TAODV: A Trust Model Based Routing Protocol for Secure Ad Hoc Networks

Li Xiaoqi, GiGiOctober 28, 2003

Oct. 28, 2003 CSE Dept. of CUHKPage 2

Outline

• Introduction• Background: Subjective logic and

AODV• Framework of TAODV• Trust model for TAODV• Routing operations in TAODV• Analysis• Conclusion and future work

Oct. 28, 2003 CSE Dept. of CUHKPage 3

Introduction to MANETs

• Mobile Ad Hoc Networks (MANETs)– No fixed infrastructure– Self-organized routing– Prone to be unstable and insecure

• Previous Secure Solutions for MANETs– Require each node to testify itself by

showing its digital signature at all times– Need a super-trusted third-party to provide

authentication

Oct. 28, 2003 CSE Dept. of CUHKPage 4

Introduction to TAODV

• Make use of trust relationships among nodes

• Need not request and verify signature at each time of communication, just like human society

• TAODV: a secure routing protocol based on trust model for MANET

Oct. 28, 2003 CSE Dept. of CUHKPage 5

Background: Subjective Logic

• Subjective logic– Represent trust relationship formally– Define how to combine different trust

information together– Map all kinds of evidences to trust

representation space

• We derive our trust model for TAODV from subjective logic

Oct. 28, 2003 CSE Dept. of CUHKPage 6

Background: AODV

• AODV– Ad Hoc On-Demand Distance Vector Rout

ing Protocol for MANETs– Two main routing messages:

• RREQ: Routing REQuest• RREP: Routing REPly

• We extend AODV by adding trust information into its routing messages

Oct. 28, 2003 CSE Dept. of CUHKPage 7

Framework of TAODV

Oct. 28, 2003 CSE Dept. of CUHKPage 8

Trust Model for TAODV: Representation of trust

• Use Opinion to represent trust:– A three-dimensional metric–

• -- Probability of node A believing in node B

• -- Probability of node A disbelieving in node B

• -- Probability of node A’s uncertainty about B

–

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1 AB

AB

AB udb

Oct. 28, 2003 CSE Dept. of CUHKPage 9

Trust Model for TAODV: Combination of trust

• Discounting Combination: – Combine trusts along one path– Combine

• Consensus Combination:– Combine trusts from several

paths– Combine

)()(

)(CA

CB

BA

),()(

)(CBA

CB

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A C

B

A

C

B

Oct. 28, 2003 CSE Dept. of CUHKPage 10

Trust Model for TAODV: Mapping from evidences to opinion space

• Mapping function:

– p : positive evidences– n : negative evidences

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Routing Operations in TAODV

• Trust Recommendation• Trust Judgement• Route Table Extension• Trust Update• Routing Messages Extensions• Trusted Routing Discovery

Oct. 28, 2003 CSE Dept. of CUHKPage 12

Trust Recommendation

• Exchange trust information• Two types of messages:

– TREQ: Trust REQuest– TREP: Trust REPly

• Message structure:

Oct. 28, 2003 CSE Dept. of CUHKPage 13

Message Structures of TREQ & TREP

TREQ TREP

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Trust Judgement

b d u Actions>0.5

Request and verify digital signature

>0.5

Distrust a node for an expiry time

>0.5

Trust a node and continue routing

≤0.5

≤0.5

≤0.5

Request and verify digital signatureb – belief d – disbelief u – uncertainty 0.5 – threshold

Oct. 28, 2003 CSE Dept. of CUHKPage 15

Route Table Extension

• Add three fields into original route table– Positive events– Negative events– Opinion

• New route table format

DestIP

… NextHop

..

.State

Expiry

PositiveEvents

NegativeEvents

Opinion

Oct. 28, 2003 CSE Dept. of CUHKPage 16

Trust Update

• Update of Evidences– Successful Communication Positive events: p++

– Failed Communication Negative events: n++• Update of opinion

– Mapping from evidence space– Combination from different recommendations

• Update fashion– Periodical update if high packets frequency– On-demand update if lower packets frequency

Oct. 28, 2003 CSE Dept. of CUHKPage 17

Routing Messages Extensions

• Add trust information into original AODV routing messages

• RREQ TRREQ• RREP TRREP• Message structure:

Oct. 28, 2003 CSE Dept. of CUHKPage 18

Message Structures of TRREQ & TRREP

TRREQ TRREP

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• N receives TRREQ from N1. It will then perform such behaviors as follows:

1. Broadcast TREQ to request N1’s opinions2. Obtain trust recommendation from N2, N3, N4:

3. Combine these three opinions together into4. Judge the next behavior using trust judgment

criteria

Trusted Routing Discovery

S

N1

N2

N

N4

N3

DTRREQ TRREQ

N receives TRREQ from N1.It will performs such behaviors:

Oct. 28, 2003 CSE Dept. of CUHKPage 20

5. If uncertainty>threshold, N requests and verifies N1’s signature

6. If N1 passes trust authentication or signature authentication, N will rebroadcast TRREQ

7. If N1 does not pass any authentication, N will not trust N1 and drop this TRREQ

8. Update the value of opinion using trust update rules

Trusted Routing Discovery

S

N1

N2

N

N4

N3

DTRREQ TRREQ TRREQ

TRREQ TRREQ

TRREPTRREP

Oct. 28, 2003 CSE Dept. of CUHKPage 21

Analysis

• Computation overheads of each set of authentication operations– Cost of each set of trust operations is O(162v) (v is the no. of average neighbors)

– Cost of each set of signature operations is O(k3) (k is the length of signature)

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Analysis (con’d)• Number of authentication

operations when given a certain traffic volume.

E.g.: n routing messages– No. of signature operations: n– No. of trust operations:

•t – average packets interval•e – trust expiry time•U will never be larger than n

Oct. 28, 2003 CSE Dept. of CUHKPage 23

Analysis (con’d)

• Security – Combination of trust authentication

and signature authentication secure

– Combination of different recommendations objective

– Customization of trust threshold flexible

Oct. 28, 2003 CSE Dept. of CUHKPage 24

Conclusion and Future Work

• TAODV is a secure routing protocol with– Less computation overheads – Flexible security levels

• Optimize trusted routing discovery algorithm

• Establish fast response mechanism when being attacked

• Perform detailed simulation evaluation

Q&A

Thank You! Thank You!