The increasing concern for identity confidentiality in the Smart City scenario has fostered research on privacy-preserving authentication based on pseudonymization. Pseudonym systems enable citizens to generate pseudo-identities and establish unlinkable anonymous accounts in cloud service providers. The citizen's identity is concealed, and his/her different anonymous accounts cannot be linked to each other. Unfortunately, current pseudonym systems require a trusted certification authority (CA) to issue the cryptographic components (e.g., credentials, secret keys, or pseudonyms) to citizens. This CA, generally a Smart City governmental entity, has the capability to grant or revoke privacy rights at will, hence posing a serious threat in case of corruption. Additionally, if the pseudonym system enables de-anonymization of misusers, a corrupted CA can jeopardize the citizens’ privacy. This paper presents a novel approach to construct a pseudonym system without a trusted issuer. The CA is emulated by a set of Smart City service providers by means of secure multi-party computation (MPC), which circumvents the requirement of assuming an honest CA. The paper provides a full description of the system, which integrates an MPC protocol and a pseudonym-based signature scheme. The system has been implemented and tested.

Attribute-based authentication is considered a cornerstone component to achieve scalable fine-grained access control in the fast growing market of cloud-based services. Unfortunately, it also poses a privacy concern. User’s attributes should not be linked to the users’ identity and spread across different organizations. To tackle this issue, several solutions have been proposed such as Privacy Attribute-Based Credentials (Privacy-ABCs), which support pseudonym-based authentication with embedded attributes. Privacy-ABCs allow users to establish anonymous accounts with service providers while hiding the identity of the user under a pseudonym. However, Privacy-ABCs require the selective disclosure of the attribute values towards service providers. Other schemes such as Attribute-Based Signatures (ABS) and mesh signatures do not require the disclosure of attributes; unfortunately, these schemes do not cater for pseudonym generation in their construction, and hence cannot be used to establish anonymous accounts. In this article, we propose a pseudonym-based signature scheme that enables unlinkable pseudonym self-generation with embedded attributes, similarly to Privacy-ABCs, and integrates a secret sharing scheme in a similar fashion to ABS and mesh signature schemes for attribute verification. Our proposed scheme also provides verifiable delegation, enabling users to share attributes according to the service providers’ policies.

Data privacy concerns are increasing significantly in the context of the Internet of Things, cloud services, edge computing, artificial intelligence applications, and other applications enabled by next-generation networks. Homomorphic encryption addresses privacy challenges by enabling multiple operations to be performed on encrypted messages without decryption. This article comprehensively addresses homomorphic encryption from both theoretical and practical perspectives. This article delves into the mathematical foundations required to understand fully homomorphic encryption ($\textsf {FHE}$). It consequently covers design fundamentals and security properties of$\textsf {FHE}$and describes the main$\textsf {FHE}$schemes based on various mathematical problems. On a more practical level, this article presents a view on privacy-preserving machine learning using homomorphic encryption and then surveys$\textsf {FHE}$at length from an engineering angle, covering the potential application of$\textsf {FHE}$in fog computing and cloud computing services. It also provides a comprehensive analysis of existing state-of-the-art$\textsf {FHE}$libraries and tools, implemented in software and hardware, and the performance thereof.

Crowdsensing requires scalable privacy-preserving authentication that allows users to send anonymously sensing reports, while enabling eventual anonymity revocation in case of user misbehavior. Previous research efforts already provide efficient mechanisms that enable conditional privacy through pseudonym systems, either based on Public Key Infrastructure (PKI) or Group Signature (GS) schemes. However, previous schemes do not enable users to self-generate an unlimited number of pseudonyms per user to enable users to participate in diverse sensing tasks simultaneously, while preventing the users from participating in the same task under different pseudonyms, which is referred to as sybil attack. This paper addresses this issue by providing a scalable privacy-preserving authentication solution for crowdsensing, based on a novel pseudonym-based signature scheme that enables unlinkable-yet-accountable pseudonymity. The paper provides a detailed description of the proposed scheme, the security analysis, the performance evaluation, and details of how it is implemented and integrated into a real crowdsensing platform.

The advances and fast spread of mobile devices and technologies, we witness today, have extended its advantages over medical and health practice supported by mobile devices, giving rise to the growing research of Internet of Things (IoT), especially the e-Health field. The features provided by mobile technologies revealed to be of major importance when we consider the continuous aging of population and the consequent increase of its debilities. In addition to the increase of lifetime span of population, also the increase of health risks and their locomotive impairments increases, requiring a close monitoring and continuous evaluation. Such monitoring should be as noninvasive as possible, in order not to compromise the mobility and the day-to-day activities of citizens. Therefore, we present the development of a noninvasive optical fiber sensor (OFS) architecture adaptable to a shoe sole for plantar pressure remote monitoring, which is suitable to be integrated in an IoT e-Health solution to monitor the well-being of individuals. This paper explores the production of the OFS multiplexed network (using fiber Bragg gratings) to monitor the foot plantar pressure distribution during gait (walking movement). From the acquired gait data, it is possible to infer health conditions of the patient's foot and spine posture. To guarantee the patients mobility, the proposed system consists of an OFS network integrated with a wireless transceiver to enable efficient ubiquitous monitoring of patients. This paper shows the calibration and measurement results, which reflect the accuracy of the proposed system, under normal walking in controlled area.

In the forthcoming Smart City scenario, Service Providers will require users to authenticate themselves and authorize their mobile applications to access their remote accounts. In this scenario, OAuth 2.0 has been widely adopted as a de facto authentication and authorization protocol. However, the current OAuth 2.0 protocol specification does not consider the user privacy issue and presents several vulnerabilities that can jeopardize users’ privacy rights. Therefore, in this paper we propose an OAuth 2.0 based protocol for Smart City mobile applications that addresses the user privacy issue by integrating a pseudonym-based signature scheme and a signature delegation scheme into the OAuth 2.0 protocol flow. The proposed solution allows users to self-generate user-specific and app-specific pseudonyms on-demand and ensure privacy-enhanced user authentication at the Service Provider side. The proposed protocol has been validated with Proverif and its performance has been evaluated in terms of time and space complexity. Results show that the proposed protocol can provide users with efficient and effective means to authenticate towards service providers while preventing user tracking and impersonation from malicious entities located in the network side or in the users’ mobile device.

Exploiting physical layer in achieving different security aspects in wireless communications has been widely encouraged. In this work, the authors propose an entity authentication scheme for mobile devices with multiple antennas, which is purely based on physical layer parameters. According to the proposed scheme, in order to authenticate a device, a number of predefined authentication signals should be detected at the receive antennas on the authenticator side. The transmitted signals are designed based on the instantaneous channel responses in order to deliver the authentication signals to the receiver. The proposed scheme works efficiently even for mobile users, which is considered a significant improvement over previous related works. Mathematical analysis of the different involved factors along with sufficient simulations show the high performance of the proposed authentication scheme.

The continuous aging of the population has increased health risks, leading to the need for close monitoring of elder citizens and patients. Fortunately, the field of e-Health has been experiencing great progress, although it still faces challenges, since it needs to be applied without compromising the mobility or lifestyle of monitored patients; i.e. non-invasive. Addressing such challenges, we present a non-invasive energy- efficient insole optical fiber sensor architecture for plantar pressure monitoring. The paper shows the design and implementation of a non-invasive "in-sole" optical fiber sensor network (using Fiber Bragg Gratings), which is able to monitor health conditions by observing plantar pressure distribution in the foot. The system integrates the optical fiber sensor network with an energy efficient wireless transceiver, in order to allow continuous monitoring of monitored patients, during their uninterrupted daily routine. The paper presents the calibration and laboratory measurements of the sensing network. The recorded measurements show the suitability and high accuracy of the proposed system in monitoring the plantar pressure distribution during walking movement (i.e. gait).

In the context of the Smart City concept, mobile e-Health applications can play a pivotal role towards the improvement of citizens' quality of life, since they can enable citizens to access personalized e-Health services, without limitations on time and location. However, accessing personalized e-Health services through citizens' mobile e-Health applications, running on their mobile devices, raises many privacy issues in terms of citizens' identity and location. These privacy issues should be addressed so that citizens, concerned about privacy leakage, will embrace Smart City mobile e-Health applications and reap their benefits. Hence, in this paper we propose an OAuth2-based protocol with strong user privacy preservation that addresses these privacy issues. Our proposed protocol follows the OAuth2 protocol flow and integrates a pseudonym-based signature scheme and a delegation signature scheme into the user authentication phase of the OAuth2 protocol. The proposed protocol enables citizens authentication towards the servers providing personalized e-Health services, while preserving their privacy from malicious mobile applications and/or eavesdroppers. Moreover, the proposed protocol does not require to store sensitive information in the citizens' mobile devices.

Security is of paramount importance for vehicular communications to verify regular updates from authorized vehicles while detecting misleading reports from malicious or malfunctioning on board units (OBUs). This should however be provided without violating the privacy of the users. Using frequently changing pseudonyms for the vehicles is an effective solution to preserve their privacy. However, in current systems the vehicles need to be always connected to the Certification Authority (CA) to receive the pseudonyms. This might be unfeasible due to the sparse infrastructure deployment, especially in the early stage of the technology, that can lead to availability and scalability problems. In this paper, we solve this issue by proposing efficient protocols for authentication, pseudonym generation, message verification and anonymity revocation that do not require permanent contact with the CA. Even in case of network availability, this feature also reduces the communication overhead for the pseudonym generation and revocation list distribution.

Abstract Cognitive radio is envisaged as a promising solution to cope with the problem of spectrum scarcity. In cognitive radio networks, users can sense the medium and opportunistically use available frequency bands. Users can cooperate in order to increase the reliability of the sensing process, which is called cooperative spectrum sensing (CSS). However, cooperative paradigms are threatened by the behavior of malicious users. Two types of attacks represent the main threats for CSS network operation, namely, spectrum sensing data falsification (SSDF) and incumbent emulation (IE). These two types of attacks have received a considerable amount of attention in the literature, but they have always been studied separately. In this paper, we propose a novel mechanism based on lightweight cryptography that considers both SSDF and IE attacks combined in a CSS network for the first time. Lightweight cryptography, in contrast to previous techniques used (such as intrusion detection or reputation systems), provides higher resilience to such attacks when a high number of mobile malicious users exist, providing better energy efficiency. Analytical and simulation results show the outperformance of the proposed algorithm compared with previous mechanisms, in terms of lower false alarm probability (i.e., higher chance of using the free frequency bands) and hence better energy ratings. Copyright © 2015 John Wiley & Sons, Ltd.

Hierarchical ad hoc networks have gained popularity due to the huge number of mobile devices, as well as the social content distribution which is frequently location based. One major issue of hierarchical networks due to mobility is the overlapping of clusters. The issue is often resolved by merging of overlapping clusters. Some efforts propose immediate merging of clusters, while others suggest contention intervals before merging without detailed analysis of the length of such intervals. The literature lacks a thorough study of the efficiency of merging procedures. This paper represents a comprehensive study of the merging procedures. The paper derives an analytical model to compare the merging procedure with and without applying contention intervals. The effect of varying the length of contention intervals on the cluster stability and energy efficiency is also studied. The results show that adopting contention intervals is not recommended. Instead, to achieve the best energy efficiency when two clusters overlap, the clusters should either merge immediately or avoid merging, depending on the characteristics of the scenario. The analytical results are supported with simulations.

Cooperative communications have been gaining huge attention lately, due to the increase in the number of mobile devices and the advancement in their capabilities. In this framework, a commonly suggested approach to benefit from cooperation is the formation of virtual groups of mobile terminals. Mobility-aware algorithms are commonly proposed, where nodes form cooperative clusters according their basic mobile characteristics. However, more detailed mobility pattern information is not used to improve the performance of these systems. The reason is the complexity of current mobility pattern recognition algorithms that require previous set up and advanced knowledge on the scenario. This paper presents a novel cognitive algorithm for the identification of mobility patterns that can be used for mobile group formation and that requires no configuration. The proposed algorithm, based on data mining techniques and cooperative optimization, can evaluate the number of mobility patterns in the scenario and classify nodes according these patterns in a distributive fashion. The algorithm is mathematically presented and tested with extended simulations in both Matlab and ns-2.