Evaluation of congestion-based certificate omission in VANETs

Telematic awareness of nearby vehicles is a basic foundation of electronic safety applications in Vehicular Ad hoc Networks (VANETs). This awareness is achieved by frequently broadcasting beacon messages to nearby vehicles that announce a vehicle's location and other data like heading and speed. Such safety-related beacons require strong integrity protection and high reliability, two properties that are hard to combine because the communication and computation overhead introduced by security mechanisms affects reliability. This applies especially to the signatures and certificates needed for authentication. We propose a mechanism to reduce the communication overhead of secure safety beacons by adaptively omitting the inclusion of certificates in messages. In contrast to similar earlier proposals, we control the omission rate based on estimated channel congestion. A simulation study underlines the advantages of the congestion-based certificate omission scheme compared to earlier approaches. Moreover, we show that the benefits of certificate omission outweigh the negative effect of cryptographically un-verifiable beacons.