Protocols for Secure Communication in Wireless Sensor Networks

14 Chapter 2. Wireless Sensor Networks and Their Security
minimal requirements. The security mechanisms still work if they are exceeded
by the actual characteristics of a network. However, in such a case other mechanisms
could be more appropriate, i.e. more cost-effective or providing better
security guarantees. For example, if a base station is available, it could act as
a trusted third party and be used for node authentication and key establishment
between nodes. This would allow end-to-end secure communication, which
would be infeasible otherwise.
Computational Resources matchbox to dust
Composition homogeneous
Infrastructure ad hoc
Topology multi-hop
Connectivity connected
Size unlimited
Tamper resistance non-neglibile
Table 2.1: General constraints on considered wireless sensor networks
We have extended the classification scheme by adding a category tamper resistance,
which is highly relevant for the security of a sensor network. If nodes
would be completely open to arbitrary manipulations, speaking of a secure sensor
network would have little meaning. We therefore require a minimum level
of tamper resistance that imposes at least a small, constant cost on an attacker
before he is able to take control of a node. This could mean as little as that
sensor nodes are hidden between rocks on an open field, or as much as them
having a shielding that is hard to penetrate.
In the remainder of this section, we discuss the properties of this model in
detail. For each category, we discuss the impact of possible configurations on
the security of the network. In some cases, using a seemingly more powerful
configuration introduces security risks that are avoided with a simple one. Of
course, one doesn’t always have the choice as the architecture of a sensor network
is governed by its application context. However, one should be aware of
the risks that a certain architecture implies. In many cases, it may be advantageous
to prefer a simple design.
2.2.1 Computational Resources
Sensor networks are demanding with regard to protocol and algorithm design
due to size and energy restrictions. Only a small amount of memory is available
for program code and data, the energy source is limited, and the communication
range is rather small. These factors indicate that algorithms for sensor networks
should be as localized as possible in order to avoid long-distance interaction as