Tools for Achieving Usable Ex Post Transparency: A Survey

Transparency of personal data processing is a basic privacy principle and a right that is well acknowledged by data protection legislation, such as the EU general data protection regulation (GDPR). The objective of ex post transparency enhancing tools (TETs) is to provide users with insight about what data have been processed about them and what possible consequences might arise after their data have been revealed, that is, ex post. This survey assesses the state of the art in scientific literature of the usability of ex post TETs enhancing privacy and discusses them in terms of their common features and unique characteristics. The article first defines the scope of usable transparency in terms of relevant privacy principles for providing transparency by taking the GDPR as a point of reference, and usability principles that are important for achieving transparency. These principles for usable transparency serve as a reference for classifying and assessing the surveyed TETs. The retrieval and screening process of the publications is then described, as is the process for deriving the subsequent classification of the characteristics of the TETs. The survey not only looks into what is made transparent by the TETs but also how transparency is actually achieved. A main contribution of this survey is a proposed classification that assesses the TETs based on their functionality, implementation and evaluation as described in the literature. It concludes by discussing the trends and limitations of the surveyed TETs in regard to the defined scope of usable TETs and shows possible directions of future research for addressing these gaps. This survey provides researchers and developers of privacy enhancing technologies an overview of the characteristics of state of the art ex post TETs, on which they can base their work.