  Vehicular ad-hoc networks (VANETs) are one of the most important components
in Intelligent Transportation System (ITS), which aims to provide secure and
efficient communication between vehicles. Safety-critical vehicular
communication requires security, privacy, and auditability. To satisfy these
requirements simultaneously, several conditional privacy-preserving
authentication schemes are proposed by employing ring signatures. However,
these methods have paid little attention to the issues like how to choose the
valid ring members or how to set up a ring. In this paper, we introduce an
efficient conditional privacy-preserving scheme which provides an appropriate
approach establishing the list of ring members with efficient revocation.
Moreover, our proposed scheme also provides batch verification to significantly
reduce the computational cost. According to the analysis of security, our
scheme is sufficiently resistant against several common attacks in VANETs. The
performance results show that the proposed scheme is efficient and practical
with both low computation and communication cost.
