This thesis is dedicated to security of client-server applications running on Windows platform. In the beginning chapters it is possible to find motivation, about why this type of security is important. Following content describes some elements of used architecture and elements of operating system Windows. The core of the work contains techniques and tools used by the attacker and protection against them. In following chapter there is a design and implementation of the security solution based on the previous theory. This solution is then tested against various threats, to verify its effectivity.

This thesis deals with an introduction to debugging and debuggers. The thesis describes principles of the debugging information, especially the DWARF format and its Call Frame Information (CFI), that enables a debugger to visualize the call stack. Furthermore, extensions of the debugger used in the Lissom project were designed and implemented. These extensions added support for call stack visualization, history value storage and step return and step over commands.

Equation-based object-oriented (EOO) modelling languages provide a convenient, declarative method for describing models of cyber-physical systems.Because of the ease of use of EOO languages, large and complex models can be built with limited effort.However, current state-of-the-art tools do not provide the user with enough information when errors appear or simulation results are wrong.It is paramount that the tools give the user enough information to correct errors or understand where the problems that lead to wrong simulation results are located.However, understanding the model translation process of an EOO compiler is a daunting task that not only requires knowledge of the numerical algorithms that the tool executes during simulation, but also the complex symbolic transformations being performed. In this work, we develop and explore methods where the EOO tool records the transformations during the translation process in order to provide better diagnostics, explanations, and analysis.This information can be used to generate better error-messages during translation.It can also be used to provide better debugging for a simulation that produces unexpected results or where numerical methods fail. Meeting deadlines is particularly important for real-time applications.It is usually important to identify possible bottlenecks and either simplify the model or give hints to the compiler that enables it to generate faster code.When profiling and measuring execution times of parts of the model the recorded information can also be used to find out why a particular system is slow.Combined with debugging information, it is possible to find out why this system of equations is slow to solve, which helps understanding what can be done to simplify the model. Finally, we provide a method and tool prototype suitable for speeding up simulations by compiling a simulation executable for a parallel platform by partitioning the model at appropriate places.

With the popularity of the World Wide Web, a large amount of data is generated and made available through the Internet everyday. To integrate and query this huge amount of heterogeneous data, the vision of Semantic Web has been recognized as a possible solution. One key technology for the Semantic Web is ontologies. Many ontologies have been developed in recent years. Meanwhile, due to the demand of applications using multiple ontologies,  mappings between entities of these ontologies are generated as well, which leads to the generation of ontology networks consisting of ontologies and mappings between these ontologies. However, neither developing ontologies nor finding mappings between ontologies is an easy task. It may happen that the ontologies are not consistent or complete, or the mappings between these ontologies are not correct or complete, or the resulting ontology network is not consistent. This may lead to problems when they are used in semantically-enabled applications. In this thesis, we address two issues relevant to the quality of the mappings and the structure in the ontology network. The first issue deals with the missing mappings between networked ontologies. Assuming existing mappings between ontologies are correct, we investigate whether and how to use these existing mappings, to find more mappings between ontologies. We propose and test several strategies of using the given correct mappings to align ontologies. The second issue deals with the missing structure, in particular missing is-a relations, in networked ontologies. Based on the assumption that missing is-a relations are a kind of modeling defects, we propose an ontology debugging approach to tackle this issue. We develop an algorithm for detecting missing is-a relations in ontologies, as well as algorithms which assist the user in repairing by generating and recommending possible ways of repairing and executing the repairing. Based on this approach, we develop a system and test its use and performance.

The World Wide Web contains large amounts of data and in most cases this data is without any explicit structure. The lack of structure makes it difficult for automated agents to understand and use such data. A step towards a more structured World Wide Web is the idea of the Semantic Web which aims at introducing semantics to data on the World Wide Web. One of the key technologies in this endeavour are ontologies which provide means for modeling a domain of interest. Developing and maintaining ontologies is not an easy task and it is often the case that defects are introduced into ontologies. This can be a problem for semantically-enabled applications such as ontology-based querying. Defects in ontologies directly influence the quality of the results of such applications as correct results can be missed and wrong results can be returned. This thesis considers one type of defects in ontologies, namely the problem of completing the is-a structure in ontologies represented in description logics. We focus on two variants of description logics, the EL family and ALC, which are often used in practice. The contributions of this thesis are as follows. First, we formalize the problem of completing the is-a structure as a generalized TBox abduction problem (GTAP) which is a new type of abduction problem in description logics. Next, we provide algorithms for solving GTAP in the EL family and ALC description logics. Finally, we describe two implemented systems based on the introduced algorithms. The systems were evaluated in two experiments which have shown the usefulness of our approach. For example, in one experiment using ontologies from the Ontology Alignment Evaluation Initiative 58 and 94 detected missing is-a relations were repaired by adding 54 and 101 is-a relations, respectively, introducing new knowledge to the ontologies.

Traditionally, when debugging a software system, developers rely on having access to the input data that caused the error. However, with data privacy concerns on the rise, it is becoming increasingly challenging to rely on input data as it might be sensitive or even classified. Telemetry is a method of collecting information about a system that can offer assistance. This thesis proposes a telemetry solution for debugging systems where input data is sensitive. The telemetry solution was implemented in a geographical 3D visualization system and evaluated based on two aspects: its effectiveness in assisting the developers working on the system to locate if and where a problem has occurred, and its ability to deduce the input data that generated the output. The results indicate that the telemetry solution is successful in helping developers identify system errors. Additionally, the system's privacy is maintained, as it is not feasible to directly ascertain the input data responsible from the output. However, no proof is presented and as such, no guarantee can be made. We conclude that telemetry can be a useful tool for developers, making the debugging process more effective while protecting sensitive input data. However, this might not be the case for different customers or systems. The thesis demonstrates the potential of using telemetry for debugging privacy-sensitive systems, with a proof-of-concept solution that can be improved upon in the future.

It is a great challenge to build reliable computer systems with unreliable hardware and buggy software. On one hand, software bugs account for as much as 40% of system failures and incur high cost, an estimate of $59.5B a year, on the US economy. On the other hand, under the current trends of technology scaling, transient faults (also known as soft errors) in the underlying hardware are predicted to grow at least in proportion to the number of devices being integrated, which further exacerbates the problem of system reliability. We propose several methods to improve system reliability both in terms of detecting and correcting soft-errors as well as facilitating software debugging. In our first approach, we detect instruction-level anomalies during program execution. The anomalies can be used to detect and repair soft-errors, or can be reported to the programmer to aid software debugging. In our second approach, we improve anomaly detection for software debugging by detecting different types of anomalies as well as by removing false-positives. While the anomalies reported by our first two methods are helpful in debugging single-threaded programs, they do not address concurrency bugs in multi-threaded programs. In our third approach, we propose a new debugging primitive which exposes the non-deterministic behavior of parallel programs and facilitates the debugging process. Our idea is to generate a time-ordered trace of events such as function calls/returns and memory accesses in different threads. In our experience, exposing the time-ordered event information to the programmer is highly beneficial for reasoning about the root causes of concurrency bugs.

As software continues to envelop traditional industries the need for increased attention to cybersecurity is higher than ever. Software security helps protect businesses and governments from financial losses due to cyberattacks and data breaches, as well as reputational damage. In theory, securing software is relatively straightforward—it involves following certain best practices and guidelines to ensure that the software is secure. In practice, however, software security is often much more complicated. It requires a deep understanding of the underlying system and code (including potentially legacy code), as well as a comprehensive understanding of the threats and vulnerabilities that could be present. Additionally, software security also involves the implementation of strategies to protect against those threats and vulnerabilities, which may involve a combination of technologies, processes, and procedures. In fact many real cyber attacks are caused not from zero day vulnerabilities but from known issues that haven't been addressed so real software security also requires ongoing monitoring and maintenance to ensure critical systems remain secure. This thesis presents a series of novel techniques that together form an enhanced software maintenance methodology from initial bug reporting all the way through patch deployment. We begin by introducing Ad Hoc Test Generation, a novel testing technique that handles when a security vulnerability or other critical bugis not detected by the developers’ test suite, and is discovered post-deployment, developers must quickly devise a new test that reproduces the buggy behavior. Then the developers need to test whether their candidate patch indeed fixes the bug, without breaking other functionality, while racing to deploy before attackers pounce on exposed user installations. This work builds on record-replay and binary rewriting to automatically generate and run targeted tests for candidate patches significantly faster and more efficiently than traditional test suite generation techniques like symbolic execution. Our prototype of this concept is called ATTUNE. To construct patches in some instances developers maintaining software may be forced to deal directly with the binary since source code is no longer available. In these instances this work presents a transformer based model called DIRECT that provides semantics related names for variables and function names that have been lost giving developers the opportunity to work with a facsimile of the source code that would otherwise be unavailable. In the event developers need even more support deciphering the decompiled code we provide another tool called REINFOREST that allows developers to search for similar code which they can use to further understand the code in question and use as a reference when developing a patch. After patches have been written, deployment remains a challenge. In some instances deploying a patch for the buggy behavior may require supporting legacy systems where software cannot be upgraded without causing compatibility issues. To support these updates this work introduces the concept of binary patch decomposition which breaks a software release down into its component parts and allows software administrators to apply only the critical portions without breaking functionality. We present a novel software patching methodology that we can recreate bugs, develop patches, and deploy updates in the presence of the typical challenges that come when patching production software including deficient test suites, lack of source code, lack of documentation, compatibility issues, and the difficulties associated with patching binaries directly.

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