Paper 2018/185 Original: eprint.iacr.org/2018/185 ↗

A privacy-preserving method for temporarily linking/revoking pseudonym certificates in vehicular networks

Abstract

Vehicular communication (V2X) technologies are expected to become increasingly common in the future. Although they enable improvements on transportation safety and efficiency, the large scale deployment of V2X requires addressing some challenges. In particular, to prevent abuse by drivers and by the system itself, V2X architectures must: (1) ensure the authenticity of messages, which is usually accomplished by means of digital certification; and (2) preserve the privacy of honest users, so owners of non-revoked certificates cannot be easily identified and tracked by eavesdroppers. A promising design to address these requirements is the Security Credential Management System (SCMS), which is currently among the main candidates for protecting V2X communications in the United States. Even though SCMS provides efficient, scalable and privacy-preserving mechanisms for managing V2X-oriented certificates, in this article we show that its certificate revocation process can be further enhanced. Namely, we present two birthday attacks against SCMS's revocation process, both of which degrade the system's security as time passes and more certificates are revoked. We then describe an alternative design to prevent such security degradation with minimal computational overhead. In complement to these security gains, we also describe a mechanism for improving the flexibility of the revocation procedure, allowing certificates (as well as their owner's privacy) to be temporarily revoked in an efficient manner. This should be useful, for example, to implement suspension mechanisms or to aid in investigations by law-enforcement authorities.