Cyber Physical Security Solutions for Pervasive Health Monitoring Systems - E-Healthcare Systems and Wireless Communications - page 160

• Proactivity : The ability to provide privileg-
es to caregivers in response to emergencies
without explicit request.
• Adaptive Risk Management : Being aware
of its environment, CAAC minimizes the
risks associated with voluntarily opening
the system, by making the opening tempo-
rary, for a specific set of caregivers only,
and dynamically varying it over time as
criticalities within the system change

• Safety : As the operation of the CPS has
direct consequence on a physical process,
safety of the process and its users is para-
mount. Safety maybe compromised as a
result of security components of the CPS
interact in an unexpected manner with oth-
ers (secure or non-secure components).
For example, increased latency in deliv-
ering medicine in a PHM-CPS due to the
overhead introduced by the secure com-
munication requirement between the base
station and the actuator. Similarly, adverse
effect on the physical element of the CPS,
due to the operation of the CPS can also be
envisioned.
• Mixed Criticality : CPS can be mixed-crit-
ical systems with both critical (those that
perform critical computations or those that
interact with the physical process) and
non-critical components (Mixed Critical
Systems). Interaction between these two
components has to be carefully considered
in order to ensure the safe operation of
the system. CYPSec solutions for mixed-
critical CPSs which use both critical and
non-critical components to function have
to be aware of this difference and ensure
that security provision does not affect the
operation of the critical aspects of the sys-
tem. One approach for handling the mixed
critical nature is to formally verify the be-
havior of CYPSec solutions under differ-
ent operational conditions of the system.
• Physical/Hybrid Attacks : As CYPSec so-
lutions depend upon the physical process
to enable security, attacks on the physical
process can be potentially used to prevent
the CYPSec solutions from functioning
correctly. For example, CPSs today are
being rapidly deployed using custom hard-
ware platforms. However, given the often
harsh environment of deployment, the
platforms often exhibit transient (soft) er-
rors. Many applications today require “x-

CYPSEC RESEARCH CHALLENGES

It can be seen that there are many advantages to
CYPSec solutions compared to the traditional
security protocols for PHM-CPS. These are
however only preliminary techniques devised
to demonstrate CYPSec's viability. In the long
run several additional research challenges need
to be considered in order to successfully deploy
CYPSec solutions. They are:

• Notion of Time : The close coupling of
CYPSec solutions with the environment
also brings to fore an important character-
istic that traditional security approaches do
not seem to consider - the notion of time.
Traditional computing usually ignores the
notion of time by abstracting the physical
process (Lee, Cyber Physical Systems:
Design Challenges, 2008). Security solu-
tions developed for such computing sys-
tems also follow the same philosophy. The
traditional WCET bounds of software are
therefore not sufficient when physical pro-
cesses are involved. Tools such as static
timing analysis which are used to establish
the WCET bounds already find it difficult
to provide tight execution bounds given the
innovation curve in the hardware (Mueller,
2006). This problem will be exacerbated
now that the dynamics of the physical pro-
cess also has to be considered.