  Previous research employing a conceptual approach with a digital twin has
demonstrated that (noise-based) dynamic watermarking is incapable of providing
unconditional security in smart electrical grid systems. However, the
implementation of digital twins can be prohibitively costly or infeasible due
to limited available data on critical infrastructure. In this study, we first
analyze the spectral properties of dynamic watermarking and its associated
protocol. Subsequently, we present a straightforward attack inspired by the
digital twin method, which extracts and utilizes the grid noises and completely
breaches the security of dynamic watermarking without requiring knowledge of
the private watermarking signal. The attacker can fully expose the grid while
evading detection by the controller. Our findings indicate that in the absence
of secure and authenticated communications, dynamic watermarking offers neither
conditional nor unconditional security. Conversely, when communication lines,
sensors, and communicators are equipped with tamper-resistant and
secure/authenticated links, dynamic watermarking becomes redundant for grid
security.
