Anonymous Authenticated Announcement Schemes in Vehicular Ad Hoc Networks

This thesis adds to the design of new announcement schemes in vehicular ad hoc networks (VANETs). An announcement scheme allows vehicles to broadcast information about their surrounding to other vehicles in their proximity. This enables neighbouring vehicles to be aware of their driving environment and appropriate action can be taken upon receiving the messages. This may enhance road safety and traffic efficiency. Safety can only be achieved if the messages announced are reliable. A message announced is considered to be reliable if a receiver can be assured it was sent unmodified by a legitimate vehicle and the content of the message reflects the actual situation. Two common techniques to achieve this property is by using threshold method and reputation-based models. In a threshold method, a message is believed to be reliable if a vehicle receives messages of the same content announced by a number of distinct legitimate vehicles of a certain threshold within a time interval. In a reputation-based models, the reliability of a message is evaluated according to the reputation of the reporting vehicles; higher reputation reflects the likelihood a vehicle is announcing reliable messages. However, verification of reliability may violate privacy. Sensitive information such as its identity such be preserved and messages announced by a vehicle should be unlinkable. This is to prevent unlawful tracing and user profiling, as otherwise, it would be difficult to attract vehicles to join the network. The issues of security and privacy have been among the main concerns in the adoption of this technology. Such concerns are justified in the context of preserving and protecting user privacy whilst benefiting from the rich tools of vehicular communication systems. On the other hand, should misbehaviour arise, malicious vehicles should be traceable where it is identified to be held accountable and liable. It should also not be able to deny of having sent the message. This motivates the work described in this thesis.

We begin by defining the system and security model of an announcement scheme in VANETs. We analyse some related existing schemes in the literature which are based on (i) threshold mechanism and (ii) trust- and reputation-based models and examine the extent to which they satisfy the contradictory requirement of reliability, privacy and accountability. Our analysis indicates that most schemes does not achieve message reliability and some schemes does not fulfil the requirement of accountability. In addition, most trust- and reputation-based schemes does not address the issue of privacy. This highlights the need to design a more efficient reliable privacy-preserving announcement schemes. Observation and comparison of different mechanisms used in some existing announcement schemes leads to our construction of a generic abstraction of an authenticated anonymous announcement scheme designed using threshold method. We also formulate a generic abstraction for an authenticated anonymous announcement scheme designed using reputation systems based on our proposed schemes. Within these abstractions, we give construction to three announcement schemes. The first scheme uses public key cryptography and reputation systems. We constructed another two schemes using certificateless signature. These schemes consider the challenging conflicting security requirements which we shall show has been achieved simultaneously in this thesis.

We analyse the security of our proposed schemes and evaluate their performance. We validate the performance of our schemes by means of simulations. We then compare instantiation of our schemes with state-of-the-art announcement schemes, demonstrating that our schemes possess the attractive properties of message reliability, user privacy and accountability while achieving system robustness and performance efficiency.