Noninterference for free

Abstract

The dependency core calculus (DCC) is a framework for studying a variety of dependency analyses (e.g., secure information flow). The key property provided by DCC is noninterference, which guarantees that a low-level observer (attacker) cannot distinguish high-level (protected) computations. The proof of noninterference for DCC suggests a connection to parametricity in System F, which suggests that it should be possible to implement dependency analyses in languages with parametric polymorphism. We present a translation from DCC into Fω and prove that the translation preserves noninterference. To express noninterference in Fω, we define a notion of observer-sensitive equivalence that makes essential use of both first-order and higher-order polymorphism. Our translation provides insights into DCC's type system and shows how DCC can be implemented in a polymorphic language without loss of the noninterference (security) guarantees available in DCC. Our contributions include proof techniques that should be valuable when proving other secure compilation or full abstraction results.