Substantial effort has been invested on secure location verification in hope to enable mobile wireless systems to optimize system performance or securely confer rights based on the participants' locations. However, most previous studies do not address the impact of, and are often susceptible to, collusion attacks in which adversaries share their private keys. In this paper, we propose a secure multilateration scheme. Given the same processing delay, detection threshold, and assuming zero synchronization error between verifiers, our proposed scheme achieves the highest rate of false-location detection by any verification system based solely on time-of-flight measurements. We also show that our scheme is resilient to collusion attacks if the verification system can detect the distance enlargement attack. We propose using other physical measurements to mitigate the distance enlargement, and thus also the collusion, attacks. To the best of our knowledge, this is the first attempt to prevent collusion attacks by mitigating the distance enlargement attack.

In a Vehicular Ad hoc NETwork (VANET), vehicles broadcast safety messages disclosing their trajectory information in order to warn drivers of impending accidents. Precise location information needed for these safety applications, combined with the need to exclude attackers through the use of authentication, creates a significant privacy risk. One method proposed to improve privacy is the use of many pseudonyms, and changing pseudonyms while in a mix zone where all other vehicles also change pseudonyms. Previous work has evaluated the effectiveness of mix zones using traces generated based on traffic theory. In this paper, we analyze the privacy obtainable from using mix zones in VANETs based on actual recordings of vehicle movements. We choose rank instead of entropy as our privacy metric because, as we will show, entropy is difficult to measure in our scenarios.

In this paper, we propose a lightweight mechanism for revoking security certificates that is appropriate for the limited bandwidth and hardware cost constraints of a VANET. A Certificate Authority (CA) issues certificates to trusted nodes, i.e., vehicles. If the CA looses trust in a vehicle (e.g., due to evidence of malfunction or malicious behavior), the CA must promptly revoke the certificates of the distrusted vehicle. To distribute revocation information quickly even during incremental deployment, we propose that CAs use Certificate Revocation Lists (CRLs). The CRL should be composed in a secure manner, and it should be exchanged in a way such that the CRL is both quickly and widely distributed. We previously proposed a mechanism for the quick distribution of CRL updates that also covers a wide area by using vehicle-to-vehicle (V2V) communication . In this paper, we additionally investigate the performance of V2V communication in partial deployment scenarios, that is, where only a certain percentage of vehicles are equipped with VANET radios. We provide simulation results that show our V2V exchange mechanism is quicker than distributing CRLs or CRL updates through road-side units (RSUs) alone. However, this revocation process, which involves both the CA and vehicles, must conform to the aforementioned bandwidth and hardware restrictions. In this paper, we present mechanisms that achieve the goals of reduced CRL size, a computationally efficient mechanism for determining if a certificate is on the CRL, and a lightweight mechanism for exchanging CRL updates. Additionally, we expand on our previous work to provide privacy to revoked vehicles prior to their revocation.

Abstract There are two underlying principles that guide how a vehicular ad hoc network (VANET) is built: there will be misbehavior and the extent to which vehicles can misbehave should be bounded. Additionally, the main use for VANETs currently is to enable safety applications where vehicles' position, velocity, and acceleration are broadcast to other vehicles in the VANET. Combining these guiding principles with this application results in the privacy of vehicles and users being an important concern for VANET design. Safety application messages are signed using keys and therefore linked to vehicles. In this work, we investigate how to assign keys to vehicles in order to preserve privacy and maintain our guiding VANET design principles. Specifically, we investigate the design space where individual keys may be given to multiple vehicles and vehicles may have multiple keys. Through a simple security analysis, we eliminate the case where all keys are common. Through mathematical and logical analysis, we conclude that keys should not be owned by multiple vehicles, that is, keys should be unique to vehicles and vehicles should be given multiple keys. Specifically, we show that it is impossible to provide good privacy and fast revocation when keys are shared among vehicles. Copyright © 2009 John Wiley & Sons, Ltd.

Previous simulations have shown substantial performance gains can be achieved by using hybrid cellular and wireless LAN (WLAN) approaches. In a hybrid system, a proxy in an area of strong connectivity (and therefore higher bandwidth) forwards traffic on behalf of a client in an area of weaker connectivity (and therefore lower bandwidth). The proxy routes traffic between the base station (over a cellular link) and the client (over a WLAN). Such approaches have had limited practical applicability due to substantial security risks, including eavesdropping, intentional performance degradation and cheating the incentive schemes. The secure unified cellular ad hoc network (SUCAN) protocol is designed to address these risks, allowing the deployment of hybrid networks. SUCAN uses incentives and cryptographic techniques to eliminate cheating by self-interested hosts, while limiting the damage caused by malicious hosts. We implemented SUCAN on Verizon's broadband access network. To our knowledge, this is the first realworld implementation of a hybrid cellular network protocol. Our implementation results show that the SUCAN system can provide substantial performance increases and protects against performance degradation even in the presence of malicious behavior.

Many results have been published in the literature based on performance measurements obtained from simulations of vehicular networks (VANETs). These simulations use as input traces of vehicle movements that have been generated by traffic simulators which are based on traffic theory models. To our knowledge, no one has published any work based on actual large-scale recordings of vehicle movements. We use recordings of actual vehicle movements on various roadways. In order to enable analysis on this scale, we have developed a new VANET simulator, which can handle many more vehicles than NS-2. To enable us to use our own simulator, we present results of a cross-validation between NS-2 and our simulator, showing that both simulators produce results that are statistically the same. We use our simulator to analyze the proposed authentication mechanism, which relies on ECDSA signatures, comparing it to broadcast authentication using TESLA. We perform our evaluations using real vehicle mobility, which we believe to be the first simulations using real vehicle mobility. Our comparison shows strengths and weaknesses for each of these authentication schemes in terms of the resulting reception rates and latency of broadcast packets.

In this paper we present fundamental results on secure clock synchronization and man-in-the-middle detection using only timing information. Under the assumption of afflne clocks, we present a clock synchronization protocol that can operate on any channel on which data can be sent. We present a clock synchronization protocol from the literature and add verification steps on top of this protocol. These verification steps force man- in-the-middle attackers, who want to delay traffic between the endpoints and yet remain undetected, to impose only constant delays on packets. In a special case, we show that it is possible to identify and ignore attacker-delayed packets. We then show three different types of attackers: a half-duplex attacker that can always be caught using timing information alone, a double full-duplex attacker that can never be caught using only timing information, and a full-duplex attacker whose capability to perform man-in-the- middle attacks depends on its location relative to the endpoints and on the turnaround times of the endpoints. In particular, we prove that certain attackers are impossible to detect using only timing, and we construct defensive protocols that prevent all other man-in- the-middle delay attacks. A particularly noteworthy result is that a single attacker using the same radio technology as the endpoints can never successfully perform a man-in-the-middle attack to delay traffic. These results form a lightweight man-in-the-middle attack detection protocol, on top of which a wide variety of protocols can be built, including routing protocols and more sophisticated heavyweight protocols.

Due to the widespread adoption of the Global Positioning System (GPS), many systems have been designed to use the location information of participants. When these systems confer rights (such as access rights) based on location, such claim must be securely verified in order to prevent attackers from gaining access to resources that should be restricted. Substantial effort has been made on secure location verification; however, previous work does not address the impact of collusion attacks where adversaries share their private keys nor do they address a possible jamming attack where attackers inject a high amount of noise to prevent successful challenge and response receptions. In this paper, we propose a secure multilateration scheme that provides maximal security achievable by any time-of-flight based system that does not employ other verification methods.