  In this paper, we introduce an efficient and trustworthy conditional
privacy-preserving communication protocol for VANETs based on proxy
re-signature. The proposed protocol is characterized by the Trusted Authority
(TA) designating the Roadside Units (RSUs) to translate signatures computed by
the On-Board Units (OBUs) into one that are valid with respect to TA's public
key. In addition, the proposed protocol offers both a priori and a posteriori
countermeasures: it can not only provide fast anonymous authentication and
privacy tracking, but guarantees message trustworthiness for vehicle-to-vehicle
(V2V) communications. Furthermore, it reduces the communication overhead and
offers fast message authentication and, low storage requirements. We use
extensive analysis to demonstrate the merits of the proposed protocol and to
contrast it with previously proposed solutions.
