Protocols for Secure Communication in Wireless Sensor Networks

22 Chapter 2. Wireless Sensor Networks and Their Security
the development of wireless communication for hand-held and portable computers.
These interfaces (e.g. IEEE 802.11, Bluetooth, ZigBee) also support
ad hoc networking, i.e. devices are able to connect to each other without a
supporting infrastructure. Although there are sensor network designs that rely
on base station support, in this work we concentrate on infrastructure-less architectures.
Here, we review the most important related network types. Peerto-peer
overlay networks are included in the presentation since they follow the
same principle as wireless ad hoc networks and provide their own supporting
services, although they are implemented on top of the Internet infrastructure.
2.3.1 Ad Hoc Networks
An important class of networks that share many similarities with sensor networks
are subsumed under the notion of ad hoc networks. As sensor networks,
ad hoc networks usually operate without infrastructural support. This
means that routing, security, and other services must be provided collaboratively.
However, there are significant differences between the network types
since their application cases are quite different. In contrast to sensor networks,
ad hoc networks are usually comprised of heterogeneous devices which are
specialized to different tasks and are under the control of different users. Also,
from a user’s point of view, they operate on a different level. Ad hoc networks
often fulfill user-controlled tasks, while sensor networks operate more
autonomously. However, sensor networks incorporate features of ad hoc networks
and vice versa, and the boundaries between both network types are
blurry. The main differences with regard to security are summarized as follows:
• Fairness Ad hoc networks are not operated nor owned by a single entity.
Usually, every participating device is associated with a different user on
whose behalf it operates. As a consequence, fairness is not easily maintained
when part of the users act selfishly, trying to exploit other users’ resources
without offering their own. Also, it is not easy to decide whether
it is advantageous for the network to admit a new device. These problems
are part of normal operation in ad hoc networks. In sensor networks,
similar problems occur only when a network is under attack.
• Group communication Often, some devices organized in an ad hoc network
need to form a closed group. This usually means they have to negotiate
a common group key in order to exclude occasional (or malicious)
passers-by from their communication. This is not common in sensor networks,
as a sensor network as a whole can be considered a closed group.