1. Trust- and Clustering-Based Authentication Service in Mobile Ad Hoc Networks Presented by Edith Ngai 28 October 2003

2. 2 Introduction A mobile ad hoc network (MANET) is a collection of nodes with no infrastructure Connected with wireless communication Dynamic Topology Nodes are often mobile Vulnerable to security attacks

3. 3 Introduction Security of networks widely relies on the use of key management mechanisms An ad hoc network is infrastructureless without centralized server Traditional solutions do not meet the requirements of mobile ad hoc networks

4. 4 Related Work Traditional network authentication solutions rely on physically present, trust third-party servers, or called certificate authorities (CAs). Partially distributed certificate authority makes use of a (k,n) threshold scheme to distribute the services of the certificate authority to a set of specialized server nodes. Fully-distributed certificate authority extends the idea of the partially-distributed approach by distributing the certificate services to every node.

5. 5 Related Work Pretty Good Privacy (PGP) is proposed by following a web-of-trust authentication model. PGP uses digital signatures as its form of introduction. When any user signs for another user's key, he or she becomes an introducer of that key. As this process goes on, a web or trust is established. Self-issued certificates issue certificates by users themselves without the involvement of any certificate authority.

6. 6 Our Work Propose a secure public key authentication service in mobile ad hoc networks with malicious nodes Prevent nodes from obtaining false public keys of the others Based on a network model and a trust model Security operations include public key certification and trust value update

7. 7 Architecture

8. 8 The Network Model Obtain a hierarchical organization of a network Minimize the amount of storage for communication information Optimize the use of network bandwidth Direct monitoring capability is limited to neighboring nodes Allow the monitoring work to proceed more naturally Improve network security

9. 9 The Network Model

10. 10 The Trust Model Define a fully-distributed trust management algorithm that is based on the web-of-trust model, in which any user can act as a certifying authority This model uses digital signatures as its form of introduction. Any node signs another's public key with its own private key to establish a web of trust Our trust model does not have any trust root certificate, it just relies on direct trust and groups of introducers in certification

11. 11 The Trust Model Define the authentication metric as a continuous value between 0.0 and 1.0 Define a direct trust relationship as the trust relationship between two nodes in the same group and a recommendation trust as the trust relationship between nodes of different groups. The first formula calculates the trust value of a new recommendation path: The second formula draws a consistent conclusion when there are several derived trust relationships between two entities:

12. 12 Security Operations Public key certification Trust value update

13. 13 Public Key Certification Authentication in our network relies on the public key certificates signed by some trustable nodes. Nodes in the same group are assumed to know each other by means of their monitoring components and the short distances among them

14. 14 Public Key Certification

15. 15 Trust Value Update

16. 16 Trust Value Update s denotes the requesting node t denotes the target node Nodes i 1, i 2, …, i n are the introducers Each V s, i* and V i*, t form a pair to make up a single trust path from s to t Compute the new trust relationship from s to t of a single path Combine trust values of different paths to give the ultimate trust value of t Insert trust value V t to the trust table of s

17. 17 Simulation Results Network simulator Glomosim Evaluate the effectiveness in providing secure public key authentication in the presence of malicious nodes Network# of nodes100 # of groups5 % of trustable nodes at initializationp % of malicious nodesm Public key request Max # of introducers for each request3 Min # of reply for each request1 SimulationTime45000s # of query cycles40 # of requests per cycle100

18. 18 Ratings to Malicious Nodes

19. 19 Ratings to Trustable Nodes at Initialization

20. 20 Comparison on Successful Rate

21. 21 Comparison on Failure Rate

22. 22 Comparison on Unreachable Rate

23. 23 Conclusion We developed a trust- and clustering-based public key authentication mechanism We defined a trust model that allows nodes to monitor and rate each other with quantitative trust values We defined the network model as clustering-based The authentication protocol proposed involves new security operations on public key certification, update of trust table, discovery and isolation on malicious nodes We conducted security evaluation We compared with the PGP approach to demonstrate the effectiveness of our scheme