abstract: The use of reactive security mechanisms in enterprise networks can, at times, provide an asymmetric advantage to the attacker. Similarly, the use of a proactive security mechanism like Moving Target Defense (MTD), if performed without analyzing the effects of security countermeasures, can lead to security policy and service level agreement violations. In this thesis, I explore the research questions 1) how to model attacker-defender interactions for multi-stage attacks? 2) how to efficiently deploy proactive (MTD) security countermeasures in a software-defined environment for single and multi-stage attacks? 3) how to verify the effects of security and management policies on the network and take corrective actions? I propose a Software-defined Situation-aware Cloud Security framework, that, 1) analyzes the attacker-defender interactions using an Software-defined Networking (SDN) based scalable attack graph. This research investigates Advanced Persistent Threat (APT) attacks using a scalable attack graph. The framework utilizes a parallel graph partitioning algorithm to generate an attack graph quickly and efficiently. 2) models single-stage and multi-stage attacks (APTs) using the game-theoretic model and provides SDN-based MTD countermeasures. I propose a Markov Game for modeling multi-stage attacks. 3) introduces a multi-stage policy conflict checking framework at the SDN network's application plane. I present INTPOL, a new intent-driven security policy enforcement solution. INTPOL provides a unified language and INTPOL grammar that abstracts the network administrator from the underlying network controller's lexical rules. INTPOL develops a bounded formal model for network service compliance checking, which significantly reduces the number of countermeasures that needs to be deployed. Once the application-layer policy conflicts are resolved, I utilize an Object-Oriented Policy Conflict checking (OOPC) framework that identifies and resolves rule-order dependencies and conflicts between security policies. / Dissertation/Thesis / Doctoral Dissertation Computer Science 2020

A recent study using reinforcement learning with a Q-functions to quantify the impact of individual player actions in ice hockey has shown promising results. The model takes into account the context of the actions and captures internal dynamic features of the play which simple common metrics e.g., counting goals or assists, do not. It also performs look ahead which is important in a low scoring game like ice hockey. However, it does not capture the chemistry between the players i.e., how well the players play together which is important in a team sport like ice hockey. In this paper, we, therefore, extend this earlier work on individual player performance with new metrics on player pairs impact when on ice together. Our resulting top pairings are compared to NHL’s official statistics and extended analysis is performed that investigate the relationship with time on ice which provides insights that could be of relevance to coaches.

Not all goals in the game of ice hockey are created equal: some goals increase the chances of winning more than others. This thesis investigates the result of constructing and using a reward function that takes this fact into consideration, instead of the common binary reward function. The two reward functions are used in a Markov Game model with value iteration. The data used to evaluate the hockey players is play-by-play data from the 2013-2014 season of the National Hockey League (NHL). Furthermore, overtime events, goalkeepers, and playoff games are excluded from the dataset. This study finds that the constructed reward, in general, is less correlated than the binary reward to the metrics: points, time on ice and, star points. However, an increased correlation was found between the evaluated impact and time on ice for center players. Much of the discussion is devoted to the difficulty of validating the results from a player evaluation due to the lack of ground truth. One conclusion from this discussion is that future efforts must be made to establish consensus regarding how the success of a hockey player should be defined.