Keywords: Why3

This paper introduces separation predicates, a technique to reuse some ideas from separation logic in the framework of program verification using a traditional first-order logic. The purpose is to benefit from existing specification languages, verification condition generators, and automated theorem provers. Separation predicates are automatically derived from user-defined inductive predicates. We illustrate this idea on a non-trivial case study, namely the composite pattern, which is specified in C/ACSL and verified in a fully automatic way using SMT solvers Alt-Ergo, CVC3, and Z3.

The use of constraints in types is quite natural. Yet, integrating constraint based types into the heart of a modern, statically typed, object-oriented programming language is quite tricky. Over the last five years we have designed and implemented the constrained types framework in the programming language X10. In this paper we review the conceptual design, the practical implementation issues, and the many new questions that are raised. We expect the pursuit of these questions to be a profitable area of future work.

Unstructured (low-level) programs tend to be challenging to prove correct, since the control flow is arbitrary complex and there are no obvious points in the code where to insert logical assertions. In this paper, we present a system to formally verify ARM programs, based on a flow sequentialization methodology and a formalized ARM semantics. This system, built upon the why3 verification platform, takes an annotated ARM program, turns it into a set of purely sequential flow programs, translates these programs' instructions into the corresponding formalized opcodes and finally calls the Why3 VCGen to generate the verification conditions that can then be discharged by provers. A prototype has been implemented and used to verify several programming examples.

Keywords: Why3

Watermarking techniques are used to help identifying copies of publicly released information. They consist in applying a slight and secret modification to the data before its release, in a way that should be robust, ie., remain recognizable even in (reasonably) modified copies of the data. In this paper, we present new results about the robustness of watermarking schemes against arbitrary attackers, and the formalization of those results in Coq. We used the ALEA library, which formalizes probability theory and models probabilistic programs using a simple monadic translation. This work illustrates the strengths and particularities of the induced style of reasoning about probabilistic programs. Our technique for proving robustness is adapted from methods commonly used for cryptographic protocols, and we discuss its relevance to the field of watermarking.

Keywords: watermarking, probabilistic algorithms, formal proofs, security, interactive theorem proving

Cubicle is a new model checker for verifying safety properties of parameterized systems. It implements a parallel symbolic backward reachability procedure using Satisfiabilty Modulo Theories. Experiments done on classic and challenging mutual exclusion algorithms and cache coherence protocols show that Cubicle is effective and competitive with state-of-the-art model checkers.

Lucy-n is a language for programming networks of processes communicating through bounded buffers. A dedicated type system, termed a clock calculus, automatically computes static schedules of the processes and the sizes of the buffers between them.

In this article, we present a new algorithm which solves the subtyping constraints generated by the clock calculus. The advantage of this algorithm is that it finds schedules for tightly coupled systems. Moreover, it does not overestimate the buffer sizes needed and it provides a way to favor either system throughput or buffer size minimization.

We present a method to discharge proof obligations from Atelier B using multiple SMT solvers. It is based on a faithful modeling of B's set theory into polymorphic first-order logic. We report on two case studies demonstrating a significant improvement in the ratio of obligations that are automatically discharged.

This paper describes a novel decision procedure for quantifier-free linear integer arithmetic. Standard techniques usually relax the initial problem to the rational domain and then proceed either by projection (e.g. Omega-Test) or by branching/cutting methods (branch-and-bound, branch-and-cut, Gomory cuts). Our approach tries to bridge the gap between the two techniques: it interleaves an exhaustive search for a model with bounds inference. These bounds are computed provided an oracle capable of finding constant positive linear combinations of affine forms. We also show how to design an efficient oracle based on the Simplex procedure. Our algorithm is proved sound, complete, and terminating and is implemented in the Alt-Ergo theorem prover. Experimental results are promising and show that our approach is competitive with state-of-the-art SMT solvers.

We report on the second verified software competition. It was organized by the three authors on a 48 hours period on November 8--10, 2011. This paper describes the competition, presents the five problems that were proposed to the participants, and gives an overview of the solutions sent by the 29 teams that entered the competition.

This article details the formal verification of a 2-line C program that computes the number of solutions to the n-queens problem. The formal proof of (an abstraction of) the C code is performed using the Why3 tool to generate the verification conditions and several provers (Alt-Ergo, CVC3, Coq) to discharge them. The main purpose of this article is to illustrate the use of Why3 in verifying an algorithmically complex program.

Keywords: Why3

Keywords: Why3

Keywords: Why3

SMT solvers can decide the satisfiability of ground formulas modulo a combination of built-in theories. Adding a built-in theory to a given SMT solver is a complex and time consuming task that requires internal knowledge of the solver. However, many theories can be easily expressed using first-order formulas. Unfortunately, since universal quantifiers are not handled in a complete way by SMT solvers, these axiomatics cannot be used as decision procedures. In this paper, we show how to extend a generic SMT solver to accept a custom theory description and behave as a decision procedure for that theory, provided that the described theory is complete and terminating in a precise sense. The description language consists of first-order axioms with triggers, an instantiation mechanism that is found in many SMT solvers. This mechanism, which usually lacks a clear semantics in existing languages and tools, is rigorously defined here; this definition can be used to prove completeness and termination of the theory. We demonstrate on two examples, how such proofs can be achieved in our formalism.

Keywords: Quantifiers, Triggers, SMT Solvers, Theories

Keywords: Why3