The successful crowdsourcing model and gamification design of Stack Overflow (SO) Q&A platform have attracted many programmers to ask and answer technical questions, regardless of their level of expertise. Researchers have recently found evidence of security vulnerable code snippets being possibly copied from SO to production software. This inspired us to study how reliable is SO in providing secure coding suggestions. In this project, we automatically extracted answer posts related to Java security APIs from the entire SO site. Then based on the known misuses of these APIs, we manually labeled each extracted code snippets as secure or insecure. In total, we extracted 953 groups of code snippets in terms of their similarity detected by clone detection tools, which corresponds to 785 secure answer posts and 644 insecure answer posts. Compared with secure answers, counter-intuitively, insecure answers has higher view counts (36,508 vs. 18,713), higher score (14 vs. 5), more duplicates (3.8 vs. 3.0) on average. We also found that 34% of answers provided by the so-called trusted users who have administrative privileges are insecure. Our finding reveals that there are comparable numbers of secure and insecure answers. Users cannot rely on community feedback to differentiate secure answers from insecure answers either. Therefore, solutions need to be developed beyond the current mechanism of SO or on the utilization of SO in security-sensitive software development. / Master of Science / Stack Overflow (SO), the most popular question and answer platform for programmers today, has accumulated and continues accumulating tremendous question and answer posts since its launch a decade ago. Contributed by numerous users all over the world, these posts are a type of crowdsourced knowledge. In the past few years, they have been the main reference source for software developers. Studies have shown that code snippets in answer posts are copied into production software. This is a dangerous sign because the code snippets contributed by SO users are not guaranteed to be secure implementations of critical functions, such as transferring sensitive information on the internet. In this project, we conducted a comprehensive study on answer posts related to Java security APIs. By labeling code snippets as secure or insecure, contrasting their distributions over associated attributes such as post score and user reputation, we found that there are a significant number of insecure answers (644 insecure vs 785 secure in our study) on Stack Overflow. Our statistical analysis also revealed the infeasibility of differentiating between secure and insecure posts leveraging the current community feedback system (eg. voting) of Stack Overflow.

Les injections de fautes laser induisent des fautes transitoires dans les circuits intégrés en générant localement des courants transitoires qui inversent temporairement les sorties des portes illuminées. L'injection de fautes laser peut être anticipée ou étudiée en utilisant des outils de simulation à différents niveaux d'abstraction: physique, électrique ou logique. Au niveau électrique, le modèle classique d'injection de fautes laser repose sur l'ajout de sources de courant aux différents nœuds sensibles des transistors MOS. Cependant, ce modèle ne prend pas en compte les grands composants de courant transitoire également induits entre le VDD et le GND des circuits intégrés conçus avec des technologies CMOS avancées. Ces courants de court-circuit provoquent un significatif IR drop qui contribue au processus d'injection de faute. Cette thèse décrit notre recherche sur l'évaluation de cette contribution. Il montre par des simulations et des expériences que lors de campagnes d'injection de fautes laser, le IR drop induite par laser est toujours présente lorsque l'on considère des circuits conçus dans des technologies submicroniques profondes. Il introduit un modèle de faute électrique amélioré prenant en compte le IR drop induite par laser. Il propose également une méthodologie qui utilise des outils CAD standard pour permettre l'utilisation du modèle électrique amélioré pour simuler des fautes induits par laser au niveau électrique dans des circuits à grande échelle. Sur la base de simulations et de résultats expérimentaux supplémentaires, nous avons constaté que, selon les caractéristiques de l'impulsion laser, le nombre de fautes injectées peut être sous-estimé par un facteur aussi grand que 3 si le IR drop induite par laser est ignorée. Cela pourrait conduire à des estimations incorrectes du seuil d'injection des fautes, ce qui est particulièrement pertinent pour la conception de techniques de contre-mesures pour les systèmes intégrés sécurisés. De plus, les résultats expérimentaux et de simulation montrent que même si l'injection de fautes laser est une technique d'injection de fautes très locale et précise, les IR drops induites ont un effet global se propageant à travers le réseau d'alimentation. Cela donne des preuves expérimentales que l'effet de l'illumination laser n'est pas aussi local que d'habitude. / Laser fault injections induce transient faults into ICs by locally generating transient currents that temporarily flip the outputs of the illuminated gates. Laser fault injection can be anticipated or studied by using simulation tools at different abstraction levels: physical, electrical or logical. At the electrical level, the classical laser-fault injection model is based on the addition of current sources to the various sensitive nodes of MOS transistors. However, this model does not take into account the large transient current components also induced between the VDD and GND of ICs designed with advanced CMOS technologies. These short-circuit currents provoke a significant IR drop that contribute to the fault injection process. This thesis describes our research on the assessment of this contribution. It shows by simulation and experiments that during laser fault injection campaigns, laser-induced IR drop is always present when considering circuits designed in deep submicron technologies. It introduces an enhanced electrical fault model taking the laser-induced IR-drop into account. It also proposes a methodology that uses standard CAD tools to allow the use of the enhanced electrical model to simulate laser-induced faults at the electrical level in large-scale circuits. On the basis of further simulations and experimental results, we found that, depending on the laser pulse characteristics, the number of injected faults may be underestimated by a factor as large as 3 if the laser-induced IR-drop is ignored. This could lead to incorrect estimations of the fault injection threshold, which is especially relevant to the design of countermeasure techniques for secure integrated systems. Furthermore, experimental and simulation results show that even though laser fault injection is a very local and accurate fault injection technique, the induced IR drops have a global effect spreading through the supply network. This gives experimental evidence that the effect of laser illumination is not as local as usually considered.