Indian Institute Of Technology, Delhi Page 1 Enhancements in Security, Performance Modeling and Optimization in Vehicular Networks Ashwin Rao 2006SIY7513 Supervisor: Arzad A. Kherani

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page Protocol Stack Data Flows and Resources Secure Message formats and their processing Network & Transport Layer Services Enhancement to the MAC

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 9 Accept/Drop Mechanism (Security Layer)

Indian Institute Of Technology, Delhi Page 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 ?

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 13 Freshness Checks

Indian Institute Of Technology, Delhi Page 14 Algorithm to Accept/Drop Messages

Indian Institute Of Technology, Delhi Page 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.

Indian Institute Of Technology, Delhi Page 16 Reduced Operating Time Of Malicious Nodes Time at which a certificate was revoked

Indian Institute Of Technology, Delhi Page 17 Impact of Freshness checks Fraction of packets from compromised nodes Fraction of packets from non-compromised nodes

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 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

Indian Institute Of Technology, Delhi Page 20 Q&A

Indian Institute Of Technology, Delhi Page 21 Extra Slides (BACKUP)

Indian Institute Of Technology, Delhi Page 22 IEEE 1609 protocol stack Resource Manager Data flows and Resources at all points Security Services Secure message formats and processing based on PKI – Networking Services Network and Transport layer services – Multi-channel operations Enhancement to IEEE MAC

Indian Institute Of Technology, Delhi Page 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.

Indian Institute Of Technology, Delhi Page 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?