An Adaptive Protocol for Efficient & Secure Multicasting in Wireless LANS Sandeep Gupta & Sriram Cherukuri Arizona State University

Overview Introduction & Background Problem Statement Related Work System Model Proposed Solution Simulation & Results References

Introduction & Background Multicasting in wireless LANS Energy and Bandwidth Constraints Advantages of Multicasting Security Primitives Location Based Access Confidentiality, Integrity, Authenticity,& Non-repudiation. Applications of Secure Multicast

Problem Statement To build multicast scheme satisfying Basic security primitives. Forward and Backward message secrecy conditions. Performs the above energy efficiently.

Related Work Little work in Secure multicast in wireless networks Kuri proposed protocols for reliable multicast. Bhargavan proposed a scheme based on unicast and public key cryptosystem.

System Model Range of base station Coverage area of base station Group member inside the coverage area Group member outside the coverage area Malicious node outside coverage area but inside the range of base station Base station Shared Wireless Channel

Key Establishment The key establishment algorithm 1. X => Y: X Hi I am X 2. Y => X: R Prove it 3. X => Y: E p (hash(R),S x ) 4. Y=>X: E p (hash(S x ), S y ) 5. K = F(S x,S y )

Proposed Solutions Three solutions presented DSK- Different Session Key Session Key is unique for each of the multicast group receivers. SSK- Single Session Key Session Key is common for all the multicast group receivers. Hybrid Scheme Session Key is common for a subset of the multicast group receivers and unique keys are used for the remainder members.

Proposed Solutions (Cont') DSK Algorithm 1. The base station establishes individual session keys with each member node using the protocol explained earlier. 2. When a member leaves the cell, no key exchange is required. The key the base station shared with the departed member is invalidated. 3. When a new member attaches to a base station, the base station establishes a new session key with it.

Proposed Solutions (Cont') SSK Algorithm 1. The base station establishes the same session key with all the members in the cell. 2. When a receiver node leaves the cell, the base station establishes a new session key with the remaining members in the cell. This ensures forward message secrecy. 3. When a new receiver node attaches to a base station, the base station establishes a new session key with all the members of the cell. This ensures backward message secrecy. Here multicasting may be used as explained in the previous section.

Proposed Solutions (Cont') Hybrid Algorithm 1. Nodes classified as stable and unstable nodes based on duration of stay(>t s or not). 2. Common key with stable nodes, unique keys with unstable nodes. 3. The re-keying action varies for stable and unstable node movement. Stable node moves out => re-key stable set. Unstable node moves out => key discarded. New( hence unstable) node enters => new key established Unstable node stabilizes => re-key stable set.

Simulations & Results Simulations performed NS with mobility patterns generated by random way point movement. Metrics: Communicating cost, Mobility Results summarized in table.

Simulation & Results ComparisonBetter at high mobility Better at low mobility DSK/SSKDSKSSK SSK/HybridHybridSSK DSK/HybridHybrid

Optimization Primitives Batch Re-Keying The requests for re-keying are aggregated over a period of time and then processed. The batch interval is parameter

Optimizations and results Group Communication for Key Distribution When a node new node enters we use the old key to multicast the new key to the older members

References ANSI/IEEE Standard , In 1999 Edition, J.Kuri and S.K.Kasera, Reliable Multicast in Multi access Wireless LANs, In IEEE INFOCOM ’99, 1999, L.R.Dondeti, S.Mukherjee, A.Samal, Scalable secure one to many communication using dual encryption, In Computer Communications, Volume 23,Issue 17, Pages (November 2000) V.Bharghavan, Secure Wireless LANs, In ACM Conference on Computers and Communications Security ’94,; Fairfax, VA. D. Bruschi and E. Rosti, Secure Multicast in Wireless Networks of Mobile Hosts:Protocols and Issues

B.Schneier Applied Cryptography,Protocols,Algorithms and source code in C Second Edition.John Wiley & Sons X.S.Li, Y.R.Yang, M.G.Gouda,S.S.Lam Batch Rekeying for Secure Group Communications Tenth international World Wide Web Conference,Hong Kong,China May J.B. Lacy, D. P. Mitchell, and W. M. Schell CryptoLib:Cryptography in software Proc USEN1X4th UN1XSecurity Symp., Oct Marc Langheinrich Privacy by Design - Principles of Privacy-Aware Ubiquitous Systems Proceedings of Ubicomp 2001, September 30 - October 2, 2001, Atlanta, GA.

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