Team Comète

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Overall Objectives
Scientific Foundations
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Section: Overall Objectives

Overall Objectives

The research of the Comète team focuses on the theoretical foundations of distributed and mobile systems. The project follows two main directions: the study, implementation and applications of the probabilistic $ \pi$ -calculus, a variant of the $ \pi$ -calculus, and the use of higher-order functional programming languages for distributed applications, in particular in the context of peer-to-peer systems.

Our main field of application are large-scale Distributed Mobile Systems (DMS) of computing devices of varying character providing diverse services. In this context, it is a daunting technical and scientific challenge to develop reasoning techniques which allow us to build systems guaranteeing that processes and data move in a secure, highly distributed network of devices which may individually exhibit failures but together work as a reliable, dependable system.

Formal Specification and Verification is of great help for system building and reasoning. The issue is to formally verifying whether a given system complies with a given specification typically expressed as temporal/spatial logic formulas, process expressions, or automata.

Model checking prevails in today's verification techniques. However, model checking usually needs a finite-state representation of systems, while most DMS are inherently open: there is no bound on the number of resources/devices that can be part of a system. In other words, many DMS's phenomena are best represented in models providing for unbounded or infinite systems. We consider the challenging problem of extending model checking techniques, possibly by combining them with deductive techniques, for the verification of DMS in unbounded or (infinite) scenarios.

Fault tolerance is a fundamental issue of DMS as they must often provide reliable services despite the occurrence of various types of failure. The use of specifications enriched with stochastic information and probabilistic reasoning provides a powerful mathematical tool for analyzing DMS that may exhibit failures. For example, stochastic information with probabilistic techniques can be used for specifying the rate at which faulty communication channels drop messages and for verifying message-delivery properties of the corresponding system. The probabilistic specification and verification of DMS is one of goals of Comète.

The highly distributed and mobile nature of the systems under consideration makes them more accessible and hence more vulnerable. Security is therefore crucial for these systems. The specification and verification of security properties has until now mainly addressed finite-state, deterministic processes (or protocols). We believe that more attention needs to be paid to infinite-state and probabilistic frameworks for the faithful modeling of features such as nonce generation , cryptographic attacks , and an open number of participants . Such features are prominently present in the DMS we are interested.

Our general goal is to provide rigorous theories and tools for the specification and verification of DMS. In particular, we shall deal with the following fundamental specific issues in the specification and verification of DMS: Infinite (or Unbounded) Systems , Probabilistic Specifications and Specification and Verification of Security . Our approach will involve the use of tools from Process Calculi, Constraint Technology and Probabilistic Methods. We shall introduce these tools before describing our project approach.


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