Cette thèse aborde différents aspects de la cryptologie, subsumant des champs aussi variés que la conception de protocoles, l’amélioration d’outils algorithmiques et les attaques. Les deux principales focales de cette étude sont : un protocole de co-signature prouvé irréfragable et un système de chiffrement authentifié à sécurité prouvée. Notre protocole de co-signature permet l’équité légale. L’équité légale est une nouvelle variante de la notion d’équité, ne reposant pas sur des tiers. Notre instanciation d’équité légale est construite à l’aide des signatures de Schnorr. Nous présenterons également un protocole d’authentification distribué de type Fiat-Shamir. La deuxième partie de cette thèse est consacrée aux améliorations algorithmiques. Nous introduisons une méthode permettant de doubler la vitesse de l’algorithme de Barrett en utilisant des modules composites spécifiques et un nouvel algorithme de multiplication à retour sur trace, particulièrement adapté aux microprocesseurs bon marché. Nous nous intéresserons ensuite à la sécurité des composants en étudiant la régulation du débit des correcteurs de von Neumann et les attaques en fautes sur des implémentations de cryptographie à courbes elliptiques. Enfin, un des actes novatoires incidents notre travail sera d’adapter aux codes correcteurs d’erreurs deux techniques empruntées à la cryptographie : un premier résultat améliore l’efficacité calculatoire des codes BCH grâce à une version de l’algorithme de Barrett étendue aux polynômes. Le second est un nouveau code correcteur d’erreurs basé sur la théorie des nombres. / This thesis addresses various topics in cryptology, namely protocol design, algorithmic improvements and attacks. In addition, we venture out of cryptography and propose two new applications of cryptographic techniques to error correcting codes. Our main results comprise a provably secure co-signature protocol and a provably secure authenticated encryption scheme. Our co-signature protocol achieves legal fairness, a novel fairness variant that does not rely on third parties. Legal fairness is implemented using Schnorr signatures. We also present a distributed Fiat-Shamir authentication protocol. The second part of the thesis is devoted to computational improvements, we discuss a method for doubling the speed of Barrett’s algorithm by using specific composite moduli, devise new BCH speed-up strategies using polynomial extensions of Barrett’s algorithm, describe a new backtracking-based multiplication algorithm suited for lightweight microprocessors and present a new number theoretic error-correcting code. Fault injection attacks are further overviewed and a new fault attack on ECC implementations is proposed.

Although terrorism is an area that has been the subject of much research, systematic searches in databases reveal that a focus on actors and movements that find their motivation in Christian beliefs, is, by and large, lacking. Ever since the 9/11 terrorist attack, Islamist terrorism has been the major focus. The purpose of this thesis is to describe and compare Christian and Islamist acts of terrorism. This will be done by using the terrorist attack of the self-proclaimed Christian crusader Anders Behring Breivik in Norway 2011 and compare it to the terrorist attack in Paris November 2015 claimed by the terrorist organisation Islamic State (IS). A content analysis is used to explore the material. The analysis is conducted with an analytical framework created from previous research on religious terrorism to explore the similarities and differences of religiously motivated terrorist acts. The study reveals that there are a lot of similarities between Breivik and the Paris attackers. Both Breivik and IS strived to change society with violence justified by their religion. In a type of “God´s executioner” fashion. A final conclusion in this thesis is that Breivik and IS share Ideological core ideas in the form of exclusivity, however, the exclusivity is expressed differently. Breivik´s exclusiveness is linked to ethnicity and skin colour, while IS´s exclusivity is solely linked to faith.

Indiana University-Purdue University Indianapolis (IUPUI) / The internet is the home for massive volumes of valuable data constantly being created, making it difficult for users to find information relevant to them. In recent times, online users have been relying on the recommendations made by websites to narrow down the options. Online reviews have also become an increasingly important factor in the final choice of a customer. Unfortunately, attackers have found ways to manipulate both reviews and recommendations to mislead users. A Recommendation System is a special type of information filtering system adapted by online vendors to provide suggestions to their customers based on their requirements. Collaborative filtering is one of the most widely used recommendation systems; unfortunately, it is prone to shilling/profile injection attacks. Such attacks alter the recommendation process to promote or demote a particular product. On the other hand, many spammers write deceptive reviews to change the credibility of a product/service. This work aims to address these issues by treating the review manipulation and shilling attack scenarios independently. For the shilling attacks, we build an efficient Reinforcement Learning-based shilling attack method. This method reduces the uncertainty associated with the item selection process and finds the most optimal items to enhance attack reach while treating the recommender system as a black box. Such practical online attacks open new avenues for research in building more robust recommender systems. When it comes to review manipulations, we introduce a method to use a deep structure embedding approach that preserves highly nonlinear structural information and the dynamic aspects of user reviews to identify and cluster the spam users. It is worth mentioning that, in the experiment with real datasets, our method captures about 92\% of all spam reviewers using an unsupervised learning approach.

In recent years, trusted execution environments like Intel SGX have allowed developers to protect sensitive code inside so called enclaves. These enclaves protect its code and data even in the cases of a compromised OS. However, SGX enclaves have been shown to be vulnerable to numerous side-channel attacks. Therefore, there is a need to investigate ways that such attacks against enclaves can be detected. This thesis investigates the viability of using performance counters to detect an SGX-targeting side-channel attack, specifically the recent Load Value Injection (LVI) class of attacks. A case study is thus presented where performance counters and a threshold-based detection method is used to detect variants of the LVI attack. The results show that certain attack variants could be reliably detected using this approach without false positives for a range of benign applications. The results also demonstrate reasonable levels of speed and overhead for the detection tool. Some of the practical limitations of using performance counters, particularly in an SGX-context, are also brought up and discussed.

This work deals with performance and security testing of blockchain protocols based on the Proof-of-Stake (PoS) consensus model. It describes properties, problems, but also the use of blockchain systems. On theoretical levels, this thesis compares the properties and resistance to various attacks of numerous PoS protocols, specifically Algorand, Casper, Gasper, Snow White, Stellar and Decred. Additionally, this work implements a protocol simulator of Algorand, Casper FFG and Gasper. The simulator is built on top of the Bitcoin Simulator simulation tool, which is based on the NS-3 discrete network event simulator. Then, it compares the properties of the implemented protocols using discrete simulation.

This thesis is focused on crypto-module RCM 3700, which is used for encrypted data transmission. Following work analyses basic network protocols and some sort of attacks in Ethernet network. The main goal of these attacks is to collect information and services about the device and to analyze transmitted data. Based on these information attacks can be done more precisely than without them. The main target of these attacks is the denial of particulary service or data abuse. Furthermore, in the diploma thesis configuration of router CISCO 2801 is applied in order to improve the LAN security. The deveploment board, which includes reset function, supplied circuit and interface for RS 232, was designed for crypto-module RCM 3700.

This work explores, analyzes and rate infuence of VoIP attacks on open source pbx functionality. It describes how voice over IP attacks are achieved according to security standards. There are described concepts and basics of VoIP networks with orientation on facts necessary to understand analyzed actions and measurements in theoretical part. In practical part, there is described realization of attack tests according to instructions with first orientation on initial checking of testing device, pbx’s and security attack possibilities and then complex creation and testing of attack scenarios types such as fuzzing and denial of service attacks.

This work describes one - way hash functions and cryptographic algorithms . It also describes their implementation regarding DOC, PDF and ZIP files contents encryption . Subsequently , the implementation analyzis is provided . Following next, the brute - force attack procedure levereging GPU is proposed and evaluated.

Widespread use of wireless networks has made security a serious issue. This thesis proposes misuse based intrusion detection system for wireless networks, which applies artificial neural network to captured frames for purpose of anomalous patterns recognition. To address the problem of high positive alarm rate, this thesis presents a method of applying two artificial neural networks.

The thesis describes a design and implementation of Nemea system module purposed on generation of records about simulated network attacks. This thesis also contains brief description of Nemea system and several network attacks. Finally, part of this work is description of simulated attacks and methods of simulations.