Doctor of Philosophy / Department of Computing and Information Sciences / Xinming (Simon) Ou / Enterprise network security management is a vitally important task, more so now than ever before. Networks grow ever larger and more complex, and corporations, universities, government agencies, etc. rely heavily on the availability of these networks. Security in enterprise networks is constantly threatened by thousands of known software vulnerabilities, with thousands more discovered annually in a wide variety of applications. An overwhelming amount of data is relevant to the ongoing protection of an enterprise network. Previous works have addressed the identification of vulnerabilities in a given network and the aggregated collection of these vulnerabilities in an attack graph, clearly showing how an attacker might gain access to or control over network resources. These works, however, do little to address how to evaluate or properly utilize this information. I have developed a comprehensive approach to enterprise network security management. Compared with previous methods, my approach realizes these issues as a uniform desire for provable mitigation of risk within an enterprise network. Attack graph simplification is used to improve user comprehension of the graph data and to enable more efficient use of the data in risk assessment. A sound and effective quantification of risk within the network produces values that can form a basis for valuation policies necessary for the application of a SAT solving technique. SAT solving resolves policy conflicts and produces an optimal reconfiguration, based on the provided values, which can be verified by a knowledgeable human user for accuracy and applicability within the context of the enterprise network. Empirical study shows the effectiveness and efficiency of these approaches, and also indicates promising directions for improvements to be explored in future works. Overall, this research comprises an important step toward a more automated security management initiative.

The first part of this dissertation examines the impact of financial development on different countries holdings of U.S securities. The difference between the US weight in the global market capitalization and the US weight in developed and developing countries is tested through a panel data analysis. We find that most countries tend to overweight their US debt portfolio which is strongly related to their financial market development. When holdings of US debts and equity are low, financial market development is high; in developing countries, holding less US equity in their portfolio causes country to get better financial development. In developed countries there is no causation effect; a simple negative relation between financial development and countries holding of US securities is observed and countries tend to hold relatively less US securities through years. The second part of this dissertation examines whether economic conditions, affect carve-outs frequency and returns. This paper investigates the effect of expansion and recession, and industry sectors on carve out issued in the US over 1982 to 2009. We find that the number of carve-outs is higher in expansion than recession. However, the cumulative abnormal returns are higher during recession which is explained by the higher adverse selection during this period. Further, we find that the difference of abnormal returns between expansion and recession is significant and we also observe that high-tech or non-high-tech industries that undertake carve-out have positive higher abnormal return during recession. Therefore, within a same industry sector, carve-out abnormal returns are impacted by the economy cycle. However difference of abnormal returns between industry sector, high-tech and non-high-tech industries, is not significant.

Container Line Supply Chain (CLSC), which transports cargo in containers and accounts for approximately 95 percent of world trade, is a dominant way for world cargo transportation due to its high efficiency. However, the operation of a typical CLSC, which may involve as many as 25 different organizations spreading all over the world, is very complex, and at the same time, it is estimated that only 2 percent of imported containers are physically inspected in most countries. The complexity together with insufficient prevention measures makes CLSC vulnerable to many threats, such as cargo theft, smuggling, stowaway, terrorist activity, piracy, etc. Furthermore, as disruptions caused by a security incident in a certain point along a CLSC may also cause disruptions to other organizations involved in the same CLSC, the consequences of security incidents to a CLSC may be severe. Therefore, security analysis becomes essential to ensure smooth operation of CLSC, and more generally, to ensure smooth development of world economy. The literature review shows that research on CLSC security only began recently, especially after the terrorist attack on September 11th, 2001, and most of the research either focuses on developing policies, standards, regulations, etc. to improve CLSC security from a general view or focuses on discussing specific security issues in CLSC in a descriptive and subjective way. There is a lack of research on analytical security analysis to provide specific, feasible and practical assistance for people in governments, organizations and industries to improve CLSC security. Facing the situation mentioned above, this thesis intends to develop a set of analytical models for security analysis in CLSC to provide practical assistance to people in maintaining and improving CLSC security. In addition, through the development of the models, the thesis also intends to provide some methodologies for general risk/security analysis problems under complex and uncertain environment, and for some general complex decision problems under uncertainty. Specifically, the research conducted in the thesis is mainly aimed to answer the following two questions: how to assess security level of a CLSC in an analytical and rational way, and according to the security assessment result, how to develop balanced countermeasures to improve security level of a CLSC under the constraints of limited resources. For security assessment, factors influencing CLSC security as a whole are identified first and then organized into a general hierarchical model according to the relations among the factors. The general model is then refined for security assessment of a port storage area along a CLSC against cargo theft. Further, according to the characteristics of CLSC security analysis, the belief Rule base Inference Methodology using the Evidential Reasoning approach (RIMER) is selected as the tool to assess CLSC security due to its capabilities in accommodating and handling different forms of information with different kinds of uncertainty involved in both the measurement of factors identified and the measurement of relations among the factors. To build a basis of the application of RIMER, a new process is introduced to generate belief degrees in Belief Rule Bases (BRBs), with the aim of reducing bias and inconsistency in the process of the generation. Based on the results of CLSC security assessment, a novel resource allocation model for security improvement is also proposed within the framework of RIMER to optimally improve CLSC security under the constraints of available resources. In addition, it is reflected from the security assessment process that RIMER has its limitations in dealing with different information aggregation patterns identified in the proposed security assessment model, and in dealing with different kinds of incompleteness in CLSC security assessment. Correspondently, under the framework of RIMER, novel methods are proposed to accommodate and handle different information aggregation patterns, as well as different kinds of incompleteness. To validate the models proposed in the thesis, several case studies are conducted using data collected from different ports in both the UK and China. From a methodological point of view, the ideas, process and models proposed in the thesis regarding BRB generation, optimal resource allocation based on security assessment results, information aggregation pattern identification and handling, incomplete information handling can be applied not only for CLSC security analysis, but also for dealing with other risk and security analysis problems and more generally, some complex decision problems. From a practical point of view, the models proposed in the thesis can help people in governments, organizations, and industries related to CLSC develop best practices to ensure secure operation, assess security levels of organizations involved in a CLSC and security level of the whole CLSC, and allocate limited resources to improve security of organizations in CLSC. The potential beneficiaries of the research may include: governmental organizations, international/regional organizations, industrial organizations, classification societies, consulting companies, companies involved in a CLSC, companies with cargo to be shipped, individual researchers in relevant areas etc.

This study examines the use of leveraged exchange traded funds (LETFs) within a portfolio insurance framework to reduce exposure to downside risk. Investors have learned the importance of mitigating this risk having experienced two “once in a century” events in the last 20 years with the tech crash in the early 2000s and the financial crisis in 2008. Current portfolio insurance strategies are either option based (Leland & Rubinstein, 1976) or constant proportional portfolio insurance (CPPI), (Black & Jones, 1987). The cost of option based strategies can be quite high while a CPPI strategy requires constant rebalancing. This study combines the advantages of each by using LETFs to attain the leverage options provide, while at the same time allowing a greater percentage of the portfolio to be invested in bonds since a position in LETFs relative to a typical market index magnifies equity exposure. Thus, where a standard CPPI strategy may require 50% of the portfolio to be invested in equities, using a 3x LETF only requires approximately 16.7%. Results suggest the use of LETFs within a portfolio insurance framework result in better returns, higher Sharpe, Sortino, Omega, and cumulative prospect values while reducing Value at Risk (VaR) and Excess Shortfall below VaR. This twist on the use of LETFs will be of interest to any investor concerned with mitigating downside risk while allowing participation in increasing markets.

I investigate a simple merger arbitrage strategy with a focus on middle-market companies. I estimate [-1, 1] buy-and-hold abnormal returns (BHARs) and long-run BHARs of prospective middle-market acquirers after they announce an acquisition and test whether [-1, 1] BHARs are predictive of subsequent long-run holding period returns (HPRs) and long-run BHARs. The [-1, 1] BHARs are calculated for 57 acquiring companies, and then separated into two equal-weight portfolios: one of positive [-1, 1] BHARs (referred to as the long portfolio) and one of negative [-1, 1] BHARs (referred to as the short portfolio). I then calculate the HPR and long-run BHARs over the following time horizons: [2, 22], [2, 43], [2, 64], [2, 127], and [2, 253]. I perform a Student’s t-test comparing the means of the HPRs of the two portfolios and find that the long and short [2, 22] and [2, 64] HPRs have statistically different mean returns. Similarly, I perform a Student’s t-test comparing the means of the BHARs of the two portfolios and find that the difference in the means are not statistically significant. I also regress the different long-run BHARs on [-1, 1] BHARs, adjusted [-1, 1] BHARs, and normalized [-1, 1] BHARs. Adjusted [-1, 1] BHARs are adjusted for the effects of known predictive factors found in prior literature such as the type of payment. For example, if the type of payment is cash, 2.40 percentage points of the [-1, 1] BHAR is attributed to the cash payment. Normalized [-1, 1] BHARs divide each [-1, 1] BHAR by each security return’s standard deviation over the following trading days: [-22, -2]. I find [-1, 1] BHARs and adjusted [-1, 1] BHARs of middle-market lack statistically significant effects on long-run BHARs over the [2, 22], [2, 43], [2, 127], and [2, 253] horizons. [-1, 1] BHARs and adjusted [-1, 1] BHARs of middle-market firms have statistically significant effects on [2, 64] BHARs. Therefore, a possible merger arbitrage strategy may exist for predicting BHARs for the [2, 64] horizon. The strategy consists of an investor going long on all acquirers that have a positive [-1, 1] BHAR and short on all acquirers that have a negative [-1, 1] BHAR over the following trading days: [2, 64]. After the [-1, 1] BHARs are normalized, however, the normalized [-1, 1] BHARs are no longer statistically significant when predicting any long-run BHAR. On the whole, I find the Efficient Market Hypothesis – which states that the market efficiently prices the information released into the market after an acquisition announcement – is correct, at least with respect to the information contained in [-1, 1] BHARs.

The explosive growth of ‘accelerators’ in the United States has given entrepreneurs and their startups the opportunity to pursue seed-stage financing. While the specific economic role of accelerators remains unclear, a study comparing the selection of portfolio companies between accelerators and venture capitalists was performed. A difference of means was performed on the responses per question between the collected 19 accelerators’ response and the 100 venture capitalists’ response, recorded from a prior study. It is found that venture capitalists place significantly more weight, than accelerators, on the potential of the startup’s product or service to be proprietary, to enter a high-growth market with little threat of competition within the first 3 years, and to deliver a high financial return within 5 to 10 years. The results also indicate that both accelerators and venture capitalists emphasize different attributes of the entrepreneur and venture team when considering selection.

Many studies have been performed on the short- and long-run abnormal returns to acquirers in acquisition attempts, but the topic of bidding wars is relatively unexplored. This piece performs an in-depth analysis of daily returns to both the public winners and losers in bidding war situations. It provides a counterargument to earlier findings that found that winners in bidding wars performed poorly compared to losers. I also fill in the gap in the analysis of short-term returns to paired winners and losers during and surrounding the bidding war. I find that winners perform significantly better than losers during certain critical periods in the bidding war, and this appears to signal the increased likelihood of the winner’s success. However, in the short-term, the market consistently misjudges the direction of the long-run benefits of the acquisition to the winner.

本論文提出了一個免憑證加密系統的方案，並且將此方案實作出來，使得此方案更具實用性。此方案主要架構為免憑證加密系統，利用此系統的特性消除傳統公開金鑰密碼系統中需要公開金鑰憑證認證的麻煩，也不會產生基於身分認證加密系統的私鑰託管問題，有效的結合了兩項系統的優點，並且提高了這兩種系統的安全性及方便性。本論文的協定中，在基於身分認證加密系統的公鑰部分還加入了階級以及時間戳記的概念，用以限制接收方取得部份私鑰的能力，並且也將接收方的部分公鑰加入其中，來增加部份私鑰的安全性。另外此協定也加入了提早解密金鑰的部分，可讓傳送方在傳出密文後更改解密時間，而不需要重新使用新的公鑰加密資訊，便可提早讓接收方取得相對應的明文資訊。 / In this paper, we propose a new certificateless public key encryption system, and implement it for securing e-mail systems. Certificateless cryptography, which is in contrast to traditional public key crypto-systems, does not require the use of certificates to guarantee the authenticity of public key. It does rely on the use of a trusted third party (TTP) who is in possession of a master key, just like the identity-based public key cryptography. However, certificateless public key crypto-system does not suffer from the key escrow property, whereas, it is a problem in the identity-based public key crypto-systems. Moreover, in our system, we add some new properties like level and time-stamp to limit the ability of receivers and to promote the safety of the system. Time-stamp ensures that the ciphertext cannot be decrypted before the indicated time and a level ensures that only the user with the corresponding identity and level can decrypt the ciphertext. In addition, a new feature is also introduced which is called the time-release encryption. Time-release encryption allows the encrypter to publish a release key so that the ciphertext can be decrypted by the receiver before the time indicated in the time-stamp when necessary.

In 1996, Sloan identified the accruals anomaly, in which the negative relationship between the accruals component of current earnings and subsequent stock returns can be exploited to generate excess returns. One would expect the accruals anomaly to dissipate and ultimately disappear as investors take advantage of the now-public information. However, nearly two decades later, it persists as one of the most prominent and contentious anomalies; its magnitude of current and future excess returns still remain controversial. The main reason for its persistence is that extreme accrual firms possess characteristics that are unappealing to most investors. These characteristics, which include insufficient analyst coverage, high idiosyncratic volatility and the presence of institutional constraints, are generally more pronounced in firms with weak internal controls. This paper finds that the accruals anomaly persists at a higher magnitude in firms with weak internal controls. This higher magnitude of excess returns survives the Fama-French five-factor (2015), the Stambaugh-Yuan four-factor (2017) and the Hou, Xue, and Zhang (2015) q-factor models.

In chapter 1, we examine the nature and scale of the relationship between returns on sector Equity Traded Funds (ETFs) and their volatility. We discuss the source and direction of the effect between returns and risk and whether behavioral biases are prominent among sector ETFs. The study has implications for financial sector practitioners and investors, as it provides more information about the risk in sector ETF and whether that risk differs from that of other investment instruments. To this end, we test three hypotheses based on the relevant literature on volatility and returns: the leverage effect hypothesis, feedback hypothesis, and behavioral biases in assets pricing. We employ two measures of volatility in this chapter; specifically, we use the GARCH (1, 1) model and the Range-based autoregressive model. Chapter 2 presents an examination of the factors that affect payout policy in a frontier market. MSCI classifies the Saudi stock exchange as a large frontier market and proposes to be reclassified as an emerging market by next year. The Saudi market is characterized by the high governmental influence and dominance of individual traders on daily transactions. By studying the 12-year panel data, we assess the effect government, board characteristics, social norms and major shareholder on Saudi firms’ decision to distribute dividends. The government presence and investor taste, especially for Islamic-compliant firms, are discussed. This chapter provides valuable information for investors and practitioners by identifying the factors that should be considered when making finance and investment decisions in frontier markets.