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Today,
security in one form or another is a requirement for an increasing
number of embedded systems, ranging from low-end systems such as
PDA's(Personal Digital Assistants), wireless handsets, networked
sensors, and smart cards, to high-end systems such as routers, gateways,
firewalls, storage servers, and web servers. Technological advances
that have spurred the development of these electronic systems have
also ushered in seemingly parallel trends in the sophistication
of security attacks. It has been observed that the cost of insecurity
in electronic systems can be very high.
In an increasing number of distributed embedded applications the
individual nodes must communicate with each other over insecure
channels like e.g. the public Internet or via wireless communication
links. Internet connections expose applications to intrusions and
malicious attacks. Unfortunately, security techniques developed
for enterprise and desktop computing might not satisfy embedded
application requirements because of the following reasons which
will be explained in detail later.
1) Cost sensitivity
2) Interactive matters
3) Energy constraints
4) Development environment
2 WHAT IS AN EMBEDDED SYSTEM?
Embedded systems cover a large range of computer systems from ultra
small computer-based devices to large systems monitoring and controlling
complex processes. IEEE has the following definition for embedded
systems:
A computer system that is part of a larger system and performs some
of the requirements of that system; for example, a computer system
used in an aircraft or rapid transit system. (IEEE, 1992).
Most of such embedded systems can also be characterized as real-time
systems, (i.e., systems in which the correctness of the system depends
not only on the logical result of the computations it performs but
also on time factors). Embedded real-time systems contain a computer
as a part of a larger system and interact directly with external
devices. They must usually meet stringent specifications for safety,
reliability, limited hardware capacity etc. The increased complexity
of embedded real-time systems leads to increasing demands with respect
to requirements engineering, high-level design, early error detection,
productivity, integration, verification and maintenance.
In many cases embedded systems are safety or mission critical systems
and hence the demands on reliability, robustness, availability and
other characteristics of dependable systems are important.
The most important requirements of an embedded system are:
> Real-time properties: The real-time system functions are time-related;
a violation of time requirements even of a proper functional response
violates the system functionality.
> Dependability: Dependability is defined as an ability of a
system to deliver service that can justifiably be trusted and an
ability of a system to avoid failures that are more severe and frequent
than is acceptable to the users. The main means to attain dependability
are related to avoidance of faults. Dependability is characterized
by several attributes such as reliability, availability, integrity,
safety, confidentiality and maintainability.
> Resource consumption: Many embedded systems have strong requirements
for low and controlled consumption of different resources. The reasons
may be the size of the systems and/or the demands on lower production
costs.
> Life cycle properties: In general embedded systems are tightly
coupled with their environment and the absence of their services
can have large consequences on the environment. In many domains
the embedded systems have very long life time running round the
clock year after year. During the lifetime of a system several generations
of hardware and software technologies can be used. The long life
systems must be able to cope with these changes introduced either
into the surrounding environment or into the systems themselves.
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