Multi-user Broadcast Authentication in Wireless Sensor Networks

1. Multi-user Broadcast Authentication in Wireless Sensor Networks ICU 20082065 MyunghanYoo

2. Contents • Introduction • Preliminaries • The Proposed Scheme • CAS • DAS • BAS • HAS • Performance Analysis • Conclusions • Discussion

3. Introduction • In Wireless Sensor Networks, broadcast/multicast from not only sink, but also a sensor node becomes crucial function • Authentication of them is highly important • Several symmetric key cryptography based μTESLA-likeschemes have been proposed

4. Introduction • Weak points of μTESLA-like schemes • All the receivers have to buffer all the messages within one time interval • Wormhole attacks • Caused by forged message, due to delay of the disclosed keys • Arbitrary flooding in current time interval • Nodes should buffer • Transmission is expensive • Denial-of-Service attacks

5. Introduction • Solutions • TIK protocol • Require a heavy burden of memory • Public key cryptography based • No longer impractical primitive

6. Preliminaries Initial Configuration Verification • The Bloom Filter • Hashing input value k times • If all bits are 1, true member • Otherwise, discard • False positive probability

7. Preliminaries The Merkle hash tree

8. CAS M: Message, tt: time-stamp, SIG{}: signature, UID: user’s ID, SK: Secret key, PK: public key, CertUID: user’s certificate, ExpT: expiration time, and h():hashed value • The Certificate-Based Authentication Scheme • Drawbacks • Communication overhead • Including Certification • Computation overhead • Two signature verification

9. DAS • The Direct Storage Based Authentication Scheme • Instead of certificate, list is used • User’s ID & public key • Scalability problem

10. BAS • The Bloom Filter Based Authentication Scheme • System Preparation • Sink construct Bloom filter & counting Bloom filter

11. BAS

12. BAS • Message Signing and Authentication • Based on ECDSA’s partial message recovery

13. BAS • Message Signing and Authentication • Broadcast • Check authenticity by verifying public key Wpub’s membership with bloom filter • Hashing { UID || Wpub} specific times • If all hashed values on the bloom filter are 1, OK • Otherwise, discard received message

14. BAS • Message Signing and Authentication • Verify signature

15. BAS Update counting bloom filter Update bloom filter Update bloom filter of every node User Revocation

16. BAS • User Addition • Generate more (ID, PK) pairs than need in system preparation phase, assign a pair when new nodes join WSN • Add user, after revocation of old members • No increasing the probability of a false positive • Procedure is same as revocation’s one

17. BAS F (The probability of False Positive) Generate PK/SK pairs: computationally feasible m/N (bits/User) m: storage space bits N: the number of users The minimum probability of a false positive regarding

18. BAS The number of users Thus, we need to consider of trade-off between the maximum supported number of users and the probability of a false positive given a fixed storage

19. HAS • The Hybrid Authentication Scheme (HAS) • Supporting more users using the Merkle Hash tree & Bloom filter • Trading the message length for the storagespace • System Preparation • Calculate trade-off • maximum number of user & false positive rate • Construct of Merkle hash tree • Each leaf is user’s public key • The sink prunes it into a small tree • Generate Bloom filter • Elements of group are small trees

20. HAS Auxiliary Authentication Information of node ID • Message Signing and Authentication • Broadcast • Received node • Calculate the corresponding root node using AAIUID • Verify the root node value using bloom filter • Verify the signature in the same way of BAS

21. Performance Analysis Communication Overhead

22. Performance Analysis • Computational Overhead • Measure energy consumption of signature verification on two processor

23. Performance Analysis • Security Strength • BAS • Instant authentication • Impossible to launch attack using authentication delay • Suitable for military application with freq=6.36*10-20 • Protection from replay attack with time stamp • Jamming attacks emitting random bits • CAS is weak, since every message has certificate • HAS and BAS are robust • Authentication using Bloom filter is cheap

24. Performance Analysis • Security Strength • Jamming attacks using valid PK attached to irregularly modified message • HAS and BAS • After verifying signature, recognize that message is bed. • Implement an alert report mechanism • When failing to authenticate messages in a row • Repot to the sink • The sink invest the network • Detection & Remedy are out of scope in this paper

25. Conclusions • Reveal the problems of SKC based multi user broadcast authentication schemes • Authentication delay • Vulnerabilities • Propose PKC based schemes using Bloom filter & Merkel hash tree • Minimizing energy dissipation • Analyze performance & security

26. Discussion • Shortcoming • Evaluate overhead of only proposed schemes • We can’t know how much energy resource is consumed compared to when μTESLA-likeschemes are used.

27. Thank you