Privacy-preserving Identity Management

With the technological advances and the evolution of online services, user privacy is becoming a crucial issue in the modern day society. Privacy in the general sense refers to individuals’ ability to protect information about themselves and selectively present it to other entities. This concept is nowadays strongly affected by everyday practices that assume personal data disclosure, such as online shopping and participation in loyalty schemes. This makes it difficult for an individual to control the outflow of her personal data and provides third parties with strong data gathering possibilities. On the other hand, the privacy-related legislation obliges the service providers to limit the collection of personal data and protect the data they collect. In rare cases, the privacy protection can be driven by the desire to build a trust relationship with customers. To achieve the described goals of protecting users’ privacy, this thesis focuses on two aspects of managing personal information. Firstly, we address the privacy-preserving design and development of information systems. The described approach coheres to the privacy-by-design principles, which assert that privacy should be embedded in a system design from the very beginning as an essential component of the core functionality, rather than being introduced as an add-on. Secondly, we develop a framework that informs the users about their privacy level and consequences of utilising a particular service or interacting with a particular service provider. That way, the user is enabled to make informed decisions about the disclosure of her personal information and remain in control of her achieved privacy. The first part of the thesis describes a reusable mechanism for achieving unlinkability and anonymity in incentive systems, such as loyalty schemes or reputation systems, while creating a certain level of assurance for the providers about the participating users. Namely, it allows the users to prove that they are registered for a particular service, that they satisfy specific requirements posed by the provider and that they cannot share their earned benefits, while remaining anonymous. The versatility of the scheme is demonstrated with its application in a privacy-preserving ticketing system for public transport services. The resulting system prevents tracking users’ movements. At the same time, the provider can impose needed restrictions on transport services utilisation. Further, this thesis presents a design of a privacy-preserving eHealth system. It is intended for commercial use, with limited trust assumptions, while protecting users’ personal and sensitive data. It allows the patients and elderly to connect to a range of caregivers and care providers. Besides describing the architectural design of the system, we also develop the protocols that describe its functioning. The latter part of this thesis focuses on ensuring user informedness about their attained privacy level. It presents a logic-based framework that allows the users to track which information is known or can be learned by which providers. This is achieved through modelling relevant credential technologies, service providers and the interactions of a user, i.e. data disclosures. The framework also evaluates which interactions can be linked together, as these links allow the providers to extend their knowledge about the user. Consequently, the user can decide on which information may be disclosed, by assessing the privacy level that would be achieved.nrpages: 206status: publishe