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Some Security Challenges for Mesh Networks

Jean-Pierre Hubaux

EPFL

Switzerland

Joint work with Imad Aad, Naouel Ben Salem, Levente Buttyan, Srdjan Capkun, Markus Jakobsson, and Maxim Raya

Funded by the MICS/Terminodes project, www.mics.org

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Some Security Challenges for Mesh Networks

Outline

1. Preventing greedy behavior at the MAC layer

2. Secure positioning

3. Cooperation between nodes

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1. Preventing greedy behavior at the MAC layer

Well-behaved node CheaterWell-behaved node

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IEEE 802.11 MAC – Brief reminder

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Misbehavior techniques – NAV

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Misbehavior techniques – DIFS

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Misbehavior techniques – Frame scrambling

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Misbehavior techniques – Backoff

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Solution 1

Detection and handling of MAC layer misbehavior in

wireless networks (Kyasanur and Vaidya, DSN 2003)

Idea: the receiver assigns backoff values to the sender

Detection: compares expected and observed backoffs

Correction: assigns penalty to the cheater

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Solution 2 DOMINO (Raya, Hubaux, and Aad, MobiSys 2004)

Idea: monitor the traffic and detect deviations by comparing average values of observed users

Detection tests: number of retransmissions, backoff, …

Features:

• Full standard compliance

• Needs to be implemented only at the Access Point

• Applicable to all CSMA/CA-based protocols

• Simple and efficient

The operator decides the amount of evidence required before taking action (in order e.g. to prevent false positives)

http://domino.epfl.ch

Game-theoretic study:M. Cagalj, S. Ganeriwal, I. Aad and J.-P. Hubaux"On Cheating in CSMA/CA Networks" Technical report No. IC/2004/27, February 2004

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Components of DOMINO

Consecutive backoff

Actual backoff

Maximum backoff: the maximum

should be close to CWmin - 1

Backoff manipulation

Comparison of the idle time after the

last ACK with DIFSTransmission before DIFS

Comparison of the declared and actual

NAV valuesOversized NAV

Number of retransmissionsFrame scrambling

Detection testCheating method

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DOMINO performance (ns-2 simulation)

Setting: uplink UDP traffic; 7 well-behaved stations + 1 cheating station;each point corresponds to 100 simulations of 10s each; confidence int: 95%

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2. Secure positioningBeing able to securely verify positions of devices can enable:

- Location-based access control- Detection of displacement of valuables- Detection of stealing- Monitoring and enforcement of policies (e.g., traffic monitoring)- Location-based charging - …

In multi-hop networks- Secure routing- Secure positioning- Secure data harvesting (sensor networks)- …

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Distance measurement by Time of Flight (ToF)

- Based on the speed of light (RF, Ir)

ts

A B(A and B are synchronized - ToF)

tr dABm=(tr-ts)c

ts

- Based on the speed of sound (Ultrasound)

(A and B are NOT synchronized – Round trip ToF)

tr dABm=(tr-ts-tprocB)c/2

ts

A B

tr(RF)

dABm=(tr(RF)-tr(US))s

ts

tstr(US)

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Attacks on RF and US ToF-based techniques

- Dishonest device: cheat on the time of sending (ts) or

time of reception (tr)

ts1. Overhear and jam

2. Replay with a delay Δt

A B(A and B are assumed

to be synchronised)

tr dABm=(tr-ts)c

ts

ts

B

tr+Δt

dABm=(tr+Δt-ts)cts+Δt

M

=> dABm>dAB

- Malicious attacker: 2 steps:

M

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Summary of possible attacks on distance measurement

Malicious attackers

RSS (Received Signal Strength)

Distance enlargement and

reduction

Distance enlargement and

reduction

Ultrasound Time of Flight

Distance enlargement and

reduction

Distance enlargement and

reduction

Radio Time of Flight

Distance enlargement and

reduction

Distance enlargement only

Dishonest nodes

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Secure positioning

- Goals:

- preventing a dishonest node from cheating about its own position

- preventing a malicious attacker from spoofing the position of an

honest node

- Our proposal: Verifiable Multilateration

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Distance Bounding (RF)

ts

BS A

NBS

tr

- Introduced in 1993 by Brands and Chaum to prevent the Mafia fraud attack

ABS NN εt procA

dreal ≤ db = (tr-ts)c/2 (db=distance bound)

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Distance bounding characteristics

RSSDistance enlargement

and reduction Distance enlargement

and reduction

US ToFDistance enlargement

and reduction

Distance enlargement and

reduction

RF ToFDistance enlargement

and reductionDistance enlargement

only

RF Distance BoundingDistance enlargement

onlyDistance enlargement

only

US Distance BoundingDistance enlargement

onlyDistance enlargement

and reduction

Malicious attackersDishonest nodes- RF distance bounding:

- nanosecond precision required, 1ns ~ 30cm

- UWB enables clock precision up to 2ns and 1m

positioning indoor and outdoor (up to 2km) with RF ToF

- US distance bounding:

- millisecond precision required,1ms ~ 35cm

- distance bounding can be enabled with 802.11 and US

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Verifiable Multilateration (Trilateration)

x

y

(x,y)

BS1

BS2

BS3

Verification triangle

Distancebounding

A

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Verifiable Multilateration (properties 1/2)

- a malicious attacker cannot spoof the position of a node such that it seems that the node is at a position different from its real position within the triangle

- a node located within the triangle cannot prove to be at another position within the triangle except at its true position.

- a node located outside the triangle formed by the verifiers cannot prove to be at any position within the triangle

- a malicious attacker cannot spoof the position of a node such that it seems that it is located at a position within the triangle, if the node is outside the triangle

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Verifiable Multilateration (properties 2/2)

- a node can show (by distance enlargement) that it is positioned outside the triangle

- an attacker can always show that the node is positioned outside the triangle

• Srdjan Capkun and Jean-Pierre HubauxSecuring position and distance verification in wireless networks     Technical report EPFL/IC/2004-43, May 2004

• Srdjan Capkun and Jean-Pierre HubauxSecure Positioning in Sensor Networks     Technical report EPFL/IC/2004-44, May 2004

The same holds in 3-D, with a triangular pyramid instead of a triangleThe same holds in 3-D, with a triangular pyramid instead of a triangle

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• Multi-hop mesh networks represent a new and promising paradigm, but …

• No incentive the network does not work :V. Srinivasan, P. Nuggehalli, C. Chiasserini, and R. Rao, Infocom 2003M. Felegyhazi, L. Buttyan, and J. P. Hubaux, PWC 2003

Why would intermediate nodes bother to relay packets forthe benefit of other nodes?

3. Cooperation between nodes

• Autonomous multi-hop networks

R. Mahajan, M. Rodrig, D. Wetherhall, and J. Zahorjan,“Encouraging Cooperation in Multi-Hop Wireless Networks,” Technical Report CSE-04-06-01, Univ. of Washington, June 2004

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Incentive techniques: other scenarios

• Multi-hop networks with permanent access to the backbone

• Solution based on lottery tickets:M. Jakobsson, J.-P. Hubaux and L. Buttyan, "A Micro-Payment Scheme Encouraging Collaboration in Multi-HopCellular Networks", Financial Crypto 2003

• Systematic payment:N. Ben Salem, L. Buttyán, J.-P. Hubaux and  M. Jakobsson, "A Charging and Rewarding Scheme for Packet Forwarding in Multi-hop Cellular Networks", MobiHoc 2003

• Multi-hop networks with sporadic access to the backbone

S. Zhong, Y. R. Yang, and J. Chen, “Sprite: A Simple, Cheat-Proof, Credit-Based System for Mobile Ad Hoc Networks,” INFOCOM 2003

A i1 BSA Bj1BSB

Initiator

Correspondent

Backbone

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Conclusion

Mesh networks must be secured prior to any commercial deployment A number of research results from the security of

wireless (ad hoc) networks can be used or adapted, notably: To prevent greedy behavior To secure positioning To stimulate cooperation between nodes

There are more challenges, in particular: Preventing denial of service attacks Stimulation of the network deployment