Upper Bounds on The Min-Entropy of RO Sum, Arbiter, Feed-Forward Arbiter, and S-ArbRO PUFs

The focus and novelty of this work is the derivation of tight upper bounds on the min-entropy of several physically unclonable funcions (PUFs), i.e., Ring Oscillator Sum, Arbiter, Feed-Forward Arbiter, and S-ArbRO PUFs. This constrains their usability for the fuzzy extraction of a secret key, as an alternative to storing keys in non-volatile memory. For example, it is shown that an ideal Arbiter PUF with 64 stages cannot provide more than 197 bits of min-entropy. At Financial Cryptography 2012, Van Herrewege et al. assume that 1785 bits of min-entropy can be extracted, which renders their 128-bit key generator instantly insecure. We also derive upper bounds that comply with nonideal PUFs, attributed to, e.g., manufacturing in silicon. As a side contribution hereby, we refute the claim that S-ArbRO PUFs are highly resistant against machine learning.