Programming with explicit security policies

Are computing systems trustworthy? To answer this, we need to know three things: what the systems are supposed to do, what they are not supposed to do, and what they actually do. All three are problematic. There is no expressive, practical way to specify what systems must do and must not do. And if we had a specification, it would likely be infeasible to show that existing computing systems satisfy it. The alternative is to design it in from the beginning: accompany programs with explicit, machine-checked security policies, written by programmers as part of program development. Trustworthy systems must safeguard the end-to-end confidentiality, integrity, and availability of information they manipulate. We currently lack both sufficiently expressive specifications for these information security properties, and sufficiently accurate methods for checking them. Fortunately there has been progress on both fronts. First, information security policies can be made more expressive than simple noninterference or access control policies, by adding notions of ownership, declassification, robustness, and erasure. Second, program analysis and transformation can be used to provide strong, automated security assurance, yielding a kind of security by construction. This is an overview of programming with explicit information security policies with an outline of some future challenges.