Optical physical unclonable keys are currently considered to be rather promising candidates for the development of entity authentication protocols, which offer security against both classical and quantum adversaries. In this work we investigate the robustness of a continuous-variable protocol, which relies on the scattering of coherent states of light from the key, against three different types of intercept-resend emulation attacks. The performance of the protocol is analysed for a broad range of physical parameters, and our results are compared to existing security bounds.