Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Group signature-based scheme <s> We construct a short group signature scheme. Signatures in our scheme are approximately the size of a standard RSA signature with the same security. Security of our group signature is based on the Strong Diffie-Hellman assumption and a new assumption in bilinear groups called the Decision Linear assumption. We prove security of our system, in the random oracle model, using a variant of the security definition for group signatures recently given by Bellare, Micciancio, and Warinschi. <s> BIB001 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Group signature-based scheme <s> An approach of membership revocation in group signatures is verifier-local revocation (VLR for short). In this approach, only verifiers are involved in the revocation mechanism, while signers have no involvement. Thus, since signers have no load, this approach is suitable for mobile environments. Although Boneh and Shacham recently proposed a VLR group signature scheme from bilinear maps, this scheme does not satisfy the backward unlikability. The backward unlikability means that even after a member is revoked, signatures produced by the member before the revocation remain anonymous. In this paper, we propose VLR group signature schemes with the backward unlinkability from bilinear maps. <s> BIB002 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Group signature-based scheme <s> Vehicular communication networking is a promising approach to facilitating road safety, traffic management, and infotainment dissemination for drivers and passengers. One of the ultimate goals in the design of such networking is to resist various malicious abuses and security attacks. In this article we first review the current standardization process, which covers the methods of providing security services and preserving driver privacy for wireless access in vehicular environments (WAVE) applications. We then address two fundamental issues, certificate revocation and conditional privacy preservation, for making the standards practical. In addition, a suite of novel security mechanisms are introduced for achieving secure certificate revocation and conditional privacy preservation, which are considered among the most challenging design objectives in vehicular ad hoc networks. <s> BIB003 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Group signature-based scheme <s> Vehicular ad hoc networks (VANETs) are being designed to improve traffic safety and efficiency. To meet this goal, the messages disseminated in VANETs must be trustworthy. We propose a privacy-preserving system that guarantees message trustworthiness in vehicle-to-vehicle (V2V) communications. Vehicle privacy is provided as long as a vehicle does not attempt to endorse the same message more than once. In spite of a message having been validly endorsed, if it is later found to be false, the system offers the possibility of a posteriori tracing the message generator and its endorsers. Our proposal demonstrates a number of distinctive features. The system is equipped with both a priori and a posteriori countermeasures. The threshold used for a priori endorsement can adaptively change according to the message urgency and traffic context, rather than being preset in the system design stage as in existing schemes. The verification of authenticated V2V messages is accelerated by batch message-processing techniques. Simulation results illustrate that the system maintains its performance under various traffic conditions. <s> BIB004
In  , Chaum and Heyst proposed a new type of signature scheme for a group of entities, called group signatures. Such a scheme allows a group member to sign a message on the group's behalf such that everybody can verify the signature but no one can find out which group member provided it. However, there is a trusted third party, called the group manager, who can reveal the identity of the originator of a signature in the case of later dispute. This act is referred to as "opening" a signature or also as revocation of a signer's anonymity. The group manager can either be a single entity or a number of coalitions of several entities (e.g., group members). Dozens of group signature schemes Boneh et al. (2004); ;  ; BIB002 have been proposed since 1991 due to its attractive features. Lin et al.L i net al. (2007; BIB003 ; proposed the group signature based (GSB) protocol, based on the efficient group signature BIB001 . With GSB, each vehicle stores only a private key and a group public key. Messages are signed using the group signature scheme without revealing any identity information to the public. Thus privacy is preserved while the trusted authority is able to expose the identity of a sender. However, the time for safety message verification grows linearly with the number of revoked vehicles in the revocation list in the entire network. Hence, each vehicle has to spend additional time on safety message verification. Furthermore, when the number of revoked vehicles in the revocation list is larger than some threshold, the protocol requires every remaining vehicle to calculate a new private key and group public key based on the exhaustive list of revoked vehicles whenever a vehicle is revoked. Lin et al.L i n et al. (2007; BIB003 ; do not explore solutions to effectively updated the system parameters for the participating to vehicles in a timely, reliable and scalable fashion. This issue is not explored and represents an important obstacle to the success of this scheme. A linkable group signature  is a variant of group signatures. In a linkable group signature, it is easy to distinguish the group signatures produced by the same signer, even though the signer is anonymous. Linkable group signatures can thwart the Sybil attack but are not compatible with vehicle privacy due to the linkability of signer identities, i.e., the various message endorsements signed by a certain vehicle can be linked. BIB004 proposed a novel protocol based on linkable group signature, which is equipped with both priori and posteriori countermeasures. However, they face the same adverse conditions in GSB protocol in which the verification time grows linearly with the number of revoked vehicles and every remaining vehicle need to update its private key and group public key when the number of revoked vehicles is larger than some threshold.