Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> k-TAA-based scheme <s> We propose an authentication scheme in which users can be authenticated anonymously so long as times that they are authenticated is within an allowable number. The proposed scheme has two features that allow 1) no one, not even an authority, identify users who have been authenticated within the allowable number, and that allow 2) anyone to trace, without help from the authority, dishonest users who have been authenticated beyond the allowable number by using the records of these authentications. Although identity escrow/group signature schemes allow users to be anonymously authenticated, the authorities in these schemes have the unnecessary ability to trace any user. Moreover, since it is only the authority who is able to trace users, one needs to make cumbersome inquiries to the authority to see how many times a user has been authenticated. Our scheme can be applied to e-voting, e-cash, electronic coupons, and trial browsing of content. In these applications, our scheme, unlike the previous one, conceals users' participation from protocols and guarantees that they will remain anonymous to everyone. <s> BIB001 </s> Anonymous Authentication Protocols for Vehicular Ad Hoc Networks: An Overview <s> k-TAA-based scheme <s> Vehicular ad hoc network (VANET) can offer various services and benefits to VANET users and thus deserves deployment effort. Misusing such network could cause destructive consequences. It is therefore necessary to discourage misbehavior and defend VANET systems against it, in order to ensure correct and smooth operations of the network. In this paper, we review the techniques for handling misbehavior in VANETs, particularly where anonymous communications are desired to conserve user privacy since it adds more complexity to the defense against misbehavior. A new scheme is proposed to punish misbehaving users and can be employed in both inter-vehicle and vehicle-to-infrastructure anonymous communications. Our scheme leverages some threshold authentication technique that dynamically revokes a user's credential, while providing the flexibility of whether to reveal the user's identity and tolerating unintentional misbehavior such as hardware malfunctioning. <s> BIB002
In a k-times anonymous authentication (k-TAA) system BIB001 , participants are a group manager (GM), a number of application providers (AP) and a group of users. The GM registers users into the group and each AP independently announces the number of times a user can access his application. A registered user can then be anonymously authenticated by APs within their allowed numbers of times (k times) and without the need to contact the GM. Dishonest users can be traced by anyone while no one, even the GM or APs, can identify honest users or link two authentication executions performed by the same user. Finally no one, even the GM, is able to successfully impersonate an honest user to an AP. In dynamic k- TAA Nguyen & Safavi-Naini (2005) , APs have more control over granting and revoking access to their services and so have the required control on their clients. Sun et al. BIB002 Sun et al. (2010c) proposed a new misbehavior defense technique leveraging the idea of dynamic revocation, to provide a means of limiting the impact of misbehavior by adjusting it to an acceptable level during the vulnerable period existing in the automatic revocation technique based on dynamic k-TAA. However, the downside of Sun et al.'s scheme is obviously the lack of capability to trace misbehaving users.