schulzrinne, M. Matuszewski, Peer-to-Peer Protocol (P2PP) (November 2007) draft-baset-p2psip-p2pp-01 (txt) • J. Hautakorpi, G. Camarillo, J. Koskela, Utilizing HIP (Host Identity Protocol) for P2PSIP (Peer-to-peer Session Initiation Protocol) (November 2007) draft-hautakorpi-p2psip-with-hip-01 (txt) • C. Jennings, B. Lowekamp, E. Rescorla, J. Rosenberg, REsource LOcation And Discovery (RELOAD) (November 2007) draft-bryan-p2psip-reload-02 (txt) (html) • E. Marocco, E. Ivov, Extensible Peer Protocol (XPP) (November 2007) draft-marocco-p2psip-xpp-01 (txt) • E. Marocco, E. Ivov, XPP Extensions for Implementing a Passive P2PSIP Overlay Network based on the CAN Distributed Hash Table (November 2007) draft-marocco-p2psip-xpp-pcan-01 • L. Li, Ch. Zhang, Y. Wang, Y. Ji, A SIP-based P2PSIP Client Protocol (November 2007) draft-li-p2psip-client-protocol-00 (txt) • E. Cooper, A. Johnston, P. Matthews, An ID/Locator Architecture for P2PSIP (November 2007) draft-matthews-p2psip-id-loc-00 (txt) • I. Baumgart, Peer-to-Peer Name Service (P2PNS) (November 2007) draft-baumgart-p2psip-p2pns-00 (txt) • D. Bryan, E. Shim, B. Lowekamp, S. Dawkins, Ed., Application Scenarios for Peer-to-Peer Session Initiation Protocol (P2PSIP) (November 2007) draft-bryan-p2psip-app-scenarios-00 (txt) • XingFeng Jiang, HeWen Zheng, Service Extensible P2P Peer Protocol (November 2007) draft-jiang-p2psip-sep-00 (txt) • Hewen Zheng, Xingfeng Jiang, P2PSIP Client Protocol (October 2007) draft-zheng-p2psip-client-protocol-00 (txt) • S. Cirani, L. Veltri, A Kademlia-based DHT for Resource Lookup in P2PSIP (October 2007) draft-cirani-p2psip-dsip-dhtkademlia-00 (txt) • G. Garcia, P2PSIP bootstrapping using DNS-SD (October 2007) draft-garcia-p2psip-dns-sd-bootstrapping-00 (txt) • M. Matuszewski, J-E. Ekberg, and P. Laitinen, Security requirements in P2PSIP (July 2007) draft-matuszewski-p2psip-security-requirements-01 (txt) • B. Lowekamp and J. Deverick, Security Extensions for RELOAD (July 2007) draft-lowekamp-p2psip-reload-security-01 (txt) (html) • M. Stiemerling, M. Brunner, Peer-to-Peer SIP Implementation Report (July 2007) draft-stiemerling-p2psip-impl-01 (txt) • D. Bryan, E. Shim, and B. Lowekamp, Use Cases for Peer-to-Peer Session Initiation Protocol (July 2007) draft-bryan-p2psip-usecases-00 (txt) (html) • C. Jennings, J. Rosenberg, and E. Rescorla, Address Settlement by Peer to Peer (July 2007) draft-jennings-p2psip-asp-00 (txt) (html) • D. Bryan, S. Baset, M. Matuszewski, and H. Sinnreich, P2PSIP Protocol Framework and Requirements (June 2007) draft-bryan-p2psip-requirements-00 (txt) • E. Cooper, A. Johnston, and P. Matthews, A Distributed Transport Function in P2PSIP using HIP for Multi-Hop Overlay Routing (June 2007) draft-matthews-p2psip-hip-hop-00 (txt) (htm) • E. Cooper and P. Matthews, The Effect of NATs on P2P SIP Overlay Architecture (March 2007) draft-matthews-p2psip-nats-and-overlays-01 (txt) • E. Marocco and D. Bryan, Interworking between P2PSIP Overlays and Conventional SIP Networks (March 2007) draft-marocco-p2psip-interwork-01 (txt) (html) • H. Sinnreich - Ed., A. Johnston, E. Shim, and K. Singh, Simple SIP Usage Scenario for Applications in the Endpoints (March 2007) draft-sinnreich-sip-tools-01 (txt) (pdf) • D. Bryan, B. Lowekamp, and C. Jennings, dSIP: A P2P Approach to SIP Registration and Resource Location (February 2007) draft-bryan-p2psip-dsip-00 (txt) (html) • M. Zangrilli and D. Bryan, A Chord-based DHT for Resource Lookup in P2PSIP (February 2007) draft-zangrilli-p2psip-dsip-dhtchord-00 (txt) (html) • E. Cooper, P. Matthews, D. Bryan, and B. Lowekamp, NAT Traversal for dSIP (February 2007) draft-matthews-p2psip-dsip-nat-traversal-00 (txt) (html) • M. Zangrilli and D. Bryan, A Bamboo-based DHT for Resource Lookup in P2PSIP (February 2007) draft-zangrilli-p2psip-dsip-dhtbamboo-00 (txt) (html) • C. Jennings, Security Mechanisms for Peer to Peer SIP (February 2007) draft-jennings-p2psip-security-00 (txt) • XingFeng Jiang, The requirement of P2PSIP Peer protocol (February 2007) draft-jiang-p2psip-peer-protocol-requirement-00 (txt) • S. Baset and H. Schulzrinne, Peer-to-Peer Protocol (February 2007) draft-baset-p2psip-p2pcommon-01 (txt) (html) • E. Cooper, A. Johnston, and P. Matthews, Bootstrap Mechanisms for P2PSIP (February 2007) draft-matthews-p2psip-bootstrap-mechanisms-00 (txt) (html) • J. Hautakorpi and G. Camarillo, The Peer Protocol for P2PSIP Networks (February 2007) draft-hautakorpi-p2psip-peer-protocol-00 (txt)
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 15
IETF P2PSIP WG: Status Quo
• Many open issues• Architecture not clearly defined yet• Nat traversal / Routing• Security / Replication of SIP registrations
• What seems to be clear...• Signalling (after locating the callee through the overlay) and Call
Content (RTP) can go directly peer-to-peer• Central Enrollment Server, but only for node-ID assignment
To protect against virtual node-Ids (so-called Sybil-attacks) and chosen location attacksCentral authority is not on every signalling pathSpecifically, the enrollment server is not involved during call setup
Ｐage <date> 16January 2008 - 16
Technical Implications of P2P Paradigm for Lawful Interception of
VoIP
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 17
Challenges for LI imposed by P2P paradigm
• No server involved in call-setup• No central component on the signalling path• No static relationship between target identity and first
application-layer signalling hop
• Routing of signalling messages• Incoming and outgoing calls take different routes• The outgoing signalling “proxy” is different for every
callee
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 18
Challenges for LI imposed by P2P paradigm
• Distributed Hash Table is highly dynamic• The node responsible for storing the location of a SIP-URI
changes frequently• Overlay links in participating nodes change frequently
For the same callee the first signalling hop may be different with every call
• Mobility• User mobility already a problem in server-based SIP
signalling• Increased problem in P2PSIP because also mobility on
signalling layer
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 19
Challenges for LI imposed by P2P paradigm
• Service Provider may not be involved in signalling• Operator role in P2PSIP deployment not defined yet• Service provided may only cover enrollment (node-ID
assignment)• Registrations of users (identity/location bindings) are possibly
stored at end-users’ terminals• Signalling will not traverse proxies once a session has been
set upAfter call-setup, all signalling can go directly peer-to-peer
Ｐage <date> 20January 2008 - 20
Possible Solutions and Standardisation Efforts
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 21
Footprint in Terminals
• Suggested solution by some government agencies for Lawful Interception of VoIP / IP traffic in general
• Advantages• VoIP signalling and media are correlated in terminals
No need to trigger media interception from signalling interception • Mobility is not a problem if interception function is embedded
in the terminal• Would also help against encryption done in terminals
• Problems with P2PSIP:• May be a feasable solution for hardphones but hard to enforce
for open source softphones• With open standards, anybody can write software
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 22
Footprint in Devices
• Currently heavily discussed in Germany• http://www.bundestrojaner.net/
“Install the Bundestrojannow and get a
one-year subscriptionof free telephone surveillance“
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 23
Intercepting all IP traffic
• Intercept all IP packets at access network and filter SIP messages containing the target URI
• Problems• User mobility
the IP-address (and thus the access network) of the target may not be known prior to a callHow to correlate dynamically in real-time the triggering of CC interception?
• Encryption controlled by end-devicesIf users have a pre-shared key and encryption is end-to-end, CC cannot be retrieved
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 24
Infiltrating P2P network
• Intentionally place nodes controlled by the LEA in the P2P network• Log lookup requests and registration update messages• Perform location lookup on target identity frequently
• Approach pursued by the music industry to find illegal sharing of content in file-sharing P2P networks• Goal for music industry is simpler: find somebody who shares
music illegally• Goal for Lawful Interception: find a specific user• P2PSIP will be designed to make chosen-location attacks hard
For LI this would be exactly the goal: try to place a node at a specific location in the P2P network
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Conclusion
3rd ETSI Security Workshop, Sophia-Antipolis, 15-16 January 2008January 2008 - 26
Conclusions
• Future VoIP service architectures may lack central servers• P2PSIP is currently standardised by the IETF
• P2P paradigm imposes new challenges to Lawful Interception• Without a central component where (at least) signalling
traverses, Lawful Interception gets technically complex• Difficult to map ETSI reference model to P2P model
• Possible Solutions (that would need to be standardised) are• Footprint in devices• Interception at access network of target and dynamic
triggering of CC interception
