A fundamental challenge in controlling the leakage of sensitive information by computer systems is the possibility of correlations between different secrets, with the result that leaking information about one secret may also leak information about a different secret. We explore such leakage, here called Dalenius leakage, within the context of the g-leakage family of leakage measures. We prove a fundamental equivalence between Dalenius min-entropy leakage under arbitrary correlations and g-leakage under arbitrary gain functions, and show how this equivalence increases the significance of the composition refinement relation. We also consider Dalenius leakage in the case when the marginal distributions induced by the correlation are known, giving techniques to compute stronger upper bounds in this case.

We consider the geo-indistinguishability approach to location privacy, and the trade-off with respect to utility. We show that, given a desired degree ofgeo-indistinguishability, it is possible to construct a mechanism that minimizes the service quality loss, using linear programming techniques. In addition we show that, under certain conditions, such mechanism also provides optimal privacy in the sense of Shokri et al. Furthermore, we propose a method to reduce the number of constraints of the linear program from cubic to quadratic, maintaining the privacy guarantees and without affecting significantly the utility of the generated mechanism. This reduces considerably the time required to solve the linear program, thus enlarging significantly the location sets for which the optimal mechanisms can be computed.

The growing popularity of location-based systems, allowing unknown/untrusted servers to easily collect huge amounts of information regarding users' location, has recently started raising serious privacy concerns. In this paper we introduce geoind, a formal notion of privacy for location-based systems that protects the user's exact location, while allowing approximate information -- typically needed to obtain a certain desired service -- to be released.