Cyber Physical Security Solutions for Pervasive Health Monitoring Systems - E-Healthcare Systems and Wireless Communications - page 154

Classes of Attacks CPS this has to change as both the attack on and

effect on physical aspect of the system has to be
considered in tandem with the cyber. An important
consequence of this realization is that as with the
traditional cyber security, it becomes imperative
to be able to detect attacks and identify attackers
who mount purely physical or hybrid attacks, this
is a non-trivial task and needs efforts in multiple
channels of operation and not cyber-alone.
In order to put the notion of security of CPSs
in perspective consider the CPS security matrix in
Figure 2. Its two axes represent mode of attack and
domain of effect, respectively. For purely cyber
systems, the mode of attack is cyber and its effect
is on the cyber element. For example, a computer
worm (cyber attack) crashing a system (cyber ef-
fect). Similarly, for a purely physical system, the
mode of attacks is usually physical and its effect
can be felt on the ability of the system to physi-
cally perform its task. For example, a stuffing a
vehicle's tail pipe (physical attack) prevents it
from starting (physical effect). With CPS, given
its tight CP-coupling, we have to consider not only
these but two additional modes of attack where
the domain of effect of not necessarily the same
as the mode of attack.

We classify the types of attacks on CPS into three
categories:

• Cyber-Attacks : These attacks are directed
at the cyber element of the CPS in order
to disrupt, alter or glean information from
its operation. Such attacks can have effect
on not only the cyber but also the physi-
cal element of the system. Example of such
an attack includes disabling of cars by an
intruder hacking into a web-based vehicle
immobilizing system (Poulsen, 2010).
• Physical Attacks : These attacks are direct-
ed at either the cyber and/or physical ele-
ment of the CPS in order to disrupt, alter
or glean information from its operation.
Example of such an attack could anything
from irradiating electronic circuitry (phys-
ical attack on cyber element) in mission
critical applications to cause soft-errors to
physically heating break-pads of vehicles
to reduce their efficiency, increasing stop
distances.
• Hybrid Attacks : These attacks are a combi-
nation of the previous two, where cyber and
physical attacks are mounted in tandem on
the cyber element or both cyber and physi-
cal element of the CPS. Example include
infection of a PHM-CPS actuator with a
malignant update causing side-channel
confidential information leakage and un-
timely actuation and selectively jamming
the channel between the sensors and base
station preventing it from knowing of such
unauthorized actuation potentially causing
serious harm to the physical process (hu-
man body).

Security Requirements

We classify the security requirements of CPS in
terms of its five main elements.

• Sensing Security : As a CPS depends upon
its constituent physical process, the valid-
ity and accuracy of the sensing process has
to be ensured. Sensing Security needs tech-
niques for physical stimuli authentication,
so that any data measured from the physi-
cal process can be trusted.
• Storage Security : Once the data has been
collected and processed it may be required
to be stored over time for future access.
Any tampering of this stored data can lead
to errors in future data processing require-

Traditional computer security work has focused
mainly on the first class of attacks in a limited way
as the consequences on the physical element due
to the cyber attack are rarely considered. With