The Unified Butterfly Effect: Efficient Security Credential Management System for Vehicular Communications

With the increasing demand for intelligent transportation systems (ITS), security and privacy requirements are paramount. This led to many proposals aimed at creating a Vehicular Public Key Infrastructure (VPKI) able to address such prerequisites. Among them, the Security Credential Management System (SCMS) is particularly promising, providing data authentication in a privacy-preserving manner and also supporting revocation of misbehaving vehicles. Despite SCMS's appealing design, in this paper we show that its certificate issuing process can be further improved. Namely, one of the main benefits of SCMS is its so-called butterfly key expansion process, which issues arbitrarily large batches of pseudonym certificates by means of a single request. Although this protocol requires the vehicle to provide two separate public/private key pairs to registration authorities, we hereby propose an improved approach that unifies them into a single key. As a result, the processing and bandwidth utilization for certificate provisioning are reduced from 10% to 50% for all entities involved in the protocol. We also show that such performance gains come with no negative impact in terms of security, flexibility or scalability when compared to the original SCMS.