## 2 Intelligent Sensors and Their Basic Security Issues  
The progress in low-power CMOS processing, communication circuits and transducer technology has enabled new possibilities and applications, including advanced processing within the nodes (**-**m**otes\") of wireless sensor networks (WSNs). Apart from a class of sensors working in WSNs, other groups exist in different application domains. Intelligent sensors can work autonomously or co-operate with control systems supervised by SCADA or different monitoring units. Some of them are designed for special applications, e.g., motion sensors for digital tachyographs. The security and safety issues are important for intelligent sensors because very often they are used for responsible technical applications in varied, high-risk environments. These issues can be considered in the context of connectivity aspects due to the fact that intelligent sensors are elements of wireless sensor networks or can communicate indirectly with other systems in a different way. Basic research fields concerning sensor systems and their applications deal with energy efficiency, network protocols, distributed databases, as well as discussed here security issues. Sensor systems designers focus on solving separate technical issues which are specific due to the resource limitation of the sensor nodes (limitations concern power sources, processing and communication capabilities). The security analysis of wireless sensor networks [3] points at the possibility of individual node interception. This problem can be solved by using advanced cryptographic and authentication algorithms which require increased processing resources. The data transmitted between nodes and data stored within nodes should be secured. An important issue is to protect a cryptographic key used for securing data stored within nodes. The denial-of-service attacks vulnerability of large scale sensor networks is discussed in the dissertation [4]. These attacks, performed from the outside or from an intercepted node, have different forms, such as: false data reports causing false alarms, excessive power consumption, and congestion of wireless channels. Due to the node computational limitation, some filtering algorithms, such as Bloom filters, are considered to solve this problem (messages can be broadcast to the selected nodes only, determined by a filter). The paper [5] discusses basic security issues of wireless sensor networks, including the routing behaviour, node tamper resistance, and implementation of commonly known security mechanisms (encryption, key management, authentication, authorization). The use of these mechanisms is very difficult due to the node resource limitations. Specific solutions for wireless sensor networks have been developed based on the set of nodes provided with sensors and with actuators. The paper [5] presents an ambient intelligence application to control the environment. Environmental data are sampled by sensors, then aggregated and processed by external servers to extract knowledge about the environment. On the basis of this knowledge, control data are elaborated and passed to actuators. The data influence environmental parameters. The problem of data reliability has been solved on the application level with the use of a trust-based decision framework. The paper discusses most of commonly known attacks on the nodes, networks and applications, which will be considered later, once the intelligent sensor security model has been worked out. A general review of security problems related to wireless sensor networks is provided in [6] with respect to both variants of networks: the hierarchical WSN (nodes of different capabilities, the network topology is known) and the distributed WSN (no fixed infrastructure, huge number of nodes, usually scattered in a hostile uncontrolled environment, the network topology is unknown).