Theses and Dissertations from UMD
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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
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Item A New Paradigm for Practical Maliciously Secure Multi-Party Computation(2018) Wang, Xiao; Katz, Jonathan; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Secure Multi-Party Computation (MPC) protocols allow a group of mutually distrusting users to compute a function jointly on their inputs without revealing any information beyond the output. For many years, implementations of MPC protocols have targeted security against semi-honest adversaries, i.e., attackers are assumed to execute the protocol honestly but try to learn private information after the fact. Protocols secure against stronger and more realistic malicious adversaries, who could behave arbitrarily during the protocol execution, were known to exist but were much less efficient. This thesis introduces a new paradigm to construct extremely efficient MPC protocols with malicious security. In particular, this thesis consists of three major contributions. 1. We introduce the authenticated garbling framework, and present an efficient concrete instantiation of the protocol. The resulting protocol partially closes the gap between semi-honest and malicious MPC protocols asymptotically; the implementation of the protocol represents the state-of-the-art system for malicious two-party computation. 2. We discuss how to apply authenticated garbling to the multi-party setting, where all-but-one parties can be corrupted by the adversary. The resulting protocol improves upon the best previous constant-round protocol by orders of magnitude. We also present a system that, for the first time, enables MPC executions among hundreds of parties, distributed globally. 3. We present a series of optimizations to two-party authenticated garbling by interpreting authenticated garbling in a new way. The improved malicious protocol has essentially the same concrete efficiency as the best semi-honest protocol in the preprocessing model. 4. We develop these protocols in EMP-toolkit, a practical and efficient MPC tool that can be used to build new protocols and to develop applications using our existing protocols.Item Functions of the Tobacco mosaic virus helicase domain: regulating formation of the virus replication complex and altering the activity of a host-encoded transcription factor(2008-04-23) Wang, Xiao; Culver, James N; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tobacco mosaic virus (TMV)-encoded 126-kDa and 183-kDa replicases are multidomain and multifunctional proteins. The helicase domain shared by both replicases has been shown to perform multiple tasks during the virus life cycle. In vitro structural and functional analyses demonstrated that monomers and dimers of the TMV helicase domain were the active forms for ATP hydrolysis. However, self-interaction of the helicase polypeptides resulted in the formation of higher-order structures that likely serve as structural scaffolds for the assembly of virus replication complexes (VRCs). Mutagenesis studies of the TMV helicase motifs showed that conserved amino acid residues played important roles in protein ATPase and/or RNA binding activities. A close correlation between ATPase activity of the helicase domain and assembly of wild-type VRC-like vesicles by the 126-kDa replicase further suggests that ATPase activity of the TMV helicase domain may modulate proper VRC assembly. In addition to helicase self-interaction, a novel virus-host interaction involving ATAF2, a NAC domain transcription factor was identified. Members within the NAC domain family are involved in plant developmental processes and stress/defense responses. In this study, transgenic plants overexpressing ATAF2 showed a strong developmental phenotype. Inoculation of TMV in these transgenic plants resulted in reduced virus accumulations. Additionally, transcriptional induction of ATAF2 occurred in response to TMV infection and salicylic acid treatment. Combined, these results suggest that ATAF2 is involved in a host defense response. One interesting finding was that in susceptible hosts, virus-directed induction of ATAF2 and PR1, a well-defined pathogenesis-related (PR) marker gene for host defense system, occurred only in locally-infected but not in systemically-infected tissues. Dynamic changes in the expression of host defense genes suggest that viruses have evolved certain mechanisms to actively modulate host gene expression. Interaction between the TMV helicase domain and ATAF2 may provide one way to suppress the ATAF2-mediated host defense signaling pathway. Combined these studies investigated the importance of the TMV helicase domain in VRC formation and in manipulating the host defense system. The results confirmed the functional versatility of the TMV helicase domain in establishing a successful virus life cycle.