  Among the available communication systems, vehicular networks are emerging as
one of the most promising and yet most challenging instantiations of mobile
ad-hoc network technologies. The deployment of such networks in large scale
requires the enforcement of stringent security mechanisms that need to abide by
the technical, societal, legal, and economical requirements of Intelligent
Transportation Systems. Authentication is an effective process for validating
user identity in vehicular netoworks. However, it cannot guarantee the network
security by itself. Available industrial standards do not consider methods to
promptly revoke misbehaving vehicles. The only available protection consists on
the \textit{revocation by expiry}, which tolerates the misbehaving vehicle to
remain trusted in the system for a long time (e.g. 3 months with certificate
pre-loading according to EU security policy). This poses a huge yet dangerous
limitation to the security of the vehicular ecosystem. In this work we propose
a Distributed Ledger-based Certificate Revocation Scheme for Vehicular Ad-hoc
Networks (VANETs) that harnesses the advantages of the underlying Distributed
Ledger Technology (DLT) to implement a privacy-aware revocation process that is
fully transparent to all participating entities and meets the critical message
processing times defined by EU and US standards. An experimental validation and
analysis demonstrates the effectiveness and efficiency of the proposed scheme,
where the DLT streamlines the revocation operation overhead and delivers an
economic solution against cyber-attacks in vehicular systems.
