International Association
for Cryptologic Research

This paper describes techniques that enable vehicles to collect local information (such as road conditions and traffic information) and report it via road-to-vehicle communications. To exclude malicious data, the collected information is signed by each vehicle. In this communications system, the location privacy of vehicles must be maintained. However, simultaneously linkable information (such as travel routes) is also important. That is, no such linkable information can be collected when full anonymity is guaranteed through the use of cryptographic tools such as group signatures. Similarly, continuous linkability (via pseudonyms, for example) may also cause problem from the viewpoint of privacy.

In this paper, we propose a road-to-vehicle communication system with relaxed anonymity by considering time-dependent linking properties via group signatures with time-token dependent linking (GS-TDL). These techniques are used to construct an anonymous time-dependent authentication system via GS-TDL. Briefly, a vehicle is unlinkable unless it generates multiple signatures simultaneously. In addition, we describe vulnerability in the anonymous authentication system proposed by Wu, Domingo-Ferrer and Gonz{\\\'a}lez-Nicol{\\\'a}s (IEEE T. Vehicular Technology 2010), where an unauthorized individual can create a valid group signature without using signing key. Moreover, our GS-TDL scheme supports verifier-local revocation (VLR), which maintains constant signing and verification costs by using the linkable part of signatures. These appear to be related to independent interests. Finally, we provide our experimental results (using the TEPLA library) and confirm that our system is feasible in practice.