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ANNALS of Faculty Engineering Hunedoara International Journal of Engineering Tome XII [2014] Fascicule 3 [August] ISSN: 1584 2673 [CD Rom, online] a free access multidisciplinary publication of the Faculty of Engineering Hunedoara 1. Ján ĎURECH, 2. Peter PENIAK, 3. Mária FRANEKOVÁ ZIGBEE AS COMMUNICATIONS PLATFORM FOR SMART HOUSE APPLICATIONS 1 3. University of Žilina, Faculty of Electrical Engineering, Department of Control and Information Systems, Žilina, SLOVAKIA Abstract: Paper deals with problem of using wireless networks in smart house applications. Main part is focused on wireless technology ZigBee, which is described and is analysed with regard to its safety features and its possibility for using in intelligent house. Solution of ZigBee network was realised on the base of development kit CC2530ZDK made by company Texas Instruments. Practical part is focusing on HW a SW realisation of several applications (control of lighting, heating and external equipment) and their testing. Keywords: Smart house, ZigBee, control, Texas Instrument kit, security 1. INTRODUCTION The last two decades of ongoing intensive research in an area of smart house applications, introduced the new technologies in the field of sensor systems and an energy management. With inserting of a sort of intelligence into buildings (intelligent house), we are able to provide a better facility management and control overall consumption of energy. Embedded sensor systems can evaluate internal and external conditions in buildings and provide the results for processing to control systems, which can optimize consumption. Since energy is becoming more expensive, this issue attracts more and more attention [1], [2]. In order to achieve the given goal, the distributed sensors have to transfer the results to control system via a suitable communication system. One of the possible solutions is to use wireless technologies that do not require cabling and enable flexible sensor distribution without dependencies on building layout and existing cabling systems. Wireless networks, intended for intelligent building, have to interconnect sensors, actuators and controllers. In the vast majority, the used applications need to transfer only a small amount of data. Widespread and popular networks such as WLAN and Bluetooth are unsatisfactory for the following reasons [3]: None of these networks meets requirements for the necessary battery life, because these protocols do not support or support only partially energy saving techniques, such as sleep mode. Both protocols are mainly working in the 2.4 GHz band which is intended mainly for multimedia applications. On contrary, applications used in intelligent buildings do not require such broad bandwidth and can work in lower frequency band, for example 868 MHz with a lower transmission power. The Table 1 shows a comparison of wireless technologies used in intelligent buildings in terms of distance, the frequency range, the speed and modulation. 2. ZIGBEE SPECIFICATION ZigBee and IEEE 802.15.4 are standards that provide the necessary network interface for sensor networks. As shown in Figure 1, IEEE 802.15.4 standard defines the physical and MAC (Medium Access Control) layer, ZigBee defines the network and application layer. ZigBee Alliance was copyright Faculty of Engineering Hunedoara, University POLITEHNICA Timisoara 89 Fascicule 3

90 Fascicule 3 ISSN: 1584-2673 [CD-Rom, online] created in 2002 as a non profit organization. IEEE 802.15.4 standard was approved in 2003 (later modified in 2006), which embraced the ZigBee Alliance and 14 December 2004 was first approved ZigBee 1.0 specification [7]. Table 1. Characteristics of wireless networks used in smart houses applications Wireless Characteristics technology Distance (m) Frequency (MHz) Speed (kbps) Modulation 6LowPan 75 2,4GHz, 868/915 MHz 216 ASK/ BPSK/ O QPSK DASH 7 250 433,04 434,79 MHz 232 FSK/GFSK EnOcean 300 868/315 MHz 232 ASK Insteon 50 902 924 MHz 224 FSK Knx RF 70 868 MHz 256 FSK ONE NET 70 868/915 MHz 4096 FSK Wavenis 1000 400/868/915 MHz 2000 GFSK Z Wave 300 868/908MHz 232 FSK ZigBee 75 2,4GHz, 868/915MHz 264 ASK/ BPSK/ O QPSK The latest version of ZIGBEE specification was released in 2007 [7]. It defines two profiles. Profile 1 is intended for home and commercial use with simple low memory footprint. Profile 2 is called as ZigBee Pro and offers additional features such as routing, multicast communication mode and high security encrypted using a key exchange SKKE (Symmetric Figure 1. Reference model of ZigBee network Key Key Exchange). The main difference between the specifications of the ZigBee 2007 and previous version ZigBee 2006 is in ability to support a fragmentation and rapid frequency agile channel. The fragmentation is the ability to process data that are greater than the available capacity. Version ZigBee 2006 and ZigBee 2007 are fully compatible, but the devices operating on the ZigBee 2006 specification can act only as end devices that cannot route packets [8]. From the logical point of view divided ZigBee devices on the network to: ZigBee Coordinator (ZC) is a primary device for each ZigBee network. It is responsible for a packet routing, network management and monitoring. It also can have a role of central security node, known as Trust center. Each network has to have only one coordinator, which requires continuous powering. ZigBee Router (ZR) is used for routing of packets between central coordinator and end devices in order to enlarge the network for longer distances. It is represented as local coordinator for end devices, although it can also serve as end device. It also requires continuous power. ZigBee End Device (ZED) can only communicate with the coordinator or a router and cannot transfer data from other devices. Because it has the lowest memory and computational demands, it can rely mostly on battery power. ZigBee uses three types of network topologies. The first supported topology is a star topology with the central coordinator node and end devices. The second topology is a tree topology, in which end devices do not communicate directly with the coordinator of the network, but can use the local router as primary local coordinator. This makes it possible to increase the distance between the end device and the central coordinator. The last topology is a mesh topology and it combines the features of previous topologies giving flexibility for network implementation [10]. In order to insure appropriate communication integrity and security, ZigBee uses AES (Advanced Encryption Standard) for encryption. ZigBee standard supports the use of the following security mechanism: Data encryption. Verification of data and devices. Protection against duplication framework.

ANNALS of Faculty Engineering Hunedoara International Journal of Engineering ZigBee network works with five different keys: Link key a common key used for encryption between two communicating devices (unicast). Network key a common key valid for the whole network, which is used for broadcast communications. Master key used to initiate communication and establish Link key between two devices. Key transport key that is used for transfer of any security key from target to destination node. Key load key used for secure transmission of main key. As already pointed out, ZigBee specifies two types of keys, Link and Network key. While Link key is shared between the two devices, the Network key is common to the whole network. Each network has a secure ZigBee device called Security Center (Trust center), which is in charge of key distribution to other devices. Data integrity is achieved by applying authentication function and adding the imprint of message to the network frames. If the MIC code given transmitter coincides with the calculated MIC recipient data, the received frame will be considered authentic. Higher level of security is achieved by increasing the number of bits in the MIC. ZigBee and IEEE 802.15.4 supports 32 bit, 64 bit and 128 bit MIC possibilities. 3. EXPERIMENTAL ZIGBEE NETWORK CONFIGURATION FOR SMART HOUSE The goal was to design and construct the appropriate hardware and software in order to evaluate and test ZigBee standard in Smart House applications. It has been realized by the development kit CC2530ZDK [11] from Texas Instruments. Texas Instrument is one of the founders of the ZigBee standard and offers a wide variety of devices including a product development kit for distribution of the subprograms that are designed to control peripherals [4] [9]. This module contains an integrated circuit IC RF (Radio Frequency Integrated Circuit), external components, filters for the highest quality radio communication and connector for 2.4 GHz antenna. The module connects to SmartRF05EB. Example of the smart house application with sensors, control system for heating, lighting and driver for remote control is shown in Fig.2, including communication system based on ZigBee tree topology [5]. Figure 2. Example of smart house application with ZigBee communication platform Figure 3. Example of the screen of Embedded Workbench Software implementation of all elements of the program was carried out in IAR Embedded Workbench, which is an integrated development environment (IDE) and contains compiler programming languages C and C + + for various devices, including the CC2530, see Figure 3 [6]. There was a necessity to create a separate program code for each device in the ZigBee network. The basic structure of this code could be implemented either by obtaining existing packages from the manufacturer of ZigBee chips, or using development tools, such as IAR Embedded Workbench. These codes were used to initialize the device and control peripherals. Plates were programmed using SmartRF Flash Programmer. Remote control program is composed of menus, which serves the user to control the device. 91 Fascicule 3

ISSN: 1584-2673 [CD-Rom, online] For network configuration, the following basic parameters of ZigBee wireless network had to be set in order to enable their communication via ZigBee: communication channel (Channel# 25), network identifier PAN ID (PANID #2013), addresses for devices (see Figure 2). 4. SECURITY EVALUATION OF EXPERIMENTAL ZIGBEE NETWORK The development kit CC2530ZDK uses AES encryption with a 64 bit MIC for the authenticity of data. The advantage of this method is that the encryption is calculated based on the sequential frame number. Therefore the encrypting of two identical texts would give two different results. This feature is known as semantic security and breaking of such the encryption method is almost impossible. The disadvantage of ZigBee networks is that all passwords must be kept in its memory in unencrypted form. As long as the attacker gets physically to the device, it can be easily copied from the memory of the program to computer, where the key can be easily found. Realized physical attack was bound to one device with a USB output, which was recorded using the whole pa have device to our computer. It was found in an unencrypted key: c0c1c2c3c4c5c6c7c8c9cacbcccdcecf (Fig. 4). To avoid to this attack devices should be in tamper resistant box and when the violation is recorded device should delete its memory. Figure 5. NONCE attack and XOR operation with identification of Figure 4. Possible physical attack with key identification original data 01 Another possible security issue can be caused, if for any reason the device sends two consecutive messages m1 and m2 with the same sequence number, the attacker has available various encrypted (E) data c1 and c2 with using of the same key. By using XOR operation (1), it can restore partial information regarding the calculation of the original messages. This attack is known as the same NONCE attack [11]. One of the possible cases to demonstrate NONCE attack can be power failure (empty battery). If the system fails to unknown status, it can be reset to the default state. This could increase the likelihood to use the same NONCE with a key that was used before the failure. Example of using XOR operations on original data after reset of device is possible to see on the fig. 5, where we can see the result of XOR operation 01. The original unencrypted transmitted data was: 66h + 67h=01. Rest of the data is XOR of the MIC function. To avoid this attack it would be necessary to store the nonce states in a non volatile memory and to recover them after each power failure [11]. 5. CONCLUSIONS The goal of the paper was to analyze the technological possibilities for implementing a wireless network for smart houses with focus on ZigBee technology. ZigBee offers a flexible network meeting specific requirements of smart houses. Its advantage is that it supports energy efficient communication with sufficient security. In addition, the manufacturers offer the possibility of creating own applications by customers. Our experimental application was created in 2.4 GHz band, with sample of devices used in intelligent building. The article described network security mechanisms such as encryption, data verification and data integrity during transmission. In laboratory conditions, it was verified that is almost impossible to break the network. The provided examples of security attacks on the ZigBee network, has illustrated theoretical option, but also proposed short term solution to mitigate possible attacks. 92 Fascicule 3

ANNALS of Faculty Engineering Hunedoara International Journal of Engineering Acknowledgements This paper was supported by the Educational grant agency (KEGA) No: 024ŽU 4/2012: Modernisation of educational technologies and methods with focus on cryptography for safety relevant applications. REFERENCES [1.] Technology of choice, smart home and intelligent bulding control [online] In: [2.] http://www.knxgebaeudesysteme.de/sto_g/english/general_documentation/technology_of_c hoice_2cdc500064m0201.pdf> [3.] KÁLLAY F., PENIAK P.: PC networks LAN,MAN, WAN and their applications. In Slovak. Monography. 2003, ISBN 80 247 0545 1 [4.] FRANEKOVÁ M. at all.: Communications safetz of industrial networks. In Slovak. Monography., EDIS ŽU Žilina 2007, ISBN 978 80 8070 715 6 http://www.inels.sk [5.] Model of inteligent house. In: http://www.jilova.cz/projekty/projekty rozvoj inteligentnibudovystudium1.pdf > [6.] http://www.inels.sk [7.] CC2530 ZigBee Development Kit User s Guide [8.] ZigBee Alliance: [online]. In: http://www.zigbee.org. [9.] ĎURECH, J. Applying ZigBee network in intellignt house. In Slovak. Diploma thesis. Žilina: University of Žilina, 2013. [10.] Open handset alliance. In: http://www.openhandsetalliance.com [11.] http://developer.android.com [12.] ĎURECH, J. FRANEKOVÁ, M.: Applications of control in intelligent house via ZigBee technology. In: XV International PhD Workshop. OWD 2013, Wisla, Poľsko, 19 22 October 2013, ISBN 978 83 935427 2 7, p. 409 414 ANNALS of Faculty Engineering Hunedoara International Journal of Engineering copyright UNIVERSITY POLITEHNICA TIMISOARA, FACULTY OF ENGINEERING HUNEDOARA, 5, REVOLUTIEI, 331128, HUNEDOARA, ROMANIA http://annals.fih.upt.ro 93 Fascicule 3