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Master of Science in Engineering - Engineering / Any software project goes through the different stages of a Software Development Life Cycle (SDLC). Like any other commercial product, software has a design stage but this stage is unique and critical to software due to its soft nature. A system that is given careful thought at the design phase results in a correct and complete system and adheres to software design principle. The “Unified Modelling Language” (UML) is a standard modelling language for object-oriented systems. Many tools are currently available to support the design and implementation of software. Generating skeletal code from a design brings down the implementation time considerably. This research report presents a list of criteria against which one can compare different UML tools, and puts forward a rating system where decisions can be made on them. It presents a comparison between four UML tools: ArgoUML, Rational Rose, Together Control Centre, and MasterCraft. An end-to-end application was developed on each of these tools as part of the evaluation process. During the design phase a detailed design was done using the ICONIX process. The different features of an ideal UML tool is analysed and used to evaluate the four selected tools. Of the four tools, Rational Rose, Together Control Centre, MasterCraft are offthe-shelf modelling softwares whereas ArgoUML is an open source modelling software. From the evaluation it is observed that Together Control Centre attains a high score with Rational Rose following just behind. MasterCraft comes third. Argo UML has the least score but it has the advantage of being an open source software.

In this work, I dealt with the field of Business Process Managent and Service Oriented Architecture. First I tried a comprehensive conceptual view of both through the definition of important principles. In BPM as a disciline I identified "life-cycle" as the most important principle for process optimization tools. For service-oriented architecture, I had to reduce the view to important principles related to composition of services. An important starting point in my work are the definitions of processes and services and their roles in BPM systems. It is a simplified view that helps connect modeled processes to Web services. Web services and orchestration is the most popular and most common usage of the service-oriented architecture. Composition is another important building block of SOA and is the basis for more realistic goals of SOA, such as greater enterprise agility, more efficient utilization of resources in the enterprise, etc. BPM discipline combines multiple elements and as it is typicaly multidisciplinary it combines process management and optimization through tools. These tools historically perform their roles well, but companies are now in a very competitive linked environment and must to behave differently. In my work I have stated firstly why would these areas could be beneficial to each other. The next part focused, what is the relationship with the life-cycle process for BPM and how it fits into the life-cycle services in SOA. Finally, I analyzed the current state mapping of BPMN, the most common notation for expressing processes in BPM, to BPEL. BPEL describes a process, but it is expressed as a programmatic sequential process, which is also executed in digital form. At work I have examined the role of the new version of the BPMN notation 2.0.

In online service systems, delay experienced by a user from the service request to the service completion is one of the most critical performance metrics. To improve user delay experience, in this thesis, we investigate a novel aspect of system design: proactive serving, where the system can predict future user request arrivals and allocate its capacity to serve these upcoming requests proactively. This approach is complementary to the conventional capacity boosting mechanism and is motivated by recent industrial and academic advances. In particular, we investigate the fundamentals of proactive serving from a queuing theory perspective. / First, most importantly, we show that under proactive serving the average user delay decreases exponentially (in the prediction window size) for a wide range of queuing models. Furthermore, the delay reduction is robust against prediction errors. We also show that both the variance of user delay and the tail of user delay decrease exponentially under proactive serving, which are also important user delay experience metrics. / We then show that proactive serving is more effective in decreasing user delay than capacity boosting in light workload regime. In particular, the average user delay decays inverse-proportionally in system capacity, but exponentially in the prediction window size in proactive serving. / Finally we demonstrate how to leverage proactive serving in system design from a optimization point of view, e.g., how many resources are dedicated to proactive serving. The results provide useful engineering insights to system designers. / Our trace-driven simulation results demonstrate the practical power of proactive serving: for example, under the YouTube data trace of 1000 different videos, the average user delay can be decreased by 50% when the system predicts 100 seconds ahead. Our results provide useful insights for proactive serving and justify its increasing applications in practical systems. / 對於在線服務系統，由於系統服務造成的用戶延遲是衡量系統性能的重要指標。提高用戶的延遲體驗的傳統方法是提高系統中服務器的性能。在本論文中，我們研究一種新穎的叫做“前瞻性服務”的方法用來提高用戶的延遲體驗。前瞻性服務是指系統在預測用戶需求的基礎上，在用戶產生需求之前，系統已經將服務送到用戶手中。前瞻性服務是傳統方法的有力補充。我們從排隊論的角度研究前瞻性服務對用戶的延遲的提高。 / 首先，對於多种排隊系統，我們證明前瞻性服務能夠指數性降低用戶的平均延遲。而且前瞻性服務對於用戶需求預測的誤差具有魯棒性。我們同時也證明了前瞻性服務能夠指數性降低用戶的延遲方差和尾概率。 / 然後，我們證明前瞻性服務在系统低负载时比傳統方法在降低用戶的平均延遲上更加有效。前瞻性服務能夠指數性降低用戶的平均延遲。而通過提高系統服務器性能，只能反比例降低用戶的平均延遲。 / 最後，我們從優化的角度分析怎樣在系統設計中利用前瞻性服務，給系統設計者提供有用的建議。 / 我們基於實際數據的仿真結果驗證了前瞻性服務在實際系統的作用。例如，基於Youtube數據的仿真表明，如果系統能提前一百秒預測用戶的需求，那麼前瞻性服務能夠降低一半的用戶延遲。 / Zhang, Shaoquan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 103-108). / Abstracts also in Chinese. / Title from PDF title page (viewed on 02, December, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

What formal guarantees should a secure messaging application provide? Do the most widely-used protocols provide them? Can we do better? In this thesis we answer these questions and with them give a formal study of modern secure messaging protocols, which encrypt the personal messages of billions of users. We give definitions and analyses of two protocols: one existing (Signal) and one new (ART). For Signal, we begin by extending and generalising classic computational models, in order to apply them to its complex ratcheting key derivations. With a threat model in mind we also define a security property, capturing strong secrecy and authentication guarantees including a new one which we call "post-compromise security". We instantiate Signal as a protocol in our model, stating its security theorem and sketching a computational reduction. Signal only supports encrypting messages between two devices, and so most implementers have built custom protocols on top of it to support group conversations. These protocols usually provide weaker security guarantees, and in particular usually do not have post-compromise security. We propose a new protocol called ART, whose goal is to bring Signal's strong security properties to conversations with multiple users and devices. We give a design rationale and a precise definition of ART, and again generalise existing computational models in order to formally specify its security properties and sketch a security reduction. ART has enjoyed widespread interest from industry, and we aim to turn it into an open standard for secure messaging. To that end, we have brought it to the IETF and formed a working group called Messaging Layer Security, with representatives from academia as well as Facebook, Google, Twitter, Wire, Cisco and more. Through MLS, we hope to bring ART's strong guarantees to practical implementations across industry. After concluding our analyses we pause for a moment, and start looking towards the future. We argue that for complex protocols like Signal and ART we are reaching the limits of computational methods, and that the future for their analysis lies with symbolic verification tools. To that end we return to the symbolic model and give a number of case studies, in each one showing how a traditional limitation of symbolic models can in fact be seen as a modelling artefact.

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Nowadays, computer networks have always been complicated deployment for both the scientific and industry groups as they attempt to comprehend and analyze network performance as well as design efficient procedures for their operation. In software-defined networking (SDN), predicting latency (delay) is essential for enhancing performance, power consumption and resource utilization in meeting its significant latency requirements. In this thesis, we present a graph-based formulation of Abilene Network and other topologies and apply a Graph Neural Network (GNN)-based model, Spatial-Temporal Graph Convolutional Network (STGCN), to predict end-to-end packet delay on this formulation. The evaluation uses STGCN to compare with other machine learning methods: Multiple Linear Regression (MLR), Extreme Gradient Boosting (XGBOOST), Random Forest (RF), and Neural Network (NN). Datasets in use include Abilene, 15-node scale-free, 24-node GEANT2, and 50-node networks. Notably, our GNN-based methodology can achieve 97.0%, 95.9%, 96.1%, and 63.1% less root mean square error (RMSE) in the most complex network situation than the baseline predictor, MLR, XGBOOST and RF, respectively. All the experiments show that STGCN has good prediction performance with small and stable prediction errors. This thesis illustrates the feasibility and benefits of a GNN approach in predicting end-to-end delay in software-defined networks.

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Idag finns det en uppsjö av meddelandeapplikationer och det kommer nya nästan varje dag. Dock finns det inte lika många meddelandeapplikationer där både klientapplikationen och serverapplikationen är öppen källkod och kan köras på egna privata servrar. Dessa meddelandeapplikationer är bra på att lösa problemet att många, upp till flera miljoner personer ska kunna kommunicera med varandra. Dock finns det ett mindre användarfall med ett mindre meddelandesystem som består av enbart ett meddelandeflöde, där alla meddelanden är synliga för alla enheter. Detta mindre användarfall gör att mindre metadata behövs. Användningsområden för ett sådant meddelandesystem kan vara bl.a. att få notifikationer från servrar eller att skriva anteckningar. Meddelandeflödet synkroniseras mellan alla enheter. Målet med detta arbete är att skapa ett End-to-End krypterat meddelandesystem som uppfyller autentisering, dataintegritet och sekretess. Forskning har granskats gällande svagheter i vissa krypteringstekniker, dessa svagheter har tagits i åtanke vid skapandet av meddelandesystemet. Syftet varför detta meddelandesystem behöver skapas är därför att något befintligt system som uppfyller vissa viktiga krav för att upprätthålla den personliga integriteten saknas. En prototyp har skapats som består av en serverapplikation och en grafisk datorapplikation. Meddelanden som skickas i meddelandesystemet är End-to-End krypterade. Kommunikation mellan klienter och server är även den krypterad och autentiserad. / Today there exists many messaging applications and new ones are released almost daily. However, there are not as many messaging applications where both the client application and the server application are open source and can be self hosted. These messaging applications are good at solving the problem that many, up to several million people can communicate with each other. However, there is a smaller more focused use case with a messaging system consisting of only one message flow, where all messages are visible to all devices. This smaller use case means that less metadata is required. Uses for such a messaging system may be to receive notifications from servers or to take personal notes. The message system is synchronized between all devices. The goal of this project is to create an End-to-End encrypted messaging system that provides authentication, data integrity and confidentiality. Research has been investigated regarding weaknesses in some encryption techniques, these weaknesses have been taken into account when creating the messaging system. The purpose why this messaging system needs to be created is because an existing system that meets certain essential requirements for maintaining maximum personal integrity is missing. A prototype has been created that consists of a server application and a graphical computer application. Messages sent in the messaging system are End-to-End encrypted. Communication between clients and the server is also encrypted and authenticated.

End-to-end encryption is becoming a standard feature in popular mobile chat appli-cations (apps) with millions of users. In the two years a number of leading chat apps have added end-end encryption features including LINE, KakaoTalk, Viber, Facebook Messenger, and WhatsApp.However, most of these apps are closed-source and there is little to no independent ver-ification of their end-to-end encryption system design. These implementations may be a major concern as proprietary chat apps may make use of non-standard cryptographic algorithms that may not follow cryptography and security best practices. In addition, governments authorities may force chat app providers to add easily decryptable export-grade cryptography to their products. Further, mainstream apps have a large attack surface as they offer a variety of features. As a result, there may be software vulnera-bilities that could be exploited by an attacker in order to compromise user’s end-to-end privacy. Another problem is that, despite being closed-source software, providers often market their apps as being so secure that even the provider is not able to decrypt messages. These marketing claims may be potentially misleading as most users do not have the technical knowledge to verify them.In this Master’s thesis we use KakaoTalk – the most popular chat app in South Korea – as a case study to perform a security and privacy assessment and audit of its “Secure Chat” opt-in end-to-end encryption feature. Also, we examine KakaoTalk’s Terms of Service policies to verify claims such as “[. . . ] Kakao’s server is unable to decrypt the encryption [. . . ]” from a technical perspective.The main goal of this work is to show how various issues in a product can add up to the potential for serious attack vectors against end-to-end privacy despite there being multiple layers of security. In particular, we show how a central public-key directory server makes the end-to-end encryption system vulnerable to well-known operator-site man-in-the-middle attacks. While this naive attack may seem obvious, we argue that (KakaoTalk) users should know about the strength and weaknesses of a particular design in order to make an informed decision whether to trust the security of a chat app or not. / End-to-end kryptering är en allt mer vanligt förekommande funktionalitet bland populära mobila chatttjänster (händanefter appar) med miljontals användare. Under de två senaste åren har många ledande chattappar, bland annat LINE, KakaoTalk, Viber, Facebook Messenger, och WhatsApp, börjat använda end-to-end kryptering. Dock så är de flesta av dessa appar closed-source och det finns begränsad, eller ingen, fristående granskning av systemdesignen för deras end-to-end kryptering. Dessa implementationer kan innebära en stor risk då proprietära chattappar kan använda sig av kryptografiska algoritmer som inte följer best practice för säkerhet eller kryptografi. Vidare så kan statliga myndigheter tvinga de som tillhandahåller chattappar att använda lättdekrypterad export-grade kryptografi för sina produkter. Lägg till det att de flesta vanliga appar har många ytor som kan attackeras, till följd av all funktionalitet de erbjuder. Som ett resultat av detta finns en risk för mjukvarubrister som kan utnyttjas av en hackare för att inkräkta på en användares end-to-end integritet. Ytterligare ett problem är att trots att det är closed-source mjukvara så marknadsför ofta appleverantörerna sina appar som att vara är så säkra att inte ens leverantörerna själva kan dekryptera användarnas meddelanden. Det som hävdas i marknadsföringen riskerar vara missledande eftersom de flesta användarna inte har den tekniska kunskap som krävs för att kunna verifiera att det som hävdas är sant. I den här Master-uppsatsen använder vi KakaoTalk – den mest populära chattappen i Sydkorea – som en fallstudie för att granska och bedömma säkerhetens- och integritets-aspekterna hos deras valbara “Secure Chat” med end-to-end krypteringsfunktionalitet. Vi granskar även KakaoTalk’s användarvillkor för att kunna verifiera påståenden som att “[. . . ] Kakao’s server is unable to decrypt the encryption [. . . ]” från ett tekniskt perspektiv. Det huvudsakliga syftet med denna studien är att belysa hur olika brister i en produkt sammantagna kan skapa en risk för allvarliga vektorattacker mot end-to-end integriteten även fast det finns flera skyddslager. Mer specifikt visar vi hur en central katalogserver för public-keys gör end-to-end krypteringssystemet sårbart mot välkända operator-site man-in-the-middle-attacker. Trots att denna naiva typ av attack kan verka uppenbar, argumenterar vi för att (KakaoTalk) användare borde veta om styrkorna och svagheterna med en särskild systemdesign för att kunna göra ett informerat val för om de ska lita på säkerheten hos en chattapplikation eller inte.