  Hybrid systems are integrations of discrete computation and continuous
physical evolution. The physical components of such systems introduce safety
requirements, the achievement of which asks for the correct monitoring and
control from the discrete controllers. However, due to denial-of-service
security attack, the expected information from the controllers is not received
and as a consequence the physical systems may fail to behave as expected. This
paper proposes a formal framework for expressing denial-of-service security
attack in hybrid systems. As a virtue, a physical system is able to plan for
reasonable behavior in case the ideal control fails due to unreliable
communication, in such a way that the safety of the system upon
denial-of-service is still guaranteed. In the context of the modeling language,
we develop an inference system for verifying safety of hybrid systems, without
putting any assumptions on how the environments behave. Based on the inference
system, we implement an interactive theorem prover and have applied it to check
an example taken from train control system.
