Enhancements in Security, Performance Modeling and Optimization in Vehicular Networks

1. Ashwin Rao 2006SIY7513 Supervisor: Arzad A. Kherani Enhancements in Security, Performance Modeling and Optimization in Vehicular Networks

2. Introduction to VANETs • Mobile ad hoc networks (MANETs) with vehicles as mobile nodes • Application classification • Safety Related - Early Warning Messages • Best Effort – Traffic Optimization • Secure Transactions – Toll collection • Application to enhance safety of passengers

3. VANET jargon • VANET – Vehicular Ad hoc networks • OBU – On Board Unit – communication equipment in vehicles • RSU – Road Side Unit - provides infrastructure • WAVE – Wireless Access in Vehicular Environment • DSRC – Dedicated Short Range Communication

4. PKI: A brief overview • Asymmetric Keys (Pu -> Public key, Pr ->Private Key) • M = Pr(Pu(M)) & M = Pu(Pr(M)) -- where M is the message to be secured • Certificate contains the public key & signature of CA • Certificate sent with signed message to verify the signature of message • Certificate shouldn't be revoked for message to be accepted

5. Security in VANETs • Security essential to the protect critical messages • Mechanism providing security need to address • Authenticity – genuine v/s malicious source • Anonymity – sender having right to privacy • Data Integrity – messages received as-is • Low Overheads – to retain usefulness of messages • Use of PKI based security proposed in IEEE 1609.2

6. 1609 Protocol Stack • Data Flows and Resources • Secure Message formats and their processing • Network & Transport Layer Services • Enhancement to the 802.11 MAC

7. Revocation of Certificates • Required to distinguish genuine and malicious nodes • When does the PKI revoke a certificate ? • It is compromised • It is used for malicious activity • Other reasons like terminating the V2V service • Problems • Revocation information to be propagated to all concerned

8. Certificate Revocation Lists (CRLs) • PKI propagates revocation information using CRLs • CRLs are signed by the CA • Problems with CRLs in VANETs • Communication with infrastructure at irregular intervals • Varying contact times with infrastructure • Number of CRLs limited to storage space in OBU • Time to search the certificate in CRLs • Operating time of malicious node = avg. CRL update interval

9. Accept/Drop Mechanism (Security Layer)

10. Confidence In Security Infrastructure • What is the probability that a certificate is a good certificate if it is not available in the CRLs at OBU? • How recent are the CRLs in the OBU? • How recent is the certificate under consideration? • With how much confidence can you accept the signed message? • On what parameters is this confidence related to ?

11. Parameters affecting CoS • r – the revocation rate • Var( T ) – variance in inter-CRL update times • E[ T ] - Expected CRL update interval • If Var(T) = 0 then

12. Freshness checks • Sender and receiver have equal access to PKI • Sender checks if one of its certificates is revoked • The CA modifies the freshness check field in the certificate if it is not revoked • Freshness check field is part of the certificate • For receiver of messages to confirm freshness checks • For non-malicious senders to validate the genuineness of their certificates

13. Freshness Checks

14. Algorithm to Accept/Drop Messages

15. Advantages of Freshness Checks • Time for verifying signed messages • Independent of number of CRLs and certificates in CRLs • OBUs need not store CRLs • Reduced storage requirement of OBU • Solves problem of CRL propagation • The validity of certificate dependent on the current value of CoS and not determined at time of issue.

16. Reduced Operating Time Of Malicious Nodes Time at which a certificate was revoked

17. Impact of Freshness checks Fraction of packets from non-compromised nodes Fraction of packets from compromised nodes

18. FutureTasks • Relation between CoS and probability of messages from non-compromised nodes getting dropped • Impact of the overheads of security on performance of secure messages • Impact of periodic transmission on the performance of secure messages • Adapting rate of transmission V/S Adapting transmission range of messages

19. Conclusion • Minimize some of the security overheads of verifying the messages by providing a constant time algorithm to accept/drop messages • Robust security infrastructure equally important for effective security

20. Q&A

21. Extra Slides (BACKUP)

22. IEEE 1609 protocol stack • 1609.1 - Resource Manager • Data flows and Resources at all points • 1609.2 - Security Services • Secure message formats and processing based on PKI • 1609.3 – Networking Services • Network and Transport layer services • 1609.4 – Multi-channel operations • Enhancement to IEEE 802.11 MAC

23. Research Agenda • Implement essential features of 1609.x protocol stack • Incorporate vehicular traffic & data traffic models • Simulate V2V messaging at each node. • Propose algorithm to accept and drop messages • Study the performance metrics across widely varying system parameters (with and without security) in V2V networks.

24. Accept/Drop Mechanism (at Security Layer) • Received message signed using a certificate present in CRLs at OBU • Drop the packet • Received message signed using a certificate absent from the CRLs at OBU • Is the certificate revoked by the PKI ? • Is the certificate compromised but not revoked at the PKI ? • Is the certificate a genuine non-compromised certificate?