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关键词： Computer science   adversary behavior   computer security   cybersecurity   public key infrastructures  

摘要： Public Key Infrastructure (PKI) is designed to guarantee the authenticity and integrity of digital assets such as messages, executable binaries, etc. In PKIs, there are two representative applications: 1) the Web PKI and 2) the Code-Signing PKI. 1) The Web PKI enables entities (e.g., clients and web service providers) to securely communicate over untrusted networks such as the Internet, and 2) the Code-Signing PKI helps protect clients from executing files of unknown origin. However, anecdotal evidence has indicated that adversaries compromised and abused the PKIs, which poses security threats to entities. For example, CAs have mis-issued digital certificates to adversaries due to their failed vetting processes. Moreover, private keys that are supposed to be securely kept were stolen by adversaries. Such mis-issued certificates or stolen private keys were used to launch impersonation attacks. In this regard, we need to have a sound understanding of such security threats and adversaries' behaviors in the PKIs to mitigate them and further to enhance the security of the PKIs. In this dissertation, we conduct a large-scale measurement study in the two representative applications---the Web PKI and the Code-Signing PKI---to better understand adversaries' behaviors and the potential security threats. First, in 1) the Web PKI, we mainly focus on phishing websites served with TLS certificates. From the measurement study, we observe that certificate authorities (CAs) often fail in their vetting process and mis-issue TLS certificates to adversaries (i.e., phishing attackers). Also, CAs rarely revoke their issued TLS certificates that have been compromised. Second, in 2) the Code-Signing PKI, we characterize the weaknesses of the three actors (i.e., CAs, software publishers, and clients) that adversaries can exploit to compromise the Code-Signing PKI. Moreover, we measure the effectiveness of the primary defense, revocation, against the Code-Signing PKI abuses. We find that err

关键词： Mathematical model   Symmetric matrices   Computational modeling   Stochastic processes   Nonlinear equations   Protocols   Computer science   DeGroot model   high exponent   consensus   MAS   transition matrix  

摘要： A nonlinear consensus model is assigned to resolve the consensus problem of multi-agent systems (MAS). Other studies have constructed consensus systems based on low-complexity computation linear equations or complex nonlinear equations. Linear equations are less efficient in reaching a consensus due to their slow computation process, where nonlinear equations are more efficient. The three major challenges in designing nonlinear consensus equations are: building a system of nonlinear equations that have solution, easy to calculate, and less time consuming. This study aims to create a consensus system that is nonlinear and easy to calculate. According to our survey, the DeGroot model (DGM) of 1974 is a linear model and the first effect consensus model with a flexible computation process for finite nodes. We examine if raising the exponential level for the initial cases of agents allows the system to achieve a consensus and move the DGM to a nonlinear level. The results show that by raising the exponent, the DGM is able to reach a consensus. The consensus of the DGM reaches a certain positive value that depends on the initial states of the agents and the transition matrix, whereas the consensus of the proposed exponential DGM (EDGM) reaches zero with a flexible and unrestricted matrix. Moreover, EDGM is a nonlinear model and reaches the consensus faster than the DGM linear model. The results are supported by theoretical evidence and numerical analysis.

关键词： Applied mathematics   Computer science  

摘要： This thesis presents an analysis of several smoothness energies (also called smoothing energies) in geometry processing, and introduces new methods as well as a mathematical proof of correctness and convergence for a well-established method. Geometry processing deals with the acquisition, modification, and output (be it on a screen, in virtual reality, or via fabrication and manufacturing) of complex geometric objects and data. It is closely related to computer graphics, but is also used by many other fields that employ applied mathematics in the context of geometry. The popular Laplacian energy is a smoothness energy that quantifies smoothness and that is closely related to the biharmonic equation (which gives it desirable properties). Minimizers of the Laplacian energy solve the biharmonic equation. This thesis provides a proof of correctness and convergence for a very popular discretization method for the biharmonic equation with zero Dirichlet and Neumann boundary conditions, the piecewise linear Lagrangian mixed finite element method. The same approach also discretizes the Laplacian energy. Such a proof has existed for flat surfaces for a long time, but there exists no such proof for the curved surfaces that are needed to represent the complicated geometries used in geometry processing. This proof will improve the usefulness of this discretization for the Laplacian energy. In this thesis, the novel Hessian energy for curved surfaces is introduced, which also quantifies the smoothness of a functions, and whose minimizers solve the biharmonic equation. This Hessian energy has natural boundary conditions that allow the construction of functions that are not significantly biased by the geometry and presence of boundaries in the domain (unlike the Laplacian energy with zero Neumann boundary conditions), while still conforming to constraints informed by the application. This is useful in any situation where the boundary of the domain is not an integral part of the pr

关键词： Computer science  

摘要： Morphology is the study of the internal word structure, and how it interacts with orthography, phonology, semantics and syntax. Morphological tagging and disambiguation are integral Natural Language Processing (NLP) tasks, and often used as enabling technologies for higher order NLP models. While many recent NLP systems model morphology implicitly as part of an end-to-end system, explicit morphological modeling is particularly important for low-resource languages and dialects, for which morphology is more difficult to learn implicitly. Different languages have different morphological systems, which hinders the direct application of existing models developed for certain languages to others. Some languages are characterized as morphologically-rich, having a high number of inflections for a given base word, like Arabic, compared to poorer languages with fewer inflections, like English. The Arabic language is also diglossic in nature: Modern Standard Arabic (MSA) is the high register of the language, commonly used in news reports and official correspondence, while Dialectal Arabic (DA) is the low register and often used in daily interactions. Despite being used for official matters, MSA is not the native language for any Arabic speakers. DA is mainly spoken and is rarely written, it therefore lacks standardized orthography guidelines. Social media platforms have dramatically increased the volume of written DA content. However, the lack of standardized orthography guidelines renders much of this content highly sparse and inconsistent. Annotated DA resources are also still very limited for most dialects, which further complicates NLP tasks in general. Morphological modeling for DA is particularly challenging, since all of the previous challenges are further aggravated with DA's morphological richness, reducing the accuracy of DA morphological models severely. Due to these different challenges, morphological modeling in DA is an active area of research, that has recently b

关键词： Computer science  

摘要： There is growing desire to parallelize software and systems due to the increasing availability and utility of multi-core platforms. Ideally, the performance is desired to scale up linearly as core count increases, if there is enough parallelism can be explored inside the system. However, with more and more cores, the inter-core coordination among those parallelized software components becomes a performance challenge. As a result, system support for scalable coordination is necessary to enable applications to efficiently harness the parallel computation capacity of multi-core platforms with a wide spectrum, from embedded devices to edge cloud to rack-scale systems in data-center. This thesis investigates scalable coordination support for three different domains, each with unique system limitations and performance requirements. RT-SMR, implementation and analysis of scalable memory reclamation which provides efficient and predictable resource sharing in real-time systems; BI, a consistency model which enables data-structures sharing in non-cache-coherency rack-scale systems; and EdgeOS, a micro-kernel baaed operating system that provides fine-grained isolation for scalable, dynamic, multi-tenant Edge Clouds.

关键词： Literature   Computer science  

摘要： This thesis seeks to establish an approach to integrate thematic cohesion in interactive narrative. Psychological AI entities have been a promising possibility for interactive narrative because they can simulate characters that react appropriately to any situation. But even though they can act like human beings, this does not necessarily make them into good actors for an interesting dramatic story. In order for this to happen, the AIs need to be directed in some way, and various other designers have built such constraints directly into their patterns. However, my approach uses a separate narrative module to affect characters in a more subliminal manner, tilting characters towards a central theme while still giving them psychological agency.

关键词： Ciphers   Encryption   Color   Sensitivity   Logistics   Computer science   Cryptography   image processing   encryption   decryption   chaos  

摘要： In real time scenarios, the single image encryption schemes are not that efficient when a bunch of color images is to be encrypted. This problem should be addressed due to computational cost incurred by multiple executions of single color-image encryption scheme. The objective of this research work is to provide a new and efficient multiple color images cipher scheme. This cipher is based on chaotic system, circular shift operations and SHA-384 hash codes. First of all, an arbitrary number of RGB images are input. They are combined in a rectangular fashion to get their hash code. Then this big color-image is decomposed into its three basic components, i.e., red, green and blue. To scramble the pixels of these components, they are shifted circularly both the row-wise and column-wise. Further, XOR operation has been performed to realize the effects of diffusion in these components. Lastly, these components are joined together to get the final RGB cipher image. Apart from the 384-hash codes, a salt key of 384-bit has also been used in the proposed cipher to heighten the security effects. The SHA-384 hash codes render the required key space and plaintext sensitivity. The simulation results and the performance analyses carried out at the end clearly prove the efficiency, effectiveness, robustness and the real-world applicability of the proposed multiple RGB images cipher. Besides, the encryption throughput 7.716 Mb/s of the proposed scheme outperforms many of the existing ones.

关键词： Computer science  

摘要： Dynamically-typed languages have improved programming experience in software development, leading to widespread adoption in the modern software ecosystem. As dynamically- typed languages continue to evolve, their implementations inevitably become more complex and error-prone. As a result, many bugs in the language implementations are found every year, and attackers try to exploit them for code-injection or code-reuse attacks. Prior work has attempted to defend against these attacks by using technologies such as data execution prevention (DEP), software diversity, control-flow integrity (CFI), etc. However, interactive scripting environments provide attackers with a unique attack surface, capable of bypassing existing defenses. In this dissertation, we explore a new attack vector that was thought to be non-exploitable: the bytecode interpreter attack. We propose four attack strategies to compromise the byte- code interpreter itself. We show that our attacks successfully lead to arbitrary code execution in three popular dynamically-typed languages (Python, Lua, and JavaScript). To address this new attack vector, we propose a new comprehensive mitigation for dynamically-typed languages: NoJitsu. NoJITsu protects complex, real-world scripting engines from not only the bytecode corruption but also prior code-injection and reuse attacks. The key idea behind our comprehensive defense is to enable fine-grained memory access control for individual memory regions based on their roles throughout the script engine’s life-cycle. We combine automated analysis, instrumentation, compartmentalization, and Intel’s Memory-Protection Keys (MPK) to secure script engines against existing and newly synthesized attacks. Further, we thoroughly test our implementation using several real-world scenarios as well as standard benchmarks. We show that NoJITsu successfully thwarts code-reuse, code-injection, and bytecode attacks against any part of the scripting engine while offering a modest run-

关键词： Applied mathematics   Mathematics   Computer science  

摘要： Determinantal Point Processes (DPPs) are probability distributions on subsets of a collection of points that tend to generate diverse configurations of points. This feature makes them suitable as a probabilistic model of diversity. Recently this idea has been exploited extensively in subset selection problems, where given a large set of items such as images, documents, or any other form of collected data, the goal is to select a small, yet diverse and representative subset. However, with the rapid growth of datasets size, in order to utilize DPPs for real-world tasks, we need to design new primitives and inference algorithms that can be run efficiently in these settings. This thesis focuses on two inference tasks for DPPs: In the first part, we study sampling algorithms for DPPs and offer efficient MCMC based algorithms which can be applied in both discrete and continuous domains. In the second part, we consider the problem of determinant maximization which is equivalent to the Maximum a Posteriori encoding for DPPs, and present scalable algorithms in a distributed setting which assumes the input data are arbitrarily split among numerous nodes.

关键词： Information technology   Information science   Computer science  

摘要： The purpose of the qualitative descriptive phenomenological study was to explore the cybersecurity experts' insights into the factors that are limiting U.S.-based SMEs from adopting the NIST CSF. The research question asked: What factors are limiting U.S.-based SMEs from implementing the NIST CSF? The conceptual framework for this study proposed analyzing the factors limiting the implementation of the NIST CSF by SMEs within the primary constructs of the Unified Theory of Acceptance and Use of Technology (UTAUT). The qualitative descriptive phenomenological study used semi-structured interviews to collect information from 12 participants with at least 10 years of cybersecurity experience in the United States. The participants were all CISOs, CTOs, or in other highly experienced cybersecurity positions. Data were analyzed utilizing the five-step method for analysis of descriptive qualitative data. Six major themes and 2 prominent topics emerged. The 6 major themes were (a) complexity, (b) lack of skillsets/staff, (c) expensive/costs, (d) not required regulatory standard, (e) lack of cybersecurity knowledge, and (f) lack of executive buy-in. The 2 prominent topics were (a) lack of harmonization and (b) lack of industry partner support/tools. The data from the study revealed that all 6 major themes correspond back to each of the 4 primary constructs of UTAUT. The key findings suggest that the factors limiting the implementation of the NIST CSF by SMEs could be reduced through an evaluation of the NIST CSF for enhancements based on the 4 primary constructs under UTAUT.