## 2 Intelligent Sensors and Their Basic Security Issues
The assumed TVAC security model (Threat-Vulnerability-Attacker-Countermeasure) can be useful to define properly threat items in the methodology presented below. While comparing these two technologies, it was pointed out that wireless sensor networks are poorly standardized. Besides, only few CC certificates concern the WSN technology. Wireless sensors developers can benefit from numerous experiences (hundreds of finalized CC certification processes) in smart card and RFID systems development because attacks on smart cards apply to WSN nodes and some node RF/Communications attacks may apply to contactless smart cards and RFIDs. Microcontroller architectures, tamper resistance, resource limitation, and communication issues are very similar in both technologies. Intelligent sensors are able to work autonomously as well. The advanced Drager Polytron 7000 Fixed gas detector [12] is an example of an intelligent sensor designed for responsible applications. It is able to detect over 100 different gases and has a modular structure. It is provided with communication facilities. The implementation of the above mentioned mechanisms, like: cryptographic or filtering algorithms, advanced specialized key management or routing protocols in sensor networks, requires right assurance because they are extremely important to provide reliable and secure operation of the entire network and network-based applications. The above mentioned works focus on specific and advanced security mechanisms, however, they do not provide a methodology how to implement these mechanisms with proper assurance, for example with the use of well known assurance methodologies, like the ISO/IEC Common Criteria methodology. Considering the intelligent sensor as a typical IT product and the networked sensor system as an IT system, the Common Criteria methodology can be applied to them as well. The works dealing with the Common Criteria application in sensors and sensor systems development are scarce, though they are becoming a new, promising Common Criteria standard application domain. The most relevant concern:  
* airplane health monitoring systems,
* safety-critical assets distribution systems,
* motion sensors of digital tachyographs,
* SCADA-related products,
* specialized firewalls used in control and automation systems, co-operating with sensor networks. The paper [13] presents a sensor system, based on a wireless network, supporting the transfer of sensor data and information onboard commercial airplanes (eEnabled airplanes) as well as between airplanes and their supporting ground systems. Such systems, called AHMMS (Airplane Health Monitoring and Management Systems), are applied in the latest generation of aircrafts to improve the safety and efficiency of air travel. AHMMS monitor permanently the health of airplane structures and board systems using embedded sensors and give timely feedback to the flight control computer working on the board and to the airline ground server for health assessment. To secure the electronic distribution of software, cryptographic key and data between airplane and ground systems the Common Criteria methodology is used. The new application of this methodology encompasses the identification of specific security threats, requirements, and mitigation mechanisms based on the Public Key Infrastructure (PKI) services and digital signatures. Securing the communication channel between the aircraft and ground system is a very important issue, though it does not concern intelligent sensors directly, but communication with the sensor-based system. A similar issue concerns asset distribution systems which should securely load the authorized software (e.g., safety standards compliant software, firmware for intelligent sensors) or contents (data, security related data, unique identifiers, cryptographic keys, _etc._) to physical objects, like airplanes [14], vehicles or other specialized equipment. The integrity and authenticity of the distributed assets is significant for the safety and security of these objects.