Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Basic scheme <s> Vehicular networks are likely to become the most relevant form of mobile ad hoc networks. In this paper, we address the security of these networks. We provide a detailed threat analysis and devise an appropriate security architecture. We also describe some major design decisions still to be made, which in some cases have more than mere technical implications. We provide a set of security protocols, we show that they protect privacy and we analyze their robustness, and we carry out a quantitative assessment of the proposed solution. <s> BIB001 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Basic scheme <s> Vehicular networks are very likely to become the most pervasive and applicable of mobile ad hoc networks in this decade. Vehicular Ad hoc NETwork (VANET) has become a hot emerging research subject, but few academic publications describing its security infrastructure. In this paper, we review the secure infrastructure of VANET, some potential applications and interesting security challenges. To cope with these security challenges, we propose a novel secure scheme for vehicular communication on VANETs. The proposed scheme not only protects the privacy but also maintains the liability in the secure communications by using session keys. We also analyze the robustness of the proposed scheme. <s> BIB002 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Basic scheme <s> Advances in wireless communications allow setting up communication links between vehicles for the exchange of information between them. Such vehicular ad hoc networks (VANETs) are important to enhance traffic safety since critical environmental conditions, such as road or traffic conditions, can be rapidly exchanged between vehicles in VANETs. However, to be useful for the driver, the information must be reliable, i.e., with great probability, the received information indeed reflects the actual situation. One approach to this is to regard information as reliable if it is confirmed by various sources. To achieve this, messages received must be distinguishable. This may become a threat against the privacy of drivers since by observing messages, vehicles may be traced. In this paper, we address the mentioned problems. We base the reliability of information on the number of different sources that confirmed specific information, and that number must be greater than a given threshold. We address the nontraceability by letting vehicles change their identity frequently. Our approach scales with respect to storage on the vehicle, as well as management of identities at a certification authority. <s> BIB003 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> Basic scheme <s> Vehicular ad hoc networks (VANETs) allow vehicle-to-vehicle communication and, in particular, vehicle-generated announcements. Provided that the trustworthiness of such announcements can be guaranteed, they can greatly increase the safety of driving. A new system for vehicle-generated announcements is presented that is secure against external and internal attackers attempting to send fake messages. Internal attacks are thwarted by using an endorsement mechanism based on threshold signatures. Our system outperforms previous proposals in message length and computational cost. Three different privacy-preserving variants of the system are also described to ensure that vehicles volunteering to generate and/or endorse trustworthy announcements do not have to sacrifice their privacy. <s> BIB004
Raya et al. BIB001  introduced the large number of anonymous key based (LAB) protocol. Their key idea is to install on each OBU a large number of private keys and their corresponding anonymous certificates. To sign each launched message, a vehicle randomly selects one of its anonymous certificates and uses its corresponding private key. The other vehicles use the public key of the sender enclosed with the anonymous certificate to authenticate the source of the message. These anonymous certificates are generated by employing the pseudo-identity of the vehicles, instead of taking any real identity information of the drivers. Each certificate has a short life time to meet the drivers'privacy requirement. Although LAB protocol can effectively meet the conditional privacy requirement, it is inefficient and may become a scalability bottleneck. The reason is that a sufficient numbers of certificates must be issued to each vehicle to maintain anonymity over a significant period of time. (Raya et al.Raya & Hubaux (2005;  suggest using large pseudo certificates for each vehicle). As a result, the certificate database to be searched by the TRC in order to match a compromised certificate to its owner's identity is huge. In addition, the protocols of  are extended for providing confidentiality in specific scenarios of VANET implementations in BIB002 . Most recently, BIB003 proposed a solution that permits vehicles to verify the reliability of information received from anonymous origins. In this solution, each vehicle can generate the public/private key pairs by itself. However, the assumption in this solution is very restricted in that additional hardware is needed on the OBU. However,  showd that the Kounga et al.'s scheme does not achieve the goals of authenticity of a message, privacy of drivers and vehicles, reliability of distributed information, and revocation of illegitimate vehicles. After that, a proposal is also presented following the priori protection paradigm based on threshold signature by BIB004 . Nevertheless, to obtain the anonymity, this protocol assumes that the OBU installed on the vehicle can be removable and multi OBUs could alternatively be used with the same vehicle (like several cards can be used within a cell phone in the same time). Thus, this assumption may enable malicious adversary to mount the so-called Sybil attack: vehicles using different anonymous key pairs from corresponding OBUs can sign multiple messages to pretend that these messages were sent by different vehicles. Since multi OBUs can be installed on the same vehicle, no one can find out whether all of these signatures come from the same vehicle or not. 