Ravi Chugh :: Fine

Encoding Stateful Authorization and Information Flow Policies in Fine

Nikhil Swamy, Juan Chen, and Ravi Chugh
ESOP 2010 [ paper | tech report ]

Proving software free of security bugs is hard. Languages that ensure that programs correctly enforce their security policies would help, but, to date, no security-typed language has the ability to verify the enforcement of the kinds of policies used in practice -- dynamic, stateful policies which address a range of concerns including forms of access control and information flow tracking.

This paper presents Fine, a new source-level security-typed language that, through the use of a simple module system and dependent, refinement, and affine types, checks the enforcement of dynamic security policies applied to real software. Fine is proven sound. A prototype implementation of the compiler and several example programs are available here.

Type-preserving Compilation for Verification of Security Enforcement

Juan Chen, Ravi Chugh, and Nikhil Swamy
PLDI 2010 [ paper ]

A number of programming languages use rich type systems to verify security properties of code. Some of these languages are meant for source programming, but programs written in these languages are compiled without explicit security proofs, limiting their utility in settings where proofs are necessary, e.g., proof-carrying authorization. Others languages do include explicit proofs, but these are generally lambda calculi not intended for source programming, that must be further compiled to an executable form. A language suitable for source programming backed by a compiler that enables end-to-end verification is missing.

In this paper, we present a type-preserving compiler that translates programs written in Fine, a source-level functional language with dependent refinements and affine types, to DCIL, a new extension of the .NET Common Intermediate Language. Fine is type checked using an external SMT solver to reduce the proof burden on source programmers. We extract explicit LCF-style proof terms from the solver and carry these proof terms in the compilation to DCIL, thereby removing the solver from the trusted computing base. Explicit proofs enable DCIL to be used in a number of important scenarios, including the verification of mobile code, proof-carrying authorization, and evidence-based auditing. We report on our experience using Fine to build reference monitors for several applications, ranging from a plugin-based email client to a conference management server.

Software

I implemented the first version of proof reconstruction for Fine by converting proofs from Z3. For more recent details, check out the project pages for Fine and F*, a language that derives from Fine.