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TAODV: A Trust Model Based Routing Protocol for Secure Ad Hoc Networks
Xiaoqi Li, Michael R. Lyu, and Jiangchuan LiuIEEE Aerospace ConferenceMarch 2004
March 2004 CSE Dept. of CUHKPage 2
Outline
• Introduction• Background: AODV and Subjective
logic• Framework of TAODV• Trust model for TAODV• Routing operations in TAODV• Analysis• Conclusion and future work
March 2004 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
March 2004 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
March 2004 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
March 2004 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
March 2004 CSE Dept. of CUHKPage 7
Framework of TAODV
March 2004 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
–
ABb
),,( AB
AB
AB
AB udb
ABdABu
1 AB
AB
AB udb
March 2004 CSE Dept. of CUHKPage 9
• Discounting Combination: – Combine trusts along one path– Combine
– Equation: Let
Trust Model for TAODV: Combination of trust
A C
B
)()(
)(CA
CB
BA
BC
AB
AB
AB
BC
AB
BC
AB
ABC
ABC
ABC
ubud
db
bb
u
d
b
),,( ABC
ABC
ABC
ABC udb
March 2004 CSE Dept. of CUHKPage 10
Trust Model for TAODV: Combination of trust
• Consensus Combination: – Combine trusts from several paths– Combine
– Equation: Let
),()(
)(CBA
CB
CA
B
C
A
C
B
C
A
Cuuuukwhere
BC
AC
AC
BC
BC
AC
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AC
BAC
BAC
BAC
kuu
kudud
kubub
u
d
b
2
,
,
,
,
/)(
/)(
/)(
),,( ,,,, BAC
BAC
BAC
BAC udb
A
C
B
March 2004 CSE Dept. of CUHKPage 11
• Mapping from evidence space to opinion space:
– p : positive evidences– n : negative evidences
Trust Model for TAODV: Mapping from evidences to opinion space
0,
2
22
2
AB
np
np
nnp
p
AB
AB
AB
uwhere
u
d
b
March 2004 CSE Dept. of CUHKPage 12
Routing Operations in TAODV
• Trust Recommendation• Trust Judgement• Routing Table Extension• Trust Update• Routing Messages Extensions• Trusted Routing Discovery
March 2004 CSE Dept. of CUHKPage 13
Trust Recommendation• Exchange trust information• Three types of message:
– TREQ: Trust REQuest– TREP: Trust REPly– TWARN: Trust WARNing
• Broadcast TWARN when a node’s disbelief value is zero
• Message structure:
March 2004 CSE Dept. of CUHKPage 14
Trust Judgement
• Predefined trust judging rules
b d u Actions>0.5 Request and verify digital
signature
>0.5 Distrust a node for an expire time
>0.5 Trust a node and continue routing
≤0.5 ≤0.5 ≤0.5 Request and verify digital signature
b – belief d – disbelief u – uncertainty 0.5 – threshold
March 2004 CSE Dept. of CUHKPage 15
Routing Table Extension
• Add three fields into original routing table– Positive events– Negative events– Opinion
• New routing table formatDestIP DestSe
q...
HopCount
..
.Lifetime Positiv
eEvents
NegativeEvents
Opinion
March 2004 CSE Dept. of CUHKPage 16
Trust Update
• Update of Evidences– Successful Communication Positive
events: p++– Failed Communication Negative events: n++
• Update of opinion - two ways: – Mapping from evidence space– Combination from different
recommendations
March 2004 CSE Dept. of CUHKPage 17
Trusted Routing Discovery: Scenario I-Beginning of TAODV
• Initial opinions are all (0,0,1)• Node A originates a RREQ to discover a route to C• Node B will authenticate A and C because of high
uncertainty (u=1) of them from its point of view• Finally, if succeeds, the opinions are all changed
to (0.33,0,0.67)
March 2004 CSE Dept. of CUHKPage 18
Trusted Routing Discovery: Scenario II-A Stable TAODV MANET
• Trust relationships have been established among almost all the nodes
• The values of uncertainty are getting smaller and smaller
• The general procedures are as follows. (e.g. N2)
March 2004 CSE Dept. of CUHKPage 19
Trusted Routing Discovery: Scenario II-A Stable TAODV MANET
March 2004 CSE Dept. of CUHKPage 20
Analysis
• Performance– No need to perform cryptographic
computations in every packet reducing computation overhead
– Trust recommendation messages and routing table extension are simple no introducing much routing overhead
March 2004 CSE Dept. of CUHKPage 21
Analysis
• Security – A malicious node will be finally denied
from the network and it’s opinion from other nodes will be (0,1,0).
– When a bad node turns to be a good one, it’s opinion in others will be changed from (0,1,0) to (0,0,1) after expiry.
March 2004 CSE Dept. of CUHKPage 22
Analysis
• Flexibility– Each node is given more flexibility to
define its own opinion threshold.– The default threshold is 0.5.– For high level security requirement,
the threshold can be increased.– For some non-critical applications, the
threshold can be decreased.
March 2004 CSE Dept. of CUHKPage 23
Conclusion
• First approach to apply the idea of trust model into the security solutions of MANETs.
• The trust among nodes can be quantified and combined.
• TAODV is a secure routing protocol with– Less computation overheads – Not introducing much routing overheads– Flexible security levels
March 2004 CSE Dept. of CUHKPage 24
Future Work
• Optimize trusted routing discovery algorithm
• Establish fast response mechanism when being attacked
• Perform detailed simulation evaluation