Trust Model Based Self-Organized Routing Protocol For Secure Ad Hoc Networks

Li XiaoqiCSE Department, CUHK29/04/2003

Outline

Introduction to Ad Hoc NetworksMotivation and Design GoalsTrust Model for Ad Hoc NetworksTrusted Self-Organized Routing ProtocolConclusionResearch Plan and Future Work

Now Come to:

Introduction to Ad Hoc NetworksMotivation and Design GoalsTrust Model for Ad Hoc NetworksTrusted Self-Organized Routing ProtocolResearch Plan and Future WorkConclusion

What is Ad Hoc Network

A kind of network without fixed infrastructure such as base stations or access points, which performs communications through wireless mediaWireless applications in:

Military OperationsDisaster ReliefMeeting Room Setup for ConferencePersonal Area Networking

Characteristics of Ad Hoc Networks

No fixed infrastructureEach node is a routerMulti-hop routing by nodes cooperationSelf-organization natureHigh mobilityProne to be attacked

Routing Protocols for Ad Hoc Networks

AODV:-Ad Hoc On-Demand Distance Vector Protocol

DSR:-The Dynamic Source Routing Protocol

DSDV: -Destination-Sequenced Distance Vector

Protocol

Overview of AODV

Discover routes when neededMainly two types of routing messages:

RREQ: Route RequestRREP: Route Reply

Fixed-length messagesOnly one mutable field: Hop Count

Route Discovery in AODV

Laptop

PDA

PDA

PDA

Laptop

Laptop

LaptopRREQ

RREPRREP

Broadcast

S

D

Now Come To:

Introduction to Ad Hoc NetworksMotivation and Design GoalsTrust Model for Ad Hoc NetworksTrusted Self-Organized Routing ProtocolConclusionResearch Plan and Future Work

Security Requirements in Ad Hoc Networks

ConfidentialityAuthenticityIntegrityAvailabilityNon-repudiationAccess Control

Attacks to Ad Hoc NetworksAttack Method Motivation/Result Influence to

Security Services

Eavesdropping Obtain contents of messages Loss of Confidentiality

Masquerading Impersonate good nodesRouting RedirectionRouting table poisoningRouting Loop, etc.

Loss of Authenticity

Modification Make a node denial of serviceObtain keys, etc.

Loss of Integrity

Tunneling Attract trafficRouting Redirection

Loss of Confidentiality and Availability

Flooding Denial of Service Loss of Availability

Dropping Destroy normal routing progress Loss of Non-reputation and Availability

Replaying/Delaying Destroy normal routing progressDestroy normal data transmission

Loss of Access Control and Integrity

Common Solutions for SecurityOften assume

A trusted authority to issue certificates.A centralized server to monitor the networks.A secret association between certain nodes.

DisadvantagesDestroy the self-organization nature of ad hoc networks.Limit the mobility of nodes.Single point of failureLess of efficiency and availability

Self-Organized Solutions for Security

PropertiesAuthenticate each other in a self-organized wayOften issue certificate of a public key by nodes cooperationOften need node monitoring mechanism

DisadvantagesNeed at least k neighbors to cooperateMonitoring mechanism is difficult to implement and is performance-consuming

Current Issues in Ad Hoc Networks

Lack of security considerationCentralized server or trusted third parties destroy the self-organization naturePure cryptographic solutions bring high overheadCurrent self-organized solutions lose flexibility

Our Solutions and Design GoalsDesign a suitable decentralized trust model that can be used for the security solutions of ad hoc networks.

Apply this trust model to design a flexible self-organized key management scheme.

Apply this trust model to design a secure and flexible self-organized routing protocol with lower overhead.

Demonstrate the principle of the trust model and the security advantages of the resulting ad hoc networks.

Now Come To:

Introduction to Ad Hoc NetworksMotivation and Design GoalsTrust Model for Ad Hoc NetworksTrusted Self-Organized Routing ProtocolResearch Plan and Future WorkConclusion

Trust Model for Ad Hoc Networks

Overview of trust theoryTrust is a basic aspect of human life.Trust is regarded as a measurable variable.Trust theory has been applied into the fields of E-Commerce

Organization of nodes in ad hoc networks is similar as human society

Apply trust theory to secure ad hoc networks

Previous Trust ModelsDirect and recommendation trust model

Continuous value to represent trust Basis of many other trust models

Recommendation protocol modelFocus on the exchange of trust information

Dempster-Shafer Theory based modelUpper and lower bound pair to represent trust Trust matrix to represent trust relationshipCombine two matrices using Dempster-Shafer theory

Previous Trust Models (Con’d)

Model using Fuzzy LogicTrust matrix to represent trust relationshipFuzzy logic to verify transactionsFuzzy logic to combine trust matrices

Model using Subjective LogicUse Opinion to represent trustOpinion includes belief, disbelief, uncertaintyCombine trust using subjective logic

Comparison of Trust Models

Single trust value vs. OpinionOpinion with belief, disbelief and uncertainty can express more information

Fuzzy logic vs. Subjective logicFuzzy logic operates on certain measures about fuzzy propositionsSubjective logic operates on uncertain measures about crisp propositions

Comparison of Trust Models (Con’d)

Shafer theory vs. Subjective logicBoth introduce uncertaintyNo need to set upper or lower bounds of trust described in Shafer theory

Design Issues of Trust Model

Definition of TrustRepresentation of TrustCombination of TrustExchange of Trust Information

Our Trust Model

Use ‘Opinion’ to define and represent trustCombine trust opinions using subjective logicDefine a trust recommendation protocol to exchange trust information

Definition and Representation of Trust

Opinion: a three-dimensional metricThe opinion about the trustworthiness of x, denoted by ωx , is the triple defined by:

b(x) represent belief: probability of believing x.d(x) represent disbelief: probability of disbelieving xu(x) represent uncertainty: probability of uncertainty about x’s trustworthiness

)(),(),( xuxdxbx

Definition and Representation of Trust (Con’d)

Property of Opinion:

b, d, u is in [0,1]b+d+u = 1

Opinion ωx

(0.4,0.1,0.5) can be represented in the right figure.

0 0

0 11

1

)5.0,1.0,4.0(x

0. 5

0. 1

0. 4

Disbelief

Uncertainty

Belief

Combination of Trust

Discounting Combination Combine trusts along one pathCombine

Consensus CombinationCombine trusts from several pathsCombine

)()(

)(CA

CB

BA

),()(

)(CBA

CB

CA

A C

B

A

C

B

An Example of Combining Trust

A want to know B’s trustworthiness

A B

N3

N2

N1

Trust Recommendation Protocol

Exchange trust informationThree types of message:

TREQ: Trust RequestTREP: Trust ReplyTWARN: Trust Warning

Message structure

T y p e Re q u e s to r Re co m m e n d e r Re co m m e n d e e O p in io n C la s s Ex p iry

Our Trust Model vs. Subjective Logic Trust Model

Simplify the representation of trust, which is more suitable for ad hoc networksPropose a trust recommendation protocol to exchange trust informationHandle the dynamic of trust which is not mentioned in subjective logic

Now Come To:

Introduction to Ad Hoc NetworksMotivation and Design GoalsTrust Model for Ad Hoc NetworksTrusted Self-Organized Routing ProtocolResearch Plan and Future WorkConclusion

Assumption of Our Trusted Routing Protocol

Ability to recover node’s neighbors.Reliability of broadcasting one-hop messages Uniqueness of node’s IDCapability of monitoring behaviors of one-hop neighbors Key management has been done before

Node ModelOne node has an opinion about othersEach node maintains a trust table. For Example, A’s trust table is:

Initial opinion of a node in others’ eyes is (0,0,1)

General Framework

Tr us t

R e c o m m e ndat i o n

P r o t o c o l

Trust M ode l

Tr us t

C o m bi nati o n

Al go r i t h m

Cr ypt o gr aphi c R o ut i ng D i s c o ve r y

and M ai nt e nan c e

Tr ust e d R o ut i ng Dis c o ve r y

an d M ai nt e nanc e

Tr us t

U pdati ng

AL go r i t h m

B as i c A O D V R o ut in g P r o t o c o l

Trus te d R outing P rotoc ol

Cryptographic Technologies

Use cryptographic schemes to do routing in the beginning of this networkAdopt ideas in SAODV [42]

Digital signature: authenticate the non-mutable fields of the messagesHash chains: secure the only mutable field ‘hop count’

Overview of Trusted Self-Organized Routing Protocol

Effective when trust relationships have been established among most nodesBased on AODV routing protocolCriteria to determine whether a node can be trusted or not is:

belief≥0.5, disbelief<0.5, uncertainty<0.5

Nodes cooperate to decide a opinion

Trusted Routing Discovery

S

N 1 N 2

N 3

T

R R E Q

R R E P

L in k s

Ro u tin g Re q u e s t: S : is su e s RREQ . N 1 : v e r if ie s o p in io n s N 1 S , N 1 T . N 2 : v e r if ie s o p in io n s N 2 N 1 , N 2 S , a n d N 2 T . N 3 : v e r if ie s o p in io n N 3 N 2 .

Ro u tin g Re p ly : N 3 : h a s ro u te e n tr y to T, th e n is su e s RREP. N 2 : v e r if ie s o p in io n N 2 N 3 . N 1 : v e r if ie s o p in io n N 1 N 2 . S : v e r if ie s o p in io n S N 1 .

Trust Update Algorithm

Each value in a opinion is logically divided into 5 levels. Every 0.25 is one level.Successful verification for ten times:

belief+=0.25, disbelief-=0.125, uncertainty-=0.125

Failed verification for each time:belief-=0.125, disbelief+=0.25, uncertainty-=0.125

No verification during expiry timebelief-=0.375, disbelief+=0.125, uncertainty+=0.25

Trust Update Algorithm (Con’d)

If in opinion A to B, belief<0 or disbelief>1

Opinion(AB) will be changed to (0,1,0) Node A broadcast this opinion using TWARN messageNeighbors will re-calculate the opinion using trust combination algorithmB will be denied from A’s communication

Trusted Key Management

Use trust model into key managementAdvantages:

Self-organizationFlexible: no limitation of at least k neighborsLower overhead

AnalysisPerformance is increased

No need to perform cryptographic calculations for every packet lower overhead

Security is enhancedCombination of trust model, cryptographic schemes and monitor mechanism

More reasonable and flexibleGood nodes who become bad will be denied from network eventuallyBad nodes who turn to good will be allowed accessing network again soon

Now Come To:

Introduction to Ad Hoc NetworksMotivation and Design GoalsTrust Model for Ad Hoc NetworksTrusted Self-Organized Routing ProtocolConclusionResearch Plan and Future Work

Conclusion

A promising idea to apply trust model to secure ad hoc networksNode uses ‘opinion’ to judge if another node is trustableNodes cooperate to obtain a more accurate opinionTrusted routing protocol is

Self-organizedLower-overhead More reasonable

More secure More flexible

Research Plan and Future Work

A better trust combination algorithmA better way to apply trust model into key managementStudy monitor or intrusion detection issuesImprove trusted routing protocol to make it prevent or stand more attacksA detailed simulation evaluation using NS-2 or Glomosim simulators

Q&A

Thank you !