Campi reali chiusi con esponenziale

Lo scopo di questa tesi è dimostrare che ogni campo reale chiuso con l'esponenziazione ammette una parte intera. Per far questo, inizialmente, definiamo le serie di potenze generalizzate ad esponenti in un gruppo ordinato e a supporto ben ordinato introdotte da Hahn (capitolo 1). Dopo aver dimostrato che tali serie formano un campo, introduciamo il concetto di chiusura per troncamento che permette di 'troncare' le serie dopo un numero fissato di elementi. Successivamente, dopo aver definito la valutazione archimedea standard, vengono fornite le ipotesi necessarie per poter immergere un campo reale chiuso R in un opportuno campo di serie formali. Tali serie hanno coefficienti nel campo residuo di R rispetto alla valutazione archimedea standard v ed esponenti nel gruppo di valutazione di R calcolato ancora rispetto a v. L'immersione definita risulta chiusa per troncamento, quindi si dimostra l'esistenza della parte intera per R. Arriviamo quindi all'argomento principale di questo lavoro. Dopo aver effettuato un cambiamento di notazioni (per poter scrivere gli elementi in forma diadica), passiamo a costruire l'immersione di un campo reale chiuso con esponenziazione in un opportuno campo di serie formali. Ne calcoliamo dunque la parte intera. Come conclusione di questa tesi, illustriamo un importante teorema dovuto a Ressayre, da cui si ha l'equivalenza tra Th(R, 2^x) e la teoria dei campi reali chiusi con l'esponenziale ristretto all'intervallo [0, 1] (Te) unita ad uno schema di assiomi. Questo risultato non solo dà una dimostrazione della model completezza di Th(R, 2^x) alternativa a quella data da Wilkie, ma riconduce il problema della decidibilità della suddetta teoria a quello della decidibilità di Te

Through Modeling to Synthesis of Security Automata

AbstractWe define a set of process algebra operators, that we call controller operators, able to mimic the behavior of security automata introduced by Schneider in [Schneider, F. B., Enforceable security policies, ACM Transactions on Information and System Security 3 (2000), pp. 30–50] and by Ligatti and al. in [Bauer, L., J. Ligatti and D. Walker, More enforceable security policies, in: I. Cervesato, editor, Foundations of Computer Security: proceedings of the FLoC'02 workshop on Foundations of Computer Security (2002), pp. 95–104]. Security automata are mechanisms for enforcing security policies that specify acceptable executions of programs.Here we give the semantics of four controllers that act by monitoring possible un-trusted component of a system in order to enforce certain security policies. Moreover, exploiting satisfiability results for temporal logic, we show how to automatically build these controllers for a given security policy

Model and Synthesize Security Automata

We define a set of process algebra operators (controllers) that mimic the security automata introduced by Schneider in [18] and by Ligatti and al. in [4], respectively. We also show how to automatically build these controllers for given security policies

Action Refinement for Security Properties Enforcement

In this paper we propose an application of the action refinement theory for enforcing security policies at different levels of abstraction by using process algebra controller operators. Let us consider a system that cooperates with a possible untrusted component managed by a programmable controller operator in such a way that the considered composed system is secure, i.e., the composed system works as expected. Firstly, the considered system is specified at a high level of abstraction. Successively, we refine it by applying a refinement function in such a way that we pass through different abstraction levels. Here we investigate on the set of features a refinement function needs to have for guaranteeing that a considered system, which is secure at high level, once refined is still secure regardless the behaviour of the implementation of the untrusted component. Indeed, by applying an action refinement function, it is possible to refine the system, the controller program and the possible untrusted component as if they were three independent entities, in such a way that their implementation does not depend on each other. Hence the capability of the controller operator to make the system secure regardless the behaviour of the untrusted component at high level, is also preserved at a lower level

Partial mode checking, process algebra operators and satisfiability procedures for (automatically) enforcing security properties

In this paper we show how the partial model checking approach for the analysis of secure systems may be also useful for enforcing security properties. We define a set of process algebra operators that act as programmable controllers of possibly insecure components. The program of these controllers may be automatically obtained through the usage of satisfiability procedures for a variant of mu-calculus

A framework for automatic security controller generation

This paper concerns the study, the development and the synthesis of mechanisms for guaranteeing the security of complex systems, i.e., systems composed by several interactive components. A complex system under analysis is described as an open system, in which a certain component has an unspecified behavior (not fixed in advance). Regardless of the unspecified behavior, the system should work properly, e.g., should satisfy a certain property. Within this formal approach, we propose techniques to enforce properties and synthesize controller programs able to guarantee that, for all possible behaviors of the unspecified component, the overall system results secure. For performing this task, we use techniques able to provide us necessary and sufficient conditions on the behavior of this unspecified component to ensure the whole system is secure. Hence, we automatically synthesize the appropriate controller programs by exploiting satisfiability results for temporal logic. We contribute within the area of the enforcement of security properties by proposing a flexible and automated framework that goes beyond the definition of how a system should behave to work properly. Indeed, while the majority of related work focuses on the definition of monitoring mechanisms, we aid in the synthesis of enforcing techniques. Moreover, we present a tool for the synthesis of secure systems able to generate a controller program directly executable on real devices as smart phones

Semiring-based Specification Approaches for Quantitative Security

Our goal is to provide different semiring-based formal tools for the specification of security requirements: we quantitatively enhance the open-system approach, according to which a system is partially specified. Therefore, we suppose the existence of an unknown and possibly malicious agent that interacts in parallel with the system. Two specification frameworks are designed along two different (but still related) lines. First, by comparing the behaviour of a system with the expected one, or by checking if such system satisfies some security requirements: we investigate a novel approximate behavioural-equivalence for comparing processes behaviour, thus extending the Generalised Non Deducibility on Composition (GNDC) approach with scores. As a second result, we equip a modal logic with semiring values with the purpose to have a weight related to the satisfaction of a formula that specifies some requested property. Finally, we generalise the classical partial model-checking function, and we name it as quantitative partial model-checking in such a way to point out the necessary and sufficient conditions that a system has to satisfy in order to be considered as secure, with respect to a fixed security/functionality threshold-value

Closing the loop of SIEM analysis to Secure Critical Infrastructures

Critical Infrastructure Protection is one of the main challenges of last years. Security Information and Event Management (SIEM) systems are widely used for coping with this challenge. However, they currently present several limitations that have to be overcome. In this paper we propose an enhanced SIEM system in which we have introduced novel components to i) enable multiple layer data analysis; ii) resolve conflicts among security policies, and discover unauthorized data paths in such a way to be able to reconfigure network devices. Furthermore, the system is enriched by a Resilient Event Storage that ensures integrity and unforgeability of events stored.Comment: EDCC-2014, BIG4CIP-2014, Security Information and Event Management, Decision Support System, Hydroelectric Da

1st International Workshop on TEchnical and LEgal aspects of data pRIvacy and Security (TELERISE 2015)

This paper is the report on the 1st International Workshop on TEchnical and LEgal aspects of data pRIvacy and SEcurity (TELERISE 2015) at the 37th International Conference on Software Engineering (ICSE 2015). TELERISE investigates privacy and security issues in data sharing from a technical and legal perspective. Keynote speech as well as selected papers presented at the event fit the topics of the workshop. This report gives the rationale of TELERISE and it provides a provisional program