Irene Eusgeld

''System-of-systems'' approach for interdependent critical infrastructures

The study of the interdependencies within critical infrastructures (CI) is a growing field of research as the importance of potential failure propagation among infrastructures may lead to cascades affecting all supply networks. New powerful methods are required to model and describe such ‘‘systems-ofsystems’’ (SoS) as a whole. An overall model is required to provide security and reliability assessment taking into account various kinds of threats and failures. A significant challenge associated with this model may be to create ‘‘what-if’’ scenarios for the analysis of interdependencies. In this paper the interdependencies between industrial control systems (ICS), in particular SCADA (Supervisory Control and Data Acquisition), and the underlying critical infrastructures to address the vulnerabilities related to the coupling of these systems are analyzed. The modeling alternatives for system-of-systems, integrated versus coupled models, are discussed. An integrated model contains detailed low level models of (sub)systems as well as a high level model, covering all hierarchical levels. On the other hand, a coupled model aggregates different simulated outputs of the low level models as inputs at a higher level. Strengths and weaknesses of both approaches are analyzed and a model architecture for SCADA and the ‘‘system under control’’ are proposed. Furthermore, the HLA simulation standard is introduced and discussed in this paper as a promising approach to represent interdependencies between infrastructures. To demonstrate the capabilities of the HLA standard for the interdependencies study, an exemplary application and some first results are also briefly presented in this paper.

The role of network theory and object-oriented modeling within a framework for the vulnerability analysis of critical infrastructures

A framework for the analysis of the vulnerability of critical infrastructures has been proposed by some of the authors. The framework basically consists of two successive stages: (i) a screening analysis for identifying the parts of the critical infrastructure most relevant with respect to its vulnerability and (ii) a detailed modeling of the operational dynamics of the identified parts for gaining insights on the causes and mechanisms responsible for the vulnerability. In this paper, a critical presentation is offered of the results of a set of investigations aimed at evaluating the potentials of (i) using network analysis based on measures of topological interconnection and reliability efficiency, for the screening task; (ii) using object-oriented modeling as the simulation framework to capture the detailed dynamics of the operational scenarios involving the most vulnerable parts of the critical infrastructure as identified by the preceding network analysis. A case study based on the Swiss high-voltage transmission system is considered. The results are cross-compared and evaluated; the needs of further research are defined.

Adopting HLA standard for interdependency study

In recent decades, modern Critical Infrastructure (CI) has become increasingly automated and interlinked as more and more resources and information are required to maintain its day-to-day operation. A system failure, or even just a service debilitation, of any CI may have significant adverse effects on other infrastructures it is connected/interconnected with. It is vital to study the interdependencies within and between CIs and provide advanced modeling and simulation techniques in order to prevent or at least minimize these adverse effects. The key limitation of traditional mathematical models such as complex network theory is their lacking the capabilities of providing sufficient insights into interrelationships between CIs due to the complexities of these systems. A comprehensive method, a hybrid approach combining various modeling/simulation techniques in a distributed simulation environment, is presented in this paper. High Level Architecture (HLA) is an open standard (IEEE standard 1516) supporting simulations composed of different simulation components, which can be regarded as the framework for implementing such a hybrid approach. The concept of adopting HLA standard for the interdependency study is still under discussion by many researchers. Whether or not this HLA standard, or even the distributed simulation environment, is able to meet desired model/simulation requirements needs to be carefully examined. This paper presents the results from our experimental test-bed, which recreates the architecture of a typical Electricity Power Supply System (EPSS) with its own Supervisory Control and Data Acquisition (SCADA) system, for the purpose of investigating the capabilities of the HLA technique as a standard to perform interdependency studies.

Analyzing vulnerabilities between SCADA system and SUC due to interdependencies

Interdependencies within and among Critical Infrastructures (CIs), e.g., between Industrial Control Systems (ICSs), in particular Supervisory Control and Data Acquisition (SCADA) system, and the underlying System Under Control (SUC), have dramatically increased the overall complexity of related systems, causing the emergence of unpredictable behaviors and making them more vulnerable to cascading failures. It is vital to get a clear understanding of these often hidden interdependency issues and tackle them with advanced modeling and simulation techniques. In this paper, vulnerabilities due to interdependencies between these two exemplary systems (SCADA and SUC) are investigated and analyzed comprehensively using a modified five-step methodical framework. Furthermore, suggestions for system performance improvements based on the investigation and analysis results, which could be useful to minimize the negative effects and improve their coping capacities, are also presented in this paper.

Creating a simulation environment for critical infrastructure interdependencies study

The critical infrastructures (CIs) on which our daily life depends are mutually interdependent. What happens to one infrastructure can directly or indirectly affect another infrastructure or maybe even more. The development of advanced techniques of modeling and simulation is significant for the interdependencies study between CIs. In this paper, an approach to model critical infrastructures as well as adopting HLA (High Level Architecture) standard to simulate the interoperations between individual models under system-of-systems design architecture is proposed. Two examples of interdependent systems (CIs), which are studied in this approach, are : Electric Power Supply (EPS) System and Supervisory Control and Data Acquisition (SCADA) System.

A Genetic Algorithm for Fault-Tolerant System Design

Due to high cost, considerable complexity and long design cycles of fault-tolerant systems, a (partial) automation of the design process becomes attractive. This paper presents an approach to automatic design by use of a genetic algorithm. Unlike typical genetic algorithms the individuals (which represent a fault-tolerant system structure each) are represented by a non-cyclic graph rather than a string. Special crossover and mutation operations modify the individuals such that reasonable fault-tolerant systems are likely to be generated. The biggest problem in using genetic algorithms lies in the definition of an appropriate fitness function one has to apply to each of the many generated individuals. A complete analysis of a single fault-tolerant system would comprise time-consuming fault-tree analysis, reachability analysis of the state space, etc. A substantial speed-up by orders of magnitude has been achieved by the development of a completely new fitness function, which can be considered as a simplified reachability analysis. For many fault tolerance techniques it visits each component only once (or very few times in the case of mechanisms like rollback, retry etc.).

Exploring impacts of single failure propagation between SCADA and SUC

Critical infrastructures (CI) deserve increased attention as our societies simply rely on most of their goods and services they are expected to continuously supply. The study of the interdependencies within and among CI is an emerging research field since modern CI are becoming increasingly vital as well as automated and interlinked in complex ways to maintain their daily operations. A failure within any CI or even loss of its continuous service may be damaging enough to society and economy while cascading failures across boundaries have the potential for multi-infrastructural collapse with unprecedented negative consequences. In this paper, the interdependencies between Industrial Control Systems (ICS), in particular SCADA (Supervisory Control and Data Acquisition), and the underlying System Under Control (SUC) are explored and studied using advanced model/simulation techniques. A single failure propagation experiment that analyzes a typical substation of the Electricity Power Supply System (EPSS), comprising components from both SUC and SCADA is developed to visualize the propagation of cascading events across boundaries and evaluate negative impacts on the service availability of the system due to interdependencies related problems.

Hidden Vulnerabilities Due to Interdependencies between Two Systems

Critical infrastructures (CIs) deserve increased attention as our societies simply rely on most of the goods and services they are expected to continuously supply. Interdependencies within and among CIs have dramatically increased the overall complexity of related infrastructure systems, making them more vulnerable to cascading failures with widespread unpredicted consequences. It is vital to get a clear understanding of these often hidden interdependency issues and tackle them through advanced techniques. In this paper, the interdependencies between Industrial Control Systems (ICS), in particular the SCADA (Supervisory Control and Data Acquisition) system, and the underlying System Under Control (SUC) are identified and assessed using modeling/simulation methods by following a modified 4-step methodical framework. This paper mainly focuses on those techniques and analytical experiments developed for the essential step of this methodical framework, the in-depth analysis, i.e., applying a hybrid modeling/simulation approach and three in-depth experiments.

Automatic design of reliable systems consisting of nano-elements

The design of nano structures is considered a challenge for design methods, which have to cope with much more elements than traditional VLSI. Moreover, such elements will be unreliable due to unavoidable physical quantum effects. The inevitable fault tolerance leads to an additional increase of the design space. An extremely high number of nano-devices can be used for various redundancy schemes and many combinations thereof, thus promising an efficient solution to the reliability problem of nano devices. This paper proposes a heuristic design method based on a specific type of genetic algorithms. It has been adapted to the design of fault-tolerant nano systems with respect to the representation of systems as well as the fitness function and the underlying fault model.