A model for I/O in equational languages with don't care non-determinism

Existing models for I/O in side-effect free languages focus on functional languages, which are usually based on a largely deterministic reduction strategy, allowing for a strict sequentialization of I/O operations. In concurrent logic programming languages a model is used which allows for don't care non-determinism; the sequentialization of I/O is extensional rather than intensional. We apply this model to equational languages, which are closely related to functional languages, but exhibit don't care non-determinism. The semantics are formulated as constrained narrowing, a relation that contains the rewrite relation, and is contained in the narrowing relation. We present constrained narrowing and some of its properties; a constructive method to transform conventional term rewriting systems to constrained narrowing systems; and a discussion on requirements for an implementation

Meta SOS - A Maude Based SOS Meta-Theory Framework

Meta SOS is a software framework designed to integrate the results from the meta-theory of structural operational semantics (SOS). These results include deriving semantic properties of language constructs just by syntactically analyzing their rule-based definition, as well as automatically deriving sound and ground-complete axiomatizations for languages, when considering a notion of behavioural equivalence. This paper describes the Meta SOS framework by blending aspects from the meta-theory of SOS, details on their implementation in Maude, and running examples.Comment: In Proceedings EXPRESS/SOS 2013, arXiv:1307.690

An Epistemic Approach to Coercion-Resistance for Electronic Voting Protocols

Coercion resistance is an important and one of the most intricate security requirements of electronic voting protocols. Several definitions of coercion resistance have been proposed in the literature, including definitions based on symbolic models. However, existing definitions in such models are rather restricted in their scope and quite complex. In this paper, we therefore propose a new definition of coercion resistance in a symbolic setting, based on an epistemic approach. Our definition is relatively simple and intuitive. It allows for a fine-grained formulation of coercion resistance and can be stated independently of a specific, symbolic protocol and adversary model. As a proof of concept, we apply our definition to three voting protocols. In particular, we carry out the first rigorous analysis of the recently proposed Civitas system. We precisely identify those conditions under which this system guarantees coercion resistance or fails to be coercion resistant. We also analyze protocols proposed by Lee et al. and Okamoto.Comment: An extended version of a paper from IEEE Symposium on Security and Privacy (S&P) 200

Linearization in parallel pCRL

AbstractWe describe a linearization algorithm for parallel pCRL processes similar to the one implemented in the linearizer of the μCRL Toolset. This algorithm finds its roots in formal language theory: the `grammar' defining a process is transformed into a variant of Greibach Normal Form. Next, any such form is further reduced to linear form, i.e., to an equation that resembles a right-linear, data-parametric grammar. We aim at proving the correctness of this linearization algorithm. To this end we define an equivalence relation on recursive specifications in μCRL that is model independent and does not involve an explicit notion of solution

Linearization in parallel pCRL

We describe a linearization algorithm for parallel pCRL processes similar to the one implemented in the linearizer of the mcrl Toolset. This algorithm finds its roots in formal language theory: the `grammar' defining a process is transformed into a variant of Greibach Normal Form. Next, any such form is further reduced to emph{linear form, i.e., to an equation that resembles a right-linear, data-parametric grammar. We aim at proving the correctness of this linearization algorithm. To this end we define an equivalence relation on recursive specifications in mcrl that is model independent and does not involve an explicit notion of solution

Unification Theory - An Introduction

Aus der Einleitung: „Equational unification is a generalization of syntactic unification in which semantic properties of function symbols are taken into account. For example, assume that the function symbol '+' is known to be commutative. Given the unication problem x + y ≐ a + b (where x and y are variables, and a and b are constants), an algorithm for syntactic unification would return the substitution {x ↦ a; y ↦ b} as the only (and most general) unifier: to make x + y and a + b syntactically equal, one must replace the variable x by a and y by b. However, commutativity of '+' implies that {x ↦ b; y ↦ b} also is a unifier in the sense that the terms obtained by its application, namely b + a and a + b, are equal modulo commutativity of '+'. More generally, equational unification is concerned with the problem of how to make terms equal modulo a given equational theory, which specifies semantic properties of the function symbols that occur in the terms to be unified.