  Given a network with the set of vulnerable actuators (and sensors), the
security index of an actuator equals the minimum number of sensors and
actuators that needs to be compromised so as to conduct a perfectly
undetectable attack using the said actuator. This paper deals with the problem
of computing actuator security indices for discrete-time LTI network systems.
Firstly, we show that, under a structured systems framework, the actuator
security index is generic. Thereafter, we provide graph-theoretic conditions
for computing the structural actuator security index. The said conditions are
in terms of existence of linkings on appropriately-defined directed
(sub)graphs. Based on these conditions, we present an algorithm for computing
the structural index.
