Abstract
Both research community and industry believe that Intelligent Transportation System (ITS) would be achievable in the next decade. ITS introduces information technology for the transportation vehicles and infrastructures and aims to improve road safety and traffic efficiency. Vehicular Communication Systems (VCS), provides a platform for the vehicles to exchange messages with network infrastructures (V2I) or other vehicles (V2V). Confidence in these messages can be achieved through secure group messaging. Furthermore, the reliability of ITS highly relies on the security level of VCS. Therefore, secure key management schemes are proposed to enhance network security, which involves two aspects, namely Group Key Management (GKM) and Key Handover which also known as key transfer. The first part manages keys among a communication group within small road area, whereas key handover transfers secret keys from one security domain to another. Three contributions related to secure key management are as follows. The first contribution focuses on managing group communication keys in an efficient way. The probability-based scheme describes a novel GKM scheme using leaving probabilities of vehicles to optimise the structure of key tree branches. The proposed scheme further decreases rekeying costs and releases network resources. The second contribution introduces the Distributed Ledger Technology (DLT) structure to simplify the key handover procedures between heterogeneous networks. The central managers are eliminated from the key handover participation list. The key handover data are encapsulated into transactions and the Blockchain is maintained by all the infrastructures distributively. Finally, the dynamic transaction collection period is replenished to further optimise the performance based on the framework in the second contribution. The collection period varies dynamically to flexibly fit the traffic level on the road. The scheme aims to raise key handover efficiency at peak hours, while reducing the computation burden at off-peak hours.