P2P Applications - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 11

device, namely Berkeley MICA2 Mote [Crossbox Technology, 2008], has
only 128 KBytes program memory.
3. Vulnerability to attacks: As WSNs are usually deployed in hostile envi-
ronments, nodes are exposed to physical attacks by the potential ad-
versaries. In most practical scenarios, it is possible for the attackers to
compromise a node physically and take full control of the node without
being detected. This is often called “node capture attack.”
4. Lack of post-deployment knowledge: Without deployment knowledge,
such as location information, the distribution of sensor nodes may follow
a randomly scattered pattern. Therefore, the network topology is hard
to be determined a priori so that the optimization of trust establishment
is very di cult.
In general, the major barrier for enhancing security in WSNs is their
weak computational and communication capabilities. These inherent prop-
erties make traditional cryptographic protocols, such as Di e-Hellman key
agreement [Di e and Hellman, 1976] and RSA signature [Rivest et al., 1978]
techniques, undesirable when compared to the symmetric key approaches [Per-
rig et al., 2002] in terms of energy and computational requirements. These
public key schemes are either too computation intensive or too large to fit
in the resource-constrained sensor nodes. We discuss more on sensor network
trust establishment in Chapter 6.
2.3 File Sharing
File sharing is probably the real starter of the P2P computing arena. The
idea is very simple—a user wants to find a certain file (e.g., a music MP3 file)
and downloads it as soon as possible. Many users share the same objective
and therefore there is a large aggregate pool of files for mutual sharing. Thus,
in essence, there are four aspects in a file sharing P2P application:
Search. The file sharing system has to support a convenient and accurate
file search user-interface.
Peer Selection. The file sharing system has to support an e cient peer-
selection mechanism so as to minimize the download time.
Connection. Peers should be able to set up more or less stable data transfer
connections so that file data packets can be exchanged e ciently.
Performance. The key performance metrics are download time and avail-
ability.