Avec l'évolution des technologies, la complexité des systèmes informatiques ne cesse de s'accroître. Parmi ces systèmes, on retrouve les logiciels critiques qui doivent offrir une garantie de sûreté de fonctionnement qui s'avère crucial et pour lesquels un dysfonctionnement peut avoir des conséquences graves. Les méthodes formelles fournissent des outils permettant de garantir mathématiquement l'absence de certaines erreurs. Ces méthodes sont indispensables pour assurer les plus hauts niveaux de sûreté. Mais l'application de ces méthodes sur un code système bas niveau se heurte à des difficultés d'ordre pratique et théorique. Les principales difficultés concernent la prise en compte des aspects bas niveau, comme les pointeurs et les interactions avec le matériel spécifique. De plus, le fait que ces systèmes soient concurrents conduit à une augmentation exponentielle du nombre de comportements possibles, ce qui rend plus difficile leur vérification. Dans cette thèse, nous proposons une méthodologie pour la spécification et la vérification par model-checking de ce type de systèmes, en particulier, ceux implémentés en C. Cette méthodologie est basée sur la traduction de la sémantique de C en TLA+, un langage de spécification formel adapté à la modélisation de systèmes concurrents. Nous avons proposé un modèle de mémoire et d'exécution d'un programme C séquentiel en TLA+. En se basant sur ce modèle, nous avons proposé un ensemble de règles de traduction d'un code C en TLA+ que nous avons implémenté dans un outil, appelé C2TLA+. Nous avons montré comment ce modèle peut s'étendre pour modéliser les programmes C concurrents et gérer la synchronisation entre plusieurs processus ainsi que leur ordonnancement. Pour réduire la complexité du model-checking, nous avons proposé une technique permettant de réduire significativement la complexité de la vérification. Cette réduction consiste pour un code C à agglomérer une suite d'instructions lors de la génération du code TLA+, sous réserve d'un ensemble de conditions.Nous avons appliqué la méthodologie proposée dans cette thèse sur un cas d'étude réel issu de l'implémentation d'un micronoyau industriel,sur lequel nous avons vérifié un ensemble de propriétés fonctionnelles. L'application de la réduction a permis de réduire considérablement le temps de la vérification, ce qui la rend utilisable en pratique.Les résultats ont permis d'étudier le comportement du système, de vérifier certaines propriétés et de trouver des bugs indétectables par des simples tests. / Software systems are critical and complex. In order to guarantee their correctness, the use of formal methodsis important. These methods can be defined as mathematically based techniques, languages and tools for specifying and reasoning about systems. But, the application of formal methods to software systems, implemented in C, is challenging due to the presence of pointers, pointer arithmetic andinteraction with hardware. Moreover, software systems are often concurrent, making the verification process infeasible. This work provides a methodology to specify and verify C software systems usingmodel-checking technique. The proposed methodology is based on translating the semantics of Cinto TLA+, a formal specification language for reasoning about concurrent and reactive systems. We define a memory and execution model for a sequential program and a set of translation rules from C to TLA+ that we developed in a tool called C2TLA+. Based on this model, we show that it can be extended to support concurrency, synchronization primitives and process scheduling. Although model-checking is an efficient and automatic technique, it faces the state explosion problem when the system becomes large. To overcome this problem, we propose a state-space reduction technique. The latter is based on agglomerating a set of C instructions during the generation phase of the TLA+ specification. This methodology has been applied to a concrete case study, a microkernel of an industrial real-time operating system, on which a set of functional properties has been verified. The application of the agglomeration technique to the case study shows the usefulness of the proposed technique in reducing the complexity of verification. The obtained results allow us to study the behavior of the system and to find errors undetectable using traditional testing techniques.

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Information technology systems are essential for most businesses as they facilitate the handling and sharing of data and the execution of tasks. Due to connectivity to the internet and other internal networks, these systems are susceptible to cyberattacks. Computer worms are one of the most significant threats to computer systems because of their fast self-propagation to multiple systems and malicious payloads. Modern worms employ obfuscation techniques to avoid detection using patterns from previous attacks. Although the best defense is to eliminate (patch) the software vulnerabilities being exploited by computer worms, this requires a substantial amount of time to create, test, and deploy the patches. Worm containment techniques are used to reduce or stop the spread of worm infections to allow time for software patches to be developed and deployed. In this dissertation, a novel blockchain-based collaborative intrusion prevention system model is introduced. This model is designed to proactively contain zero-day and obfuscated computer worms. In this model, containment is achieved by creating and distributing signatures for the exploited vulnerabilities. Blockchain technology is employed to provide liveness, maintain an immutable record of vulnerability-based signatures to update peers, accomplish trust in confirming the occurrence of a malicious event and the corresponding signature, and allow a decentralized defensive environment. A consensus algorithm based on the Practical Byzantine Fault Tolerance (PBFT) algorithm is employed in the model. The TLA+ formal method is utilized to check the correctness, liveness, and safety properties of the model as well as to assert that it has no behavioral errors. A blockchain-based automatic worm containment system is implemented. A synthetic worm is created to exploit a network-deployed vulnerable program. This is used to evaluate the effectiveness of the containment system. It is shown that the system can contain the worm and has good performance. The system can contain 100 worm attacks a second by generating and distributing the corresponding vulnerability-based signatures. The system latency to contain these attacks is less than 10 ms. In addition, the system has low resource requirements with respect to memory, CPU, and network traffic. / Graduate

This item contains the agenda, minutes, and attachments for the Faculty Senate meeting on this date. There may be additional materials from the meeting available at the Faculty Center.

<p>A great deal of the research on cross-linguistic phonetic influence demonstrates that a speaker’s knowledge of their first language (L1) significantly affects their ability to perceive and produce sounds in any other language. While current studies show that cross-linguistic transfer occurs at the L3 level, some research suggests that properties of both L1 and L2 are present in the production of L3 (Ionin, Montrul & Santos, 2011). Many studies have addressed perception, production and factors that influence foreign speech in Second Language Acquisition (SLA) (Watkins, Rauber & Baptista, 2009). As the number of multilingual individuals rises, so does the need for studies that investigate not only SLA but also that of additional languages (i.e., Third Language Acquisition). This dissertation examines how cross-linguistic influence (CLI) occurs among English, Spanish, and Brazilian Portuguese (BP), examining instances of vowel reduction, an aspect of phonological production. English and BP are assumed as vowel reducing languages, whereas Spanish displays negligible vowel reduction in comparison. The vowel productions in L3 BP of two multilingual groups, L1English-L2Spanish-L3BP (ESP) and L1 Spanish-L2 English-BP (SEP) were investigated in two tasks: a paragraph reading task (PRT) and a carrier phrase task (CPT). The study sought to determine whether i) a native speaker of a vowel reducing L1 and a non-vowel reducing L2 displays more or less vowel reduction in a vowel reducing L3 than a native speaker of a non-vowel reducing L1 and vowel reducing L2 and ii) how length of exposure to an L3 affects phonological production. Three fixed effects were considered: duration ratio, intensity ratio and height (F1). The goal was to ascertain whether the Typological Primacy Model (TPM) (Rothman 2011, 2015) or the L2 Status Factor Model (Bardel & Falk 2007, 2012; Hammarberg, 2001) would be a better predictor for how vowel reduction would occur in the L3. Results for duration ratio and vowel height showed no significant difference between groups ESP and SEP. Results for intensity ratio suggest L2 Status as a better predictor, as group SEP displayed more phonological transfer than the ESP group. A hybrid approach to L3 acquisition models is proposed. </p>