  Advances in computing have resulted in an emerging need for multi-factor
authentication using an amalgamation of cryptographic and physical keys. This
letter presents a novel authentication approach using a combination of signal
and antenna activation sequences, and most importantly, perturbed antenna array
geometries. Possible degrees of freedom in perturbing antenna array geometries
affected physical properties and their detection are presented. Channel
estimation for the plurality of validly authorized arrays is discussed.
Accuracy is investigated as a function of signal-to-noise ratio (SNR) and
number of authorized arrays. It is observed that the proposed authentication
scheme can provide 1% false authentication rate at 10 dB SNR, while it is
achieving less than 1% missed authentication rates.
