Transient Response of Hybrid Boolean Networks as Physical Unclonable Functions
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Physical unclonable functions are devices that exploit small, random variations in a manufacturing process to create unique and stable identifying behavior. These devices have found a variety of security applications, from intellectual property protection to secret key generation. In this work, we propose a framework for constructing physical unclonable functions from hybrid Boolean networks realized on field-programmable gate arrays. These networks are highly sensitive to propagation delay and other non-ideal behavior introduced by the silicon fabrication process and thus provide a source of entropy generation that is amplified by chaotic dynamics. We leverage this behavior in the context of physical unclonable functions by setting the initial state of the network to a specified Boolean string (the challenge) and measuring the state of the network some time later (the response). Due to the non-equilibrium nature of the proposed protocol, challenge-response pairs can be collected at a rapid rate of up to 100 MHz. Moreover, we collect multiple response bits per challenge, in contrast to many proposed techniques. We find a high degree of reliability and uniqueness from the proposed devices, respectively characterized by μ_intra=6.68% and μ_inter=47.25% for a moderately sized device. We estimate the available entropy in devices of varying size with several statistical tests and find that the entropy scales exponentially with the size of the network.
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