Effective and robust operations, as well as security and privacy are critical for the deployment of vehicular ad hoc networks (VANETs). Efficient and easy-to-manage security and privacy-enhancing mechanisms are essential for the wide-spread adoption of the VANET technology. In this paper, we are concerned with this problem; and in particular, how to achieve efficient and robust pseudonym-based authentication. We design mechanisms that reduce the security overhead for safety beaconing, and retain robustness for transportation safety, even in adverse network settings. Moreover, we show how to enhance the availability and usability of privacy-enhancing VANET mechanisms: Our proposal enables vehicle on-board units to generate their own pseudonyms, without affecting the system security.

Vehicular Communication (VC) systems are on the verge of practical deployment. Nonetheless, their security and privacy protection is one of the problems that have been tackled only recently. In order to show the feasibility of secure VC, implementations are required. In [8] we have discussed the design of a VC security system that has emerged as a result of the European SeVeCom project. In this second paper, we discuss various issues related to the implementation and deployment aspects of secure VC systems. Moreover, we provide an outlook on open security research issues, which will arise as VC systems develop from today's simple prototypes to full-fledged systems.

Abstract-Vehicular communication (VC) systems are being developed primarily to enhance transportation safety and efficiency. Vehicle-to-vehicle communication, in particular, frequent cooperative awareness messages or safety beacons, has been considered over the past years as a main approach. Meanwhile, the need to provide security and to safeguard users' privacy is well understood, and security architectures for VC systems have been proposed. Although technical approaches to secure VC have several commonalities and a consensus has formed, there are critical questions that have remained largely unanswered: Are the proposed security and privacy schemes practical? Can the secured VC systems support the VC-enabled applications as effectively as unsecured VC would? How should security be designed so that its integration into a VC system has a limited effect on the system's performance? In this paper, we provide answers to these questions, investigating the joint effect of a set of system parameters and components. We consider the state-ofthe-art approach in secure VC, and we evaluate analytically and through simulations the interdependencies among components and system characteristics. Overall, we identify key design choices for the deployment of efficient, effective, and secure VC systems.

Transportation safety, one of the main driving forces of the development of vehicular communication (VC) systems, relies on high-rate safety messaging (beaconing). At the same time, there is consensus among authorities, industry, and academia on the need to secure VC systems. With specific proposals in the literature, a critical question must be answered: can secure VC systems be practical and satisfy the requirements of safety applications, in spite of the significant communication and processing overhead and other restrictions security and privacy-enhancing mechanisms impose? To answer this question, we investigate in this paper the following three dimensions for secure and privacy-enhancing VC schemes: the reliability of communication, the processing overhead at each node, and the impact on a safety application. The results indicate that with the appropriate system design, including sufficiently high processing power, applications enabled by secure VC can be in practice as effective as those enabled by unsecured VC. I. INTRODUCTIONVehicular communication (VC) systems are developed as a means to enhance transportation safety and efficiency. Vehicles and road-side infrastructure units (RSUs) are equipped with on-board sensors, computers, and wireless transceivers. Vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication enable primarily safety applications. Many research and development projects, including the Car-to-Car Communication Consortium in Europe and the US Department of Transportation VII initiative, converge towards a design with vehicles frequently beaconing their position along with warnings on their condition or the environment. Typical beaconing periods considered are in the order of one beacon per 100 milliseconds per vehicle.At the same time, it has been understood that VC systems are vulnerable to attacks and that the privacy of their users is at stake. For example, an attacker could inject messages with false information, or collect vehicle messages to track their locations and infer sensitive user data. As a result, the research community in industry and academia, with the endorsement of authorities, has undertaken three major efforts to design security and privacy enhancing solutions for VC: the NoW project [8], the IEEE 1609.2 working group [9], and the SeVeCom project [11].A few basic ideas transcend all these efforts to develop VC security architectures. They all build on top of a currently

WiFi's dependability requirements are growing as its usage spreads to public hotspots and personal home networks. Authentication and confidentiality are crucial issues for corporate WiFi use, but privacy and availability tend to dominate pervasive usage. This article discusses dependability and its impact on WiFi usage scenarios.