CKMI: Comprehensive Key Management Infrastructure Design for Industrial Automation and Control Systems  
Thejas G.  
The model consists of three levels: field network, control network and plant network. IACS includes the various devices in the industrial plant to perform automation and monitor the industrial facilities. The resource constraints at different levels of the automation system are different. The devices at each level differ in their capacities such as storage, communication, computation, accessibility, power requirement and latency. The various types of devices situated at different levels are as follows:  
* _Field level network_: It includes sensors (optical, magnetic, thermal, etc. ), IEDs and actuators (magnetic valves, motor stats, power switches, etc.). Sensors help to monitor leakages in the pipes, to monitor pipe pressure, to monitor the flow rate, to check boilers temperature, etc. [2]. They help the IACS operator to maintain the functionality of the system in normal condition. Hence, they are called as the eyes and ears of industrial control systems. * _Control level network_: It includes PLCs, RTUs, ICS servers and controllers such as AC800M, AC800C, etc. RTUs are field level equipment used for data acquisition from sensor devices and actuators. They are located remotely with respect to the control center. PLC functions similar to RTU. RTUs are normally used for collecting data from a large geographical areas, whereas PLCs are used in the case of local control. * _Plant level network_: It includes connectivity server, aspect server, application server, monitoring stations, domain controller, OPC operator workplaces, third-party application servers, ICS users, engineering and monitoring stations and other servers. The industrial network can be associated with the web for remote observing via firewall and VPN. For the last few years, industrial control systems security is a hot topic in the research community. The catch of malicious activities (Stuxnet [3], Duqu, Flame, Havex [4; 5], etc.) and their massive damage on the real-time systems enforce the plant owners and the nations to consider the security for industrial automation systems as a high priority issue [6]. The attacks occurred on SCADA systems are discussed in [4]. The communications in the IACS are real-time in nature. Based on the data obtained from the field network, the control network takes a proper decision and sends suitable commands to the field devices to sustain the normal functioning of the industrial plant and to avoid interruption. For example, in the case of water management systems, communications include OPEN/CLOSE the valves; SWITCH_ON/SWITCH_OFF the device; RAISE/LOW the levels of the water tank; acquire data such as water flow rate, water level in storage tanks, pressure in water pipes, temperature inside  
Figure 1: Industrial automation and control systems. the boiler, speed of actuators; and read the characteristics such as acidity, purity, chlorine residual in the water, etc. The communication messages contain sensitive data; if an attacker captures or modifies the message contents, it results in severe consequences [4; 7]. The following are some of the malicious actions that the attacker may perform:  
1. Modify the transmitted readings
2. Send invalid commands or to send valid commands at a false time
3. Send wrong information to the control unit
4. Create situations leading to packet loss
5. Overwrite the existing programs of the remote devices
6. Introduce a delay in the communication
7. Try to block the information
8. Replay the data, modify the configurations of the devices, etc. Therefore, there exists a strong requirement of communication security that protects the communication between the devices of the industrial plant. For communication security, secret keys are required between the communicating entities. Due to the large size of IACS networks, involving devices with varying capabilities, managing secret keys associated with all the communicating entities is a challenging task [8; 9].