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PERFORMANCE EVALUATION OF SECURE COMMUNICATION IN VEHICULAR NETWORKS

This dissertation attempts to evaluate the performance of the Public Key Infrastructure (PKI) based security mechanisms proposed to secure the messages exchanged in vehicular networks, and the performance of communication considering the various overheads of security. Vehicular networks are not expected to guarantee on-demand connectivity between the principals of the network and the infrastructure responsible for issuing certificates to the principals of network, and revocation of compromised certificates. We propose a metric called Confidence on Security Infrastructure to quantify the confidence the principals of vehicular networks can have on the PKI based security given the delays in access to the revocation information due to such sporadic connectivity. We then propose an accept/drop mechanism at the security layer called Freshness Checks aimed at controlling these delays. Further, we show that the security performance of vehicular networks is independent of the density of the vehicles if one only takes vehicle reliability into account however, intentional malicious activities could require an increase in infrastructure presence. The proposed safety applications rely heavily on secure exchange of data using the broadcast services of the MAC layer. Further, any security mechanism comes with overheads in terms of computation and communication. We show that the computational overheads of the proposed PKI based security result in packet processing and not packet transmission becoming a bottle-neck. Further, broadcast packets that undergo collisions are not retransmitted. We obtain this collision probability by initially assuming low rates of packet generation at the application layer resulting in our nodes being bufferless at the MAC layer and then extend our model for finite buffers to study the system under higher data traffic loads. We show that adapting packet generation rates and the time for which a message is transmitted over the air have a greater impact on packet losses due to collisions as compared to adapting the probability of attempting a transmission and buffer sizes at the MAC layer.