From fine- to coarse-grained dynamic information flow control and back

Abstract

We show that fine-grained and coarse-grained dynamic information-flow control (IFC) systems are equally expressive. To this end, we mechanize two mostly standard languages, one with a fine-grained dynamic IFC system and the other with a coarse-grained dynamic IFC system, and prove a semantics-preserving translation from each language to the other. In addition, we derive the standard security property of non-interference of each language from that of the other, via our verified translation. This result addresses a longstanding open problem in IFC: whether coarse-grained dynamic IFC techniques are less expressive than fine-grained dynamic IFC techniques (they are not!). The translations also stand to have important implications on the usability of IFC approaches. The coarse-to fine-grained direction can be used to remove the label annotation burden that fine-grained systems impose on developers, while the fine-to coarse-grained translation shows that coarse-grained systemsÐwhich are easier to design and implementÐcan track information as precisely as fine-grained systems and provides an algorithm for automatically retrofitting legacy applications to run on existing coarse-grained systems. CCS Concepts: • Security and privacy → Formal security models;

Mechanized logical relations for termination-insensitive noninterference

“…Our semantic handling of label polymorphism is also different due to our use of semantic worlds. Rajani and Garg use their relation to prove that the fine-grained and coarse-grained static IFC systems are equivalent; Vassena et al [2019] show a similar result for dynamic information-flow control systems.…”

A Dependently Typed Library for Static Information-Flow Control in Idris

“…Their approach is different to the coarse-grained approach taken in our work where only some computations and values have associated security labels. Rajani and Garg [32] show that both approaches are equally expressive for static IFC techniques and Vassena et al [47] show the same for dynamic IFC techniques.…”

Nontransitive Policies Transpiled

“…They show that fine-grained type systems that track the propagation of values are as expressive as coarse-grained type systems that track the propagation of context. Vassena et al [31] expand the study to the dynamic setting. Xiang and Chong [33] use opaque labeled values in their study of dynamic coarse-grained information flow control for Java-like languages.…”