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Real-time operating systems for mixed-criticality systems
must support different types of software, such as
real-time applications and general purpose applications,
and, at the same time, must provide strong spatial and
temporal isolation between independent software components.
Therefore, state-of-the-art real-time operating systems
focus mainly on predictability and bounded worst-case behavior.
However, general purpose operating systems such as Linux
often feature more efficient---but less deterministic---mechanisms
that significantly improve the average execution time.
This thesis addresses the combination of the two contradicting
requirements and shows thread synchronization mechanisms
with efficient average-case behavior, but without sacrificing
predictability and worst-case behavior.
This thesis explores and evaluates the design space of fast paths
in the implementation of typical blocking synchronization
mechanisms, such as mutexes, condition variables, counting
semaphores, barriers, or message queues. The key technique here
is to avoid unnecessary system calls, as system calls have high
costs compared to other processor operations available in user
space, such as low-level atomic synchronization primitives.
In particular, the thesis explores futexes, the state-of-the-art
design for blocking synchronization mechanisms in Linux
that handles the uncontended case of thread synchronization
by using atomic operations in user space and calls into the
kernel only to suspend and wake up threads. The thesis also
proposes non-preemptive busy-waiting monitors that use an
efficient priority ceiling mechanism to prevent the lock holder
preemption problem without using system calls, and according
low-level kernel primitives to construct efficient wait and
notify operations.
The evaluation shows that the presented approaches
improve the average performance comparable
to state-of-the-art approaches in Linux.
At the same time, a worst-case timing analysis shows
that the approaches only need constant or bounded temporal
overheads at the operating system kernel level.
Exploiting these fast paths is a worthwhile approach
when designing systems that not only have to fulfill
real-time requirements, but also best-effort workloads.
Data-minimization and fairness are fundamental data protection requirements to avoid privacy threats and discrimination. Violations of data protection requirements often result from: First, conflicts between security, data-minimization and fairness requirements. Second, data protection requirements for the organizational and technical aspects of a system that are currently dealt with separately, giving rise to misconceptions and errors. Third, hidden data correlations that might lead to influence biases against protected characteristics of individuals such as ethnicity in decision-making software. For the effective assurance of data protection needs,
it is important to avoid sources of violations right from the design modeling phase. However, a model-based approach that addresses the issues above is missing.
To handle the issues above, this thesis introduces a model-based methodology called MoPrivFair (Model-based Privacy & Fairness). MoPrivFair comprises three sub-frameworks: First, a framework that extends the SecBPMN2 approach to allow detecting conflicts between security, data-minimization and fairness requirements. Second, a framework for enforcing an integrated data-protection management throughout the development process based on a business processes model (i.e., SecBPMN2 model) and a software architecture model (i.e., UMLsec model) annotated with data protection requirements while establishing traceability. Third, the UML extension UMLfair to support individual fairness analysis and reporting discriminatory behaviors. Each of the proposed frameworks is supported by automated tool support.
We validated the applicability and usability of our conflict detection technique based on a health care management case study, and an experimental user study, respectively. Based on an air traffic management case study, we reported on the applicability of our technique for enforcing an integrated data-protection management. We validated the applicability of our individual fairness analysis technique using three case studies featuring a school management system, a delivery management system and a loan management system. The results show a promising outlook on the applicability of our proposed frameworks in real-world settings.
Nowadays, almost any IT system involves personal data processing. In
such systems, many privacy risks arise when privacy concerns are not
properly addressed from the early phases of the system design. The
General Data Protection Regulation (GDPR) prescribes the Privacy by
Design (PbD) principle. As its core, PbD obliges protecting personal
data from the onset of the system development, by effectively
integrating appropriate privacy controls into the design. To
operationalize the concept of PbD, a set of challenges emerges: First, we need a basis to define privacy concerns. Without such a basis, we are not able to verify whether personal data processing is authorized. Second, we need to identify where precisely in a system, the controls have to be applied. This calls for system analysis concerning privacy concerns. Third, with a view to selecting and integrating appropriate controls, based on the results of system analysis, a mechanism to identify the privacy risks is required. Mitigating privacy risks is at the core of the PbD principle. Fourth, choosing and integrating appropriate controls into a system are complex tasks that besides risks, have to consider potential interrelations among privacy controls and the costs of the controls.
This thesis introduces a model-based privacy by design methodology to handle the above challenges. Our methodology relies on a precise definition of privacy concerns and comprises three sub-methodologies: model-based privacy analysis, modelbased privacy impact assessment and privacy-enhanced system design modeling. First, we introduce a definition of privacy preferences, which provides a basis to specify privacy concerns and to verify whether personal data processing is authorized. Second, we present a model-based methodology to analyze a system model. The results of this analysis denote a set of privacy design violations. Third, taking into account the results of privacy analysis, we introduce a model-based privacy impact assessment methodology to identify concrete privacy risks in a system model. Fourth, concerning the risks, and taking into account the interrelations and the costs of the controls, we propose a methodology to select appropriate controls and integrate them into a system design. Using various practical case studies, we evaluate our concepts, showing a promising outlook on the applicability of our methodology in real-world settings.
Absicherung der analytischen Interpretation von Geolokalisierungsdaten in der Mobilfunkforensik
(2019)
Abstract
Location based services maybe are within one of the most outstanding features of modern mobile devices. Despite the fact, that cached geolocation data could be used to reconstruct motion profiles, the amount of devices capable to provide these information in the field of criminal investigations is growing.
Motivation
The aim of this work is to generate in-depth knowledge to questions concerning geolocation in the field of mobile forensics, making especially somehow cached geolocation data forensically valuable. On top, tools meeting the specific requirements of law enforcement personnel shall be developed.
Problems
Geolocation processes within smartphones are quite complex. For the device to locate its position, different reference systems like GPS, cell towers or WiFi hot\-spots are used in a variety of ways. The whole mobile geolocation mechanism is proprietary to the device manufacturer and not build with forensic needs in mind. One major problem regarding forensic investigations is, that mainly reference points are being extracted and processed instead of real life device location data. In addition, these geolocation information only consist of bits and bytes or numeric values that have to be securely assigned to their intended meaning. The location data recovered are full of gaps providing only a part of the process or device usage. This possible loss of data has to be determined deriving a reliable measurement for the completeness, integrity and accuracy of data. Last but not least, as for every evidence within a criminal investigation, it has to be assured, that manipulations of the data or errors in position estimation have no disadvantageous effect on the analysis.
Research Questions
In the context of localisation services in modern smartphones, it always comes back to similar questions during forensic everyday life:
* Can locations be determined at any time?
* How accurate is the location of a smartphone?
* Can location data from smartphones endure in court?
Approach
For a better understanding of geolocation processes in modern smartphones and to evaluate the quality and reliability of the geolocation artefacts, information from different platforms shall be theoretically analysed as well as observed in-place during the geolocation process. The connection between data points and localisation context will be examined in predefined live experiments as well as desktop- and native applications on smartphones.
Results
Within the scope of this thesis self developed tools have been used for forensic investigations as well as analytical interpretation of geodata from modern smartphones. Hereby a generic model for assessing the quality of location data has emerged, which can be generally applied to geodata from mobile devices.
Software systems have an increasing impact on our daily lives. Many systems process sensitive data or control critical infrastructure. Providing secure software is therefore inevitable. Such systems are rarely being renewed regularly due to the high costs and effort. Oftentimes, systems that were planned and implemented to be secure, become insecure because their context evolves. These systems are connected to the Internet and therefore also constantly subject to new types of attacks. The security requirements of these systems remain unchanged, while, for example, discovery of a vulnerability of an encryption algorithm previously assumed to be secure requires a change of the system design. Some security requirements cannot be checked by the system’s design but only at run time. Furthermore, the sudden discovery of a security violation requires an immediate reaction to prevent a system shutdown. Knowledge regarding security best practices, attacks, and mitigations is generally available, yet rarely integrated part of software development or covering evolution.
This thesis examines how the security of long-living software systems can be preserved taking into account the influence of context evolutions. The goal of the proposed approach, S²EC²O, is to recover the security of model-based software systems using co-evolution.
An ontology-based knowledge base is introduced, capable of managing common, as well as system-specific knowledge relevant to security. A transformation achieves the connection of the knowledge base to the UML system model. By using semantic differences, knowledge inference, and the detection of inconsistencies in the knowledge base, context knowledge evolutions are detected.
A catalog containing rules to manage and recover security requirements uses detected context evolutions to propose potential co-evolutions to the system model which reestablish the compliance with security requirements.
S²EC²O uses security annotations to link models and executable code and provides support for run-time monitoring. The adaptation of running systems is being considered as is round-trip engineering, which integrates insights from the run time into the system model.
S²EC²O is amended by prototypical tool support. This tool is used to show S²EC²O’s applicability based on a case study targeting the medical information system iTrust.
This thesis at hand contributes to the development and maintenance of long-living software systems, regarding their security. The proposed approach will aid security experts: It detects security-relevant changes to the system context, determines the impact on the system’s security and facilitates co-evolutions to recover the compliance with the security requirements.
Data flow models in the literature are often very fine-grained, which transfers to the data flow analysis performed on them and thus leads to a decrease in the analysis' understandability. Since a data flow model, which abstracts from the majority of implementation details of the program modeled, allows for potentially easier to understand data flow analyses, this master thesis deals with the specification and construction of a highly abstracted data flow model and the application of data flow analyses on this model. The model and the analyses performed on it have been developed in a test-driven manner, so that a wide range of possible data flow scenarios could be covered. As a concrete data flow analysis, a static security check in the form of a detection of insufficient user input sanitization has been performed. To date, there's no data flow model on a similarly high level of abstraction. The proposed solution is therefore unique and facilitates developers without expertise in data flow analysis to perform such analyses.
Für die Entwicklung sicherer Softwaresysteme erweitert UMLsec die UML durch die Definition von Sicherheitsanforderungen, die erfüllt sein müssen. In Klassendiagrammen können Attribute und Methoden von Klassen Sicherheitseigenschaften wie secrecy oder integrity haben, auf die nicht authorisierte Klassen keinen Zugriff haben sollten. Vererbungen zwischen Klassen erzeugen eine Komplexität und werfen die Frage auf, wie man mit der Vererbung von Sicherheitseigenschaften umgehen sollte. Neben der Option in sicherheitskritischen Fällen auf Vererbungen zu verzichten, gibt es im Gebiet der objektorientierten Datenbanken bereits viele allgemeine Recherchen über die Auswirkungen von Vererbung auf die Sicherheit. Das Ziel dieser Arbeit ist es, Ähnlichkeiten und Unterschiede von der Datenbankseite und den Klassendiagrammen zu identifizieren und diese Lösungsansätze zu übertragen und zu formalisieren. Eine Implementierung des Modells evaluiert, ob die Lösungen in der Praxis anwendbar sind.
Over the past few decades society’s dependence on software systems has grown significantly. These systems are utilized in nearly every matter of life today and often handle sensitive, private data. This situation has turned software security analysis into an essential and widely researched topic in the field of computer science. Researchers in this field tend to make the assumption that the quality of the software systems' code directly affects the possibility for security gaps to arise in it. Because this assumption is based on properties of the code, proving it true would mean that security assessments can be performed on software, even before a certain version of it is released. A study based on this implication has already attempted to mathematically assess the existence of such a correlation, studying it based on quality and security metric calculations. The present study builds upon that study in finding an automatic method for choosing well-fitted software projects as a sample for this correlation analysis and extends the variety of projects considered for the it. In this thesis, the automatic generation of graphical representations both for the correlations between the metrics as well as for their evolution is also introduced. With these improvements, this thesis verifies the results of the previous study with a different and broader project input. It also focuses on analyzing the correlations between the quality and security metrics to real-world vulnerability data metrics. The data is extracted and evaluated from dedicated software vulnerability information sources and serves to represent the existence of proven security weaknesses in the studied software. The study discusses some of the difficulties that arise when trying to gather such information and link it to the difference in the information contained in the repositories of the studied projects. This thesis confirms the significant influence that quality metrics have on each other. It also shows that it is important to view them together as a whole and suppose that their correlation could influence the appearance of unwanted vulnerabilities as well. One of the important conclusions I can draw from this thesis is that the visualization of metric evolution graphs, helps the understanding of the values as well as their connection to each other in a more meaningful way. It allows for better grasp of their influence on each other as opposed to only studying their correlation values. This study confirms that studying metric correlations and evolution trends can help developers improve their projects and prevent them from becoming difficult to extend and maintain, increasing the potential for good quality as well as more secure software code.
Since software influences nearly every aspect of everyday life, the security of software systems is more important than ever before. The evaluation of the security of a software system still poses a significant challenge in practice, mostly due to the lack of metrics, which can map the security properties of source code onto numeric values. It is a common assumption, that the occurrence of security vulnerabilities and the quality of the software design stand in direct correlation, but there is currently no clear evidence to support this. A proof of an existing correlation could help to optimize the measurements of program security, making it possible to apply quality measurements to evaluate it. For this purpose, this work evaluates fifty open-source android applications, using three security and seven quality metrics. It also considers the correlations between the metrics. The quality metrics range from simple code metrics to high-level metrics such as object-oriented anti-patterns, which together provide a comprehensive picture of the quality. Two visibility metrics, along with a metric that computes the minimal permission request for mobile applications, were selected to illustrate the security. Using the evaluation projects, it was found that there is a clear correlation between most quality metrics. By contrast, no significant correlations were found using the security metrics. This work discusses the correlations and their causes as well as further recommendations based on the findings.
Mapping ORM to TGraph
(2017)
Object Role Modeling (ORM) is a semantic modeling language used to describe objects and their relations amongst each other. Both objects and relations may be subject to rules or ORM constraints.
TGraphs are ordered, attributed, typed and directed graphs. The type of a TGraph and its components, the edges and vertices, is defined using the schema language graph UML (grUML), a profiled version of UML class diagrams. The goal of this thesis is to map ORM schemas to grUML schemas in order to be able to represent ORM schema instances as TGraphs.
Up to this point, the preferred representation for ORM schema instances is in form of relational tables. Though mappings from ORM schemas to relational schemas exist, those publicly available do not support most of the constraints ORM has to offer.
Constraints can be added to grUML schemas using the TGraph query language GReQL, which can efficiently check whether a TGraph validates the constraint or not. The graph library JGraLab provides efficient implementations of TGraphs and their query language GReQL and supports the generation of grUML schemas.
The first goal of this work is to perform a complete mapping from ORM schemas to grUML schemas, using GReQL to sepcify constraints. The second goal is to represent ORM instances in form of TGraphs.
This work gives an overview of ORM, TGraphs, grUML and GReQL and the theoretical mapping from ORM schemas to grUML schemas. It also describes the implementation of this mapping, deals with the representation of ORM schema instances as TGraphs and the question how grUML constraints can be validated.
While real-time applications used to be executed on highly specialized hardware and individually developed operation systems, nowadays more often regular off-the-shelf hardware is used, with a variation of the Linux kernel running on top.
Within the scope of this thesis, test methods have been developed and implemented as a real-time application to measure several performance properties of the Linux kernel with regards to its real-time capability.
These tests have been run against three different versions of the Linux kernel. Afterwards, the results of the test series were compared to each other.
101worker is the modular knowledge engineering component of the 101companies project. It has developed maintainability and performance problems due to growing organically, rather than following best software design practices. This thesis lays out these problems, drafts a set of requirements for refactoring the system and then describes and analyzes the resulting implementation. The solution involves collation of scattered and redundant information, setup of unit and functional test suites and incrementalization of the bus architecture of 101worker.
Web application testing is an active research area. Garousi et al. did a systematic mapping study and classified 79 papers published between 2000-2011. However, there seems to be a lack of information exchange between the scientific community and tool developers.
This thesis systematically analyzes the field of functional, system level web application testing tools. 194 candidate tools were collected in the tool search and screened, with 23 tools being selected as foundation of this thesis. These 23 tools were systematically used to generate a feature model of the domain. The methodology to support this is an additional contribution of this thesis. It processes end user documentation of tools belonging to an examined domain and creates a feature model. The feature model gives an overview over the existing features, their alternatives and their distribution. It can be used to identify trends and problems, extraordinary features, help decision making of tool purchase or guide scientists how to focus research.
Code package managers like Cabal track dependencies between packages. But packages rarely use the functionality that their dependencies provide. This leads to unnecessary compilation of unused parts and to speculative conflicts between package versions where there are no conflicts. In two case studies we show how relevant these two problems are. We then describe how we could avoid them by tracking dependencies not between packages but between individual code fragments.
Im Rahmen dieser Arbeit wird untersucht, wie sich Modellfehler auf die Positionsgenauigkeit und Handhabbarkeit beim Rangieren mit einem Fahrerassistenzsystem auswirken. Besonderer Wert wird dabei auf die Bestimmung von Fehlergrenzen gelegt. Es wird der Frage nachgegangen, wie groß der Eingangsfehler sein darf, damit die Assistenz noch hinreichende Qualitätseigenschaften hinsichtlich ihrer Präzision und Robustheit aufweist. Dazu erfolgt zunächst eine quantitative Betrachtung der Fehler anhand des kinematischen Modells. Danach wird eine qualitative Betrachtung anhand von systematischen Experimenten durchgeführt. Es wird zunächst ein Controller entwickelt, mit dem sich ein Manöver mithilfe der visuellen Informationen der Assistenz simulieren lässt.
Dann wird eine Methode vorgestellt, mit deren Hilfe man das Manöver anhand definierter Fehlergrenzen bewerten kann. Um einen großen Raum möglicher Fehlerkombinationen effizient zu durchsuchen, wird das probabilistische Verfahren des Annealed Particle Filters benutzt. Mithilfe einer Testumgebung werden schließlich systematische Experimente durchgeführt. Zur weiteren Evaluation des Assistenzsystems in einer kontrollierten Umgebung erfolgte in Zusammenarbeit mit dem Fraunhofer ITWM in Kaiserslautern die Portierung des Assistenzsystems auf die dortige Simulationsumgebung RODOS.
Diese Bachelorarbeit behandelt die Zusammenführung der bereits vorliegenden Winkelrekonstruktions- und Simulationskomponente und erweitert diese mit Funktionen, um die Durchführung von systematischen Tests zu ermöglichen. Hierzu wird die Übergabe von Bildern aus der Simulationskomponente an die Winkelrekonstruktionskomponente ermöglicht. Des weiteren wird eine GUI zur Testlaufsteuerung und Parameterübergabe sowie eine Datenbankanbindung zur Speicherung der verwendeten Einstellungen und erzeugter Daten angebunden. Durch die Analyse der erzeugten Daten zeigt sich eine ausreichende durchschnittliche Präzision von 0.15° und eine maximale Abweichung der einzelnen Winkel von 0.6°. Der größte Gesamtfehler beläuft sich in den Testläufen auf 0.8°. Der Einfluss von fehlerhaften Parametern hat von variable zu Variable unterschiedliche Auswirkungen. So verstärkt ein Fehler in Höhe den Messfehler um ein vielfaches mehr, als ein Fehler in der Länge der Deichsel.
Im Rahmen dieser Arbeit wurde die Effizienz von Anfragen an OWL-Ontologien und Anfragen an TGraphen evaluiert. Dabei wurden die zwei unterschiedlichen Transformationsverfahren Schema-Aware Mapping und Simple Mapping getestet. Bei der Transformation einer OWL-Ontologie in einen TGraphen über Schema-Aware Mapping werden ein TGraph-Schema und ein TGraph erzeugt. Im Gegensatz zu Schema-rnAware Mapping besitzt Simple Mapping ein schon vordefiniertes TGraph-Schema, das für alle OWLOntologien anwendbar ist. Damit wird bei der Transformation einer OWL-Ontologie in einen TGraphen über Simple Mapping nur ein TGraph - kein TGraph-Schema - generiert. Mit den Verfahren wurden entsprechend auch SPARQL-Anfragen in GReQL-Anfragen transformiert.
Im Rahmen dieser Diplomarbeit wird eine Datenbank-Persistenzlösung für die TGraphenbibliothek JGraLab entwickelt. Diese erlaubt das Persistieren von TGraphen in Datenbanken ausgewählter Technologien und sorgt gleichzeitig dafür, dass die Datenbankpersistenz eines TGraphen für den Benutzer transparent bleibt. Nach der Anforderungserhebung und der Recherche zur Bewertung der Tauglichkeit von bereits bestehenden Werkzeugen für dieses Projekt, wird die Anwendungsdomäne erläutert. Anschließend wird dargelegt wie die Persistierung von TGraphen mit allen ihren Eigenschaften in Datenbanken ermöglicht werden kann. Dem schließt sich der konzeptuelle Entwurf an, in dem die Details der Lösung beschrieben werden. Als nächstes wird der objektorientierte Feinentwurf zur Integration der Lösung in die TGraphenbibliothek JGraLab entwickelt, der die Grundlage der programmatischen Umsetzung bildet. Eine Anleitung zur Verwendung der Lösung und eine Bewertung des Laufzeitverhaltens der umgesetzten Implementation schließen die Arbeit ab.
Im Rahmen dieser Diplomarbeit wird erforscht, wie bestehende Tools zur Berechnung von Softwaremetriken über COBOL-Quelltexte mit den vorhandenen Entwicklerwerkzeugen der Debeka Versicherungsgruppe interoperabel gemacht werden können. Der Text richtet sich primär an Leser aus dem Bereich der Informatik. Zum Verständnis wird ein Wissensstand vergleichbar dem eines Informatikers mit abgeschlossenem Bachelorstudium oder Vordiplom vorausgesetzt.
