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We present the first formal verification of a networked server implemented in C. Interaction trees, a general structure for representing reactive computations, are used to tie together disparate verification and testing tools (Coq, VST, and QuickChick) and to axiomatize the behavior of the operating system on which the server runs (CertiKOS). The main theorem connects a specification of acceptable server behaviors, written in a straightforward "one client at a time" style, with the CompCert semantics of the C program. The variability introduced by low-level buffering of messages and interleaving of multiple TCP connections is captured using network refinement, a variant of observational refinement., 13 pages + references

Bidirectional transformations between different data representations occur frequently in modern software systems. They appear as serializers and deserializers, as database views and view updaters, and more. Manually building bidirectional transformations---by writing two separate functions that are intended to be inverses---is tedious and error prone. A better approach is to use a domain-specific language in which both directions can be written as a single expression. However, these domain-specific languages can be difficult to program in, requiring programmers to manage fiddly details while working in a complex type system. To solve this, we present Optician, a tool for type-directed synthesis of bijective string transformers. The inputs to Optician are two ordinary regular expressions representing two data formats and a few concrete examples for disambiguation. The output is a well-typed program in Boomerang (a bidirectional language based on the theory of lenses). The main technical challenge involves navigating the vast program search space efficiently enough. Unlike most prior work on type-directed synthesis, our system operates in the context of a language with a rich equivalence relation on types (the theory of regular expressions). We synthesize terms of a equivalent language and convert those generated terms into our lens language. We prove the correctness of our synthesis algorithm. We also demonstrate empirically that our new language changes the synthesis problem from one that admits intractable solutions to one that admits highly efficient solutions. We evaluate Optician on a benchmark suite of 39 examples including both microbenchmarks and realistic examples derived from other data management systems including Flash Fill, a tool for synthesizing string transformations in spreadsheets, and Augeas, a tool for bidirectional processing of Linux system configuration files., 127 Pages, Extended Version with Appendix

This paper presents an embedded security sublanguage for enforcing information-flow policies in the standard Haskell programming language. The sublanguage provides useful information-flow control mechanisms including dynamic security lattices, run-time code privileges and declassification all without modifying the base language. This design avoids the redundant work of producing new languages, lowers the threshold for adopting security-typed languages, and also provides great flexibility and modularity for using security-policy frameworks.The embedded security sublanguage is designed using a standard combinator interface called arrows. Computations constructed in the sublanguage have static and explicit control-flow components, making it possible to implement information-flow control using static-analysis techniques at run time, while providing strong security guarantees. This paper presents a formal proof that our embedded sublanguage provides noninterference, a concrete Haskell implementation and an example application demonstrating the proposed techniques.11This paper is an expanded version of an earlier paper that appeared in IEEE CSFW (Li and Zdancewic, 2006 [4]).

We introduce a Hoare-style logic for probabilistic programs, called VPHL , that has been formally verified in the Coq proof assistant. VPHL features propositional, rather than additive, assertions and a simple set of rules for reasoning about these assertions using the standard axioms of probability theory. VPHL 's assertions are partial correctness assertions , meaning that their conclusions are dependent upon (deterministic) program termination. The underlying simple probabilistic imperative language, PrImp , includes a probabilistic toss operator, probabilistic guards and potentially-non-terminating while loops.