## 2 Security Issues in WSN  
As wireless sensor networks gain relevance as an important element of the Internet of Things world, security becomes a major design issue. There are many vulnerabilities that can be exploited to compromise the network operation or to obtain unauthorized access to relevant information [8]. In general, security threats for scalar sensor networks must also be considered for wireless image sensor networks.  
Security in wireless sensor networks may be hard to achieve due to many factors [9, 10]. The first of them is the resource-constrained nature of sensor nodes. In order to make sensor nodes economically viable and due to energy restrictions, computation and communication capabilities are limited. In fact, every security approach will require a certain amount of resources. Another relevant issue is the fact that wireless channels are inherently unreliable. Although many wireless visual sensor networks will require some level of reliability for the transmission of visual data, scalar and control data may flow in an unreliable way in a large set of monitoring and control scenarios [4]. Such unreliable channels may also add undesired latency to the communication, which may prejudice synchronization mechanisms. As duty-cycle protocols, such as IEEE 802.15.4, will be highly desired for WSN in order to allow a more efficient use of the limited energy resources, efficient synchronization will be required. At last, as sensor nodes may be deployed in unattended and human-accessible areas, they may be subject to physical attacks [9].  
Monitoring and control applications may have different security requirements, which will demand different defense measures. The main security requirements for wireless image sensor networks are described as follows:  
* Confidentiality: Sensed data and control information may be confidential, since their content must not be accessible by intruders or external elements. Control information, such as sensors' locations and even cryptography keys, is confidential in the sense that it may be exploited to compromise the network. Moreover, some sensed data, as in military applications, may be highly confidential.
* Integrity: While confidentiality avoids attackers stealing data, integrity will be concerned with data changing. If data are manipulated, this may compromise the network operation or even allow the exploitation of other vulnerabilities.
* Authenticity: Since additional packets may be inserted into the network, there should be a way to authenticate their origins. It is then not only necessary to assure that sensed data comes from valid nodes, but also to avoid malicious control information from foreign nodes being processed.
* Freshness: Control messages may propagate information that should only be valid in a defined time scope. Attackers should not be able to exploit old messages, containing, for example, cryptography keys.
* Localization: Sensor localization is a key functionality of wireless sensor networks, especially when they are randomly deployed. Secure localization is then required to allow only accurate information to be considered.  
* Availability: Wireless sensor networks are subject to different availability attacks, which may severely compromise the network operation. Such attacks can disconnect nodes, part of the network or even avoid relevant areas of a monitored field being sensed by any sensor node [11].