Covert channels are used for the secret transfer of information. Encryption only protects communication from being decoded by unauthorised parties, whereas covert channels aim to hide the very existence of the communication. Initially, covert channels were identified as a security threat on monolithic systems i.e. mainframes. More recently focus has shifted towards covert channels in computer network protocols. The huge amount of data and vast number of different protocols in the Internet seems ideal as a high-bandwidth vehicle for covert communication. This article is a survey of the existing techniques for creating covert channels in widely deployed network and application protocols. We also give an overview of common methods for their detection, elimination, and capacity limitation, required to improve security in future computer networks.

https://researchbank.swinburne.edu.au/file/5de97ea6-fcdf-43e5-98ae-0567cdd495f6/1/PDF (Published version).pdf

A survey of covert channels and countermeasures in computer network protocols

In this note, the robust output regulation problem of a multi-agent system is considered. An internal model based distributed control scheme is adopted to achieve the objectives of asymptotic tracking and disturbance rejection in an uncertain multi-agent system where both the reference inputs and disturbances are generated by an exosystem.

A Distributed Control Approach to A Robust Output Regulation Problem for Multi-Agent Linear Systems

http://foresight.ifmo.ru/ict/shared/files/201311/1_123.pdf

Decentralized control: An overview

The Statecharts formalism supports the development of intuitive graphical specifications for reactive systems. Nevertheless, some serious problems became apparent in the original Statecharts formalism so that many different Statecharts variants were proposed to overcome them. These problems are thoroughly described and approaches for solving them are evaluated. Furthermore, a set of distinctive features is elaborated which is used for a detailed comparison of the Statecharts variants. Finally, the feature set is used to characterize a new hypothetical Statecharts variant.

A Comparison of Statecharts Variants

There is a population explosion among the logical systems being used in computer science. Examples include first order logic (with and without equality), equational logic, Horn clause logic, second order logic, higher order logic, infinitary logic, dynamic logic, process logic, temporal logic, and modal logic; moreover ~, there is a tendency for each theorem prover to have its own idiosyncratic logical system. Yet it is usual to give many of the same results and applications for each logical system; of course, this is natural in so far as there are basic results in computer science that are independent of the logical system in which they happen to be expressed. But we should not have to do the same things over and over again; instead, we should generalize, and do the essential things once and for all! Also, we should ask what are the relationships among all these different logical systems. This paper shows how some parts of computer science can be done in any suitable logical system, by introducing the notion of an ins t i tu t ion as a precise generalization of the informal notion of a mlogical system, m A first main result shows that if an institution is such that interface declarations expressed in it can be glued together, then theories {which are just sets of sentences) in that institution can also be glued together. A second main result gives conditions under which a theorem prover for one institution can be validly used on theories from another; this uses the notion of an institution morphism. A third main result shows that institutions admiting free models can be extended to institutions whose theories may include, in addition to the original sentences, various kinds of constraints upon interpretations; such constraints are useful for defining abstract data types, and include so-called • data," "hierarchy, • and regenerating" constraints. Further results show how to define insitutions that mix sentences from one institution with constraints from another, and even mix sentences and {various kinds of) constraints from several different institutions. It is noted that general results about institutions apply to such mmultiplex" institutions, including the result mentioned above about gluing together theories. Finally, this paper discusses some applications of these results to specification languages, showing that much of that subject is in fact independent of the institution used.

Introducing Institutions

We describe the Calculus of Looping Sequences (CLS) which is suitable for modeling microbiological systems and their evolution. We present two extensions, CLS with links (LCLS) and Stochastic CLS. LCLS simplifies the description of protein interaction at a lower level of abstraction, namely at the domain level. Stochastic CLS allows us to describe quantitative aspects of the modeled systems, such as the frequency of chemical reactions. As examples of application to real biological systems, we show the simulation of the activity of the lactose operon in E.coli and the quorum sensing process in P.aeruginosa, both described with Stochastic CLS.

/pdf/the-calculus-of-looping-sequences-4yvjch1w3s.pdf

The calculus of looping sequences

Dynamic Graphs

We develop a model of parametric probabilistic transition Systems (PPTSs), where probabilities associated with transitions may be parameters. We show how to find instances of the parameters that satisfy a given property and instances that either maximize or minimize the probability of reaching a certain state. As an application, we model a probabilistic non-repudiation protocol with a PPTS. The theory we develop allows us to find instances that maximize the probability that the protocol ends in a fair state (no participant has an advantage over the others).

/pdf/parametric-probabilistic-transition-systems-for-system-2sdjwfkrci.pdf

Parametric probabilistic transition systems for system design and analysis

The paper presents the Calculus of Looping Sequences (CLS) suitable to describe microbiological systems and their evolution. The terms of the calculus are constructed by basic constituent elements and operators of sequencing, looping, containment and parallel composition. The looping operator allows tying up the ends of a sequence, thus creating a circular sequence which can represent a membrane. We show that a membrane calculus recently proposed can be encoded into CLS. We use our calculus to model interactions among bacteria and bacteriophage viruses, and to reason on their properties.

/pdf/a-calculus-of-looping-sequences-for-modelling-1jhp94h96k.pdf

Andrea Maggiolo-Schettini

Papers

The calculus of looping sequences

Dynamic Graphs

Parametric probabilistic transition systems for system design and analysis

A Calculus of Looping Sequences for Modelling Microbiological Systems

A Calculus of Looping Sequences for Modelling Microbiological Systems