Learn More
We address the problem of characterising the security of a program against unauthorised information flows. Classical approaches are based on non-interference models which depend ultimately on the notion of process equivalence. In these models confidentiality is an absolute property stating the absence of any illegal information flow. We present a model in(More)
Synopsis Algorithms where the ow of information is determined by an element of random choice (a \coin ipping" device), aka randomised algorithms, have known in the last decade a tremendous growth of interest, especially in the eld of complexity theory. Up to now such algorithms have been implemented mostly by means of probabilistic programs written in(More)
This paper investigates a probabilistic version of the concurrent constraint programming paradigm (CCP). The aim is to introduce the possibility to formulate so called \randomised algorithms" within the CCP framework. Our approach incorporates randomness directly within the (operational) semantics instead of referring to an \external" function or procedure(More)
We present a technique for measuring the security of a system which relies on a probabilistic process algebraic formalisation of noninterference. We define a mathematical model for this technique which consists of a linear space of processes and linear transformations on them. In this model the measured quantity corresponds to the norm of a suitably defined(More)
We introduce a quantitative approach to the analysis of distributed systems which relies on a linear operator based network semantics. A typical problem in a distributed setting is how information propagates through a network, and a typical qualitative analysis is concerned with establishing whether some information will eventually be transmitted from one(More)
We present a method for approximating the semantics of probabilistic programs to the purpose of constructing semantics based analyses of such programs. The method resembles the one based on Galois connection as developed in the Cousot framework for abstract interpretation. The main difference between our approach and the standard theory of abstract(More)
We introduce a characterisation of probabilistic transition systems (PTS) in terms of linear operators on some suitably defined vector space representing the set of states. Various notions of process equivalences can then be re-formulated as abstract linear operators related to the concrete PTS semantics via a probabilistic abstract interpretation. These(More)
In this paper we lay the semantic basis for a quantitative security analysis of proba-bilistic systems by introducing notions of approximate confinement based on various process equivalences. We re-cast the operational semantics classically expressed via probabilistic transition systems (PTS) in terms of linear operators and we present a technique for(More)