31-07-2013, 03:38 PM
SECURITY SOLUTIONS FOR CYBER-PHYSICAL SYSTEMS
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ABSTRACT
Cyber-Physical Systems (CPS) are sensing, communication and processing platforms, deeply embedded
in physical processes and provide real-time monitoring and actuation services. Such systems are becoming
increasing common in enabling many of the pervasive computing technologies that are becoming available
today such as, smart-homes, smart-vehicles, pervasive health monitoring systems. Given the automation that
CPSs introduce in managing physical processes, and the detail of information available to them for carrying
out their tasks, securing them is of prime importance.
In this dissertation, a novel security paradigm for CPSs is proposed, called Cyber-Physical Security
(CYPSec). CYPSec solutions are unique in that they take they take into account the environmentally-coupled
nature of CPSs in enabling security solutions. This dissertation explores CYPSec solutions for two diverse
but related problems. The first is a usable and secure key agreement protocol called Physiological Signal
based Key Agreement (PSKA), which combines signal processing and cryptographic primitives to enable
automated key agreement between sensors in a Body Area Network (BAN) without any form of external user
involvement. It uses specific physiological stimuli-based features (Photoplethsymogram and Electrocardio-
gram) from the human body for its task.
INTRODUCTION
Our society has been facing considerable challenges in recent years. Increasing traffic congestion,
energy scarcity, rising medical costs, climate change and many other issues have taken a turn for the worse and
need urgent attention. Technology can play a major role in alleviating these problems through the development
of smart-infrastructures.
The idea behind smart-infrastructures is to incorporate intelligence in everyday objects/services in order
to improve the efficiency of performing certain rudimentary but crucial tasks. For example, a smart coffee pot
can detect the decrease in temperature of its contents (coffee) and alert the user so that the coffee does not have
to be unnecessarily re-heated; thereby saving energy. This trend of developing intelligent systems has already
begun. A recent survey found that a typical household has at least 100 microprocessors while a typical new
model car has more than 100 of its own [12]. In fact, most of microprocessors are now embedded in systems
which are not computers [65]. The crucial technology that has made this leap possible are miniature sensing,
communication and processing platforms which can be embedded as a part of larger systems/processes for
providing real-time monitoring and feedback control services [40]. Such platforms, deeply embedded in
physical processes, are called cyber-physical systems [120].
Need for CPS Security
CPSs, given their environmental coupling, diverse capabilities and lack of isolation are often used for
monitoring and controlling mission critical, processes. Therefore any security compromise of the CPS can
have profound consequences. Further, the mission critical nature also makes them more susceptible to tar-
geted attacks. The case in point is the pace-makers CPSs which have been targeted to not only reveal a
patient’s electrocardiogram (EKG) data but also to actuate an untimely shock [28]. Further, CPSs have the
ability to monitor the physical process they are embedded in. This makes them privy to detailed and often
sensitive information about the process. If this information is available to malicious entities, it can be ex-
ploited leading to loss of privacy, abuse and discrimination. For example, unauthorized knowledge of the
electricity consumption of a neighborhood from a power-management CPS in the wrong hands can result in
socket bombing attacks on households perceived to be using excessive electricity. Finally, CPSs have the
ability to actuate changes to the environment they are a part of. Allowing unauthorized parties to actuate
untimely changes to the environment can cause harm to the process itself.
Security Requirements
Given the recent trend toward complex and open design, use of completely-off-the-shelf (COTS) com-
ponents and interconnection with existing insecure global communication infrastructure such as the Internet,
security for CPSs has become very important. It can be seen that CPSs are expected to perform diverse set
of operations not just directed toward modifying the physical process but also to change its own behavior as
well. The workflow and the aforementioned characteristics of CPS illustrate many of the principal security
requirements of CPSs, which any security architecture for CPSs should be designed to meet:
Sensing Security: As CPSs are closely related to the physical process they are embedded in, the validity
and accuracy of the sensing process has to be ensured. Sensing Security needs techniques for physical stimuli
authentication, so that any data measured from the physical process can be trusted.
Securing Information Access in Smart-Infrastructures
Importance of Problem: Smart-infrastructures are becoming increasingly common with the embedding
of computational capabilities into mundane entities surrounding us. Such an infrastructure has the ability to
monitor itself and its users and provide context-aware information and services to them. Applications such as
the active spaces [112] and pervasive health monitoring systems [113] [133] [129] are examples of this trend.
Smart-infrastructures due to their “self-aware” nature can be used to detect, provide useful and real-time infor-
mation about the state of such emergencies to the planners and relief-workers and facilitate response, thereby
improving the chances of saving lives and property. Given the amount of sensitive information available in
such systems, in order to prevent a malicious entity from accessing information or services from such a system
in an unauthorized manner, access control schemes are used. However, during emergencies, traditional access
control models are disabled to enable emergency management. Such an approach is ill-advised as it allows
anyone to simulate an emergency and get open access to it. Therefore an access control model is needed
specifically designed for smart-infrastructures, that not only has the ability to control access to patient data
in normal situations, but also dynamically adapt its behavior to handle critical/emergency situations in an
effective manner.
BACKGROUND
In this chapter, we present some general concepts and definitions pertaining to the notion of security
which we use throughout the dissertation. Though the notion of security has many connotations, for the pur-
poses of this work, we define it as preventing unauthorized entities from viewing or modifying data generated
within a system. We use the term system (in this chapter alone) in a generic sense to mean a computing system
which takes an input, processes it and provides an output. We begin this chapter by defining the requirements
of security, the potential attack vectors, the approach to addressing them and how CYPSec can be used in this
enabling these approaches.