A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item SYMMETRIC-KEY CRYPTOGRAPHY AND QUERY COMPLEXITY IN THE QUANTUM WORLD(2024) Bai, Chen; Katz, Jonathan; Alagic, Gorjan; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quantum computers are likely to have a significant impact on cryptography. Many commonly used cryptosystems will be completely broken once large quantum computers are available. Since quantum computers can solve the factoring problem in polynomial time, the security of RSA would not hold against quantum computers. For symmetric-key cryptosystems, the primary quantum attack is key recovery via Grover search, which provides a quadratic speedup. One way to address this is to double the key length. However, recent results have shown that doubling the key length may not be sufficient in all cases. Therefore, it is crucial to understand the security of various symmetric-key constructions against quantum attackers. In this thesis, we give the first proof of post-quantum security for certain symmetric primitives. We begin with a fundamental block cipher, the Even-Mansour cipher, and the tweakable Even-Mansour construction. Our research shows that both are secure in a realistic quantum attack model. For example, we prove that 2^{n/3} quantum queries are necessary to break the Even-Mansour cipher. We also consider the practical applications that our work implies. Using our framework, we derive post-quantum security proofs for three concrete symmetric-key schemes: Elephant (an Authenticated Encryption (AE) finalist of NIST’s lightweight cryptography standardization effort), Chaskey (an ISO-standardized Message Authentication Code), and Minalpher (an AE second-round candidate of the CAESAR competition). In addition, we consider the two-sided permutation inversion problem in the quantum query model. In this problem, given an image y and quantum oracle access to a permutation P (and its inverse oracle), the goal is to find its pre-image x such that P(x)=y. We prove an optimal lower bound \Omega(\sqrt{2^n}) for this problem against an adaptive quantum adversary. Moreover, we apply our lower bound above to show that a natural encryption scheme constructed from random permutations is secure against quantum attacks.Item A Complexity-Based Approach to Intra-Organizational Team Selection(2013) Hsu, Shu-Chien; Cui, Qingbin; Skibniewski, Miroslaw; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Early studies recognized the significance of team's work capacity and suggested the selection of team members based on individual skills and performance in alignment with task characteristics. The equitable team selection method, for example, assigns people to different tasks with even skill distributions for the best overall performance. Recent advancement in organization science also identifies the importance of contextual skills. However, work teams are complex adaptive systems with interdependence between workers and social environment, and exhibit surprising, nonlinear behavior. Optimizing individual stages without taking organizational complexity into account is unlikely to yield a high performing new combination of teams. The objectives of this study can be stated as: a) Utilizing complex system theory to better understand the processes of team selection including forming teams with considering worker's interdependence and replacing the unsuitable members through a time frame; b) Comparing different team selection methods, including random selection, equity method, using knowledge of interdependence in different economic conditions through simulation; c) Comparing different policies of replacing members of teams. This study utilizes a computational model to understand the complexity of project team selection and to examine how diversity of capability and interdependence between workers to effect team performance in different economic conditions. The NK model, a widely used theory for complex systems is utilized here to illustrate the worker's interdependence and fed into an Agent-Based Model. This study uses a small design firm as a case implementation to examine the performance of a variety of team selection approaches and replacement policies. Project data, task assignment, and individual and team performance information were collected for the period of 2009-2011. The simulation results show that while the equity selection method can increase the diversity of capabilities of teams, the net performance is often worse than optimizing worker interdependencies. This study suggests that managers should protect their higher-performing workers with minimal interdependence disruption when they considered team selection. Thus taking the advantages and disadvantages of all three policies into account, transferring low contributors or least supported members are recommended to be enacted before hiring new workers to avoid this last policy's especially large additional costs.Item Characterization of gradient estimators for stochastic activity networks(2011) Manterola, Renato Mauricio; Fu, Michael C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis aims to characterize the statistical properties of Monte Carlo simulation-based gradient estimation techniques for performance measures in stochastic activity networks (SANs) using the estimators' variance as the comparison criterion. When analyzing SANs, both performance measures and their sensitivities (gradient, Hessian) are important. This thesis focuses on analyzing three direct gradient estimation techniques: infinitesimal perturbation analysis, the score function or likelihood ratio method, and weak derivatives. To investigate how statistical properties of the different gradient estimation techniques depend on characteristics of the SAN, we carry out both theoretical analyses and numerical experiments. The objective of these studies is to provide guidelines for selecting which technique to use for particular classes of SANs based on features such as complexity, size, shape and interconnectivity. The results reveal that a specific weak derivatives-based method with common random numbers outperforms the other direct techniques in nearly every network configuration tested.