@phdthesis{Huendling2008,
  author    = {H{\"u}ndling, Jens},
  title     = {Modellierung von Qualit{\"a}tsmerkmalen f{\"u}r Services},
  pages     = {XVI, 216 S.},
  year      = {2008},
  language  = {de}
}
@phdthesis{Bensch2008,
  author    = {Bensch, Suna},
  title     = {Parallel systems as mildly context-sensitive grammar formalisms},
  pages     = {I, 103 S.},
  year      = {2008},
  language  = {en}
}
@phdthesis{Glubudum2008,
  author    = {Glubudum, Prisana},
  title     = {Clones of tree languages and non-deterministic hypersubstitutions},
  pages     = {3,IV, 74 Bl.},
  year      = {2008},
  language  = {en}
}
@phdthesis{Romeike2008,
  author    = {Romeike, Ralf},
  title     = {Kreativit{\"a}t im Informatikunterricht},
  pages     = {153 S.},
  year      = {2008},
  language  = {de}
}
@phdthesis{Mueller2012,
  author    = {M{\"u}ller, J{\"u}rgen J.},
  title     = {A real-time in-memory discovery service},
  address   = {Potsdam},
  pages     = {XXV, 172 S.},
  year      = {2012},
  language  = {en}
}
@phdthesis{Repp2009,
  author    = {Repp, Stephan},
  title     = {Extraktion von semantischen Informationen aus audivisuellen Vorlesungsaufzeichnungen : Sprachskripte der Vorlesungsvideos als Informationsressource},
  address   = {Potsdam},
  pages     = {183 S.},
  year      = {2009},
  language  = {de}
}
@phdthesis{Maass2009,
  author    = {Maaß, Stefan},
  title     = {Techniken zur automatisierten Annotation interaktiver geovirtueller 3D-Umgebungen},
  address   = {Potsdam},
  pages     = {111 S.},
  year      = {2009},
  language  = {de}
}
@phdthesis{Quasthoff2011,
  author    = {Quasthoff, Matthias},
  title     = {Effizientes Entwickeln von Semantic-Web-Software mit Object Triple Mapping},
  address   = {Potsdam},
  pages     = {138 S.},
  year      = {2011},
  language  = {de}
}
@phdthesis{Schaffner2013,
  author    = {Schaffner, Jan},
  title     = {Multi tenancy for cloud-based in-memory column databases : workload management and data placement},
  address   = {Potsdam},
  pages     = {135 S.},
  year      = {2013},
  language  = {en}
}
@phdthesis{Alnemr2011,
  author    = {Alnemr, Rehab},
  title     = {Reputation object representation model for enabling reputation interoperability},
  address   = {Potsdam},
  pages     = {179 S.},
  year      = {2011},
  language  = {en}
}
@phdthesis{Schuenemann2011,
  author    = {Sch{\"u}nemann, Bj{\"o}rn},
  title     = {The V2X simulation runtime infrastructure: VSimRTI},
  address   = {Potsdam},
  pages     = {163 S.},
  year      = {2011},
  language  = {en}
}
@phdthesis{Scherfenberg2012,
  author    = {Scherfenberg, Ivonne},
  title     = {A logic-based Framwork to enable Attribute Assurance for Digital Identities in Service-oriented Architectures and the Web},
  address   = {Potsdam},
  pages     = {126 S.},
  year      = {2012},
  language  = {en}
}
@phdthesis{Richter2011,
  author    = {Richter, Michael},
  title     = {Anwendung nichtlinearer Codes zur Fehlererkennung und -korrektur},
  address   = {Potsdam},
  pages     = {134 S.},
  year      = {2011},
  language  = {de}
}
@phdthesis{Alsadeh2013,
  author    = {Alsadeh, Ahmad},
  title     = {Augmented secure neighbor discovery: aligning security, privacy and usability},
  address   = {Potsdam},
  pages     = {114 S.},
  year      = {2013},
  language  = {en}
}
@phdthesis{Kreutel2010,
  author    = {Kreutel, J{\"o}rn},
  title     = {Metamodell und Beschreibungssprache f{\"u}r sprechgesteuerte Nutzerschnittstellen},
  address   = {Potsdam},
  pages     = {451 S.},
  year      = {2010},
  language  = {de}
}
@phdthesis{Rafiee2014,
  author    = {Rafiee, Hosnieh},
  title     = {Privacy and security issues in IPv6 networks},
  address   = {Potsdam},
  pages     = {141 S.},
  year      = {2014},
  language  = {en}
}
@phdthesis{Hentschel2013,
  author    = {Hentschel, Uwe},
  title     = {Steuerung der Daten{\"u}bertragung in {\"o}ffentlichen zellularen Funknetzen im Kontext telemedizinischer Anwendung},
  address   = {Potsdam},
  pages     = {224 S.},
  year      = {2013},
  language  = {de}
}
@phdthesis{Schumacher2017,
  author    = {Schumacher, Kinga},
  title     = {Hybride semantische Suche - eine Kombination aus Fakten- und Dokumentretrieval},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-405973},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 187},
  year      = {2017},
  abstract  = {Das Thema der vorliegenden Arbeit ist die semantische Suche im Kontext heutiger Informationsmanagementsysteme. Zu diesen Systemen z{\"a}hlen Intranets, Web 3.0-Anwendungen sowie viele Webportale, die Informationen in heterogenen Formaten und Strukturen beinhalten. Auf diesen befinden sich einerseits Daten in strukturierter Form und andererseits Dokumente, die inhaltlich mit diesen Daten in Beziehung stehen. Diese Dokumente sind jedoch in der Regel nur teilweise strukturiert oder vollst{\"a}ndig unstrukturiert. So beschreiben beispielsweise Reiseportale durch strukturierte Daten den Zeitraum, das Reiseziel, den Preis einer Reise und geben in unstrukturierter Form weitere Informationen, wie Beschreibungen zum Hotel, Zielort, Ausflugsziele an. Der Fokus heutiger semantischer Suchmaschinen liegt auf dem Finden von Wissen entweder in strukturierter Form, auch Faktensuche genannt, oder in semi- bzw. unstrukturierter Form, was {\"u}blicherweise als semantische Dokumentensuche bezeichnet wird. Einige wenige Suchmaschinen versuchen die L{\"u}cke zwischen diesen beiden Ans{\"a}tzen zu schließen. Diese durchsuchen zwar gleichzeitig strukturierte sowie unstrukturierte Daten, werten diese jedoch entweder weitgehend voneinander unabh{\"a}ngig aus oder schr{\"a}nken die Suchm{\"o}glichkeiten stark ein, indem sie beispielsweise nur bestimmte Fragemuster unterst{\"u}tzen. Hierdurch werden die im System verf{\"u}gbaren Informationen nicht ausgesch{\"o}pft und gleichzeitig unterbunden, dass Zusammenh{\"a}nge zwischen einzelnen Inhalten der jeweiligen Informationssysteme und sich erg{\"a}nzende Informationen den Benutzer erreichen.
 Um diese L{\"u}cke zu schließen, wurde in der vorliegenden Arbeit ein neuer hybrider semantischer Suchansatz entwickelt und untersucht, der strukturierte und semi- bzw. unstrukturierte Inhalte w{\"a}hrend des gesamten Suchprozesses kombiniert. Durch diesen Ansatz werden nicht nur sowohl Fakten als auch Dokumente gefunden, es werden auch Zusammenh{\"a}nge, die zwischen den unterschiedlich strukturierten Daten bestehen, in jeder Phase der Suche genutzt und fließen in die Suchergebnisse mit ein. Liegt die Antwort zu einer Suchanfrage nicht vollst{\"a}ndig strukturiert, in Form von Fakten, oder unstrukturiert, in Form von Dokumenten vor, so liefert dieser Ansatz eine Kombination der beiden. Die Ber{\"u}cksichtigung von unterschiedlich Inhalten w{\"a}hrend des gesamten Suchprozesses stellt jedoch besondere Herausforderungen an die Suchmaschine. Diese muss in der Lage sein, Fakten und Dokumente in Abh{\"a}ngigkeit voneinander zu durchsuchen, sie zu kombinieren sowie die unterschiedlich strukturierten Ergebnisse in eine geeignete Rangordnung zu bringen. Weiterhin darf die Komplexit{\"a}t der Daten nicht an die Endnutzer weitergereicht werden. Die Darstellung der Inhalte muss vielmehr sowohl bei der Anfragestellung als auch bei der Darbietung der Ergebnisse verst{\"a}ndlich und leicht interpretierbar sein. Die zentrale Fragestellung der Arbeit ist, ob ein hybrider Ansatz auf einer vorgegebenen Datenbasis die Suchanfragen besser beantworten kann als die semantische Dokumentensuche und die Faktensuche f{\"u}r sich genommen, bzw. als eine Suche die diese Ans{\"a}tze im Rahmen des Suchprozesses nicht kombiniert. Die durchgef{\"u}hrten Evaluierungen aus System- und aus Benutzersicht zeigen, dass die im Rahmen der Arbeit entwickelte hybride semantische Suchl{\"o}sung durch die Kombination von strukturierten und unstrukturierten Inhalten im Suchprozess bessere Antworten liefert als die oben genannten Verfahren und somit Vorteile gegen{\"u}ber bisherigen Ans{\"a}tzen bietet. Eine Befragung von Benutzern macht deutlich, dass die hybride semantische Suche als verst{\"a}ndlich empfunden und f{\"u}r heterogen strukturierte Datenmengen bevorzugt wird.},
  language  = {de}
}
@phdthesis{Smirnov2011,
  author    = {Smirnov, Sergey},
  title     = {Business process model abstraction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-60258},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Business process models are used within a range of organizational initiatives, where every stakeholder has a unique perspective on a process and demands the respective model. As a consequence, multiple process models capturing the very same business process coexist. Keeping such models in sync is a challenge within an ever changing business environment: once a process is changed, all its models have to be updated. Due to a large number of models and their complex relations, model maintenance becomes error-prone and expensive. Against this background, business process model abstraction emerged as an operation reducing the number of stored process models and facilitating model management. Business process model abstraction is an operation preserving essential process properties and leaving out insignificant details in order to retain information relevant for a particular purpose. Process model abstraction has been addressed by several researchers. The focus of their studies has been on particular use cases and model transformations supporting these use cases. This thesis systematically approaches the problem of business process model abstraction shaping the outcome into a framework. We investigate the current industry demand in abstraction summarizing it in a catalog of business process model abstraction use cases. The thesis focuses on one prominent use case where the user demands a model with coarse-grained activities and overall process ordering constraints. We develop model transformations that support this use case starting with the transformations based on process model structure analysis. Further, abstraction methods considering the semantics of process model elements are investigated. First, we suggest how semantically related activities can be discovered in process models-a barely researched challenge. The thesis validates the designed abstraction methods against sets of industrial process models and discusses the method implementation aspects. Second, we develop a novel model transformation, which combined with the related activity discovery allows flexible non-hierarchical abstraction. In this way this thesis advocates novel model transformations that facilitate business process model management and provides the foundations for innovative tool support.},
  language  = {en}
}
@phdthesis{Mahr2012,
  author    = {Mahr, Philipp},
  title     = {Resource efficient communication in network-based reconfigurable on-chip systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59914},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {The constantly growing capacity of reconfigurable devices allows simultaneous execution of complex applications on those devices. The mere diversity of applications deems it impossible to design an interconnection network matching the requirements of every possible application perfectly, leading to suboptimal performance in many cases. However, the architecture of the interconnection network is not the only aspect affecting performance of communication. The resource manager places applications on the device and therefore influences latency between communicating partners and overall network load. Communication protocols affect performance by introducing data and processing overhead putting higher load on the network and increasing resource demand. Approaching communication holistically not only considers the architecture of the interconnect, but communication-aware resource management, communication protocols and resource usage just as well. Incorporation of different parts of a reconfigurable system during design- and runtime and optimizing them with respect to communication demand results in more resource efficient communication. Extensive evaluation shows enhanced performance and flexibility, if communication on reconfigurable devices is regarded in a holistic fashion.},
  language  = {en}
}
@phdthesis{Heinze2015,
  author    = {Heinze, Theodor},
  title     = {Analyse von Patientendaten und Entscheidungsunterst{\"u}tzung in der Telemedizin},
  school      = {Universit{\"a}t Potsdam},
  pages     = {173},
  year      = {2015},
  language  = {de}
}
@phdthesis{Albrecht2013,
  author    = {Albrecht, Alexander},
  title     = {Understanding and managing extract-transform-load systems},
  pages     = {107},
  year      = {2013},
  language  = {en}
}
@phdthesis{Schacht2014,
  author    = {Schacht, Alexander},
  title     = {Konzepte und Strategien mobiler Plattformen zur Erfassung und Anlayse von Vitalparametern in heterogenen Telemonotoring-Systemen},
  pages     = {215},
  year      = {2014},
  language  = {de}
}
@phdthesis{Thomas2002,
  author    = {Thomas, Marco},
  title     = {Informatische Modellbildung : modellieren von Modellen als ein zentrales Element der Informatik f{\"u}r den allgemeinbildenden Schulunterricht},
  pages     = {98 S.},
  year      = {2002},
  language  = {de}
}
@phdthesis{Kersting2002,
  author    = {Kersting, Oliver},
  title     = {Interaktive, dynamische 3D-Karten zur Kommunikation r{\"a}umlicher Information},
  pages     = {105 S.},
  year      = {2002},
  language  = {de}
}
@phdthesis{Rostock2002,
  author    = {Rostock, Gisbert},
  title     = {Ein polynomialer Algorithmus zur Erkennung von Isomorphie von Graphen},
  pages     = {63 S.},
  year      = {2002},
  language  = {de}
}
@phdthesis{Hartje2001,
  author    = {Hartje, Hendrik},
  title     = {Schaltungsoptimierung durch Logiktransformationen w{\"a}hrend des Layoutentwurfs},
  pages     = {113 S.},
  year      = {2001},
  language  = {de}
}
@phdthesis{Kalkbrenner2001,
  author    = {Kalkbrenner, Gerrit},
  title     = {Lernen und Lehren an der virtuellen Universit{\"a}t},
  pages     = {169 S.},
  year      = {2001},
  language  = {de}
}
@phdthesis{Huong2001,
  author    = {Huong, Dinh Thi Thanh},
  title     = {Correctness proofs and probabilistic tests for constructive specifications and functional programs},
  pages     = {154 S.},
  year      = {2001},
  language  = {en}
}
@phdthesis{Kupries2000,
  author    = {Kupries, Mario},
  title     = {Interagentenkonnektionen in Multi-Agentensystemen},
  pages     = {104 S. : Anl.},
  year      = {2000},
  language  = {de}
}
@phdthesis{Petrasch1999,
  author    = {Petrasch, Roland},
  title     = {Entwicklung von Modelltypen f{\"u}r das Qualit{\"a}tsmanagement in der Software-Entwicklung am Beispiel von ausgew{\"a}hlten Qualit{\"a}tssicherungsmaßnahmen},
  pages     = {Bl. i - viii; 173 Bl. : graph. Darst.},
  year      = {1999},
  language  = {de}
}
@phdthesis{Moschanin1999,
  author    = {Moschanin, Wladimir},
  title     = {Entwurf selbstdualer digitaler Schaltungen zur Fehlererkennung},
  address   = {Potsdam},
  pages     = {III, 94 S. : graph. Darst.},
  year      = {1999},
  language  = {de}
}
@phdthesis{Tiwari2019,
  author    = {Tiwari, Abhishek},
  title     = {Enhancing Users' Privacy: Static Resolution of the Dynamic Properties of Android},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 111},
  year      = {2019},
  abstract  = {The usage of mobile devices is rapidly growing with Android being the most prevalent mobile operating system. Thanks to the vast variety of mobile applications, users are preferring smartphones over desktops for day to day tasks like Internet surfing. Consequently, smartphones store a plenitude of sensitive data. This data together with the high values of smartphones make them an attractive target for device/data theft (thieves/malicious applications). Unfortunately, state-of-the-art anti-theft solutions do not work if they do not have an active network connection, e.g., if the SIM card was removed from the device. In the majority of these cases, device owners permanently lose their smartphone together with their personal data, which is even worse. Apart from that malevolent applications perform malicious activities to steal sensitive information from smartphones. Recent research considered static program analysis to detect dangerous data leaks. These analyses work well for data leaks due to inter-component communication, but suffer from shortcomings for inter-app communication with respect to precision, soundness, and scalability. This thesis focuses on enhancing users' privacy on Android against physical device loss/theft and (un)intentional data leaks. It presents three novel frameworks: (1) ThiefTrap, an anti-theft framework for Android, (2) IIFA, a modular inter-app intent information flow analysis of Android applications, and (3) PIAnalyzer, a precise approach for PendingIntent vulnerability analysis. ThiefTrap is based on a novel concept of an anti-theft honeypot account that protects the owner's data while preventing a thief from resetting the device. We implemented the proposed scheme and evaluated it through an empirical user study with 35 participants. In this study, the owner's data could be protected, recovered, and anti-theft functionality could be performed unnoticed from the thief in all cases. IIFA proposes a novel approach for Android's inter-component/inter-app communication (ICC/IAC) analysis. Our main contribution is the first fully automatic, sound, and precise ICC/IAC information flow analysis that is scalable for realistic apps due to modularity, avoiding combinatorial explosion: Our approach determines communicating apps using short summaries rather than inlining intent calls between components and apps, which requires simultaneously analyzing all apps installed on a device. We evaluate IIFA in terms of precision, recall, and demonstrate its scalability to a large corpus of real-world apps. IIFA reports 62 problematic ICC-/IAC-related information flows via two or more apps/components. PIAnalyzer proposes a novel approach to analyze PendingIntent related vulnerabilities. PendingIntents are a powerful and universal feature of Android for inter-component communication. We empirically evaluate PIAnalyzer on a set of 1000 randomly selected applications and find 1358 insecure usages of PendingIntents, including 70 severe vulnerabilities.},
  language  = {en}
}
@phdthesis{Decker2009,
  author    = {Decker, Gero},
  title     = {Design and analysis of process choreographies},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-40761},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {With the rise of electronic integration between organizations, the need for a precise specification of interaction behavior increases. Information systems, replacing interaction previously carried out by humans via phone, faxes and emails, require a precise specification for handling all possible situations. Such interaction behavior is described in process choreographies. Choreographies enumerate the roles involved, the allowed interactions, the message contents and the behavioral dependencies between interactions. Choreographies serve as interaction contract and are the starting point for adapting existing business processes and systems or for implementing new software components. As a thorough analysis and comparison of choreography modeling languages is missing in the literature, this thesis introduces a requirements framework for choreography languages and uses it for comparing current choreography languages. Language proposals for overcoming the limitations are given for choreography modeling on the conceptual and on the technical level. Using an interconnection modeling style, behavioral dependencies are defined on a per-role basis and different roles are interconnected using message flow. This thesis reveals a number of modeling "anti-patterns" for interconnection modeling, motivating further investigations on choreography languages following the interaction modeling style. Here, interactions are seen as atomic building blocks and the behavioral dependencies between them are defined globally. Two novel language proposals are put forward for this modeling style which have already influenced industrial standardization initiatives. While avoiding many of the pitfalls of interconnection modeling, new anomalies can arise in interaction models. A choreography might not be realizable, i.e. there does not exist a set of interacting roles that collectively realize the specified behavior. This thesis investigates different dimensions of realizability.},
  language  = {en}
}
@phdthesis{Boehne2019,
  author    = {B{\"o}hne, Sebastian},
  title     = {Different degrees of formality},
  doi       = {10.25932/publishup-42379},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423795},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 167},
  year      = {2019},
  abstract  = {In this thesis we introduce the concept of the degree of formality. It is directed against a dualistic point of view, which only distinguishes between formal and informal proofs. This dualistic attitude does not respect the differences between the argumentations classified as informal and it is unproductive because the individual potential of the respective argumentation styles cannot be appreciated and remains untapped. This thesis has two parts. In the first of them we analyse the concept of the degree of formality (including a discussion about the respective benefits for each degree) while in the second we demonstrate its usefulness in three case studies. In the first case study we will repair Haskell B. Curry's view of mathematics, which incidentally is of great importance in the first part of this thesis, in light of the different degrees of formality. In the second case study we delineate how awareness of the different degrees of formality can be used to help students to learn how to prove. Third, we will show how the advantages of proofs of different degrees of formality can be combined by the development of so called tactics having a medium degree of formality. Together the three case studies show that the degrees of formality provide a convincing solution to the problem of untapped potential.},
  language  = {en}
}
@phdthesis{Przybylla2018,
  author    = {Przybylla, Mareen},
  title     = {From Embedded Systems to Physical Computing: Challenges of the "Digital World" in Secondary Computer Science Education},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418339},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 277},
  year      = {2018},
  abstract  = {Physical computing covers the design and realization of interactive objects and installations and allows learners to develop concrete, tangible products of the real world, which arise from their imagination. This can be used in computer science education to provide learners with interesting and motivating access to the different topic areas of the subject in constructionist and creative learning environments. However, if at all, physical computing has so far mostly been taught in afternoon clubs or other extracurricular settings. Thus, for the majority of students so far there are no opportunities to design and create their own interactive objects in regular school lessons. Despite its increasing popularity also for schools, the topic has not yet been clearly and sufficiently characterized in the context of computer science education. The aim of this doctoral thesis therefore is to clarify physical computing from the perspective of computer science education and to adequately prepare the topic both content-wise and methodologically for secondary school teaching. For this purpose, teaching examples, activities, materials and guidelines for classroom use are developed, implemented and evaluated in schools. In the theoretical part of the thesis, first the topic is examined from a technical point of view. A structured literature analysis shows that basic concepts used in physical computing can be derived from embedded systems, which are the core of a large field of different application areas and disciplines. Typical methods of physical computing in professional settings are analyzed and, from an educational perspective, elements suitable for computer science teaching in secondary schools are extracted, e. g. tinkering and prototyping. The investigation and classification of suitable tools for school teaching show that microcontrollers and mini computers, often with extensions that greatly facilitate the handling of additional components, are particularly attractive tools for secondary education. Considering the perspectives of science, teachers, students and society, in addition to general design principles, exemplary teaching approaches for school education and suitable learning materials are developed and the design, production and evaluation of a physical computing construction kit suitable for teaching is described. In the practical part of this thesis, with "My Interactive Garden", an exemplary approach to integrate physical computing in computer science teaching is tested and evaluated in different courses and refined based on the findings in a design-based research approach. In a series of workshops on physical computing, which is based on a concept for constructionist professional development that is developed specifically for this purpose, teachers are empowered and encouraged to develop and conduct physical computing lessons suitable for their particular classroom settings. Based on their in-class experiences, a process model of physical computing teaching is derived. Interviews with those teachers illustrate that benefits of physical computing, including the tangibility of crafted objects and creativity in the classroom, outweigh possible drawbacks like longer preparation times, technical difficulties or difficult assessment. Hurdles in the classroom are identified and possible solutions discussed. Empirical investigations in the different settings reveal that "My Interactive Garden" and physical computing in general have a positive impact, among others, on learner motivation, fun and interest in class and perceived competencies. Finally, the results from all evaluations are combined to evaluate the design principles for physical computing teaching and to provide a perspective on the development of decision-making aids for physical computing activities in school education.},
  language  = {en}
}
@phdthesis{Holz2013,
  author    = {Holz, Christian},
  title     = {3D from 2D touch},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-67796},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {While interaction with computers used to be dominated by mice and keyboards, new types of sensors now allow users to interact through touch, speech, or using their whole body in 3D space. These new interaction modalities are often referred to as "natural user interfaces" or "NUIs." While 2D NUIs have experienced major success on billions of mobile touch devices sold, 3D NUI systems have so far been unable to deliver a mobile form factor, mainly due to their use of cameras. The fact that cameras require a certain distance from the capture volume has prevented 3D NUI systems from reaching the flat form factor mobile users expect. In this dissertation, we address this issue by sensing 3D input using flat 2D sensors. The systems we present observe the input from 3D objects as 2D imprints upon physical contact. By sampling these imprints at very high resolutions, we obtain the objects' textures. In some cases, a texture uniquely identifies a biometric feature, such as the user's fingerprint. In other cases, an imprint stems from the user's clothing, such as when walking on multitouch floors. By analyzing from which part of the 3D object the 2D imprint results, we reconstruct the object's pose in 3D space. While our main contribution is a general approach to sensing 3D input on 2D sensors upon physical contact, we also demonstrate three applications of our approach. (1) We present high-accuracy touch devices that allow users to reliably touch targets that are a third of the size of those on current touch devices. We show that different users and 3D finger poses systematically affect touch sensing, which current devices perceive as random input noise. We introduce a model for touch that compensates for this systematic effect by deriving the 3D finger pose and the user's identity from each touch imprint. We then investigate this systematic effect in detail and explore how users conceptually touch targets. Our findings indicate that users aim by aligning visual features of their fingers with the target. We present a visual model for touch input that eliminates virtually all systematic effects on touch accuracy. (2) From each touch, we identify users biometrically by analyzing their fingerprints. Our prototype Fiberio integrates fingerprint scanning and a display into the same flat surface, solving a long-standing problem in human-computer interaction: secure authentication on touchscreens. Sensing 3D input and authenticating users upon touch allows Fiberio to implement a variety of applications that traditionally require the bulky setups of current 3D NUI systems. (3) To demonstrate the versatility of 3D reconstruction on larger touch surfaces, we present a high-resolution pressure-sensitive floor that resolves the texture of objects upon touch. Using the same principles as before, our system GravitySpace analyzes all imprints and identifies users based on their shoe soles, detects furniture, and enables accurate touch input using feet. By classifying all imprints, GravitySpace detects the users' body parts that are in contact with the floor and then reconstructs their 3D body poses using inverse kinematics. GravitySpace thus enables a range of applications for future 3D NUI systems based on a flat sensor, such as smart rooms in future homes. We conclude this dissertation by projecting into the future of mobile devices. Focusing on the mobility aspect of our work, we explore how NUI devices may one day augment users directly in the form of implanted devices.},
  language  = {en}
}
@phdthesis{Mueller2016,
  author    = {Mueller, Stefanie},
  title     = {Interacting with personal fabrication devices},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-100908},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxi, 108},
  year      = {2016},
  abstract  = {Personal fabrication tools, such as 3D printers, are on the way of enabling a future in which non-technical users will be able to create custom objects. However, while the hardware is there, the current interaction model behind existing design tools is not suitable for non-technical users. Today, 3D printers are operated by fabricating the object in one go, which tends to take overnight due to the slow 3D printing technology. Consequently, the current interaction model requires users to think carefully before printing as every mistake may imply another overnight print. Planning every step ahead, however, is not feasible for non-technical users as they lack the experience to reason about the consequences of their design decisions. In this dissertation, we propose changing the interaction model around personal fabrication tools to better serve this user group. We draw inspiration from personal computing and argue that the evolution of personal fabrication may resemble the evolution of personal computing: Computing started with machines that executed a program in one go before returning the result to the user. By decreasing the interaction unit to single requests, turn-taking systems such as the command line evolved, which provided users with feedback after every input. Finally, with the introduction of direct-manipulation interfaces, users continuously interacted with a program receiving feedback about every action in real-time. In this dissertation, we explore whether these interaction concepts can be applied to personal fabrication as well. We start with fabricating an object in one go and investigate how to tighten the feedback-cycle on an object-level: We contribute a method called low-fidelity fabrication, which saves up to 90\% fabrication time by creating objects as fast low-fidelity previews, which are sufficient to evaluate key design aspects. Depending on what is currently being tested, we propose different conversions that enable users to focus on different parts: faBrickator allows for a modular design in the early stages of prototyping; when users move on WirePrint allows quickly testing an object's shape, while Platener allows testing an object's technical function. We present an interactive editor for each technique and explain the underlying conversion algorithms. By interacting on smaller units, such as a single element of an object, we explore what it means to transition from systems that fabricate objects in one go to turn-taking systems. We start with a 2D system called constructable: Users draw with a laser pointer onto the workpiece inside a laser cutter. The drawing is captured with an overhead camera. As soon as the the user finishes drawing an element, such as a line, the constructable system beautifies the path and cuts it--resulting in physical output after every editing step. We extend constructable towards 3D editing by developing a novel laser-cutting technique for 3D objects called LaserOrigami that works by heating up the workpiece with the defocused laser until the material becomes compliant and bends down under gravity. While constructable and LaserOrigami allow for fast physical feedback, the interaction is still best described as turn-taking since it consists of two discrete steps: users first create an input and afterwards the system provides physical output. By decreasing the interaction unit even further to a single feature, we can achieve real-time physical feedback: Input by the user and output by the fabrication device are so tightly coupled that no visible lag exists. This allows us to explore what it means to transition from turn-taking interfaces, which only allow exploring one option at a time, to direct manipulation interfaces with real-time physical feedback, which allow users to explore the entire space of options continuously with a single interaction. We present a system called FormFab, which allows for such direct control. FormFab is based on the same principle as LaserOrigami: It uses a workpiece that when warmed up becomes compliant and can be reshaped. However, FormFab achieves the reshaping not based on gravity, but through a pneumatic system that users can control interactively. As users interact, they see the shape change in real-time. We conclude this dissertation by extrapolating the current evolution into a future in which large numbers of people use the new technology to create objects. We see two additional challenges on the horizon: sustainability and intellectual property. We investigate sustainability by demonstrating how to print less and instead patch physical objects. We explore questions around intellectual property with a system called Scotty that transfers objects without creating duplicates, thereby preserving the designer's copyright.},
  language  = {en}
}
@phdthesis{Jiang2007,
  author    = {Jiang, Chunyan},
  title     = {Multi-visualization and hybrid segmentation approaches within telemedicine framework},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12829},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {The innovation of information techniques has changed many aspects of our life. In health care field, we can obtain, manage and communicate high-quality large volumetric image data by computer integrated devices, to support medical care. In this dissertation I propose several promising methods that could assist physicians in processing, observing and communicating the image data. They are included in my three research aspects: telemedicine integration, medical image visualization and image segmentation. And these methods are also demonstrated by the demo software that I developed. One of my research point focuses on medical information storage standard in telemedicine, for example DICOM, which is the predominant standard for the storage and communication of medical images. I propose a novel 3D image data storage method, which was lacking in current DICOM standard. I also created a mechanism to make use of the non-standard or private DICOM files. In this thesis I present several rendering techniques on medical image visualization to offer different display manners, both 2D and 3D, for example, cut through data volume in arbitrary degree, rendering the surface shell of the data, and rendering the semi-transparent volume of the data. A hybrid segmentation approach, designed for semi-automated segmentation of radiological image, such as CT, MRI, etc, is proposed in this thesis to get the organ or interested area from the image. This approach takes advantage of the region-based method and boundary-based methods. Three steps compose the hybrid approach: the first step gets coarse segmentation by fuzzy affinity and generates homogeneity operator; the second step divides the image by Voronoi Diagram and reclassifies the regions by the operator to refine segmentation from the previous step; the third step handles vague boundary by level set model. Topics for future research are mentioned in the end, including new supplement for DICOM standard for segmentation information storage, visualization of multimodal image information, and improvement of the segmentation approach to higher dimension.},
  language  = {en}
}
@phdthesis{Hu2006,
  author    = {Hu, Ji},
  title     = {A virtual machine architecture for IT-security laboratories},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7818},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {This thesis discusses challenges in IT security education, points out a gap between e-learning and practical education, and presents a work to fill the gap. E-learning is a flexible and personalized alternative to traditional education. Nonetheless, existing e-learning systems for IT security education have difficulties in delivering hands-on experience because of the lack of proximity. Laboratory environments and practical exercises are indispensable instruction tools to IT security education, but security education in conventional computer laboratories poses particular problems such as immobility as well as high creation and maintenance costs. Hence, there is a need to effectively transform security laboratories and practical exercises into e-learning forms. In this thesis, we introduce the Tele-Lab IT-Security architecture that allows students not only to learn IT security principles, but also to gain hands-on security experience by exercises in an online laboratory environment. In this architecture, virtual machines are used to provide safe user work environments instead of real computers. Thus, traditional laboratory environments can be cloned onto the Internet by software, which increases accessibility to laboratory resources and greatly reduces investment and maintenance costs. Under the Tele-Lab IT-Security framework, a set of technical solutions is also proposed to provide effective functionalities, reliability, security, and performance. The virtual machines with appropriate resource allocation, software installation, and system configurations are used to build lightweight security laboratories on a hosting computer. Reliability and availability of laboratory platforms are covered by a virtual machine management framework. This management framework provides necessary monitoring and administration services to detect and recover critical failures of virtual machines at run time. Considering the risk that virtual machines can be misused for compromising production networks, we present a security management solution to prevent the misuse of laboratory resources by security isolation at the system and network levels. This work is an attempt to bridge the gap between e-learning/tele-teaching and practical IT security education. It is not to substitute conventional teaching in laboratories but to add practical features to e-learning. This thesis demonstrates the possibility to implement hands-on security laboratories on the Internet reliably, securely, and economically.},
  subject      = {Computersicherheit},
  language  = {en}
}
@phdthesis{Ghasemzadeh2005,
  author    = {Ghasemzadeh, Mohammad},
  title     = {A new algorithm for the quantified satisfiability problem, based on zero-suppressed binary decision diagrams and memoization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6378},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Quantified Boolean formulas (QBFs) play an important role in theoretical computer science. QBF extends propositional logic in such a way that many advanced forms of reasoning can be easily formulated and evaluated. In this dissertation we present our ZQSAT, which is an algorithm for evaluating quantified Boolean formulas. ZQSAT is based on ZBDD: Zero-Suppressed Binary Decision Diagram , which is a variant of BDD, and an adopted version of the DPLL algorithm. It has been implemented in C using the CUDD: Colorado University Decision Diagram package. The capability of ZBDDs in storing sets of subsets efficiently enabled us to store the clauses of a QBF very compactly and let us to embed the notion of memoization to the DPLL algorithm. These points led us to implement the search algorithm in such a way that we could store and reuse the results of all previously solved subformulas with a little overheads. ZQSAT can solve some sets of standard QBF benchmark problems (known to be hard for DPLL based algorithms) faster than the best existing solvers. In addition to prenex-CNF, ZQSAT accepts prenex-NNF formulas. We show and prove how this capability can be exponentially beneficial.},
  subject      = {Bin{\"a}res Entscheidungsdiagramm},
  language  = {en}
}
@phdthesis{Linckels2008,
  author    = {Linckels, Serge},
  title     = {An e-librarian service : supporting explorative learning by a description logics based semantic retrieval tool},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17452},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Although educational content in electronic form is increasing dramatically, its usage in an educational environment is poor, mainly due to the fact that there is too much of (unreliable) redundant, and not relevant information. Finding appropriate answers is a rather difficult task being reliant on the user filtering of the pertinent information from the noise. Turning knowledge bases like the online tele-TASK archive into useful educational resources requires identifying correct, reliable, and "machine-understandable" information, as well as developing simple but efficient search tools with the ability to reason over this information. Our vision is to create an E-Librarian Service, which is able to retrieve multimedia resources from a knowledge base in a more efficient way than by browsing through an index, or by using a simple keyword search. In our E-Librarian Service, the user can enter his question in a very simple and human way; in natural language (NL). Our premise is that more pertinent results would be retrieved if the search engine understood the sense of the user's query. The returned results are then logical consequences of an inference rather than of keyword matchings. Our E-Librarian Service does not return the answer to the user's question, but it retrieves the most pertinent document(s), in which the user finds the answer to his/her question. Among all the documents that have some common information with the user query, our E-Librarian Service identifies the most pertinent match(es), keeping in mind that the user expects an exhaustive answer while preferring a concise answer with only little or no information overhead. Also, our E-Librarian Service always proposes a solution to the user, even if the system concludes that there is no exhaustive answer. Our E-Librarian Service was implemented prototypically in three different educational tools. A first prototype is CHESt (Computer History Expert System); it has a knowledge base with 300 multimedia clips that cover the main events in computer history. A second prototype is MatES (Mathematics Expert System); it has a knowledge base with 115 clips that cover the topic of fractions in mathematics for secondary school w.r.t. the official school programme. All clips were recorded mainly by pupils. The third and most advanced prototype is the "Lecture Butler's E-Librarain Service"; it has a Web service interface to respect a service oriented architecture (SOA), and was developed in the context of the Web-University project at the Hasso-Plattner-Institute (HPI). Two major experiments in an educational environment - at the Lyc{\´e}e Technique Esch/Alzette in Luxembourg - were made to test the pertinence and reliability of our E-Librarian Service as a complement to traditional courses. The first experiment (in 2005) was made with CHESt in different classes, and covered a single lesson. The second experiment (in 2006) covered a period of 6 weeks of intensive use of MatES in one class. There was no classical mathematics lesson where the teacher gave explanations, but the students had to learn in an autonomous and exploratory way. They had to ask questions to the E-Librarian Service just the way they would if there was a human teacher.},
  subject      = {Terminologische Logik},
  language  = {en}
}
@phdthesis{Huang2006,
  author    = {Huang, Wanjun},
  title     = {Temporary binding for dynamic middleware construction and web services composition},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7672},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {With increasing number of applications in Internet and mobile environments, distributed software systems are demanded to be more powerful and flexible, especially in terms of dynamism and security. This dissertation describes my work concerning three aspects: dynamic reconfiguration of component software, security control on middleware applications, and web services dynamic composition. Firstly, I proposed a technology named Routing Based Workflow (RBW) to model the execution and management of collaborative components and realize temporary binding for component instances. The temporary binding means component instances are temporarily loaded into a created execution environment to execute their functions, and then are released to their repository after executions. The temporary binding allows to create an idle execution environment for all collaborative components, on which the change operations can be immediately carried out. The changes on execution environment will result in a new collaboration of all involved components, and also greatly simplifies the classical issues arising from dynamic changes, such as consistency preserving etc. To demonstrate the feasibility of RBW, I created a dynamic secure middleware system - the Smart Data Server Version 3.0 (SDS3). In SDS3, an open source implementation of CORBA is adopted and modified as the communication infrastructure, and three secure components managed by RBW, are created to enhance the security on the access of deployed applications. SDS3 offers multi-level security control on its applications from strategy control to application-specific detail control. For the management by RBW, the strategy control of SDS3 applications could be dynamically changed by reorganizing the collaboration of the three secure components. In addition, I created the Dynamic Services Composer (DSC) based on Apache open source projects, Apache Axis and WSIF. In DSC, RBW is employed to model the interaction and collaboration of web services and to enable the dynamic changes on the flow structure of web services. Finally, overall performance tests were made to evaluate the efficiency of the developed RBW and SDS3. The results demonstrated that temporary binding of component instances makes slight impacts on the execution efficiency of components, and the blackout time arising from dynamic changes can be extremely reduced in any applications.},
  subject      = {Middleware},
  language  = {en}
}
@phdthesis{Menzel2011,
  author    = {Menzel, Michael},
  title     = {Model-driven security in service-oriented architectures : leveraging security patterns to transform high-level security requirements to technical policies},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59058},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Service-oriented Architectures (SOA) facilitate the provision and orchestration of business services to enable a faster adoption to changing business demands. Web Services provide a technical foundation to implement this paradigm on the basis of XML-messaging. However, the enhanced flexibility of message-based systems comes along with new threats and risks. To face these issues, a variety of security mechanisms and approaches is supported by the Web Service specifications. The usage of these security mechanisms and protocols is configured by stating security requirements in security policies. However, security policy languages for SOA are complex and difficult to create due to the expressiveness of these languages. To facilitate and simplify the creation of security policies, this thesis presents a model-driven approach that enables the generation of complex security policies on the basis of simple security intentions. SOA architects can specify these intentions in system design models and are not required to deal with complex technical security concepts. The approach introduced in this thesis enables the enhancement of any system design modelling languages - for example FMC or BPMN - with security modelling elements. The syntax, semantics, and notion of these elements is defined by our security modelling language SecureSOA. The metamodel of this language provides extension points to enable the integration into system design modelling languages. In particular, this thesis demonstrates the enhancement of FMC block diagrams with SecureSOA. To enable the model-driven generation of security policies, a domain-independent policy model is introduced in this thesis. This model provides an abstraction layer for security policies. Mappings are used to perform the transformation from our model to security policy languages. However, expert knowledge is required to generate instances of this model on the basis of simple security intentions. Appropriate security mechanisms, protocols and options must be chosen and combined to fulfil these security intentions. In this thesis, a formalised system of security patterns is used to represent this knowledge and to enable an automated transformation process. Moreover, a domain-specific language is introduced to state security patterns in an accessible way. On the basis of this language, a system of security configuration patterns is provided to transform security intentions related to data protection and identity management. The formal semantics of the security pattern language enable the verification of the transformation process introduced in this thesis and prove the correctness of the pattern application. Finally, our SOA Security LAB is presented that demonstrates the application of our model-driven approach to facilitate a dynamic creation, configuration, and execution of secure Web Service-based composed applications.},
  language  = {en}
}
@phdthesis{Schnjakin2014,
  author    = {Schnjakin, Maxim},
  title     = {Cloud-RAID},
  pages     = {137},
  year      = {2014},
  language  = {de}
}
@phdthesis{Saleh2016,
  author    = {Saleh, Eyad},
  title     = {Securing Multi-tenant SaaS Environments},
  school      = {Universit{\"a}t Potsdam},
  pages     = {108},
  year      = {2016},
  abstract  = {Software-as-a-Service (SaaS) offers several advantages to both service providers and users. Service providers can benefit from the reduction of Total Cost of Ownership (TCO), better scalability, and better resource utilization. On the other hand, users can use the service anywhere and anytime, and minimize upfront investment by following the pay-as-you-go model. Despite the benefits of SaaS, users still have concerns about the security and privacy of their data. Due to the nature of SaaS and the Cloud in general, the data and the computation are beyond the users' control, and hence data security becomes a vital factor in this new paradigm. Furthermore, in multi-tenant SaaS applications, the tenants become more concerned about the confidentiality of their data since several tenants are co-located onto a shared infrastructure. To address those concerns, we start protecting the data from the provisioning process by controlling how tenants are being placed in the infrastructure. We present a resource allocation algorithm designed to minimize the risk of co-resident tenants called SecPlace. It enables the SaaS provider to control the resource (i.e., database instance) allocation process while taking into account the security of tenants as a requirement. Due to the design principles of the multi-tenancy model, tenants follow some degree of sharing on both application and infrastructure levels. Thus, strong security-isolation should be present. Therefore, we develop SignedQuery, a technique that prevents one tenant from accessing others' data. We use the Signing Concept to create a signature that is used to sign the tenant's request, then the server can verifies the signature and recognizes the requesting tenant, and hence ensures that the data to be accessed is belonging to the legitimate tenant. Finally, Data confidentiality remains a critical concern due to the fact that data in the Cloud is out of users' premises, and hence beyond their control. Cryptography is increasingly proposed as a potential approach to address such a challenge. Therefore, we present SecureDB, a system designed to run SQL-based applications over an encrypted database. SecureDB captures the schema design and analyzes it to understand the internal structure of the data (i.e., relationships between the tables and their attributes). Moreover, we determine the appropriate partialhomomorphic encryption scheme for each attribute where computation is possible even when the data is encrypted. To evaluate our work, we conduct extensive experiments with di↵erent settings. The main use case in our work is a popular open source HRM application, called OrangeHRM. The results show that our multi-layered approach is practical, provides enhanced security and isolation among tenants, and have a moderate complexity in terms of processing encrypted data.},
  language  = {en}
}
@phdthesis{SadrAzodi2015,
  author    = {Sadr-Azodi, Amir Shahab},
  title     = {Towards Real-time SIEM-based Network monitoring and Intrusion Detection through Advanced Event Normalization},
  school      = {Universit{\"a}t Potsdam},
  pages     = {144},
  year      = {2015},
  language  = {en}
}
@phdthesis{Gericke2014,
  author    = {Gericke, Lutz},
  title     = {Tele-Board - Supporting and analyzing creative collaboration in synchronous and asynchronous scenario},
  pages     = {186},
  year      = {2014},
  language  = {en}
}
@phdthesis{AlSaffar2016,
  author    = {Al-Saffar, Loay Talib Ahmed},
  title     = {Analysing prerequisites, expectations, apprehensions, and attitudes of university students studying Computer science},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98437},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 131},
  year      = {2016},
  abstract  = {The main objective of this dissertation is to analyse prerequisites, expectations, apprehensions, and attitudes of students studying computer science, who are willing to gain a bachelor degree. The research will also investigate in the students' learning style according to the Felder-Silverman model. These investigations fall in the attempt to make an impact on reducing the "dropout"/shrinkage rate among students, and to suggest a better learning environment. The first investigation starts with a survey that has been made at the computer science department at the University of Baghdad to investigate the attitudes of computer science students in an environment dominated by women, showing the differences in attitudes between male and female students in different study years. Students are accepted to university studies via a centrally controlled admission procedure depending mainly on their final score at school. This leads to a high percentage of students studying subjects they do not want. Our analysis shows that 75\% of the female students do not regret studying computer science although it was not their first choice. And according to statistics over previous years, women manage to succeed in their study and often graduate on top of their class. We finish with a comparison of attitudes between the freshman students of two different cultures and two different university enrolment procedures (University of Baghdad, in Iraq, and the University of Potsdam, in Germany) both with opposite gender majority. The second step of investigation took place at the department of computer science at the University of Potsdam in Germany and analyzes the learning styles of students studying the three major fields of study offered by the department (computer science, business informatics, and computer science teaching). Investigating the differences in learning styles between the students of those study fields who usually take some joint courses is important to be aware of which changes are necessary to be adopted in the teaching methods to address those different students. It was a two stage study using two questionnaires; the main one is based on the Index of Learning Styles Questionnaire of B. A. Solomon and R. M. Felder, and the second questionnaire was an investigation on the students' attitudes towards the findings of their personal first questionnaire. Our analysis shows differences in the preferences of learning style between male and female students of the different study fields, as well as differences between students with the different specialties (computer science, business informatics, and computer science teaching). The third investigation looks closely into the difficulties, issues, apprehensions and expectations of freshman students studying computer science. The study took place at the computer science department at the University of Potsdam with a volunteer sample of students. The goal is to determine and discuss the difficulties and issues that they are facing in their study that may lead them to think in dropping-out, changing the study field, or changing the university. The research continued with the same sample of students (with business informatics students being the majority) through more than three semesters. Difficulties and issues during the study were documented, as well as students' attitudes, apprehensions, and expectations. Some of the professors and lecturers opinions and solutions to some students' problems were also documented. Many participants had apprehensions and difficulties, especially towards informatics subjects. Some business informatics participants began to think of changing the university, in particular when they reached their third semester, others thought about changing their field of study. Till the end of this research, most of the participants continued in their studies (the study they have started with or the new study they have changed to) without leaving the higher education system.},
  language  = {en}
}
@phdthesis{Prasse2016,
  author    = {Prasse, Paul},
  title     = {Pattern recognition for computer security},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-100251},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 75},
  year      = {2016},
  abstract  = {Computer Security deals with the detection and mitigation of threats to computer networks, data, and computing hardware. This thesis addresses the following two computer security problems: email spam campaign and malware detection. Email spam campaigns can easily be generated using popular dissemination tools by specifying simple grammars that serve as message templates. A grammar is disseminated to nodes of a bot net, the nodes create messages by instantiating the grammar at random. Email spam campaigns can encompass huge data volumes and therefore pose a threat to the stability of the infrastructure of email service providers that have to store them. Malware -software that serves a malicious purpose- is affecting web servers, client computers via active content, and client computers through executable files. Without the help of malware detection systems it would be easy for malware creators to collect sensitive information or to infiltrate computers. The detection of threats -such as email-spam messages, phishing messages, or malware- is an adversarial and therefore intrinsically difficult problem. Threats vary greatly and evolve over time. The detection of threats based on manually-designed rules is therefore difficult and requires a constant engineering effort. Machine-learning is a research area that revolves around the analysis of data and the discovery of patterns that describe aspects of the data. Discriminative learning methods extract prediction models from data that are optimized to predict a target attribute as accurately as possible. Machine-learning methods hold the promise of automatically identifying patterns that robustly and accurately detect threats. This thesis focuses on the design and analysis of discriminative learning methods for the two computer-security problems under investigation: email-campaign and malware detection. The first part of this thesis addresses email-campaign detection. We focus on regular expressions as a syntactic framework, because regular expressions are intuitively comprehensible by security engineers and administrators, and they can be applied as a detection mechanism in an extremely efficient manner. In this setting, a prediction model is provided with exemplary messages from an email-spam campaign. The prediction model has to generate a regular expression that reveals the syntactic pattern that underlies the entire campaign, and that a security engineers finds comprehensible and feels confident enough to use the expression to blacklist further messages at the email server. We model this problem as two-stage learning problem with structured input and output spaces which can be solved using standard cutting plane methods. Therefore we develop an appropriate loss function, and derive a decoder for the resulting optimization problem. The second part of this thesis deals with the problem of predicting whether a given JavaScript or PHP file is malicious or benign. Recent malware analysis techniques use static or dynamic features, or both. In fully dynamic analysis, the software or script is executed and observed for malicious behavior in a sandbox environment. By contrast, static analysis is based on features that can be extracted directly from the program file. In order to bypass static detection mechanisms, code obfuscation techniques are used to spread a malicious program file in many different syntactic variants. Deobfuscating the code before applying a static classifier can be subjected to mostly static code analysis and can overcome the problem of obfuscated malicious code, but on the other hand increases the computational costs of malware detection by an order of magnitude. In this thesis we present a cascaded architecture in which a classifier first performs a static analysis of the original code and -based on the outcome of this first classification step- the code may be deobfuscated and classified again. We explore several types of features including token \$n\$-grams, orthogonal sparse bigrams, subroutine-hashings, and syntax-tree features and study the robustness of detection methods and feature types against the evolution of malware over time. The developed tool scans very large file collections quickly and accurately. Each model is evaluated on real-world data and compared to reference methods. Our approach of inferring regular expressions to filter emails belonging to an email spam campaigns leads to models with a high true-positive rate at a very low false-positive rate that is an order of magnitude lower than that of a commercial content-based filter. Our presented system -REx-SVMshort- is being used by a commercial email service provider and complements content-based and IP-address based filtering. Our cascaded malware detection system is evaluated on a high-quality data set of almost 400,000 conspicuous PHP files and a collection of more than 1,00,000 JavaScript files. From our case study we can conclude that our system can quickly and accurately process large data collections at a low false-positive rate.},
  language  = {en}
}