Benjamin Erb

Abstract: Slow-running attacks against network applications are often not easy to detect, as the attackers behave according to the specification. The servers of many network applications are not prepared for such attacks, either due to missing countermeasures or because their default configurations ignores such attacks. The pressure to secure network services against such attacks is shifting more and more from the service operators to the network operators of the servers under attack. Recent technologies such as software-defined networking offer the flexibility and extensibility to analyze and influence network flows without the assistance of the target operator. Based on our previous work on a network-based mitigation, we have extended a framework to detect and mitigate slow-running DDoS attacks within the network infrastructure, but without requiring access to servers under attack. We developed and evaluated several identification schemes to identify attackers in the network solely based on network traffic information. We showed that by measuring the packet rate and the uniformity of the packet distances, a reliable identificator can be built, given a training period of the deployment network.

Abstract: State changes over time are inherent characteristics of stateful applications. So far, there are almost no attempts to make the past application history programmatically accessible or even modifiable. This is primarily due to the complexity of temporal changes and a difficult alignment with prevalent programming primitives and persistence strategies. Retroactive computing enables powerful capabilities though, including computations and predictions of alternate application timelines, post-hoc bug fixes, or retroactive state explorations. We propose an event-driven programming model that is oriented towards serverless computing and applies retroaction to the event sourcing paradigm. Our model is deliberately restrictive, but therefore keeps the complexity of retroactive operations in check. We then introduce retro-λ, a runtime platform that implements the model and provides retroactive capabilites to its applications. While retro-λ only shows negligible performance overheads compared to similar solutions for running regular applications, it enables its users to execute retroactive computations on the application histories as part of its programming model.

Abstract: Event sourcing is increasingly used and implemented in event-based systems for maintaining the evolution of application state. However, unbounded event logs are impracticable for many systems, as it is difficult to align scalability requirements and long-term runtime behavior with the corresponding storage requirements. To this end, we explore the design space of log pruning approaches suitable for event-sourced systems. Furthermore, we survey specific log pruning mechanisms for event-sourced logs. In a brief evaluation, we point out the trade-offs when applying pruning to event logs and highlight the applicability of log pruning to event-sourced systems.

Abstract: An increasing number of distributed, event-based systems adopt an architectural style called event sourcing, in which entities keep their entire history in an event log. Event sourcing enables data lineage and allows entities to rebuild any previous state. Restoring previous application states is a straightforward task in event-sourced systems with a global and totally ordered event log. However, the extraction of causally consistent snapshots from distributed, individual event logs is rendered non-trivial due to causal relationships between communicating entities. High dynamicity of entities increases the complexity of such reconstructions even more. We present approaches for retrospective and global state extraction of event-sourced applications based on distributed event logs. We provide an overview on historical approaches towards distributed debugging and breakpointing, which are closely related to event log-based state reconstruction. We then introduce and evaluate our approach for non-local state extraction from distributed event logs, which is specifically adapted for dynamic and asynchronous event-sourced systems.

Abstract: There are many high-speed TCP variants with different congestion control algorithms, which are designed for specific settings or use cases. Distinct features of these algorithms are meant to optimize different aspects of network performance, and the choice of TCP variant strongly influences application performance. However, setting up tests to help with the decision of which variant to use can be problematic, as many systems are not designed to deal with high bandwidths, such as 10 Gbps or more. This paper provides an overview of pitfalls and challenges of realistic network analysis to help in the decision making process.

Abstract: The actor model is an established programming model for distributed applications. Combining event sourcing with the actor model allows the reconstruction of previous states of an actor. When this event sourcing approach for actors is enhanced with additional causality information, novel types of actor-based, retroactive computations are possible. A globally consistent state of all actors can be reconstructed retrospectively. Even retroactive changes of actor behavior, state, or messaging are possible, with partial recomputations and projections of changes in the past. We believe that this approach may provide beneficial features to actor-based systems, including retroactive bugfixing of applications, decoupled asynchronous global state reconstruction for recovery, simulations, and exploration of distributed applications and algorithms.

Abstract: Privacy strategies and privacy patterns are fundamental concepts of the privacy-by-design engineering approach. While they support a privacy-aware development process for IT systems, the concepts used by malicious, privacy-threatening parties are generally less understood and known. We argue that understanding the ``dark side'', namely how personal data is abused, is of equal importance. In this paper, we introduce the concept of privacy dark strategies and privacy dark patterns and present a framework that collects, documents, and analyzes such malicious concepts. In addition, we investigate from a psychological perspective why privacy dark strategies are effective. The resulting framework allows for a better understanding of these dark concepts, fosters awareness, and supports the development of countermeasures. We aim to contribute to an easier detection and successive removal of such approaches from the Internet to the benefit of its users.

Abstract: Web architectures are an important asset for various large-scale web applications, such as social networks or e-commerce sites. Being able to handle huge numbers of users concurrently is essential, thus scalability is one of the most important features of these architectures. Multi-core processors, highly distributed backend architectures and new web technologies force us to reconsider approaches for concurrent programming in order to implement web applications and fulfil scalability demands. While focusing on different stages of scalable web architectures, we provide a survey of competing concurrency approaches and point to their adequate usages.

Tags: PROJEKT, AA, BA, MA, BenjaminErb, FrankKargl, sidgraph, distributed, DominikMeissner

Abstract: Blockchain technology allows for decentralized, distributed, and secure ledgers that store records (e.g., transactions). Popular blockchain-based systems such as Bitcoin and Etherum have emerged as so-called crypto-currencies. As the ledger maintains the full history of transactions, interactions within the system are always persisted. In this work, the student is asked to design and implement online and offline transaction analyses based on Chronograph, a data processing platform for evolving graphs developed at our Institute. Therefore, different blockchain-based systems should be surveyed and appropriate analysis mechanisms should be conducted.

Tags: PROJEKT, AA, BA, BenjaminErb, FrankKargl, sidgraph, distributed, DominikMeissner

Abstract: Event sourcing is an alternative persistence approach that maintains a log of state-changing events instead of altering states directly. Event-sourced architectures require an event store for efficiently appending and retrieving log entries. In this project, an evaluation of different key/value stores and alternative (No)SQL stores is to be conducted in order to identify stores appropriate for event sourcing.

Tags: PROJEKT, AA, BA, BenjaminErb, FrankKargl, sidgraph, distributed, DominikMeissner

Abstract: As part of an ongoing research project at our institute, we are currently developing a novel distributed computing platform prototype. The systems provides a graph-based, asynchronous programming model and takes advantage of event sourcing for history-aware computations. The aim of this student work is the identification and evaluation of appropriate secondary index structures, in order to provide fast access onto specific notes of the graph topology. Also, a prototypical implementation is part of this work.

Tags: AA, BA, BenjaminErb, FrankKargl, sidgraph, distributed

Abstract: As part of an ongoing research project at our institute, we are currently developing a novel distributed computing platform prototype. The systems provides a graph-based, asynchronous programming model and takes advantage of event sourcing for history-aware computations. The aim of this student work is to compile a survey of data mining mechanisms that can be executed on graphs. Specifically, asynchronicity has to be considered here. As a result, our current prototype should be evaluated on how it suits existing graph mining approaches.

Abstract: Distributed event-sourced systems adopt a fairly new architectural style for data-intensive applications that maintain the complete history of the application state. However, the performance implications of such systems is not yet well explored, let alone how the performance of these systems can be improved. A central issue is the lack of systematic performance engineering approaches that incorporate the specific properties of distributed event-sourced systems, such as messaging and event persistence. To address this problem, we developed a methodology for performance engineering and performance analysis of distributed event-sourced systems as part of a software engineering process. This approach helps developers to identify bottlenecks and resolve performance issues based on specific micro benchmarks and subsequent targeted optimizations. To show the practicality of our methology, we applied it to the \cg platform to improve the overall performance of its current research prototype. Using our structured approach, we improved the performance of the prototype system and made it more than twice as fast for certain workloads.

Abstract: Event sourcing is a style of software architecture wherein state altering operations to an application are captured as immutable events. Each event is appended to an event log, with the current state of a system derived from this series of events. This thesis addresses the utilization of retroactive capabilities in event-sourced systems: computing alternate application states, post hoc bug fixes, or the support of algorithms which have access to their own history, for example. The possibility of retroactively accessing and modifying this event log is a potential capability of an event-sourced system, but a detailed exploration how these operations can be facilitated and supported has not yet been conducted. We examine how retroaction can be applied to event-sourced systems and discuss conceptual considerations. Furthermore, we demonstrate how different architectures can be used to provide retroaction and describe the prototypical implementation of an appropriate programming model. These findings are applied in the Chronograph research project, in order to utilize potential temporal aspects of this platform.

Abstract: Man-made disasters, earthquakes, floods, and other natural disasters come with a great number of casualties, which have to be treated as quickly as possible by emergency services to minimize fatalities. Due to the large number of casualties and aid workers, it is difficult to maintain an accurate overview of the situation. To improve the clarity of the situation, a comprehensive support system can be used for the forces on-site, which supports them in information gathering and distribution to all involved parties. Previous work has failed to implement independency of public infrastructure (e.g. power grid, cellular network) or suffer data loss due to single node failures. To solve this problem, we propose a fault-tolerant design that fully distributes information to all devices in a mobile ad hoc network, while allowing offline work outside of it. We present a proof-of-concept prototype for the proposed design and show that its data distribution component behaves as designed using a series of trials. To the best of our knowledge, there is currently no DAN system that uses multi master replication to fully distribute data, where every node has an individual copy of every piece of information.

Abstract: This bachelor thesis presents a catalog of communication patterns for concurrent and distributed computations. We compose this catalog by reviewing the inter-process communication in common concurrency models and surveying existing pattern resources, such as professional books and weblogs. In addition to the selection and composition of patterns, we determine our own pattern template structure and an appropriate visualization, specifically matching the requirements of communication patterns. The catalog itself consists of a variety of patterns, intended for the reader to get a grasp of proven solutions for recurring problems in the field of concurrent programming. We provide simplified examples for every solution by the means of message-passing.

Abstract: NoSQL-Datenbanken werden immer häufiger produktiv eingesetzt, um die steigenden Datenmengen bewältigen zu können. Derzeit ist allerdings noch nicht klar, ob diese die notwendigen Sicherheitsanforderungen erfüllen. Zu diesem Zweck stellt die vorliegende Arbeit eine Methodik zur Sicherheitsanalyse von NoSQL-Datenbanken vor. Hierzu werden die wichtigsten Sicherheitsrisiken identifiziert und es wird aufgezeigt, wie eine NoSQL-Datenbank auf diese überprüft werden kann. Die Methodik wird auf die NoSQL-Vertreter Neo4j und CouchDB angewendet. Es zeigt sich hierbei, dass beide Datenbanken schwerwiegende Sicherheitsdefizite aufweisen. Deshalb werden Empfehlungen zur Steigerung der Informationssicherheit gegeben, die bei Beachtung die ermittelten Schwachstellen beheben.

Abstract: In dieser Arbeit wurde eine Plattform zur kollaborativen Dokumentation von Patterns entworfen und prototypisch implementiert. Hierfür wurden die Anforderungen für eine generische Plattform gesammelt und Konzepte für die kollaborative Nutzung erörtert. Die Implementierung verwendet verschiedene Konzepte des Web 2.0 zur Kollaboration und zeigt prototypisch den Funktionsumfang einer Plattform für Patterns verschiedener Anwendungsgebiete.

Abstract: In a common software system we occasionally want to know how we got to the current application state without making the system more complicated. Mostly, this question can not be answered because the software just saves the newest application state. Even if the software architects implement their own history support later, it can not tell anything about the previous changes. This is where Event Sourcing and Command Query Responsibility Segregation come into play. Event Sourcing saves every change as an event and Command Query Responsibility Segregation helps to handle the increased complexity. Therefore, we can build a system which provides a history support and which is still maintainable. If we use Event Sourcing and Command Query Responsibility Segregation, we just have to make small changes to a traditional architecture in order to fix that problem. By saving all changes as events we can evaluate everything we want.

Abstract: Datenbanksysteme stellen in Anwendungen die zentrale Komponente zur Persistierung von Daten dar. Die Speicherung der Daten kann über verschieden Datenmodelle, welche die Literatur in die Kategorien relational und NoSQL einteilt, realisiert werden. Die Datenmodelle bieten unterschiedliche Funktionalitäten in Bereichen wie Konsistenz, Verteilung und Skalierbarkeit. Skalierbarkeit stellt besonders für Datenbanken innerhalb Webanwendungen eine wichtige Anforderungen dar, da zum einen die Nutzeranzahl von Webanwendungen immer weiter steigt und zum anderen die Webanwendungen starke Lastschwankungen bewältigen müssen. Um diese Lastschwankungen verarbeiten zu können, werden flexible Ressourcen benötigt, die das Cloud-Computing verspricht. Diese Arbeit betrachtet die Cloud-Computing-Architektur des DBaaS, welche Datenbanken als abstrakte Ressource bereitstellt. Der Schwerpunkt liegt hierbei auf skalierenden DBaaS-Systemen. Das Ziel dieser Arbeit besteht aus dem Design und der Implementierung eines DBaaS-Dienstes, der eine automatisierte Skalierung bietet und auf frei verfügbarer Software basiert. Hierfür werden die Anforderungen eines solchen DBaaS-Dienstes anhand eines Anwendungsfalls herausgearbeitet und die Skalierbarkeit existierender Datenbanken auf Basis von Benchmarks untersucht. Aus diesen Ergebnissen wird ein prototypisches DBaaS-System umgesetzt.

Abstract: Gegenstand dieser Arbeit ist die Erstellung eines aktuellen Surveys von bestehenden Netzwerksimulatoren, insbesondere für VANET-Simulationen.

Abstract: Computational power for content filtering in high-speed networks reaches a limit, but many applications as intrusion detection systems rely on such processes. Especially signature based methods need extraction of header fields. Hence we created an parallel protocol-stack parser module on the NetFPGA 10G architecture with a framework for simple adaption to custom protocols. Our measurements prove that the appliance operates at 9.5 Gb/s with a delay in order of any active hop. The work provides the foundation to use for application specific projects in the NetFPGA context.

Tags: PROJEKT, AA, BA, MA, BenjaminErb, FrankKargl, sidgraph, distributed, DominikMeissner

Abstract: Blockchain technology allows for decentralized, distributed, and secure ledgers that store records (e.g., transactions). Popular blockchain-based systems such as Bitcoin and Etherum have emerged as so-called crypto-currencies. As the ledger maintains the full history of transactions, interactions within the system are always persisted. In this work, the student is asked to design and implement online and offline transaction analyses based on Chronograph, a data processing platform for evolving graphs developed at our Institute. Therefore, different blockchain-based systems should be surveyed and appropriate analysis mechanisms should be conducted.

Tags: PROJEKT, AA, BA, BenjaminErb, FrankKargl, sidgraph, distributed, DominikMeissner

Abstract: Event sourcing is an alternative persistence approach that maintains a log of state-changing events instead of altering states directly. Event-sourced architectures require an event store for efficiently appending and retrieving log entries. In this project, an evaluation of different key/value stores and alternative (No)SQL stores is to be conducted in order to identify stores appropriate for event sourcing.

Tags: PROJEKT, AA, BA, BenjaminErb, FrankKargl, sidgraph, distributed, DominikMeissner

Abstract: As part of an ongoing research project at our institute, we are currently developing a novel distributed computing platform prototype. The systems provides a graph-based, asynchronous programming model and takes advantage of event sourcing for history-aware computations. The aim of this student work is the identification and evaluation of appropriate secondary index structures, in order to provide fast access onto specific notes of the graph topology. Also, a prototypical implementation is part of this work.