  This paper investigates the performance of physical layer security (PLS) in
fluid antenna-aided communication systems under arbitrary correlated fading
channels. In particular, it is considered that a single fixed-antenna
transmitter aims to send confidential information to a legitimate receiver
equipped with a planar fluid antenna system (FAS), while an eavesdropper, also
taking advantage of a planar FAS, attempts to decode the desired message. For
this scenario, we first present analytical expressions of the equivalent
channel distributions at the legitimate user and eavesdropper by using copula,
so that the obtained analytical results are valid for any arbitrarily
correlated fading distributions. Then, with the help of Gauss-Laguerre
quadrature, we derive compact analytical expressions for the average secrecy
capacity (ASC), the secrecy outage probability (SOP), and the secrecy energy
efficiency (SEE) for the FAS wiretap channel. Moreover, for exemplary purposes,
we also obtain the compact expression of ASC, SOP, and SEE by utilizing the
Gaussian copula under correlated Rayleigh fading channels as a special case.
Eventually, numerical results indicate that applying the fluid antenna with
only one active port to PLS can guarantee more secure and reliable
transmission, when compared to traditional antenna systems (TAS) exploiting
maximal ratio combining (MRC).
