559 research outputs found
Soft Constraint Programming to Analysing Security Protocols
Security protocols stipulate how the remote principals of a computer network
should interact in order to obtain specific security goals. The crucial goals
of confidentiality and authentication may be achieved in various forms, each of
different strength. Using soft (rather than crisp) constraints, we develop a
uniform formal notion for the two goals. They are no longer formalised as mere
yes/no properties as in the existing literature, but gain an extra parameter,
the security level. For example, different messages can enjoy different levels
of confidentiality, or a principal can achieve different levels of
authentication with different principals.
The goals are formalised within a general framework for protocol analysis
that is amenable to mechanisation by model checking. Following the application
of the framework to analysing the asymmetric Needham-Schroeder protocol, we
have recently discovered a new attack on that protocol as a form of retaliation
by principals who have been attacked previously. Having commented on that
attack, we then demonstrate the framework on a bigger, largely deployed
protocol consisting of three phases, Kerberos.Comment: 29 pages, To appear in Theory and Practice of Logic Programming
(TPLP) Paper for Special Issue (Verification and Computational Logic
Soft Concurrent Constraint Programming
Soft constraints extend classical constraints to represent multiple
consistency levels, and thus provide a way to express preferences, fuzziness,
and uncertainty. While there are many soft constraint solving formalisms, even
distributed ones, by now there seems to be no concurrent programming framework
where soft constraints can be handled. In this paper we show how the classical
concurrent constraint (cc) programming framework can work with soft
constraints, and we also propose an extension of cc languages which can use
soft constraints to prune and direct the search for a solution. We believe that
this new programming paradigm, called soft cc (scc), can be also very useful in
many web-related scenarios. In fact, the language level allows web agents to
express their interaction and negotiation protocols, and also to post their
requests in terms of preferences, and the underlying soft constraint solver can
find an agreement among the agents even if their requests are incompatible.Comment: 25 pages, 4 figures, submitted to the ACM Transactions on
Computational Logic (TOCL), zipped file
Soft constraint abstraction based on semiring homomorphism
The semiring-based constraint satisfaction problems (semiring CSPs), proposed
by Bistarelli, Montanari and Rossi \cite{BMR97}, is a very general framework of
soft constraints. In this paper we propose an abstraction scheme for soft
constraints that uses semiring homomorphism. To find optimal solutions of the
concrete problem, the idea is, first working in the abstract problem and
finding its optimal solutions, then using them to solve the concrete problem.
In particular, we show that a mapping preserves optimal solutions if and only
if it is an order-reflecting semiring homomorphism. Moreover, for a semiring
homomorphism and a problem over , if is optimal in
, then there is an optimal solution of such that
has the same value as in .Comment: 18 pages, 1 figur
Quantitative mu-calculus and CTL Based on Constraint Semirings
Model checking and temporal logics are boolean. The answer to the model checking question does a system satisfy a property? is either true or false, and properties expressed in temporal logics are defined over boolean propositions. While this classic approach is enough to specify and verify boolean temporal properties, it does not allow to reason about quantitative aspects of systems. Some quantitative extensions of temporal logics has been already proposed, especially in the context of probabilistic systems. They allow to answer questions like with which probability does a system satisfy a property?
We present a generalization of two well-known temporal logics: CTL and the [mu]-calculus. Both extensions are defined over c-semirings, an algebraic structure that captures many problems and that has been proposed as a general framework for soft constraint satisfaction problems (CSP). Basically, a c-semiring consists of a domain, an additive operation and a multiplicative operation, which satisfy some properties. We present the semantics of the extended logics over transition systems, where a formula is interpreted as a mapping from the set of states to the domain of the c-semiring, and show that the usual connection between CTL and [mu]-calculus does not hold in general. In addition, we reason about the feasibility of computing the logics and illustrate some applications of our framework, including boolean model checking
La scrittura dell'esilio : militari ed intellettuali italiani in Catalogna durante il Trienio Liberal 1820-1823
Il lavoro descrive le scritture lasciate dagli esuli italiani che hanno partecipato al Trienio per ricostruirne l'esperienza individuale e il rapporto con la societĂ in cui si calarono. La prospettiva è storica: incrociata con la letteratura storiografica, la loro produzione può dare nuove informazioni sulle relazioni politiche tra Italia e Spagna, sulla vita sociale della penisola nel Trienio, sulle guerre. L'uso di lettere, dichiarazioni testimoniali, memorie e produzione è quindi proposto come problema di analisi della fonti (produttori e destinatari della scrittura, tempi) perchĂ© oltre a determinare stili e contenuti, danno informazioni sui processi individuali di costruzione dell'identitĂ che accompagna il percorso risorgimentale.This paper describes texts left by Italian exiles who participated in the Trienio (Triennium) in order to reconstruct their personal experience and relationship with the society in which they were immersed. The perspective is historical: when intertwined with historiographiÂcal literature, their production may give new insights into political relations between Italy and Spain, peninsular social life during the Trienio, and wars. The use of letters, witness statements, pleadings and other texts is therefore proposed as a source of analysis (authors and recipients of texts, dates), which, apart from determining style and content, provides information on individual processes of identity construction that took place during the Risorgimento period
Timed Soft Concurrent Constraint Programs: An Interleaved and a Parallel Approach
We propose a timed and soft extension of Concurrent Constraint Programming.
The time extension is based on the hypothesis of bounded asynchrony: the
computation takes a bounded period of time and is measured by a discrete global
clock. Action prefixing is then considered as the syntactic marker which
distinguishes a time instant from the next one. Supported by soft constraints
instead of crisp ones, tell and ask agents are now equipped with a preference
(or consistency) threshold which is used to determine their success or
suspension. In the paper we provide a language to describe the agents behavior,
together with its operational and denotational semantics, for which we also
prove the compositionality and correctness properties. After presenting a
semantics using maximal parallelism of actions, we also describe a version for
their interleaving on a single processor (with maximal parallelism for time
elapsing). Coordinating agents that need to take decisions both on preference
values and time events may benefit from this language. To appear in Theory and
Practice of Logic Programming (TPLP)
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