Frédéric Prost

Security policy in a declarative style

We address the problem of controlling information leakage in a concurrent declarative programming setting. Our aim is to define verification tools in order to distinguish between authorized, or declared, information flows such as password testing (e.g., ATM, login processes, etc.) and non-authorized ones. In this paper, we first propose a way to define security policies as confluent and terminating rewrite systems. Such policies define how the privacy levels of information evolve. Then, we provide a formal definition of secure processes with respect to a given security policy. We also define an actual verification algorithm of secure processes based on constraint solving.

Modeling Pointer Redirection as Cyclic Term-graph Rewriting

We tackle the problem of data-structure rewriting including global and local pointer redirections. Each basic rewrite step may perform three kinds of actions: (i) Local redirection, the aim of which is to redirect specific pointers determined by means of a pattern; (ii) Replacement, that may add new information to data-structures; (iii) Global redirection, which is aimed at redirecting all pointers targeting a node towards another one. We define a new framework, following the double-pushout approach, where graph rewrite rules may mix these three kinds of actions in a row. We define first the category of graphs we consider and then we define rewrite rules as pairs of graph homomorphisms of the form L R. In our setting, graph K is not arbitrary, it is used to encode pointer redirection. Furthermore, pushouts do not always exist and complement pushouts, when they exist, are not unique. Despite these concerns, our definition of rewriting steps is such that a rewrite rule can always be fired, once a matching is found.

Handling declared information leakage: extended abstract

We address the problem of controlling information leakage in a concurrent declarative programming setting. Our aim is to define formal tools in order to distinguish between authorized, or declared, information flows such as password testing (e.g., ATM, login processes, etc.) and non-authorized ones. We propose to define security policies as rewriting systems. Such policies define how the privacy levels of information evolve. A formal definition of secure processes with respect to a given security policy is given.

Specializing narrowing for timetable generation: a case study

An important property of strategies used to solve goals in functional logic programming (FLP) languages is the complete exploration of the solution space. Integrating constraints into FLP proved to be useful in many cases, as the resulting constraint functional logic programming (CFLP) offers more facilities and more efficient operational semantics. CFLP can be achieved by means of conditional rewrite systems with a narrowing-based operational semantics. A common idea to improve the efficiency of such operational semantics is to use specific algorithms from operations research as constraint solvers. If the algorithm does not return a complete set of solutions, the property of completeness might be lost. We present a real world timetabling problem illustrating this approach. We propose an algorithm, obtained as an integration of three known optimization algorithms for the linear assignment problem (LAP), enumerating solutions to the LAP in order of increasing weight, such that resolution of goals is complete again. We show, how the narrowing process can be tailored to use this algorithm and provide an efficient way to solve the timetable generation problem.

A formalization of Static Analyses in System F

In this paper, we propose a common theoretical framework for type based static analyses. The aim is the study of relationships between typing and program analysis. We present a variant of Girards System F called F≤:Π. We prove standard properties of F≤:Π. We show how it can be used to formalize various program analyses like binding time and dead code. We relate our work to previous analyses in terms of expressivness (often only simply typed calculi are considered) and power (more information can be inferred). F≤:Π features polymorphism as well as subtyping at the level of universe extending previous author work where only universe polymorphism (on a simply typed calculus) was considered.

Adjunction for garbage collection with application to graph rewriting

We investigate garbage collection of unreachable parts of rooted graphs from a categorical point of view. First, we define this task as the right adjoint of an inclusion functor. We also show that garbage collection may be stated via a left adjoint, hence preserving colimits, followed by two right adjoints. These three adjoints cope well with the different phases of a traditional garbage collector. Consequently, our results should naturally help to better formulate graph transformation steps in order to get rid of garbage (unwanted nodes). We illustrate this point on a particular class of graph rewriting systems based on a double pushout approach and featuring edge redirection. Our approach gives a neat rewriting step akin to the one on terms, where garbage never appears in the reduced term.