  One of the major challenges about cyber physical systems is how to prevent
cyber attacks to ensure system integrity. There has been a large number of
different types of attacks discussed in the modern control and computer science
communities. In this paper we aim to investigate one special type of attacks in
the discrete-event system framework, where an attacker can arbitrarily alter
sensor readings after intercepting them from a target system in order to trick
a given supervisor to issue control commands improperly, driving the system to
an undesirable state. We first consider the cyber attack problem from an
attacker point of view, and formulate an attack with bounded sensor reading
alterations (ABSRA) problem. We then show that the supremal (or least
restrictive) ABSRA exists and can be synthesized, as long as the plant model
and the supervisor model are regular, i.e., representable by finite-state
automata. Upon the synthesis of the supremal ABSRA, we present a synthesis
algorithm, which ensures that a computed supervisor will be ABSRA-robust ,
i.e., either an ABSRA will be detectable or will not lead the system to an
undesirable state.
