  Nanoscale communication systems operating in Ter-ahertz (THz) band are
anticipated to revolutionise the healthcaresystems of the future. Global
wireless data traffic is undergoinga rapid growth. However, wireless systems,
due to their broad-casting nature, are vulnerable to malicious security
breaches. Inaddition, advances in quantum computing poses a risk to
existingcrypto-based information security. It is of the utmost importanceto
make the THz systems resilient to potential active and passiveattacks which may
lead to devastating consequences, especiallywhen handling sensitive patient
data in healthcare systems. Newstrategies are needed to analyse these malicious
attacks and topropose viable countermeasures. In this manuscript, we presenta
new authentication mechanism for nanoscale communicationsystems operating in
THz band at the physical layer. We assessedan impersonation attack on a THz
system. We propose usingpath loss as a fingerprint to conduct authentication
via two-stephypothesis testing for a transmission device. We used hiddenMarkov
Model (HMM) viterbi algorithm to enhance the outputof hypothesis testing. We
also conducted transmitter identificationusing maximum likelihood and Gaussian
mixture model (GMM)expectation maximization algorithms. Our simulations
showedthat the error probabilities are a decreasing functions of SNR. At 10 dB
with 0.2 false alarm, the detection probability was almostone. We further
observed that HMM out-performs hypothesistesting at low SNR regime (10%
increase in accuracy is recordedat SNR =5 dB) whereas the GMM is useful when
groundtruths are noisy. Our work addresses major security gaps facedby
communication system either through malicious breachesor quantum computing,
enabling new applications of nanoscalesystems for Industry 4.0.
