Lenient array operations for practical secure information flow

Our goal in this paper is to make secure information flow typing more practical. We propose simple and permissive typing rules for array operations in a simple sequential imperative language. Arrays are given types of the form τ₁ arr τ₂, where τ₁ is the security class of the array´s contents and τ₂ is the security class of the array´s length. To keep the typing rules permissive, we propose a novel, lenient semantics for out-of-bounds array indices. We show that our type system ensures a noninterference property, and we present an example that suggests that it will not be too difficult in practice to write programs that satisfy the typing rules.