Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Understanding of Adversary Behavior and Security Threats in Public Key Infrastructures(2020) Kim, Doowon; Dumitras, Tudor; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)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 erroneous revocations (e.g., wrong effective revocation date setting) can pose additional security threats to clients who execute binaries because the revocations become ineffective. Such security threats stem from an inherent challenge of setting an effective revocation date in the Code-Signing PKI and CAs' misunderstanding of the PKI. These findings help Anti-Virus companies and a CA fix their flaws.Item Quality and Inequity in Digital Security Education(2019) Redmiles, Elissa M; Mazurek, Michelle L; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Few users have a formal, authoritative introduction to digital security. Rather, digital security skills are often learned haphazardly, as users filter through an overwhelming quantity of security education from a multitude of sources, hoping they're implementing the right set of behaviors that will keep them safe. In this thesis, I use computational, interview, and survey methods to investigate how users learn digital security behaviors, how security education impacts security outcomes, and how inequity in security education can create a digital divide. As a first step toward remedying this divide, I conduct a large-scale measurement of the quality of the digital security education content (i.e., security advice) that is available to users through one of their most cited sources of education: the Internet. The results of this evaluation suggest a security education ecosystem in crisis: security experts are unable or unwilling to narrow down which behaviors are most important for users' security, leaving end-users -- especially those with the least resources -- to attempt to implement the hundreds of security behaviors advised by educational materials.Item Evaluating Host Intrusion Detection Systems(2007-11-28) Molina, Jesus; Cukier, Michel; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Host Intrusion Detection Systems (HIDSs) are critical tools needed to provide in-depth security to computer systems. Quantitative metrics for HIDSs are necessary for comparing HIDSs or determining the optimal operational point of a HIDS. While HIDSs and Network Intrusion Detection Systems (NIDSs) greatly differ, similar evaluations have been performed on both types of IDSs by assessing metrics associated with the classification algorithm (e.g., true positives, false positives). This dissertation motivates the necessity of additional characteristics to better describe the performance and effectiveness of HIDSs. The proposed additional characteristics are the ability to collect data where an attack manifests (visibility), the ability of the HIDS to resist attacks in the event of an intrusion (attack resiliency), the ability to timely detect attacks (efficiency), and the ability of the HIDS to avoid interfering with the normal functioning of the system under supervision (transparency). For each characteristic, we propose corresponding quantitative evaluation metrics. To measure the effect of visibility on the detection of attacks, we introduce the probability of attack manifestation and metrics related to data quality (i.e., relevance of the data regarding the attack to be detected). The metrics were applied empirically to evaluate filesystem data, which is the data source for many HIDSs. To evaluate attack resiliency we introduce the probability of subversion, which we estimate by measuring the isolation between the HIDS and the system under supervision. Additionally, we provide methods to evaluate time delays for efficiency, and performance overhead for transparency. The proposed evaluation methods are then applied to compare two HIDSs. Finally, we show how to integrate the proposed measurements into a cost framework. First, mapping functions are established to link operational costs of the HIDS with the metrics proposed for efficiency and transparency. Then we show how the number of attacks detected by the HIDS not only depends on detection accuracy, but also on the evaluation results of visibility and attack resiliency.