**2.4. Defense mechanisms**

Different types of WSN applications require different security requirements. In an environment of temperature monitoring, where researchers collect data for research, it may be that safety requirements are not very important, but the monitoring of radiation near a nuclear power plant requires authenticity assurance, confidentiality, availability and integrity. Various architectures have been developed to provide security in WSNs, among them are: SPINS, TinySec MiniSec and besides these the IEEE 802.15.4 include a security framework to meet the services of data integrity, confidentiality and authenticity [3].

SPINS (Security Protocols for Sensor Networks) developed by Perrig [15] consists of a set of security protocols that acts through encryption and message authentication codes. The TinySec was designed and implemented in the TinyOS operating system to be a mechanism for providing confidentiality, integrity and authenticity of the data link layer. It uses the CBC mode of operation that may be combined with various block ciphers as RC5 and skipjack [16]. The MiniSec is a protocol layer of security to WSN using OCB (Offset Codebook) mode for operating the block cipher, which eliminates the need of adding filler to the clear text blocks [17]. The standard IEEE 802.15.4 provides integrity, access control, confidentiality and replay protection in the link layer. The cryptographic algorithm used in this standard is AES [18].

According to Loureiro [4], a WSN tends to be autonomous and requires a high degree of cooperation to perform the tasks defined for the network. This means that traditional distributing algorithms, such as communication protocols and election of leader, should be reviewed for this type of environment before being used directly. Taking account also the limited computational power and especially of limited energy of devices is possible to deduce that not everything that works efficiently in traditional computer networks can be used in WSNs The computational limitations of a device restricting the choice of cryptographic algorithms and protocols safety. Furthermore, the lifetime of the batteries using techniques preclude the complex of security because it drastically decreases the life span of the network. [18].

Encryption is the security solution most applicable in computing. In recent years asymmetric algorithms have been extensively studied in embedded systems with low computational power. The next section discusses concepts of cryptography, and the description of the algorithms RSA, ECC, HECC and MQQ.
