PH.D. IN COMPUTER SCIENCE, UNIVERSITY OF VENICE A PH.D. THESIS PROPOSAL

In present-day computing environments, a user often employs programs which are sent or fetched from different sites to achieve his/her goals, either privately or in an organization. Such programs may be run as a code to do a simple calculation task or as interactive parallel programs doing IO operations or communications between resources located almost everywhere in the world. To face up such a complex situation we need frameworks for the formalization, analysis and verification of distributed and mobile systems properties. A process on a network can be influenced by the environment surrounding it, possibly modifying the intended behaviour of the process. Traditional correctness properties and methodologies for sequential systems are no more applicable in presence of distributed and mobile systems. Hence the necessity of designing new formal models for the description of and the reasoning on properties of distributed processes. This necessity has been recently recognized by several authors; milestones papers on this subject are [19, 7]. In particular, the π-calculus [4, 17, 19] is a process calculus where processes interact by sending communication links to each other. The basic computational step is the transfer of a communication link between two processes; the recipient can then use the link for further interaction with other parties. This makes the calculus suitable for modelling systems where the accessible resources vary over time. Following the traditional approaches for the analysis of concurrent systems, properties of mobile processes can be expressed in terms of observational equivalences [20] or modal logics [8, 25]. Traditional verification methods such as type systems, model checking and control flow analysis can been applied also to distributed processes [15, 16, 22]. Although correctness and security issues motivated the studies of abstract models for distributed systems, there are still few works dealing with the verification of correctness or security properties of concurrent and mobiles systems. We propose to study semantic characterizations of distributed systems which are suitable to analyze processes in dynamic environments. Our purpose is to specify a logical/formal tool which makes it easier to deal with concurrent or mobile systems. A logical formalism should simplify the definition of correctness and security properties for a distributed system. A logical formula defines a property and so it detects a class of processes, the processes that enjoys that property. Moreover the logical framework helps in deriving new properties as well as connections between different characterization of process properties. Our purpose is to individuate a logical language which is able to describe the the behaviour and spatial structure of concurrent systems, and thus it is a useful instrument in deriving correct systems in a compositional way. A candidate language is Spatial Logic [5, 6] which provides a powerful language to formally describe the structure of concurrent processes. Our principal intention is to play on Spatial Logic, or logic in general, to describe process behaviour w.r. t mobility and in particular security. In fact security is a basic property for distributed systems [23]. To this aim we started by analyzing the definition of secure process in other formalisms, such as SPA [20] and π calculi. First of all we are studying how security properties are defined in SPA [1, 2, 3, 10, 11, 12], especially noninterference [13, 14]. In particular in SPA we are extending the notion of noninterference to contexts, i.e. processes with a variable subprocess (a hole) that can be replaced by any process, in order to characterize the environments in which such properties can be guaranteed. This will lead us to a notion of “well formed” context. We believe that a “well formed” context is a context which cannot change in unpredictable ways, but follows some predetermined rules. These behavioral constraints should be reflected in the structure of the context itself.