Peer-to-Peer Intrusion Detection Systeme für den Schutz sensibler IT-Infrastrukturen

Vortrag der GI-Jahrestagung: Sicherheit in komplexen, vernetzten Umgebungen, Workshop im Rahmen der Jahrestagung 2005 der Gesellschaft für Informatik Informatik LIVE!, 19. - 22. September 2005 in Bonn, Deutschlan

Bisimilarity and Behaviour-Preserving Reconfigurations of Open Petri Nets

We propose a framework for the specification of behaviour-preserving reconfigurations of systems modelled as Petri nets. The framework is based on open nets, a mild generalisation of ordinary Place/Transition nets suited to model open systems which might interact with the surrounding environment and endowed with a colimit-based composition operation. We show that natural notions of bisimilarity over open nets are congruences with respect to the composition operation. The considered behavioural equivalences differ for the choice of the observations, which can be single firings or parallel steps. Additionally, we consider weak forms of such equivalences, arising in the presence of unobservable actions. We also provide an up-to technique for facilitating bisimilarity proofs. The theory is used to identify suitable classes of reconfiguration rules (in the double-pushout approach to rewriting) whose application preserves the observational semantics of the net.Comment: To appear in "Logical Methods in Computer Science", 41 page

A generic user interface for energy management in smart homes

Abstract Building operating systems play an important role in monitoring energy consumption of devices and improving energy efficiency in household buildings. From this arises a need for a preferably flexible and full-featured user interface to visualize the energy data in the building and allow residents to collect and realize various needs and preferences to the system. This article introduces a generic user interface for building operating systems which is presented from aspects of design, implementation and evaluation. To ensure the user interface can be flexibly adapted to various types of buildings, we design a series of generic data models which are independent of any building operating system. Besides, three roles with different permissions and a number of functional components of the user interface are also introduced in the article. Based on the design, a prototype of such a generic user interface named Building Operating System User Interface (BOS UI) has been implemented to operate the Energy Smart Home Lab (ESHL) at the Karlsruhe Institute of Technology (KIT). We evaluate the design, functionality and usability of the BOS UI qualitatively and quantitatively. The evaluation results show that the BOS UI meets a set of desired requirements (except for system configuration) for a generic user interface of building operating systems. Besides this, the evaluation experiments yielded very positive feedback in many aspects including improvement of energy efficiency and user experience. More than 90% of the test users agreed that the BOS UI provided them with enough information and functionalities that they would need in their daily lives and it can help them to save money. Furthermore, the mean score of the System Usability Scale (SUS) is 79.0, which indicates a good usability. The experiments prove that the user interface is still easy to use, despite abundant features are integrated into the system

Deriving bisimulation congruences in the DPO approach to graph rewriting. Long version

Motivated by recent work on the derivation of labelled transitions and bisimulation congruences from unlabelled reaction rules, we show how to solve this problem in the DPO (double-pushout) approach to graph rewriting. Unlike in previous approaches, we consider graphs as objects, instead of arrows, of the category under consideration. This allows us to present a very simple way of deriving labelled transitions (called rewriting steps with borrowed context) which smoothly integrates with the DPO approach, has a very constructive natureand requires only a minimum of category theory. The core part of this paper is the proof sketch that the bisimilarity based on rewriting with borrowed contexts is a congruence relation

Ein Schlüsselverteilungsprotokoll für kleine geschlossene Peer-to-Peer Systeme

Vertraulichkeit ist eine der Schlüsselanforderungen für geschäftliche Kommunikation über das Internet. In einer zunehmend mobilen Gesellschaft sind dabei zunehmend spontane Beratungen in Ad hoc-Umgebungen, mitunter mit wechselnden Partnern, erforderlich. Um die Vertraulichkeit der Beratung zu sichern, müssen sich die Partner auf einen gemeinsamen Schlüssel einigen, mit dem sie ihre Kommunikation verschlüsseln. Audio- und Videokonferenzsysteme, die auf einem zentralistischen Ansatz beruhen, bieten dafür praktikable Lösungen an. Dezentrale Lösungen, die dem Peer-to-Peer-Ansatz folgen, bieten hierfür flexiblere Lösungen, die Spontaneität und Flexibilität besser unterstützen. Ein effizienter Schlüsselaustausch stellt für solche Systeme noch eine Herausforderung dar. In diesem Beitrag stellen wir das Schlüsselverteilungsprotokoll VTKD vor, das speziell für den Schlüsselaustausch von kleinen dynamischen Peer-Gruppen mit bis zu 100 Partnern entworfen wurde. Es besteht aus zwei Bestandteilen: einer gegenseitigen Authentifizierung der Partner und einer sicheren Verteilung des Sitzungsschlüssels an die Partner. Das Protokoll nutzt ein virtuelles Token, um den Partner zu bestimmen, der im Fall des Schlüsselwechsels den neuen Schlüssel generiert und verteilt. Wir beschreiben den Protokollverlauf und untersuchen seine Sicherheit. Eine abschließende Leistungsanalyse zeigt, dass VTKD eine geringere Verzögerung für die Schlüsselerneuerung benötigt als existierende Schlüsselaustauschprotokolle

A Resolved Simulation Approach to Investigate the Separation Behavior in Solid Bowl Centrifuges Using Material Functions

The separation of finely dispersed particles from liquids is a basic operation in mechanical process engineering. On an industrial scale, continuously operating decanter centrifuges are often used, whose separation principle is based on the density difference between the solid and the liquid phase due to high g-forces acting on both phases. The design of centrifuges is based on the experience on the individual manufacturer or simplified black box models, which only consider a stationary state. Neither the physical behavior of the separation process nor the sediment formation and its transport is considered. In this work, a computationally-efficient approach is proposed to simulate the separation process in decanter centrifuges. Thereby, the open-source computation software OpenFOAM was used to simulate the multiphase flow within the centrifuge. Sedimentation, consolidation of the sediment, and its transport are described by material functions which are derived from experiments. The interactions between the particles and the fluid are considered by locally defined viscosity functions. This work shows that the simulation method is suitable for describing the solid-liquid separation in a simplified test geometry of a decanter centrifuge. In addition, the influence of the rheological behavior on the flow in the test geometry can be observed for the first time

{Bis[2-(diphenyl­phosphan­yl)phen­yl] ether-κ2 P,P′}(1,1′-dibenz­yl-1H,1′H-4,4′bi-1,2,3-triazole-κ2 N3,N 3′)copper(I) hexa­fluorido­phosphate dichloro­methane hemisolvate

In the crystal structure of the title compound, [Cu(C18H16N6)(C36H28OP2)]PF6·0.5CH2Cl2 or [Cu(DPEPhos)(Bn-bta)]PF6·0.5CH2Cl2 {DPEPhos = bis­[(diphenyl­phosphan­yl)phen­yl] ether and Bn-bta = 1,1′-dibenzyl-1H,1′H-4,4′-bi-1,2,3triazol­e}, the Cu atom is coordinated by two N and two P atoms of the ligands in a strongly distorted tetra­hedral environment. There are two crystallographically independent complex cations present, which differ significantly in their geometrical parameters. The solvent molecule is disordered but satisfactory atomic positions could not be determined

Annual Report 1999 / Department for Computer Science

Selbstdarstellung des Instituts für Informatik der BTU Cottbus und Berichte der Lehrstühle für das Jahr 1999.Presentation of the Department for Computer Science of the BTU Cottbus and reports of the chairs at the department for the year 1999

Characterizing Van Kampen Squares via Descent Data

Categories in which cocones satisfy certain exactness conditions w.r.t. pullbacks are subject to current research activities in theoretical computer science. Usually, exactness is expressed in terms of properties of the pullback functor associated with the cocone. Even in the case of non-exactness, researchers in model semantics and rewriting theory inquire an elementary characterization of the image of this functor. In this paper we will investigate this question in the special case where the cocone is a cospan, i.e. part of a Van Kampen square. The use of Descent Data as the dominant categorical tool yields two main results: A simple condition which characterizes the reachable part of the above mentioned functor in terms of liftings of involved equivalence relations and (as a consequence) a necessary and sufficient condition for a pushout to be a Van Kampen square formulated in a purely algebraic manner.Comment: In Proceedings ACCAT 2012, arXiv:1208.430

Spatially Resolved Study of Backscattering in the Quantum Spin Hall State

The discovery of the quantum spin Hall (QSH) state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the quantum spin Hall state have confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples, and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using scanning gate microscopy to perturb the QSH edge states on a submicron scale, we identify well-localized scattering sites which likely limit the expected nondissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed, as expected for an ideal QSH system, and are found to be robust against weak induced potential fluctuations