Browsing by Author "Dr. S. Purushothaman Iyer, Committee Chair"

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A Conformance Review Strategy for Regulating Safety-Critical Software.
(2006-09-24) Jetley, Raoul Praful; Dr. S. Purushothaman Iyer, Committee Chair; Dr. Laurie Williams, Committee Member; Dr. Matthias Stallmann, Committee Member; Dr. Alexander Dean, Committee Member
Safety is an important concern for software used in life-critical systems such as air transport, nuclear power and medical devices. The critical nature of these systems necessitates that the software used therein be reliable and free of errors. It becomes imperative, therefore, to have a stringent review process in place to ascertain the correctness of the software and to ensure that it meets all requirements and standards. Regulatory agencies encourage the use of formal methods based techniques in the development of safety critical software. However, most manufacturers are reluctant to use these techniques, citing them as too complex and time consuming. As a result, (potentially life-threatening) errors are often not discovered until the software is already on the market. When such an error is eventually discovered, it becomes essential to trace the failure to its exact source in the implementation and to assure that the error correction restores the overall safety and effectiveness of the device. In this dissertation, we present how efficient premarket and postmarket reviews of designs and implementations can be carried out using formal methods based techniques, to enable the process of reviewing software in safety-critical devices. To facilitate premarket conformance reviews, we introduce the notion of usage models -- standardized formal models that serve as design templates. We present an approach to conformance checking of safety-critical software through formal verification and automated test case sequences derived from these standardized models. To provide for efficient postmarket reviews, we establish a methodology based on integrating program slicing with model abstraction to trace software failures to their root cause. We formalize this methodology by presenting an iterative algorithm for abstraction-driven slicing and realize this algorithm through the implementation of the CAdS -- a forensic analysis tool for C programs. We provide case studies involving typical medical device software to illustrate the various concepts involved and present results from these studies to gauge the effectiveness of our proposed approach.
Improving Software Comprehension In Regulating Safety-Critical Systems
(2008-06-06) Zhang, Yi; Dr. Tao Xie, Committee Member; Dr. Laurie Williams, Committee Member; Dr. Matthias Stallmann, Committee Member; Dr. S. Purushothaman Iyer, Committee Chair
Improving Webs of Trust Through Predetermined Graph Structure
(2006-05-19) Kohler, Damon; Dr. Ting Yu, Committee Member; Dr. Khaled Harfoush, Committee Member; Dr. S. Purushothaman Iyer, Committee Chair
Parallel computing topographies and webs of trust (WoTs) share many of the same goals: minimum distance routing, an abundance of quickly determinable parallel paths, uniform structure, and fault tolerance. The structure of WoTs follows that of the social interaction between members of the WoT and are thus appropriately modeled by random graphs. However, it is the random structure of WoTs that contributes significantly to their insecurity. When using a WoT in a small, closed or secret society, such as a darknet, the random structure can be replaced with certain orderly structures, like the hypercube, which are commonly used for parallel computing networks. Imposing structure on the WoT, at its inception and throughout its lifetime, improves both security and the efficiency. To this end, I define the hypercube of trust (HoT).