P2P Applications - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 10

The development of WSNs was originally motivated by the military sens-
ing and tracking arena, such as battlefield surveillance. When sensor nodes
are deployed in hostile areas, security becomes extremely important as nodes
are subjected to different kind of threats [Fu et al., 2005, Newsome et al.,
2004,Parno et al., 2005,Wang and Bhargava, 2004,Wood and Stankovic, 2002].
Nodes may be captured and the communications among them may be eaves-
dropped or altered. Therefore, messages transmitted between sensor nodes
must be encrypted using various cryptographic protection schemes to guard
against different types of malicious attacks. Hence, trust establishment is one
of the most critical components to set up a secure communication environment
in a WSN-based information system [Kwok, 2007].
Although many traditional trust establishment schemes have been pro-
posed, a WSN is unique due to its distributed and resource-constrained prop-
erties. Some methods such as using a master key or pairwise private sharing
of keys are proposed [Kwok, 2007], but they are either too insecure or im-
practical [Chan et al., 2005a] for WSNs. Currently, many trust establishment
schemes have been developed for wireless sensor networks [Anderson et al.,
2004,Kwok, 2007]. Among them, key pre-distribution schemes are widely con-
sidered as practicable solutions in WSNs [Chan et al., 2003, Chan and Perrig,
2005, Du et al., 2005, Eschenauer and Gligor, 2002, Kwok, 2007, Liu and Ning,
2003]. A typical key pre-distribution scheme works by having keys distributed
to all nodes prior to deployment. Eschenauer et al. [Eschenauer and Gligor,
2002] pioneered this field of research by proposing a randomized key pre-
distribution scheme, which relies on probabilistic key sharing among nodes
using random graph theory [Erdos and Renyi, 1960].
From a system's point of view, WSNs are often regarded as a kind of Mo-
bile Ad-hoc Network (MANET). In order to make sensor nodes cheaper and
smaller so as to facilitate large scale deployment, heavyweight and computa-
tion intensive programs are not expected to be executed on the tiny sensor
devices. These limitations make the design of trust establishment schemes in
WSNs highly challenging. A brief summary of the constraints is described
below:
1. Energy limitation: Sensor devices are usually small in size and battery-
powered. The limited supply of power restricts the computational and
communication capabilities of sensor nodes. Indeed, an effective energy
conservation scheme is vital for maximizing the lifetime of operation
from a single node to the entire network [Raghunathan et al., 2006].
Nowadays, a typical sensor node can operate for a week (under full
operation) to several months.
2. Memory storage limitation: Due to the small size, sensor nodes are
equipped with limited amount of memory. Apart from storing key ma-
terials, it is still necessary to store the key management program and
many other applications for operation. For instance, a popular sensor