  With growing security threats to the evolving wireless systems, protecting
user privacy becomes progressively challenging. Even if the transmitted
information is encrypted and the potential wiretap channel is physically
limited (e.g. through information-theoretic security approaches), the raw data
itself, such as transmitter position and transmission pattern, could expose
confidential information. In this context, covert communication that intends to
hide the existence of transmission from an observant adversary by exploiting
the physical characteristics of the wireless medium has been actively
investigated. However, existing covertness techniques ineluctably consume
additional resources such as bandwidth and energy, which burdens system
deployment. In view of this concern, we propose an intelligent reflecting
surface (IRS)-based approach to enhance communication covertness. The core idea
is making use of a smartly controlled metasurface to reshape undesirable
propagation conditions which could divulge secret messages. To facilitate the
understanding of the proposed idea, we first provide an overview of the
state-of-the-art covert communication techniques. Then, we introduce the
fundamentals of IRS and elaborate on how an IRS can be integrated to benefit
communication covertness. We also demonstrate a case study of the joint
configuration of the IRS and the legitimate transmitter, which is of pivotal
importance in designing an IRS-enhanced covert communication system. Finally,
we shed light on some open research directions.

Networking and Internet Architecture;Signal Processing