Publications Details

PUF Entropy

Cordwell, William R.; Torgerson, Mark D.

This note discusses aspects of fuzzy extraction: in particular, how the interplay between PUF entropy and the revelation of helper data affects the entropy of the underlying secret. We examine the theory behind a scheme by Dodis et alii to develop exact formulas for the entropy of the given seed, given that an adversary knows the helper data. We also give a simple lower bound on the security of the Dodis scheme that is achieved exactly in many instances. By way of several examples, we quantify the amount of entropy that can be lost due to interactions between imperfect PUF implementations and given error correction methods. We repeatedly show that understanding the details of the error correction scheme and the interaction with the PUF response is crucial to being able to estimate the entropy of the system.