Vehicular communications are bringing a new wave of applications under the umbrella of the Cooperative Intelligent Transportation Systems (C-ITS). To this end, on-board units are expected to send messages periodically or upon the appearance of a relevant event, to feed an awareness ecosystem that enables safety or traffic efficiency services. This is the case of Cooperative Awareness Messages (CAMs) in Europe, which contain basic vehicle information such as its position or speed, among other parameters. From a network security perspective, CAMs are broadcasted unencrypted over an unprotected radio channel, hence enabling their potential interception and the disclosure of sensitive data. Although public key infrastructures (PKI)- like solutions have been proposed, high computational cost of asymmetric cryptography to cipher application data remains a challenge and a confidentiality alternative is needed. In this work, we present the implementation and evaluation of a symmetric encryption scheme based on disjoint security domains distributed in geographical areas. In the solution, vehicles are able to coordinate and agree on common keys to be used in different security zones. Simulation results show the validity of the zone encryption scheme in diverse vehicular scenarios with different traffic densities. A potential issue in the zone key redistribution consisting in the propagation of wrongly-generated duplicated keys is also detected, which is discussed in detail and a reliable solution based on the support of third-party data-forwarders is proposed and tested. Evaluations reveal good performance of the zone encryption mechanism in terms of robustness and latency, guaranteeing the efficient access to a secured channel while maintaining low computing load.

This work has been supported by the Spanish Ministry of Science, Innovation and Universities, under the Ramon y Cajal Program (Grant No. RYC-2017-23823) and the projects PERSEIDES, Spain (Grant No. TIN2017-86885-R with ERDF funds) and Go2Edge, Spain (RED2018- 102585-T); and by the European Commission, under the projects 5G- MOBIX (Grant No. 825496) and INSPIRE-5Gplus (Grant No. 871808).