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Discovery and Evaluation of Finite State Machines in Hardware Security

In the decades since the invention of the integrated circuit (IC), IC's have become ubiquitous, complex, and networked. High transistor density and the low cost of production at scale have made it economically feasible to use complex custom IC's in almost any engineering application. While IC's provide a powerful tool for solving many engineering problems, the low cost comes from outsourcing production and reusing existing design components. Both of these dependencies introduce security risk; unwanted functionality may be inserted either from opaque third party libraries used in a design or by any outside vendor involved in the fabrication process. As it is far easier to verify that specified functionality works as intended than to discover unwanted functionality, verifying that a design has not been tampered with is an important, difficult problem. In stateful designs, Finite State Machines (FSM's) choreograph the operation of the design. With knowledge of the primary inputs and the current state, an FSM instructs other subsystems what to do next. Given this central role, an FSM is an obvious target for malicious exploitation. A bad actor can add states to an FSM that may only be entered via a non-obvious sequence of inputs; these states may then leak information via a side channel, or corrupt operation of the device in a denial of service attack. Such exploitation can be avoided both proactively and reactively. This dissertation introduces methods for discovering, extracting, modifying, and analyzing FSM's in post-compilation netlists. Such netlists may be acquired either in house directly after a design is compiled, or recovered by microscopy techniques post-fabrication. This dissertation introduces several methods applicable to the problem. In order to study FSM's in a netlist, the FSM's must first be located. One method to find FSM's is to search for the control signals which drive it. A proposed algorithm for discovering control signals, RELIC-FUN, provides more accurate results than other algorithms on specific designs. Once an FSM is discovered, state transition enumeration is key to comparing the FSM's behavior to the original design. This dissertation introduces two new tools, RECUT and REFSM-SAT, which provide significantly better performance than existing enumeration algorithms. Noting that FSM's, both structurally and semantically, are graph theoretical constructs, a new graphical environment, NetViz, is introduced. NetViz is an environment for hardware security which allows chaining of analysis algorithms and graphical display of, and interaction with, analysis results. Finally, an existing logic locking algorithm, SANSCrypt, is shown to be insecure due to structural FSM analysis techniques.
Date01 January 2023
CreatorsGeist, James
Source SetsUniversity of Central Florida
Detected LanguageEnglish
SourceElectronic Theses and Dissertations, 2020-

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