On Data-Centric Trust Establishment in Ephemeral Ad Hoc Networks

Maxim Raya, Panos Papadimitratos, Virgil D. Gligor, Jean-Pierre Hubaux

INFOCOM 2008

Ephemeral networks

Definition• No prior associations• Short-lived contacts• Volatile environment• Example: VANET

Trust Properties• Trust in entities can be pre-

established• Reputation is hard to build• Trust in data is important

Trust establishment needs to be rethought

2

What is data trust?

Data Trust in Networks

• Packet forwarding• Security associations• Reputation

AM

B

Data disseminationInsufficientHard

4

Traditional ad hoc networks Ephemeral networks

Data Trust = Entity Trust Data Trust = F(Entity Trust, context)

Event-specific trust

Dynamic trust metricSecurity status

)),(( jkvf ),( jkl v )( kvs

)),(),),((),(( jkljkk vvfvsF

AC

B

M

General FrameworkTrust Computation

Weights (data-centric trust levels)

( )kv is the default trustworthiness

LocationTime

Event reports of type

from nodes jkv

jke

AC

B

M

General FrameworkEvidence Evaluation

( )jBF e

Decision Logic

Evidence Evaluation Output: Decision on Reported Event

Evidence

Event reportsof type

from nodes jkv

jke

( )jCF e ( )jMF e

Decision Logics (1)

• Most trusted report

Decision Logics (2)

• Most trusted report• Weighted voting

Decision Logics (3)

• Most trusted report• Weighted voting• Bayesian inference– Takes into account prior knowledge

Decision Logics (4)

• Most trusted report• Weighted voting• Bayesian inference• Dempster-Shafer Theory– probability is bounded by belief and plausibility– Uncertainty (lack of evidence) does not refute nor

support evidence

Decision Logics (4)

• Most trusted report• Weighted voting• Bayesian inference• Dempster-Shafer Theory

1( ) ( )

K

i k ik

bel m

11

basic belief assignment

( ) ( )ik i km F e trust level

eventreport on event

Decision Logics (4)

• Most trusted report• Weighted voting• Bayesian inference• Dempster-Shafer Theory

1 2, :

1 21 2

, :

( ) ( )

( ) ( )1 ( ) ( )

q r i

q r

q rq r

i iq r

q r

m m

m mm m

12

Dempster’s rule for combination:

1( ) ( )

K

i k ik

bel m

supporting evidence

conflicts

Case Study: VANET

13

Data Trust

Decision on event

Performance comparison

• MATLAB and ns2• 100 simulation runs• 95% confidence intervals• Broadcast environment

Effect of Data Trust (1)

Honest nodes (0.8) are more trustworthy than attackers (0.6)

Effect of Data Trust (2)

Honest nodes (0.6) are less trustworthy than attackers (0.8)

Effect of Uncertainty

Honest nodes (0.4) are more trustworthy than attackers (0.2)

Evolution in Time

Highway scenario; 50% of reports are false (received first);Honest nodes (0.8) are more trustworthy than attackers (0.6)

Conclusions

• Trust in traditional MANETs pertains exclusively to entities

• Data-centric trust is more representative and useful in ephemeral networks (e.g., VANETs)

• Several decision logics can be used, notably:– Bayesian inference if there is prior knowledge– Dempster-Shafer Theory if there is uncertainty

Effect of Prior Knowledge

10 nodes vs. 50 before