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See detailLocation Assurance and Privacy in Location-based Services
Chen, Xihui UL

Doctoral thesis (2014)

Due to the development of global navigation satellite systems (GNSS), people are able to obtain their precise locations in real time. This in turn leads to a wide range of location-based services (LBS ... [more ▼]

Due to the development of global navigation satellite systems (GNSS), people are able to obtain their precise locations in real time. This in turn leads to a wide range of location-based services (LBS), through which a user can acquire information customised to locations. However, the vulnerabilities of GNSS systems and the exposure of information such as locations and queries in LBS requests impose a strong need from users on security. In this thesis, we study two security requirements in LBSs: location assurance and privacy. Location assurance expresses users’ requirement for trustworthy locations in terms of correctness and precision while privacy addresses users’ concern about personal information leakage in LBSs. First, we present a trust framework to detect spoofing by evaluating the integrity of GNSS signals. The framework combines existing spoofing detection methods to generate an overall quantitative evaluation of the integrity of received signals. Based on this evaluation, users can determine the extent to which they can trust their locations. We implement a prototype based on our framework and develop a public service called location assurance certification. In this service, a trusted agent is introduced to issue certificates for users’ locations according to the integrity of their received signals. Second, we propose a general approach to protect users’ query privacy when the adversary has access to various contextual information. We present a probabilistic framework, in which we formally define the attacks to infer the issuers of LBS queries by exploring various contextual information. With this framework, we propose a series of query privacy metrics. These metrics not only measure query privacy from different perspectives but also enable users to express their requirements for query privacy flexibly and precisely. Our framework finally allows us to develop new mechanisms which provide protection for users’ query privacy satisfying their requirements. Third, we address location privacy. Many location privacy preserving methods (LPPM) have been proposed to protect users’ location privacy. A user will make use of them to break the link between his identity and his locations when requesting LBSs. We propose a new attack on location privacy based on the adversary’s observation on users’ locations protected by LPPMs. Compared to existing attacks which target at where users went, our attack provides the adversary with sufficient information to infer what users did, i.e., their activities. Specifically, through our attack, the adversary learns the places where users performed activities and their beginning and ending time of each activity. To achieve this goal, we explore the patterns of users with respect to movements and requesting LBSs, i.e., user profiles. [less ▲]

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See detailProtecting query privacy in location-based services
Chen, Xihui UL; Pang, Jun UL

in GeoInformatica (2014), 18(1), 95-133

The popularity of location-based services (LBSs) leads to severe concerns on users’ privacy. With the fast growth of Internet applications such as online social networks, more user information becomes ... [more ▼]

The popularity of location-based services (LBSs) leads to severe concerns on users’ privacy. With the fast growth of Internet applications such as online social networks, more user information becomes available to the attackers, which allows them to construct new contextual information. This gives rise to new challenges for user privacy protection and often requires improvements on the existing privacy-preserving methods. In this paper, we classify contextual information related to LBS query privacy and focus on two types of contexts – user profiles and query dependency: user profiles have not been deeply studied in LBS query privacy protection, while we are the first to show the impact of query dependency on users’ query privacy. More specifically, we present a general framework to enable the attackers to compute a distribution on users with respect to issuing an observed request. The framework can model attackers with different contextual information. We take user profiles and query dependency as examples to illustrate the implementation of the framework and their impact on users’ query privacy. Our framework subsequently allows us to show the insufficiency of existing query privacy metrics, e.g., k-anonymity, and propose several new metrics. In the end, we develop new generalisation algorithms to compute regions satisfying users’ privacy requirements expressed in these metrics. By experiments, our metrics and algorithms are shown to be effective and efficient for practical usage. [less ▲]

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See detailDEMO: Demonstrating a Trust Framework for Evaluating GNSS Signal Integrity
Chen, Xihui UL; Harpes, Carlo; Lenzini, Gabriele UL et al

in Proceedings of 20th ACM Conference on Computer and Communications Security (CCS'13) (2013, November)

Through real-life experiments, it has been proved that spoofing is a practical threat to applications using the free civil service provided by Global Navigation Satellite Systems (GNSS). In this paper, we ... [more ▼]

Through real-life experiments, it has been proved that spoofing is a practical threat to applications using the free civil service provided by Global Navigation Satellite Systems (GNSS). In this paper, we demonstrate a prototype that can verify the integrity of GNSS civil signals. By integrity we intuitively mean that civil signals originate from a GNSS satellite without having been artificially interfered with. Our prototype provides interfaces that can incorporate existing spoofing detection methods whose results are then combined into an overall evaluation of the signal’s integrity, which we call integrity level. Considering the various security requirements from different applications, integrity levels can be calculated in many ways determined by their users. We also present an application scenario that deploys our prototype and offers a public central service – localisation assurance certification. Through experiments, we successfully show that our prototype is not only effective but also efficient in practice. [less ▲]

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See detailDesign and formal analysis of a group signature based electronic toll pricing system
Chen, Xihui UL; Lenzini, Gabriele UL; Mauw, Sjouke UL et al

in Journal of Wireless Mobile Networks, Ubiquitous Computing, and Dependable Applications (2013), 4(1), 55-75

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See detailExploring dependency for query privacy protection in location-based services
Chen, Xihui UL; Pang, Jun UL

in Proc. 3rd ACM Conference on Data and Application Security and Privacy (2013)

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See detailA trust framework for evaluating GNSS signal integrity
Chen, Xihui UL; Lenzini, Gabriele UL; Martins, Miguel et al

in Proceedings of 26th IEEE Computer Security Foundations Symposium (CSF'13) (2013)

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See detailConstructing and comparing user mobility profiles for location-based services
Chen, Xihui UL; Pang, Jun UL; Xue, Ran

in Proc. 28th ACM Symposium on Applied Computing (2013)

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See detailPost-hoc analysis of user traceability in electronic toll collection systems
Chen, Xihui UL; Fonkwe, David; Pang, Jun UL

in Proc. 7th International Workshop on Data Privacy Management (2013)

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See detailGuidelines for the use and interpretation of assays for monitoring autophagy.
Klionsky, Daniel J.; Abdalla, Fabio C.; Abeliovich, Hagai et al

in Autophagy (2012), 8(4), 445-544

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field ... [more ▼]

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field. [less ▲]

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See detailA group signature based electronic toll pricing system
Chen, Xihui UL; Lenzini, Gabriele UL; Mauw, Sjouke UL et al

in Proc. 7th International Conference on Availability, Reliability and Security (2012)

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See detailImplementation and Validation of a Localisation Assurance Service Provider
Chen, Xihui UL; Harpes, Carlo; Lenzini, Gabriele UL et al

in Proc. 6th ESA Workshop on Satellite Navigation Technologies (2012)

Existing Global Navigation Satellite Systems offer no authentication to the open service signals and so stand-alone receivers are vulnerable to meaconing and spoofing attacks. These attacks interfere with ... [more ▼]

Existing Global Navigation Satellite Systems offer no authentication to the open service signals and so stand-alone receivers are vulnerable to meaconing and spoofing attacks. These attacks interfere with the integrity and authenticity of satellite signals: they can delay signals, or re-broadcast signals. Positioning is thus compromised and location-based services are at risk.This paper describes a solution to mitigate this risk. It is a trusted third-party Localisation Assurance service that informs location-based services providers up to which level a location claimed by client can be trusted. It runs several tests over the localisation data of client receivers and certifies the level of assurance of locations. An assurance level expresses the amount of trust the third-party has that a receiver's location is calculated from integral and authentic satellite signals. [less ▲]

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See detailMeasuring query privacy in location-based services
Chen, Xihui UL; Pang, Jun UL

in Proc. 2nd ACM Conference on Data and Application Security and Privacy (2012)

The popularity of location-based services leads to serious concerns on user privacy. A common mechanism to protect users’ location and query privacy is spatial generalisation. As more user information ... [more ▼]

The popularity of location-based services leads to serious concerns on user privacy. A common mechanism to protect users’ location and query privacy is spatial generalisation. As more user information becomes available with the fast growth of Internet applications, e.g., social networks, attackers have the ability to construct users’ personal profiles. This gives rise to new challenges and reconsideration of the existing privacy metrics, such as k-anonymity. In this paper, we propose new metrics to measure users’ query privacy taking into account user profiles. Furthermore, we design spatial generalisation algorithms to compute regions satisfying users’ privacy requirements expressed in these metrics. By experimental results, our metrics and algorithms are shown to be effective and efficient for practical usage. [less ▲]

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See detailImproving automatic verification of security protocols with XOR
Chen, Xihui UL; van Deursen, Ton UL; Pang, Jun UL

in Proc. 11th International Conference on Formal Engineering Methods (2009)

Detailed reference viewed: 54 (2 UL)