Cette thèse étudie la problématique de l’indexation et de la recherche dans les tables de hachage distribuées –Distributed Hash Table (DHT). Elle propose un système de stockage distribué des résumés de documents en se basant sur leur contenu. Concrètement, la thèse utilise les Filtre de Blooms (FBs) pour représenter les résumés de documents et propose une méthode efficace d’insertion et de récupération des documents représentés par des FBs dans un index distribué sur une DHT. Le stockage basé sur contenu présente un double avantage, il permet de regrouper les documents similaires afin de les retrouver plus rapidement et en même temps, il permet de retrouver les documents en faisant des recherches par mots-clés en utilisant un FB. Cependant, la résolution d’une requête par mots-clés représentée par un filtre de Bloom constitue une opération complexe, il faut un mécanisme de localisation des filtres de Bloom de la descendance qui représentent des documents stockés dans la DHT. Ainsi, la thèse propose dans un deuxième temps, deux index de filtres de Bloom distribués sur des DHTs. Le premier système d’index proposé combine les principes d’indexation basée sur contenu et de listes inversées et répond à la problématique liée à la grande quantité de données stockée au niveau des index basés sur contenu. En effet, avec l’utilisation des filtres de Bloom de grande longueur, notre solution permet de stocker les documents sur un plus grand nombre de serveurs et de les indexer en utilisant moins d’espace. Ensuite, la thèse propose un deuxième système d’index qui supporte efficacement le traitement des requêtes de sur-ensembles (des requêtes par mots-clés) en utilisant un arbre de préfixes. Cette dernière solution exploite la distribution des données et propose une fonction de répartition paramétrable permettant d’indexer les documents avec un arbre binaire équilibré. De cette manière, les documents sont répartis efficacement sur les serveurs d’indexation. En outre, la thèse propose dans la troisième solution, une méthode efficace de localisation des documents contenant un ensemble de mots-clés donnés. Comparé aux solutions de même catégorie, cette dernière solution permet d’effectuer des recherches de sur-ensembles en un moindre coût et constitue est une base solide pour la recherche de sur-ensembles sur les systèmes d’index construits au-dessus des DHTs. Enfin, la thèse propose le prototype d’un système pair-à-pair pour l’indexation de contenus et la recherche par mots-clés. Ce prototype, prêt à être déployé dans un environnement réel, est expérimenté dans l’environnement de simulation peersim qui a permis de mesurer les performances théoriques des algorithmes développés tout au long de la thèse. / This thesis examines the problem of indexing and searching in Distributed Hash Table (DHT). It provides a distributed system for storing document summaries based on their content. Concretely, the thesis uses Bloom filters (BF) to represent document summaries and proposes an efficient method for inserting and retrieving documents represented by BFs in an index distributed on a DHT. Content-based storage has a dual advantage. It allows to group similar documents together and to find and retrieve them more quickly at the same by using Bloom filters for keywords searches. However, processing a keyword query represented by a Bloom filter is a difficult operation and requires a mechanism to locate the Bloom filters that represent documents stored in the DHT. Thus, the thesis proposes in a second time, two Bloom filters indexes schemes distributed on DHT. The first proposed index system combines the principles of content-based indexing and inverted lists and addresses the issue of the large amount of data stored by content-based indexes. Indeed, by using Bloom filters with long length, this solution allows to store documents on a large number of servers and to index them using less space. Next, the thesis proposes a second index system that efficiently supports superset queries processing (keywords-queries) using a prefix tree. This solution exploits the distribution of the data and proposes a configurable distribution function that allow to index documents with a balanced binary tree. In this way, documents are distributed efficiently on indexing servers. In addition, the thesis proposes in the third solution, an efficient method for locating documents containing a set of keywords. Compared to solutions of the same category, the latter solution makes it possible to perform subset searches at a lower cost and can be considered as a solid foundation for supersets queries processing on over-dht index systems. Finally, the thesis proposes a prototype of a peer-to-peer system for indexing content and searching by keywords. This prototype, ready to be deployed in a real environment, is experimented with peersim that allowed to measure the theoretical performances of the algorithms developed throughout the thesis.

Current needs of human communication came to status, when most of transferred messages are considered as private and transition over non-secured communication lines in open form is not possible. That originated a lot of different methods for securing of messages and transfers in ciphered form. Two mainstreams were established, symmetric cryptography and asymmetric cryptography. Second of mentioned groups is based on usage of two information – keys, when one of then is broadly known and is public and second, well protected and private. Using a public key it is possible to establish a cryptogram of message, but for deciphering it is necessary to know private key. Asymmetric methods are based on mathematical problems, for which there is not an effective computing algorithm. This thesis are focused for asymmetric cryptosystems based on discrete logarithm problem, where ciphering of message using public key is very easy and quick, but deciphering without knowledge of private key is extremely time consuming process. Work describes a mathematical base of discrete logarithm problem, its’ properties and methods developed for solving of this problem. Descriptions of particular cryptosystems are given, i.e. ElGamal cryptosystem, Diffie-Hellman protocol and DSA. Second part of thesis is focused for web application developed as study support of discrete logarithm problem and of cryptosystems using this problem. It describes functional and graphical interface, work with it and options given to user working with application. Mentions also lessons for user which should help with understanding of described problems and practicing.

The main goal of this master's thesis is building of web portal for presentation basic cryptography algorithms. Those algorithms would be explained in the theoretical page in the first place. After that, they would be demonstrated by scripts. One part of this project is designing simplified theoretical element for basic impletion portal of information. Next part is creating web portal by one of the free available CMS´s systems. Programming language JAVA would be used as an instrument for creating demonstration scripts. For creating animations will be used the Flash animation tool. Target of formed web portal is creating community of expert public. It would make new articles, scripts and knowledge. This way, the portal would be kept current. The section which would include failure the most widely used algorithms and instructions how to eliminate it will be part of portal.

Hash tables are fast associative array implementations which became part of modern world of information technology and thanks to its simplicity became very popular among computer programmers. The choice of proper hash function is very important. Improperly selected hash function can result in poor hash table performance and its application. Currently there are many exceptional implementations of general hash functions. Such functions are not constrained to a concrete set of inputs, they perform on any input. On the other hand if we know the input domain we can design a specific hash function for desired application thus reaching better levels of performance compare to a general hash function. However hash function design is not trivial. There are no rules, standards, guides nor automated tools that would help us with such a task. In case of manual design the hash function author has to rely on his/her knowledge, experience, inventiveness and intuition. In case of such complicated tasks there is sometimes advantageous to choose a different path and use techniques such as evolution algorithms. Natural computing is an approach of certain problem solutions that are inspired by the process of species reproduction as defined by Charles Darwin. In this thesis we will design hash functions for the domain of IP addresses, that serve as an unique network device interface identifier in internet protocol networks. The chosen subset of natural computing is the genetic programming, a very specific technique that is an adequate approach to our problem thanks to its properties. Evolutionary designed hash functions offer good properties. They outperform state-of-the-art generic, human-created hash functions in terms of speed and collision resistance.

The dissertation thesis deals with cryptographic protocols for secure authentication of communicating parties, which are intended primarily for low-cost devices used in Internet of Things. Low-cost devices represent computationally, memory and power constrained devices. The thesis focuses mainly on the possibilities of using mathematically undemanding cryptographic resorces for ensuring integrity of transmitted dat, authenticity of and secured transmission of data on low-cost devices. The main goals of the thesis focus on the design of new advanced cryptographic protocols for ensuring integrity of transmitted data, authenticity, confidentiality of transmitted data between low-cost devices and authenticity with non-repudiation of done events. The thesis describes proposal of three authentication protocols, one unilateral authentication protocol and two mutual authentication protocols. The thesis also describes proposals of two protocols for secured transmission of data between two devices, one protocol without a proof of receipt data and one protocol with proof of receipt data. In this thesis is also performed a security analysis and a discussion to proposed protocols.

Die Zope Object Database, kurz ZODB, ist eine Open-Source-Datenbank für Python. Im Gegensatz zu den meisten relationalen Datenbanken verfügt die ZODB allerdings nicht über eine Anfragesprache zur gezielten Selektion von Objekten. <br /> Aufgabe dieser Diplomarbeit ist es, effiziente Ad-Hoc-Anfragemöglichkeiten zu evaluieren und eine geeignete als Zusatzprodukt in Python zu implementieren. <br /> Folgende Themen sind zu bearbeiten: <ul> <li>Vergleich und Auswahl einer Anfragesprache für Objektgraphen</li> <li>Auswahl von Indexstrukturen zur Unterstützung der gewählten Anfragesprache</li> <li>Implementation eines Zusatzprodukts zur ZODB, die eine Anfragesprache sowie unterstützende Indizes bereitstellt</li> <li>Testen und Bewerten der Implementierung</li> </ul>

Web 2.0 has significantly transformed the way how modern society works now-a-days. In today‘s Web, information not only flows top down from the web sites to the readers; but also flows bottom up contributed by mass user. Hugely popular Web 2.0 applications like Wikis, social applications (e.g. Facebook, MySpace), media sharing applications (e.g. YouTube, Flickr), blogging and numerous others generate lots of user generated contents and make heavy use of the underlying storage. Data storage system is the heart of these applications as all user activities are translated to read and write requests and directed to the database for further action. Hence focus is on the storage that serves data to support the applications and its reliable and efficient design is instrumental for applications to perform in line with expectations. Large scale storage systems are being used by popular social networking services like Facebook, MySpace where millions of users‘ data have been stored and fully accessed by these companies. However from users‘ point of view there has been justified concern about user data ownership and lack of control over personal data. For example, on more than one occasions Facebook have exercised its control over users‘ data without respecting users‘ rights to ownership of their own content and manipulated data for its own business interest without users‘ knowledge or consent. The thesis proposes, designs and implements a large scale, robust and fault-tolerant key-value data storage prototype that is peer-to-peer based and intends to back away from the client-server paradigm with a view to relieving the companies from data storage and management responsibilities and letting users control their own personal data. Several read and write APIs (similar to Yahoo!‘s P NUTS but different in terms of underlying design and the environment they are targeted for) with various data consistency guarantees are provided from which a wide range of web applications would be able to choose the APIs according to their data consistency, performance and availability requirements. An analytical comparison is also made against the PNUTS system that targets a more stable environment. For evaluation, simulation has been carried out to test the system availability, scalability and fault-tolerance in a dynamic environment. The results are then analyzed and conclusion is drawn that the system is scalable, available and shows acceptable performance.

Structured overlay networks form a major classof peer-to-peer systems, which are touted for their abilitiesto scale, tolerate failures, and self-manage. Any long livedInternet-scale distributed system is destined to facenetwork partitions. Although the problem of network partitionsand mergers is highly related to fault-tolerance andself-management in large-scale systems, it has hardly beenstudied in the context of structured peer-to-peer systems.These systems have mainly been studied under churn (frequentjoins/failures), which as a side effect solves the problemof network partitions, as it is similar to massive nodefailures. Yet, the crucial aspect of network mergers has beenignored. In fact, it has been claimed that ring-based structuredoverlay networks, which constitute the majority of thestructured overlays, are intrinsically ill-suited for mergingrings. In this thesis, we present a number of research papers representing our work on handling network partitions and mergers in structured overlay networks. The contribution of this thesis is threefold. First, we provide a solution for merging ring-based structured overlays. Our solution is tuneable, by a {\em fanout} parameter, to achieve a trade-off between message and time complexity. Second, we provide a network size estimation algorithm for ring-based structured overlays. We believe that an estimate of the current network size can be used for tuning overlay parameters that change according to the network size, for instance the fanout parameter in our merger solution.Third, we extend our work from fixing routing anomalies to achieving data consistency. We argue that decreasing lookup inconsistencies on the routing level aids in achieving data consistency in applications built on top of overlays. We study the frequency of occurence of lookup inconsistencies and discuss solutions to decrease the affect of lookup inconsistencies.

L'objectif de cette thèse est de fournir des algorithmes d'optimisation pour l'accès aux services vidéo qu’ils soient non-gérés (Internet TV) ou gérés (IPTV). Nous étudions des statistiques récentes concernant les services vidéo non-gérés comme YouTube et nous proposons des techniques d'optimisation appropriées qui pourraient améliorer l'accès aux fichiers vidéos et réduire le coût de cet accès. En outre, l’analyse des coûts joue un rôle important dans les décisions qui concernent la mise en cache des fichiers vidéos et celles liées au choix des périodes temporelles d'hébergement de ces fichiers sur les serveurs. En ce qui concerne les services vidéo gérés appelés IPTV, nous avons mené des expériences sur une architecture ouverte IPTV-collaboration entre différents opérateurs. Ce modèle est analysé selon un critère de coût d’investissement et d'exploitation à l'intérieur de la sphère domestique. En outre, nous avons introduit une solution d’optimisation dynamique de l'arbre « minimum spanning tree » (MST) pour le service IPTV multicast. Lors d’un accès nomade, les arbres statiques pourraient être incapables de fournir le service de manière efficace vu que l'utilisation de la bande passante augmente aux côté des points de streaming (racines de la topologie). Finalement, nous étudions des mesures de sécurité fiables en streaming vidéo basées sur la méthodologie de la chaîne de hachage et nous proposons un nouvel algorithme hybride. Nous effectuons des comparaisons entre les différentes manières utilisées dans la réalisation de la fiabilité des chaînes de hachage basées sur les classifications génériques / The aim of this thesis is to provide optimization algorithms for accessing video services either in unmanaged or managed ways. We study recent statistics about unmanaged video services like YouTube and propose suitable optimization techniques that could enhance files accessing and reduce their access costs. Moreover, this cost analysis plays an important role in decision making about video files caching and hosting periods on the servers. Under managed video services called IPTV, we conducted experiments for an open-IPTV collaborative architecture between different operators. This model is analyzed in terms of CAPEX and OPEX costs inside the domestic sphere. Moreover, we introduced a dynamic way for optimizing the Minimum Spanning Tree (MST) for multicast IPTV service. In nomadic access, the static trees could be unable to provide the service in an efficient manner as the utilization of bandwidth increases towards the streaming points (roots of topologies). Finally, we study reliable security measures in video streaming based on hash chain methodology and propose a new algorithm. Then, we conduct comparisons between different ways used in achieving reliability of hash chains based on generic classifications

In this thesis there is description of cryptographic algorithms. Their properties are being compared, weak and strong points and right usage of particular algorithms. The main topics are safeness of algorithms, their bugs and improvements and difficulty of breaching. As a complement to ciphers there are also hash functions taken in consideration. There are also showed the most common methods of cryptanalysis. As a practical application of described algorithms I analyze systems for secure data transfer SSH and SSL/TLS and demonstrate an attack on SSL connection. In conclusion there is recommendation of safe algorithms for further usage and safe parameters of SSH and SSL/TLS connections.