Cities are growing as a result of the worldwide urbanization process. With the aim to become more efficient and manage their citizens' needs, governments have had to take action and, as a result, smart cities are no longer a fancy idea but a real issue in most political agendas. Most smart cities are equipped with sets of sensors and actuators that form an Internet of Things (IoT) ecosystem. IoT devices enable the collection of sheer amounts of data, which can be used to provide citizens with services in a more efficient, sustainable and economically-friendly way. Amongst those services, the provision of healthcare is especially relevant, and smart health (s-health) models have been already proposed. Despite its benefits, s-health services pose privacy problems related to the large amounts of sensitive data that they manage. In this article we advocate for the use of attribute-based credentials (ABCs) to cope with privacy issues arising from the collection of health-related data through IoT devices in smart cities. We analyze several s-health applications and show that ABCs could be properly used to address those privacy problems. With this research we set the ground for the further study and application of ABCs in smart health and other privacy-aware IoT-based smart cities' services.Local governments struggle to provide citizens with efficient services and to transform cities into more livable places. With the aim to become smarter, cities adopt information and communication technologies (ICTs) that help them make better decisions. Thus, ICTs are the linchpin of the infrastructure that allows the transformation of cities into smart cities. Many definitions of the concept of smart city have been suggested, each of which emphasizing a specific dimension of the overall idea. A commonly accepted definition of a smart city was proposed by Caragliu et al., augmented by Pérez et al. and served as inspiration to define the concept of smart health in [1]: "Smart cities are cities strongly founded on information and communication technologies that invest in human and social capital to improve the quality of life of their citizens by fostering economic growth, participatory governance, wise management of resources, sustainability, and efficient mobility, whilst they guarantee the privacy and security of their citizens"

Smart cities involve the provision of advanced services for road traffic users. Vehicular ad hoc networks (VANETs) are a promising communication technology in this regard. Preservation of privacy is crucial in these services to foster their acceptance. Previous approaches have mainly focused on PKI-based or ID-based cryptography. However, these works have not fully addressed the minimum information disclosure principle. Thus, questions such as how to prove that a driver is a neighbour of a given zone, without actually disclosing his identity or real address, remain unaddressed. A set of techniques, referred to as Attribute-Based Credentials (ABCs), have been proposed to address this need in traditional computation scenarios. In this paper, we explore the use of ABCs in the vehicular context. For this purpose, we focus on a set of use cases from European Telecommunications Standards Institute (ETSI) Basic Set of Applications, specially appropriate for the early development of smart cities. We assess which ABC techniques are suitable for this scenario, focusing on three representative ones-Idemix, U-Prove and VANETupdated Persiano systems. Our experimental results show that they are feasible in VANETs considering state-of-theart technologies, and that Idemix is the most promising technique for most of the considered use cases.

Technologies based on attribute-based credentials (Privacy-ABC) enable identity management systems that require minimal disclosure of personal information and provide unlinkability of user's transactions. However, underlying characteristics of and differences between Privacy-ABC technologies are currently not well understood. In this paper, we present our efforts in defining a framework for benchmarking Privacy-ABC technologies, and identifying an extensive set of benchmarking criteria and factors impacting such benchmarks. In addition, we identify important challenges in the adoption of Privacy-ABC technologies, indicating directions for future research. The research leading to these results has received funding from the European Communitys Seventh Framework Programme (FP7/2007-2013) under Grant Agreement no. 257782 for the project Attribute-based Credentials for Trust (ABC4Trust).

Privacy-enhancing attribute-based credential (Privacy-ABC) technologies use different cryptographic methods to enhance the privacy of the users. This results in important practical differences between these technologies, especially with regard to efficiency, which have not been studied in depth, but is necessary for assessing their suitability for different user devices and for highly dynamic scenarios. In this paper, we compare the computational efficiency of two prominent Privacy-ABC technologies, IBM's Idemix and Microsoft's U-Prove, covering all known Privacy-ABC features. The results show that overall presentation is in general is more efficient with Idemix, whereas U-Prove is more efficient for the User side (proving) operations during the presentation, and overall when there are more attributes in a credential. For both technologies we confirmed that inspectability, non-revocation proofs, and inequality predicates are costly operations. Interestingly, the study showed that equality predicates, the number of attributes in a credential, and attribute disclosure are done very efficiently. Finally, we identified a number of specific trust issues regarding Privacy-ABC technologies.

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