Recent Developments in Quantitative Information Flow (Invited Tutorial)

In computer security, it is frequently necessary in practice to accept some leakage of confidential information. This motivates the development of theories of Quantitative Information Flow aimed at showing that some leaks are "small" and therefore tolerable. We describe the fundamental view of channels as mappings from prior distributions on secrets to hyper-distributions, which are distributions on posterior distributions, and we show how g-leakage provides a rich family of operationally-significant measures of leakage. We also discuss two approaches to achieving robust judgments about leakage: notions of capacity and a robust leakage ordering called composition refinement.