@inproceedings{BergerReiser2018, author = {Berger, Christian and Reiser, Hans P.}, title = {Scaling Byzantine Consensus: A Broad Analysis}, series = {SERIAL'18 Proceedings of the 2nd Workshop on Scalable and Resilient Infrastructures for Distributed Ledgers}, booktitle = {SERIAL'18 Proceedings of the 2nd Workshop on Scalable and Resilient Infrastructures for Distributed Ledgers}, publisher = {ACM}, address = {New York, NY, USA}, isbn = {978-1-4503-6110-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-7526}, pages = {6 Seiten}, year = {2018}, abstract = {Blockchains and distributed ledger technology (DLT) that rely on Proof-of-Work (PoW) typically show limited performance. Several recent approaches incorporate Byzantine fault-tolerant (BFT) consensus protocols in their DLT design as Byzantine consensus allows for increased performance and energy efficiency, as well as it offers proven liveness and safety properties. While there has been a broad variety of research on BFT consensus protocols over the last decades, those protocols were originally not intended to scale for a large number of nodes. Thus, the quest for scalable BFT consensus was initiated with the emerging research interest in DLT. In this paper, we first provide a broad analysis of various optimization techniques and approaches used in recent protocols to scale Byzantine consensus for large environments such as BFT blockchain infrastructures. We then present an overview of both efforts and assumptions made by existing protocols and compare their solutions.}, language = {en} } @phdthesis{Awwad2018, author = {Awwad, Tarek}, title = {Context-Aware Worker Selection For Efficient Quality Control In Crowdsourcing}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-7409}, school = {Universit{\"a}t Passau}, pages = {106 Seiten}, year = {2018}, abstract = {In the last decade, crowdsourcing has proved its ability to address large scale data collection tasks, such as labeling large data sets, at a low cost and in a short time. However, the performance and behavior variability between workers as well as the variability in task designs and contents, induce an unevenness in the quality of the produced contributions and, thus, in the final output quality. In order to maintain the effectiveness of crowdsourcing, it is crucial to control the quality of the contributions. Furthermore, maintaining the efficiency of crowdsourcing requires the time and cost overhead related to the quality control to be at its lowest. While effective, current quality control techniques such as contribution aggregation, worker selection, context-specific reputation systems, and multi-step workflows, suffer from fairly high time and budget overheads and from their dependency on prior knowledge about individual workers. In this thesis, we address this challenge by leveraging the similarity between completed and incoming tasks as well as the correlation between the worker declarative profiles and their performance in previous tasks in order to perform an efficient task-aware worker selection. To this end, we propose CAWS (Context AwareWorker Selection) method which operates in two phases; in an offline phase, completed tasks are clustered into homogeneous groups for each of which the correlation with the workers declarative profile is learned. Then, in the online phase, incoming tasks are matched to one of the existing clusters and the correspondent, previously inferred profile model is used to select the most reliable online workers for the given task. Using declarative profiles helps eliminate any probing process, which reduces the time and the budget while maintaining the crowdsourcing quality. Furthermore, the set of completed tasks, when compared to a probing task split, provides a larger corpus from which a more precise profile model can be learned. This translates to a better selection quality, especially for harder tasks. In order to evaluate CAWS, we introduce CrowdED (Crowdsourcing Evaluation Dataset), a rich dataset to evaluate quality control methods and quality-driven task vectorization and clustering. The generation of CrowdED relies on a constrained sampling approach that allows to produce a task corpus which respects both, the budget and type constraints. Beside helping in evaluating CAWS, and through its generality and richness, CrowdED helps in plugging the benchmarking gap present in the crowdsourcing quality control community. Using CrowdED, we evaluate the performance of CAWS in terms of the quality of the worker selection and in terms of the achieved time and budget reduction. Results shows the following: first, automatic grouping is able to achieve a learning quality similar to job-based grouping. And second, CAWS is able to outperform the state-of-the-art profile-based worker selection when it comes to quality. This is especially true when strong budget and time constraints are present on the requester side. Finally, we complement our work by a software contribution consisting of an open source framework called CREX (CReate Enrich eXtend). CREX allows the creation, the extension and the enrichment of crowdsourcing datasets. It provides the tools to vectorize, cluster and sample a task corpus to produce constrained task sets and to automatically generate custom crowdsourcing campaign sites.}, subject = {Qualit{\"a}tssicherung}, language = {en} } @phdthesis{Berndl2018, author = {Berndl, Emanuel}, title = {Embedding a Multimedia Metadata Model into a Workflow-driven Environment Using Idiomatic Semantic Web Technologies}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6708}, school = {Universit{\"a}t Passau}, pages = {xix, 301 Seiten}, year = {2018}, abstract = {The Semantic Web exists for about 20 years by now, but its applicability as well as its presence does not live up to the standards of its original idea. Incorporated Semantic Web Technologies do have an initial barrier to learn and apply, which can discourage many potential users. This leads to less available data overall in addition to decreased data quality. This work solves parts of the aforementioned problem by supporting idiomatic entry to those Semantic Web Technologies, allowing for "easier" accessibility and usability. Anno4j is a Java library that implements a form of Object-Relational Mapping for RDF data. With its application, RDF data can be created via a mapping by simply instantiating Java objects - an object-oriented programming concept the user is familiar with. On the other side, requesting persisted data is supported by a path-based querying possibility, while other features like transactional behaviour, code generation, and automated validation of input contribute to a more effective, comprehensive, and straightforward usage. A use-case is provided by the MICO Platform, a centralized software instance that connects autonomous multimedia extractors in a workflow-driven fashion. This leads to a rich metadata background for the inserted multimedia files, enabling them to be used in diverse scenarios as well as unlocking yet hidden semantics. For this task it was necessary to design and implement a metadata model that is able to aggregate and merge the varying extractor results under a common denominator: the MICO Metadata Model. The results of this work allow the use case to incorporate idiomatic Semantic Web Technologies which are then usable natively by non-Semantic Web experts. Additionally, an increase has been achieved in forms of data integration, synchronisation, integrity and validity, as well as an overall more comprehensive and rich implementation of the multimedia extractors.}, subject = {Multimedia}, language = {en} } @inproceedings{ParraRodriguezPosegga2018, author = {Parra Rodriguez, Juan D. and Posegga, Joachim}, title = {Local Storage on Steroids: Abusing Web Browsers for Hidden Content Storage and Distribution}, series = {International Conference on Security and Privacy in Communication Systems}, booktitle = {International Conference on Security and Privacy in Communication Systems}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-01704-0}, doi = {10.1007/978-3-030-01704-0_19}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6572}, pages = {20 Seiten}, year = {2018}, abstract = {Analysing security assumptions taken for the WebRTC and postMessage APIs led us to find a novel attack abusing the browsers' persistent storage capabilities. The presented attack can be executed without the website's visitor knowledge, and it requires neither browser vulnerabilities nor additional software on the browser's side. To exemplify this, we study how can an attacker use browsers to create a network for persistent storage and distribution of arbitrary data. In our proof of concept, the total storage of the network, and therefore the space used within each browser, grows linearly with the number of origins delivering the malicious JavaScript code. Further, data transfers between browsers are not restricted by the Same Origin Policy, which allows for a unified cross-origin browser network, regardless of the origin from which the script executing the functionality is loaded from. In the course of our work, we assess the feasibility of a real-life deployment of the network by running experiments using Linux containers and browser automation tools. Moreover, we show how security mechanisms against third-party tracking, cross-site scripting and click-jacking can diminish the attack's impact, or even prevent it.}, language = {en} } @inproceedings{ParraRodriguezPosegga2018, author = {Parra Rodriguez, Juan D. and Posegga, Joachim}, title = {RAPID: Resource and API-Based Detection Against In-Browser Miners}, series = {Proceedings of the 34th Annual Computer Security Applications Conference}, booktitle = {Proceedings of the 34th Annual Computer Security Applications Conference}, publisher = {ACM}, address = {New York, NY, USA}, isbn = {978-1-4503-6569-7}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6550}, pages = {[14] Seiten}, year = {2018}, abstract = {Direct access to the system's resources such as the GPU, persistent storage and networking has enabled in-browser crypto-mining. Thus, there has been a massive response by rogue actors who abuse browsers for mining without the user's consent. This trend has grown steadily for the last months until this practice, i.e., CryptoJacking, has been acknowledged as the number one security threat by several antivirus companies. Considering this, and the fact that these attacks do not behave as JavaScript malware or other Web attacks, we propose and evaluate several approaches to detect in-browser mining. To this end, we collect information from the top 330.500 Alexa sites. Mainly, we used real-life browsers to visit sites while monitoring resource-related API calls and the browser's resource consumption, e.g., CPU. Our detection mechanisms are based on dynamic monitoring, so they are resistant to JavaScript obfuscation. Furthermore, our detection techniques can generalize well and classify previously unseen samples with up to 99.99\\% precision and recall for the benign class and up to 96\\% precision and recall for the mining class. These results demonstrate the applicability of detection mechanisms as a server-side approach, e.g., to support the enhancement of existing blacklists. Last but not least, we evaluated the feasibility of deploying prototypical implementations of some detection mechanisms directly on the browser. Specifically, we measured the impact of in-browser API monitoring on page-loading time and performed micro-benchmarks for the execution of some classifiers directly within the browser. In this regard, we ascertain that, even though there are engineering challenges to overcome, it is feasible and beneficial for users to bring the mining detection to the browser.}, language = {en} } @phdthesis{Seidler2018, author = {Seidler, Anna-Raissa}, title = {Changing for the Better? Essays on the Role of Institutional Logics and Information System in Organizational Sustainability Transformations}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6330}, school = {Universit{\"a}t Passau}, pages = {XXXV, 207 Seiten}, year = {2018}, abstract = {An increasing number of companies report that eco-sustainable initiatives have a positive impact on firms' economic performance and concurrently allow the combination of social and commercial goals by optimizing environmental and economic decisions simultaneously. These initiatives are considered an integral part of organizational sustainability transformations, which are a special case of multilayered, complex organizational change efforts that relate to environmental, organizational, and individual factors. Institutional logics and information systems (IS) have shown to be two important perspectives from which to explore mechanisms and processes central to organizational sustainability transformations. Institutional logics offer a unique perspective to investigate organizational change for sustainability because they provide a new approach to organizational change that incorporates macro structures, culture, and agency to explain how actions are enabled or constrained. It thus allows for insights into the complex and miscellaneous interplay of external and internal determinants that govern organizational transformation processes towards sustainability. By providing insights into institutional changes of practice and behaviors, an institutional logic perspective allows for a detailed analysis of organizational transformations. Within these change processes, IS have shown to be an efficient and pervasive tool to leverage sustainability by integrating human and technological factors. Since IS have become a key resource for the encouragement of organizational sustainability transformations, adopting an IS perspective allows for an understanding of mechanisms and processes that enable IS to foster sustainability in organizations. Thus, this dissertation draws on four studies by investigateing an institutional logic perspective as well as an IS perspective to explore organizational sustainability transformations and facilitate an in-depth understanding of organizational, human, and technological factors that encourage sustainability in organizational transformations.}, subject = {Informationssystem}, language = {en} } @phdthesis{Wimmer2018, author = {Wimmer, Tristan}, title = {Information in Online Purchase Decision Processes: Information Extraction, Data Analysis and Economic Impact}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6327}, school = {Universit{\"a}t Passau}, pages = {ix, 108, xiii Seiten}, year = {2018}, abstract = {Information has a particular importance in online purchase decision processes. As opposed to consumers in online markets, consumers in online markets cannot inspect the physical product to evaluate it and reduce their perceived risk. Hence, consumers in online markets are dependent upon the information that they can gather about a product in which they are interested. Therefore, they have two primary sources of information: Product descriptions and customer reviews. Both sources affect consumers' purchase decision processes and hence have an economic impact for consumers, shop providers and manufacturers. It is important to know how these sources of information influence a customer's online purchase decision and how to extract the relevant information. To examine these research objectives, several studies applying different methodological approaches have been conducted. The results are presented in this dissertation.}, subject = {Kaufentscheidung}, language = {en} } @phdthesis{Giermindl2018, author = {Giermindl, Lisa}, title = {Lost in Digital Transformation? The role of Enterprise Social Networks in facilitating digital collaboration}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6157}, school = {Universit{\"a}t Passau}, pages = {194 Seiten}, year = {2018}, abstract = {In the age of globalization, exponential growth and digitalization, organizations need to make faster decisions, as well as continually innovate and adapt to changing customer needs to ensure their long-term competitiveness (Kammerlander et al. 2018; Magnusson and Martini 2008). Notably, large and established companies find it difficult to keep up with start-ups and smaller companies as well as with digital transformation (Christensen et al. 2015). Thus, organizations are increasingly providing their workforce with Enterprise Social Networks (ESNs) as intra-organizational social software platforms. Although ESNs hold great promises for organizations and their employees (M{\"a}ntym{\"a}ki and Riemer 2016), most ESN initiatives fail to leverage the intended benefits (Chin et al. 2015). This dissertation seeks to open up the black box behind this seemingly paradoxical relationship. It comprises four studies that are guided by the following research questions: R 1: How do different types of users (posters and lurkers) differ in their motivations for participating in ESNs? (= Paper 1) R 2: Why do employees deliberately not use the ESN? (= Paper 2) R 3: How can ESNs be successfully implemented and improved to overcome the challenges perceived by employees? (= Paper 3) R 4: Does ESN usage impact on individual task performance? And how can ESNs be used effectively to increase performance outcomes? (= Paper 4) Overall, the four studies contribute to a better understanding of the non-adoption phenomenon of ESNs, provide rich insights on employees' underlying reasons and challenges regarding ESN usage, while underscoring the potential value of ESNs.}, subject = {Digitalisierung}, language = {en} } @phdthesis{Yakouchyk2018, author = {Yakouchyk, Katsiaryna}, title = {Post-Soviet Region, Authoritarian Stability, and Autocracy Promotion: Limits to the European Union's External Governance}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6146}, school = {Universit{\"a}t Passau}, pages = {x, 5 Seiten}, year = {2018}, abstract = {This cumulative thesis consists of six single contributions: five independent essays and an introductory chapter. All of the conributions have been published or accepted for publication. The overarching scope of these essays is to analyze different factors accounting for the stability of post-Soviet authoritarian regimes and the obstacles, which Western democracy promoters can face when dealing with autocrats. The starting point for these enquiries has been the striking inability of Western democracies and in particular of the European Union to encourage and to assist political transformation in the majority of the post-Soviet republics.}, language = {en} } @phdthesis{Paffhausen2018, author = {Paffhausen, Anna Luisa}, title = {Three empirical essays on micro-, small and medium-sized enterprises and entrepreneurship promotion in developing countries}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6096}, school = {Universit{\"a}t Passau}, pages = {212 Seiten}, year = {2018}, abstract = {In this thesis I empirically assess a wide range of constraints faced by different types of entrepreneurs in developing countries and the effectiveness of different policy interventions aimed at removing them. Thereby, the thesis contributes to the growing literature on enterprises and entrepreneurial activities in developing countries, by producing valuable evidence on which are the constraints faced by which types of entrepreneurs in starting, surviving, and growing, as well as on which interventions work, and for whom. The thesis hence provides important insights for policy formulation aimed at inclusive growth. It consists of three self-contained papers, which put different emphasis on three different areas in which important research gaps remain. The first paper, which is presented in chapter 2, focuses on interventions aimed at removing firm-level shocks. It consists of a systematic review of evaluations of targeted programs and broader policies that intend to promote micro-, small and medium-sized enterprises (MSMEs) in developing countries, and assesses which of these interventions are effective in creating jobs. The paper presented in chapter 3 considers death of small, mainly one-person and household businesses. Together with my co-author, I collated panel data on more than 14,000 small firms from 16 firm panel surveys conducted in 12 developing countries. We use this unique panel dataset to provide answers to the following questions: What is the rate of firm death over different horizons? Which firms are more likely to die? Why do they die and what happens afterwards? In chapter 4, I take a closer look at household-level shocks and non-separability between the household and the firm, and assess whether extending health insurance to previously uninsured households leads to increased investment in productive activities, by assessing the impact of a large national health insurance scheme, the Mexican Seguro Popular, on investment in productive agricultural and non-agricultural assets and activities in rural areas. Using panel data from the Mexican rural evaluation surveys of the Oportunidades cash transfer program, I estimate the effect of the program on out-of-pocket health care expenditures and productive assets and account for possible self-selection of households into the program, using difference-in-differences estimation, as well as a propensity score matched difference-in-differences specification.}, language = {en} } @phdthesis{Satur2018, author = {Satur, Luzile Mae}, title = {Vibrancy of Public Spaces: Inclusivity and Participation Amidst the Challenges in Transformative Process in the City of Cagayan de Oro, Philippines}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6136}, school = {Universit{\"a}t Passau}, pages = {V, 206 Seiten}, year = {2018}, abstract = {This study examines the dynamics which lead to revitalization of everyday life in the public spaces of Cagayan de Oro, a medium-sized urban center in Northern Mindanao, the Philippines. By employing the oriental philosophies together with western thoughts such as Henri Lefebvre, Alain Touraine and J{\"u}rgen Habermas, this study elucidates that the core of perceived, lived and conceived spaces is 'the Subject.' Once the Subject utilizes the public sphere to instill social action, social space is ultimately produced. Hawkers, grassroots environmental activists, street readers and artists are the social Subjects who partake in the vibrancy of public spaces. The social Subjects utilize public spaces as venues of social transformation. Thus, this study argues that the social Subjects' role in democratic process lead to inclusivity of the marginalized sector in the public spaces of the city.}, subject = {{\"O}ffentlicher Raum}, language = {en} } @phdthesis{Kinseher2018, author = {Kinseher, Josef}, title = {New Methods for Improving Embedded Memory Manufacturing Tests}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6017}, school = {Universit{\"a}t Passau}, pages = {119 Seiten}, year = {2018}, abstract = {Due to the need for fast and energy-efficient accesses to growing amounts of data, the share and number of embedded memories inside modern microchips has been continuously increasing within the last years. Since embedded memories have the highest integration density of a fabrication technology they pose special test challenges due to complex manufacturing defects as well as strong transistor aging phenomena. This necessitates efficient methods for detecting more subtle defects while keeping test costs low. This work presents novel methods and techniques for improving the efficiency of embedded memory manufacturing tests. The proposed methods are demonstrated in an industrial setting based on production-proven transistor, memory as well as chip models and their benefits over the current state-of-the art is worked out.}, subject = {Speicher }, language = {en} } @unpublished{Yakouchyk2018, author = {Yakouchyk, Katsiaryna}, title = {Belarusian State Ideology: A Strategy of Flexible Adaptation}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-6028}, pages = {20 Seiten}, year = {2018}, abstract = {While in some Eastern European countries a wave of colored revolutions challenged existing political orders, Belarus has remained largely untouched by mass protests. In Minsk, the diffusion of democratic ideas leading to the mobilization of population meets a stable authoritarian regime. Nevertheless, the stagnating democratization process cannot be only attributed to the strong authoritarian rule and abuse of power. Indeed, Belarusian president Alexander Lukashenko still enjoys popularity by a large part of the population. Although international observers report that elections in Belarus have never been free and fair, few commentators doubt that Lukashenko would not have won in democratic elections. This evidence suggests that the regime succeeded in building a strong legitimizing basis, which has not been seriously challenged during the last two decades. This paper explores the authoritarian stability in Belarus by looking at the patterns of state ideology. The government effectively spreads state ideology since the early 2000s. Ideology departments have been created in almost all state institutions. The education sector has been affected by the introduction of the compulsory course "The Fundamentals of Belarusian State Ideology" at all universities, and increasing attention to the patriotic education at schools. Based on document analysis, I trace the creation of "ideological vertical" in Belarus and focuse on the issue of ideology in education and youth policy sectors.}, language = {en} } @article{GrafLambsdorffGiamatteiWerneretal.2018, author = {Graf Lambsdorff, Johann and Giamattei, Marcus and Werner, Katharina and Schubert, Manuel}, title = {Team reasoning - Experimental evidence on cooperation from centipede games}, series = {PloS ONE}, volume = {13}, journal = {PloS ONE}, number = {11}, publisher = {PLOS}, address = {San Francisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0206666}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5913}, year = {2018}, abstract = {Previous laboratory studies on the centipede game have found that subjects exhibit surprisingly high levels of cooperation. Across disciplines, it has recently been highlighted that these high levels of cooperation might be explained by "team reasoning", the willingness to think as a team rather than as an individual. We run an experiment with a standard centipede game as a baseline. In two treatments, we seek to induce team reasoning by making a joint goal salient. First, we implement a probabilistic variant of the centipede game that makes it easy to identify a joint goal. Second, we frame the game as a situation where a team of two soccer players attempts to score a goal. This frame increases the salience even more. Compared to the baseline, our treatments induce higher levels of cooperation. In a second experiment, we obtain similar evidence in a more natural environment-a beer garden during the 2014 FIFA Soccer World Cup. Our study contributes to understanding how a salient goal can support cooperation.}, subject = {Spieltheorie}, language = {en} } @phdthesis{Poehls2018, author = {P{\"o}hls, Henrich C.}, title = {Increasing the Legal Probative Value of Cryptographically Private Malleable Signatures}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5823}, school = {Universit{\"a}t Passau}, pages = {540, LXXVIII Seiten}, year = {2018}, abstract = {Die Arbeit befasst sich mit der Erarbeitung von technischen Vorgaben und deren Umsetzung in kryptographisch sichere Verfahren von datenschutzfreundlichen, veränderbaren digitalen Signaturverfahren (private malleable signature schemes oder MSS) zur Erlangung möglichst hoher rechtlicher Evidenz. Im Recht werden bestimmte kryptographische Algorithmen, Schl{\"u}ssellängen und deren korrekte organisatorische Anwendungen zur Erzeugung elektronisch signierter Dokumente als rechtssicher eingestuft. Dies kann zu einer Beweiserleichterung mithilfe signierter Dokumente f{\"u}hren. So gelten nach Verordnung (EU) Nr. 910/2014 (eIDAS) qualifiziert signierte elektronische Dokumente entweder als Anscheinsbeweis der Echtheit oder ihnen wird gar eine gesetzliche Vermutung der Echtheit zuteil. Gesetzlich anerkannte technische Verfahren, die einen solch erhöhten Beweiswert erreichen, erf{\"u}llen mithilfe von Kryptographie im wesentlichen zwei Eigenschaften: Integritätsschutz (integrity), also die Erkennung der Abwesenheit von unerw{\"u}nschten Änderungen und die Zurechenbarkeit des unveränderten Dokumentes zum Signaturersteller (accountability). Hingegen ist der größte Vorteil veränderbarer digitaler Signaturverfahren (MSS) die „privacy" genannte Eigenschaft: Eine autorisierte Änderung verbirgt den vorherigen Inhalt. Des Weiteren bleibt die Signatur solange valide wie ausschliesslich autorisierte Änderungen vorgenommen werden. Wird diese Eigenschaft kryptographisch nachweislich sicher erf{\"u}llt, so spricht man von einem private malleable signature scheme. In der Arbeit werden zwei verbreitete Formen, die sogenannten redactable signature schemes (RSS) und die sanitizable signature schemes (SSS), eingehend betrachtet. Diese erlauben vielfältige Einsatzmöglichkeiten, zum Beispiel eine autorisierte spätere Veränderung zur Wahrung von Geschäftsgeheimnissen oder zum Datenschutz: Der Unterzeichner delegiert so beispielsweise {\"u}ber ein private redactable signature scheme nur das nachträgliche Schwärzen (redaction). Dies schränkt die Veränderbarkeit auf das Entfernen von Informationen ein, erlaubt aber wirksam die Wahrung des Datenschutzes oder den Schutz von (Geschäfts)geheimnissen indem diese Informationen irreversibel f{\"u}r Angreifer entfernt werden. Die kryptographische privacy Eigenschaft besagt, dass es nun nicht mehr effizient möglich ist, aus dem geschwärzten Dokument Wissen {\"u}ber die geschwärzten Informationen zu erlangen, auch und gerade nicht f{\"u}r den Signaturpr{\"u}fer. Die Arbeit geht im Kern der Frage nach, ob ein MSS sowohl die kryptographische Eigenschaft „privacy" als auch gleichzeitig die Eigenschaften „integrity" und „accountability" mit ausreichend hohen Sicherheitsniveaus erf{\"u}llen kann. Das Ziel ist es, dass ein MSS gleichzeitig ein solch ausreichend hohen Grad an Sicherheit erf{\"u}llt, dass (1) die autorisierten nachträglichen Änderungen zum Schutze von Geschäftsgeheimnissen oder personenbezogenen Daten eingesetzt werden können, und dass (2) dem Dokument, welches mit dem speziellen Signaturverfahren signiert wurde, ein erhöhter Beweiswert beigemessen werden kann. In Bezug auf letzteres stellt die Arbeit sowohl die technischen Vorgaben, welche f{\"u}r qualifizierte elektronische Signaturen (nach Verordnung (EU) Nr. 910/2014) gelten, in Bezug auf die nachträgliche Änderbarkeit dar, als auch konkrete kryptographische Eigenschaften und Verfahren um diese Vorgaben kryptographisch beweisbar zu erreichen. Insbesondere weisen veränderbare Signaturen (MSS) einen anderen Integritätsschutz als traditionelle digitale Signaturen auf: Eine signierte Nachricht darf nachträglich durch eine definierte dritte Partei in einer definierten Art modifiziert werden. Diese sogenannte autorisierte Änderung (authorized modification) kann auch ohne Kenntnis des geheimen Signaturschl{\"u}ssels des Unterzeichners durchgef{\"u}hrt werden. Bei der Verifikation der digitalen Signatur durch den Signaturpr{\"u}fer bleibt der urspr{\"u}ngliche Signierende und dessen Einwilligung zur autorisierten Änderung kryptographisch verifizierbar, auch wenn autorisierte Änderungen vorgenommen wurden. Die Arbeit umfasst folgende Bereiche: 1. Analyse der Rechtsvorgaben zur Ermittlung der rechtlich relevanten technischen Anforderungen hinsichtlich des geforderten Integritätsschutzes (integrity protection) und hinsichtlich des Schutzes von personenbezogenen Daten und (Geschäfts)geheimnissen (privacy protection), 2. Definition eines geeigneten Integritäts-Begriffes zur Beschreibung der Schutzfunktion von existierenden malleable signatures und bereits rechtlich anerkannten Signaturverfahren, 3. Harmonisierung und Analyse der kryptographischen Eigenschaften existierender malleable signature Verfahren in Hinblick auf die rechtlichen Anforderungen, 4. Entwicklung neuer und beweisbar sicherer kryptographischer Verfahren, 5. abschließende Bewertung des rechtlichen Beweiswertes (probative value) und des Datenschutzniveaus anhand der technischen Umsetzung der rechtlichen Anforderungen. Die Arbeit kommt zu dem Ergebnis, dass zunächst einmal jedwede (autorisierte wie auch unautorisierte) Änderung von einem kryptographisch sicheren malleable signature Verfahren (MSS) ebenfalls erkannt werden muss um Konformität mit Verordnung (EU) Nr. 910/2014 (eIDAS) zu erlangen. Eine solche Änderungserkennung durch die der Signaturpr{\"u}fer, ohne Zuhilfe weiterer Parteien oder Geheimnisse, die Abwesenheit von autorisierten und unautorisierten Änderungen erkennt wurde im Rahmen der Arbeit entwickelt (non-interactive public accountability (PUB)). Diese neue kryptographische Eigenschaft wurde veröffentlicht und bereits von Arbeiten Anderer aufgegriffen. Des Weiteren werden neue kryptographische Eigenschaften und redactable signature und sanitizable signature Verfahren vorgestellt, welche zusätzlich zu dieser Änderungerkennung einen starken Schutz gegen die Aufdeckung des Orginals ermöglichen. Werden geeignete Eigenschaften erf{\"u}llt so wird f{\"u}r bestimmte Fälle ein technisches Schutzniveau erzielt, welches mit klassischen Signaturen vergleichbar ist. Damit lässt sich die Kernfrage positiv beantworten: Private MSS können ein Integritätsschutzniveau erreichen, welches dem rechtlich anerkannter digitaler Signaturen technisch entspricht, aber dennoch nachträgliche Änderungen autorisieren kann, welche einen starken Schutz gegen die Wiederherstellung des Orginals ermöglichen.}, subject = {Integrit{\"a}t}, language = {en} } @article{KronawitterLengauer2018, author = {Kronawitter, Stefan and Lengauer, Christian}, title = {Polyhedral Search Space Exploration in the ExaStencils Code Generator}, series = {ACM Transactions on Architecture and Code Optimization}, volume = {15}, journal = {ACM Transactions on Architecture and Code Optimization}, number = {4}, issn = {1544-3973}, doi = {10.1145/3274653}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5778}, year = {2018}, abstract = {Performance optimization of stencil codes requires data locality improvements. The polyhedron model for loop transformation is well suited for such optimizations with established techniques, such as the PLuTo algorithm and diamond tiling. However, in the domain of our project ExaStencils, stencil codes, it fails to yield optimal results. As an alternative, we propose a new, optimized, multi-dimensional polyhedral search space exploration and demonstrate its effectiveness: we obtain better results than existing approaches in several cases. We also propose how to specialize the search for the domain of stencil codes, which dramatically reduces the exploration effort without significantly impairing performance.}, language = {en} } @phdthesis{Sui2018, author = {Sui, Zhiyuan}, title = {Security and Privacy Schemes for Demand Response in Smart Grids}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5809}, school = {Universit{\"a}t Passau}, pages = {xx, 153 Seiten}, year = {2018}, abstract = {Smart Grids integrate currently isolated power and communications networks, while introducing several new technologies on the hardware and software sides. One of the most important ingredients is the potential for demand-response programs, which offer the possibility of sending instructions to consumers to adapt their power consumption over a certain period of time. However, high-frequency data collection exposes consumers' usage behaviors, leading to security and privacy challenges for Smart Grids. In this thesis, three cryptographic schemes are constructed for different demand-response programs. In the mandatory incentive-based demand-response program, privacy preservation depends on the power consumption of consumers. An anonymous authentication scheme is constructed for overload auditing and privacy preservation. Consumers' identities are anonymous during normal operation. The operation center defines an acceptable consumption threshold at times of power shortage. Consumers must follow the instruction and curtail their power consumption to meet the threshold. If they do so, the consumers keep their anonymity, while disobedient consumers, whose power consumption exceeds the threshold, can be identified. Security analysis demonstrates that the constructed anonymous authentication scheme is secure in a random oracle model. In the voluntary incentivebased demand-response program, consumers are categorized as either obedient or disobedient consumers according to their consumption curtailment. Consumers utilize a homomorphic encryption algorithm to encrypt their usage and report the ciphertexts to the operation center periodically. At a time of grid instability, the obedient consumers reduce their consumption and prove their curtailment by using a range proof. Both the usage reports and the proofs from obedient consumers concerning their consumption are reported without leaking private information. In order to achieve the real-time requirement, a security model is proposed and a batch verification algorithm is constructed, which is proved to be secure in the defined oracle model. Apart from reward and penalty detection in demand-response programs, theft detection is also an important requirement in Smart Grids. In order to achieve theft detection, this thesis employs the dynamic k-times anonymous authentication and blind signatures to create an efficient theft detection mechanism in the prepaid card system, where consumers pay for their consumption in advance and obtain credentials. A consumer sends the credentials anonymously and obtains corresponding credentials during times of consumption. If a thief tries to send reused credentials to steal electricity, his anonymity will be revoked. Finally, this thesis proves that the proposed mechanism finds the real identities of power thieves, without sacrificing the privacy of honest consumers under the random oracle model.}, subject = {Intelligentes Stromnetz}, language = {en} } @phdthesis{LoperaGonzalez2018, author = {Lopera Gonzalez, Luis Ignacio}, title = {Mining Functional and Structural Relationships of Context Variables in Smart-Buildings}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5737}, school = {Universit{\"a}t Passau}, pages = {viii, 99 Seiten}, year = {2018}, abstract = {The Internet of Things (IoT) is a network of computational services, devices, and people, which share information with each other. In IoT, inter-system communication is possible and human interaction is not required. IoT devices are penetrating the home and office building environments. According to current estimates, about 35 billion IoT devices will be connected by the year 20212. In the IoT business model, value comes from integrating devices into applications, e.g., home and office automation. In general, an IoT application associates different information sources with actions which can modify the environment, e.g., change the room's temperature, inform a person, e.g., send an e-mail, or activate other services, e.g., buy milk on-line. In this thesis, we focus on the commissioning and verification processes of IoT devices used in building automation applications. Within a building's lifespan, new devices are added, interior spaces are refurbished, and faulty devices are replaced. All of these changes are currently made manually. Furthermore, consider that a context-aware Building Management System (BMS) is an IoT application, which measures direct-context from the building's sensors to characterize environmental conditions, user locations, and state. Additionally, a BMS combines sensor information to derive inferred-context, such as user activity. Similar to IoT devices, inferred-context instances have to be created manually. As the number of devices and inferred-context instances increases, keeping track of all associations becomes a time-consuming and error-prone task. The hypothesis of the thesis is that users who interact with the building create use-patterns in the data, which describe functional relations between devices and inferred-context instances, e.g., which desk-movement sensor is used to infer desk-presence and controls which overhead light; additionally, use-patterns can also provide structural relations, e.g., the relative position of spatial sensors. To test the hypothesis, this thesis presents an extension to the new IoT class rule programming paradigm, which simplifies rule creation based on classes. The proposed extension uses a semantic compiler to simplify the device and inferred-context associations. Using direct-context information and template classes, the compiler creates all possible inferredcontext instances. Buildings using context-aware BMSs will have a dynamic response to user behaviour, e.g., required illumination for computer-work is provided by adjusting blinds or increasing the dim setting of overhead ceiling lamps. We propose a rule mining framework to extract use-patterns and find the functional and structural relationships between devices. The rule mining framework uses three stages: (1) event extraction, (2) rule mining, (3) structure creation. The event extraction combines the building's data into a time-series of device events. Then, in the rule mining stage, rules are mined from the time series, where we use the established algorithm temporal interval tree association rule learner. Additionally, we proposed a rule extraction algorithm for spatial sensor's data. The algorithm is based on statistical analysis of user transition times between adjacent sensors. We also introduce a new rule extraction algorithm based on increasing belief. In the last stage, structure creation uses the extracted rules to produce device association groups, hierarchical representation of the building, or the relative location of spatial sensors. The proposed algorithms were tested using a year-long installation in a living-lab consisting of a four-person office, a 12-person open office, and a meeting room. For the spatial sensors, four locations within public buildings were used: a meeting room, a hallway, T-crossing, and a foyer. The recording times range from two weeks to two months depending on scenario complexity. We found that user-generated patterns appear in building data. The rule mining framework produced structures that represent functional and spatial relationships of building's devices and provide sufficient information to automate maintenance tasks, e.g., automatic device naming. Furthermore, we found that environmental changes are also a source of device data patterns, which provide additional associations. For example, using the framework we found the fa{\c{c}}ade group for exterior light sensors. The fa{\c{c}}ade group can be used to automatically find an alternative signal source to replace broken outdoor light sensors. Finally, the rule mining framework successfully retrieved the relative location of spatial sensors in all locations but the foyer.}, subject = {Internet der Dinge}, language = {en} } @phdthesis{Woelfl2018, author = {W{\"o}lfl, Andreas}, title = {Data Management in Certified Avionics Systems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5758}, school = {Universit{\"a}t Passau}, pages = {xi, 177 Seiten}, year = {2018}, abstract = {Data management is a cornerstone for any kind of information system - including the aerospace and aviation sector. In contrast to conventional domains, software development in the avionics domain must adhere to a legally binding certification process, called qualification. The success of the process depends on compliance with international standards, such as DO-178: Software Considerations in Airborne Systems and Equipment Certification. From a software developer's perspective, challenges arise in terms of methods and tools. Techniques that have a potential impact on the deterministic and predictable execution of avionics software are prohibited. The objective of this thesis' research is to develop a scalable method to realize data-management for multi-variant avionics software under the restrictions and constraints of the domain. Since avionics software faces very long-term life-cycles (up to 75 years), a particular focus is being placed on maintenance and evolution. Based on the insights gained in a semi-structured interview at Airbus Helicopters, industrial established approaches to implement qualified avionics software are assessed at first and compared with respect to strengths and weaknesses for data-management afterwards. As a result, a novel development approach is proposed, combining model-based techniques and product-line technology to derive the source code of highly specific data-management variants, as well as the majority of assets required for the qualification process, from a declarative system specification. In order to demonstrate the practicability of the approach in industry, a framework is presented that is deployed and applied at Airbus Helicopters to generate qualifiable data-management components for the variants of the NH90 helicopter. The maintainability is shown by means of a domain-specific optimization, in which the model-based and generative approach is used to establish safe memory overlays at compile-time. Key findings reveal a substantially reduced memory footprint (29,1\% in case of a real-world scenario), as well as an significantly facilitated implementation process, which would not be accomplishable using conventional methods for software development in the avionics domain.}, subject = {Avionik}, language = {en} } @phdthesis{Hanauer2018, author = {Hanauer, Kathrin}, title = {Linear Orderings of Sparse Graphs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-5524}, school = {Universit{\"a}t Passau}, pages = {vii, 282 Seiten}, year = {2018}, abstract = {The Linear Ordering problem consists in finding a total ordering of the vertices of a directed graph such that the number of backward arcs, i.e., arcs whose heads precede their tails in the ordering, is minimized. A minimum set of backward arcs corresponds to an optimal solution to the equivalent Feedback Arc Set problem and forms a minimum Cycle Cover. Linear Ordering and Feedback Arc Set are classic NP-hard optimization problems and have a wide range of applications. Whereas both problems have been studied intensively on dense graphs and tournaments, not much is known about their structure and properties on sparser graphs. There are also only few approximative algorithms that give performance guarantees especially for graphs with bounded vertex degree. This thesis fills this gap in multiple respects: We establish necessary conditions for a linear ordering (and thereby also for a feedback arc set) to be optimal, which provide new and fine-grained insights into the combinatorial structure of the problem. From these, we derive a framework for polynomial-time algorithms that construct linear orderings which adhere to one or more of these conditions. The analysis of the linear orderings produced by these algorithms is especially tailored to graphs with bounded vertex degrees of three and four and improves on previously known upper bounds. Furthermore, the set of necessary conditions is used to implement exact and fast algorithms for the Linear Ordering problem on sparse graphs. In an experimental evaluation, we finally show that the property-enforcing algorithms produce linear orderings that are very close to the optimum and that the exact representative delivers solutions in a timely manner also in practice. As an additional benefit, our results can be applied to the Acyclic Subgraph problem, which is the complementary problem to Feedback Arc Set, and provide insights into the dual problem of Feedback Arc Set, the Arc-Disjoint Cycles problem.}, subject = {Graphentheorie}, language = {en} }