  A physically unclonable function (PUF) is an embedded hardware security
measure that provides protection against counterfeiting. Here we present our
work on using an array of randomly-magnetized micron-sized ferromagnetic bars
(micromagnets) as a PUF. We employ a 4 $\mu$m thick surface layer of
nitrogen-vacancy (NV) centers in diamond to image the magnetic fields from each
micromagnet in the array, after which we extract the magnetic polarity of each
micromagnet using image analysis techniques. After evaluating the randomness of
the micromagnet array PUF and the sensitivity of the NV readout, we conclude by
discussing the possible future enhancements for improved security and magnetic
readout.
