  We apply formal methods to lay and streamline theoretical foundations to
reason about Cyber-Physical Systems (CPSs) and physics-based attacks, i.e.,
attacks targeting physical devices. We focus on a formal treatment of both
integrity and denial of service attacks to sensors and actuators of CPSs, and
on the timing aspects of these attacks. Our contributions are fourfold. (1)~We
define a hybrid process calculus to model both CPSs and physics-based attacks.
(2)~We formalise a threat model that specifies MITM attacks that can manipulate
sensor readings or control commands in order to drive a CPS into an undesired
state, and we provide the means to assess attack tolerance/vulnerability with
respect to a given attack. (3)~We formalise how to estimate the impact of a
successful attack on a CPS and investigate possible quantifications of the
success chances of an attack. (4)~We illustrate our definitions and results by
formalising a non-trivial running example in Uppaal SMC, the statistical
extension of the Uppaal model checker; we use Uppaal SMC as an automatic tool
for carrying out a static security analysis of our running example in isolation
and when exposed to three different physics-based attacks with different
impacts.
