**2. Wireless sensor network**

Sensor nodes are electronic devices that have as main components units of storage, processing, sensing and transmission. Usually, these devices have low computational power, nevertheless play an important role in ubiquitous computing, because they have function of collecting data in a given environment, passing them through a wireless network. According to [4] WSNs can be seen as a special type of MANET (Mobile Ad hoc NETwork) that tend to run a collaborative basis where the elements (sensor nodes) provide data that are processed (or consumed) by special nodes called sink nodes.

The operation area of a WSN is very large and can be used in environmental monitoring, control temperature and humidity, vehicle traffic control, monitoring of human body organs, among others. Figure 1 illustrates a scenario of WSNs in the medical area where patients that are being monitored can be in a hospital, at home, or anywhere else performing an activity routine. Sensing data are sent to health professionals through the Internet.

**Figure 1.** Scenario of Wireless Sensor Network [5]

Some application areas of WSNs require security in the information transport, such as the scenario illustrated by figure 1, where sensor nodes implanted in the human body reporting to a hospital. According to [5] in the health field, authentication and access control are the main challenges of a mobile dynamic network topology with limited resources. Besides medical area, several other areas also need security in their transmissions as: industry, asset security and military applications. A U.S. security agency called DARPA2 has been developed numerous studies involving security in WSNs for military purposes.
