The Use of NFC and Android Technologies to Enable a KNX-based Smart Home

7/26/2019 The Use of NFC and Android Technologies to Enable a KNX-based Smart Home

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The use of NFC and Android technologies to enable

a KNX-based Smart Home

Gabriele De Luca, Paolo Lillo, Luca Mainetti, Vincenzo Mighali, Luigi Patrono, Ilaria Sergi

Dept. of Innovation Engineering

University of Salento

Lecce, ITALY

Abstract — In recent years, due the improvement of humans’

living standard, smart homes are receiving an increasing interest.

They can provide several useful services such as support for the

elderly and disabled people, access control, environmental

monitoring, and home automation. Furthermore, with the

widespread diffusion of mobile devices (i.e., smartphones, tablets)

and their integration with new auto-identification technologies

(such as the NFC technology), the need to control and manage the

smart home through these devices is increasing. In this context,the main goal of this work is to develop and validate an

architecture, both hardware and software, able to monitor and

manage a KNX-based home automation system through an

Android mobile device in an efficient and safe way. More in

detail, a software system able to configure an Android

application consistently with the home automation implant was

designed and implemented as well as an Android application able

to manage the entire home automation system based on the KNX

standard. A further Android module, which exploits NFC

technology, was developed in order to address the access control

issue. A real use case is presented, which demonstrate the

effectiveness of the proposed software system.

Keywords— KNX; Android; NFC; Building Automation;

Security.

I. I NTRODUCTION

The increasing success of the Internet of Things (IoT) [1]has encouraged a rapid movement from the Human-to-Machine (H2M) to the new Machine-to-Machine (M2M)

paradigm, so that the end-to-end communication can beexecuted without human intervention. Indeed, the IoT visionrefers to the extension of the Internet to the world of concreteobjects and places, which can communicate data aboutthemselves and access aggregated information from otherobjects or places. The IoT concept grows and develops hand inhand with "Smart Home" vision. In fact, due to the

improvement of humans’ living standard, people areincreasingly interested in solutions that allow users to not onlymake more comfortable their living environment, but also toremotely monitor the status of their home and reduce theenergy consumption. In this perspective, a smart home should

be able to utilize private and public networks to connect homedevices to each other and to the outside Internet world. It hasto provide a total integration among security systems,environmental monitoring and management, homeautomation, home entertainment, and access control systems,

by reporting the status of all home devices in an intuitive and

user-friendly interface and allowing the user to interact withthem. Moreover, the concept of the smart home is a promisingway of improving home care for the elderly and disabled in anon-obtrusive way, allowing greater independence,maintaining good health and preventing social isolation [2].Smart homes are often equipped with environmental sensors,actuators, and/or biomedical monitors. The devices operate ina network connected to a remote center for data collection and

processing. The remote center diagnoses the ongoing situationand initiates assistance procedures as required [3].

In the recent literature, there are several works addressingthe issue of the management of smart homes. In [4], a softwaremodule able to detect and solve interaction among users

policies, in smart homes based on KNX standard [5], isdesigned and implemented as part of the Engineering ToolSoftware (ETS) [6], a software tool used to configure a KNX-

based implant.

Furthermore, as the mobile devices are increasinglyubiquitous in our society, the trend to use these devices for thecontrol of smart homes is becoming more widespread, with

particular attention to home automation services management.In [7], for instance, the authors present a system to monitorand control several home system parameters by establishing aconnection among home devices and the user via hissmartphone. The proposed solution is able to provide instantnotification of any failures that may occur in the home. In [8],an application for mobile devices, in particular for iOS

phones, which combines home automation and securityservices, is presented. Again, for the iOS Operating System(OS), an application for the supervision and control of a homeautomation system is also developed in [9]. In addition tothese solutions for iOS devices, other works in the literaturedeal with the implementation of systems for home automationimplant management by exploiting the Android OS [10].

Finally, the use of modern mobile devices, which integrateauto-identification technologies, such as the Near FieldCommunications (NFC) [11], offers the possibility to developnew services for a smart home. The NFC technology buildsupon Radio Frequency Identification (RFID) [12], [13]systems by allowing two-way communication betweenendpoints. By using this technology, “dummy” things become“smart” things able to communicate information to the user(e.g., identification for access control, instruction for use of anappliance, dosage of a drug, etc.) [14].



The aim of the present work is to design and develop asystem able to control and manage a smart home by using anAndroid smartphone in a flexible, simple, and safe mode. In

particular, on the one hand, it allows controlling, both locallyand remotely, a KNX-based home automation system by

providing a high-level abstraction of real devices, and, on theother hand, it provides a control access system based on the

NFC technology. More in detail, we present a system that

mainly consists of two components: a Java application that builds the configuration file for the Android application inaccordance with users’ requirements, and the Androidapplication itself that provides the user with intuitive interfacefor managing home automation system and home access. Toevaluate the effectiveness of the proposed system, a use case is

presented that demonstrates how our software system is ableto control in real-time each KNX device.

First details of the proposed architecture, related only tohome automation component, are reported in [15]. It does notinclude some architecture extensions able to integrate alsoauto-identification technologies in Radio Frequency (RF). Onthe contrary, in the current work, both major implementing

details of the home automation system and the extensionrelated to NFC are presented.

The paper is structured as follows. In Section II, the proposed system architecture is presented, whereas in SectionIII, the details of the Home Automation component arereported. In Section IV, the Control Access component isdescribed. The use case aimed to validate the HomeAutomation system is described in Section V. Conclusions aredrawn in Section VI.

II. PROPOSED SYSTEM ARCHITECTURE

The proposed system architecture, shown in Fig. 1, mainlyconsists of two different sub-systems: (i) Home Automationmodule, and (ii) Access Control module. One of the keyelements of this architecture is the KNX/IP router, whichrepresents a tunnel that links the KNX world to the Internet, soallowing remote devices (e.g., smartphones, tablets, etc.) tosend, anytime and anywhere, messages to KNX-based homeautomation system.

The Home Automation module is split into two different

components: Editor Application, and Android Application(App). The Editor component is a Java software applicationthat has been designed in order to create the configuration filethat customizes the Android App in accordance to the userneeds. Before the technician can leverage the functionalities ofthe Editor, he must have configured and put into operation theKNX implant through the ETS tool. Then, he can use theEditor application to set up the access parameters, build the

Android App screens, and bind the control components to thecreated screens. Instead, by using the App, the user is able tocontrol the home environment both locally and remotelythrough his Android mobile device. More in detail, when alocal connection is established between the mobile device andthe home automation system, the smartphone is used as asmart remote control since it allows an easy management ofdevices that are in the same local network. Instead, if the userexploits the Android App to connect to the home automationsystem remotely (that is, when he is away from his ownhome), he can monitor and manage home devices anytime andanywhere, achieving a real advantage in terms of comfort andsafety. Indeed, on the one hand, the user can adapt thedomestic environment to his needs before returning home, on

the other hand, he can verify that no dangerous events happensuch as active electrical loads, undesirable intrusions, and soon.

The Access Control module exploits the NFC technologyto allow the management of the access attempts. An NFCreader is located in the house, just near the door and it isconnected to a Linux authentication server. The user can enterhis own home by approaching the smartphone to the NFCreader so that it can transfer the necessary authenticationinformation to the server. In order to provide an adequatesecurity level, the access control module guarantees twosuccessive security steps. First, the application requires theuser to insert a secret Personal Identification Number (PIN).

Then, it automatically collects a combination of informationrelated to the smartphone (e.g., MAC address or serial numberof the CPU) and encrypts them according to a public-keysecurity algorithm. This message, which represents thefootprint of the Android device, is sent to the authenticationserver through the NFC reader. The server, after decoding theauthentication message, compares the access credentials witha list of authorized terminals stored in its memory. If theapplicant's identity is successfully verified, the server sends aKNX message to the actuator that controls the electronic lockon the door in order to open it.

III. DESCRIPTION OF THE HOME AUTOMATION COMPONENT

A. Editor

By using the Editor application, the technician can buildthe structure of the Android App, i.e., the screens containingthe controls (lights, blinds, thermostats, etc.) for managing thehome automation system. This structure is not fixed and

predefined, but it is totally based on the end-userrequirements.

As first step, the technician imports, in the Editor, theKNX devices that the user wishes to control through theAndroid App. This operation can be executed in two ways: by

Fig. 1. The proposed system architecture.



directly importing the list of devices from the ETS project(Fig. 2) or by manually adding them to the Editor project (Fig.3). After this first step, the Editor project contains all the homeautomation devices that the user wishes to manage bysmartphone, and the corresponding addresses, i.e., the uniqueidentifiers through which the App sends commands to devicesor requires their status. About addresses, it is important toemphasize that each device can have multiple addresses, each

of which allows accessing one of its features. For example, anactuator that controls the state of a light has only twoaddresses, one for switching the state of the light and one forreading it. In contrast, a complex device, such as a thermostat,can have many addresses: an address to read the detectedtemperature, an address to read the type of actualthermoregulation (i.e., hot/cold), an address to write the typeof thermoregulation, an address to set the thermoregulation

profile (e.g., comfort, pre-comfort, and economy), etc.

One of the peculiar characteristics of the Editor applicationis that all devices, even those with more functions, andtherefore more addresses, are managed at high level, that is,considering them as a single entity, without the need of

composing them as a set of basic features. This aspectrepresents a very significant advantage, as it allows thetechnician to configure the project in a much more simple andintuitive way. Another interesting aspect is that the features ofeach device are not implemented in the source code of theEditor application, but they are parameterized in aconfiguration file written in XML language that is processedwhen the application starts. In this way, in order to handle newdevices on the market, it is sufficient to update the XML filewith the characteristics of the new device. The abstraction and

parameterization features of the Editor application arehighlighted in the class diagram shown in Fig. 4. In thisdiagram, there is no indication of specific home automationdevices, but only the generic object device (in the data

section) is defined. To manage individual devices, the Editorapplication refers to the XML configuration file, which isshown in Fig. 4 as readConfig (in the persistence section).From the class diagram, it is also clear that, in accordance withthe software engineering principles, the graphical userinterface (GUI) elements, the business logic, the data, and the

persistence mechanisms were kept separate each other.

In the last step, the technician builds the App screens inaccordance with the user requirements. To do so, there are two

possibilities, which are not mutually exclusive between them:the technician can build a hierarchy of screens thatcorresponds to the building structure or he can realize fullycustomized screens that contain the home automation devicesregardless of their actual dislocation in the home. In the firstcase, the technician can automatically extracts this informationfrom the ETS project (Fig. 5), whereas in the second case each

screen is manually defined. For example, the user may wish tohave all the home lights on one screen.

Once the whole procedure is completed, the Editorapplication provides an output file that is used to configure theAndroid App. This file is in the JSON [16] format, chosen forits simplicity and flexibility.

B. Android App

The application dedicated to the management of the homeautomation system is initially downloaded from the GooglePlay as a generic application. Obviously, it is originally notable to offer any function as it is not associated with any homeautomation system. To customize the application according tothe user requirements, the technician sends to the user’ssmartphone (or smartphones) the JSON file generated asoutput by the Editor application. This file is sent through areliable and secure communication service (e.g., a certifiedemail service).

Once the user has completed the uploading of the JSONfile, the application parses it using the JSON-simple library[17]. This operation leads to both the making of Java objectsrequired for the management of the home automation devicesand the configuration of the App screens in accordance withthe user requirements. After this easy and fast setting

procedure, the user is able to manage his home automationsystem (both locally and remotely) and to monitor, anytimeand anywhere, the status of his home, by using the feedbackssent from the KNX implant to the Android App. About thecommunication between the Android OS and the KNXimplant, a Java library called Calimero [18] has been used. Itis a very straightforward and easy to use library and it waschosen because it is open source, flexible, modular, andstrongly stable. Furthermore, among all libraries aimed atcommunicating with KNX systems, Calimero seems to be themost constantly updated and improved. The configuration

phase just described and the interaction between the AndroidApp and the used libraries are shown in Fig. 6.Fig. 2. Automatic import of the KNX devices from the ETS output file.

Fig. 3. Manually input of the KNX devices.



Since the management (especially the remotemanagement) of a home automation system represents a verysensitive service from a security point of view, variousmechanisms to ensure a secure usage of the application have

been implemented. More in detail, while the local access isguaranteed by connecting the smartphone to the local Wi-FiAccess Point, the remote access is carried out in a safe waythrough a Virtual Private Network (VPN) tunnel between themobile device and the local IP router. The establishment ofthis secure connection is possible without the need to usespecialized software, since this feature is already provided byall operating systems for mobile devices.

In order to guarantee an additional security level, a PINthat the user must enter in order to access the system functions

protects the application. When the application is started for thefirst time (after it has been configured through the JSON file),it asks the user to choose the PIN. In this way, if thesmartphone is lost or stolen, any fraudulent user cannot access

the application and then the home management features.

Finally, it is interesting to highlight another useful featureof the application for the home automation, i.e. themanagement of electrical loads. By using a power meter onone or more power lines, it is possible to control theinstantaneous power consumption of each device connected toelectrical network. In this way, if any of them is leftinadvertently switched on, the App provides the capability,also remotely, to act on the corresponding actuator in order toswitch off the device (e.g., hair straightener, iron, etc.), soavoiding the occurrence of dangerous consequences. In thisway, the App is able to improve the safety level of the house.

IV. DESCRIPTION OF THE ACCESS SYSTEM BASED ON NFC

TECHNOLOGY

The Access Control module exploits the NFC technologyin Peer-to-Peer (P2P) mode to exchange data. In the proposedsolution, the chosen devices are a NFC enabled smartphone(i.e., a Samsung Galaxy Nexus) and the SCM MicrosystemsSCL3711 USB Dongle NFC reader, as the latter is the best-supported reader by NFCPY software libraries [19]. Theselibraries have been chosen because they are the most advanced

NFC P2P desktop libraries. The NFC reader has beenconnected to a Linux authentication server placed in the

Fig. 4. Editor Class Diagram

Fig. 5. Building of the Android application screens.Fig. 6. Configuration phase and modules interaction.



house. In this server, a list containing all authorized users isstored (i.e., a list containing all the identification of theauthorized smartphone).

When the user initiates the Access Control module, hechooses a PIN code that is encrypted by using the MD5algorithm, a widely exploited cryptographic hash function that

produces a 128-bit (16-byte) hash value (MD5 checksum).This checksum is stored in the smartphone memory. In thisway, if the user loses the smartphone, the access in his ownhome is protected against ill-intentioned people: only thesmartphone owner knows the PIN, and this code is not clearlyreadable from the smartphone memory. Then, in order to enterthe home, the user starts the Access Control module and entersthe personal PIN. The application encrypts the inserted PIN byusing the MD5 algorithm and compare the obtained checksumwith that stored in the smartphone memory. If the comparisonsucceeds, then an alert popup on the smartphone prompts theuser to approach the mobile device at the door lock. At this

point, data transfer between the two NFC devices via the P2Plink starts. More in detail, the smartphone transfers anidentification code (ID) to the server in order to uniquely

identify itself. This ID could be the smartphone CPU serialnumber, the Bluetooth card MAC address, or a combination ofthese parameters.

In order to add a further security level to the system, thisID is sent to the server by using a double level Public KeyInfrastructure (PKI), that is, the RSA algorithm. Through thismechanism, the smartphone ID is first encrypted by using theuser’s private key and then by using the public key of theserver. Once transferred to the server via the P2P link, theencrypted message is decrypted by the server by using first its

private key, and then the user’s public key. The first securitylevel (i.e. the user’s public/private keys pair) is used in orderto guarantee the information authenticity. Instead, the second

security level, guarantees the information confidentiality.If the ID matches one of the IDs stored in the server list,

then a KNX message is sent by the server to the KNX implant,i.e., to the KNX actuator that controls the door lock: the dooris therefore open.

In order to prevent the eavesdropping attack, a counter isencrypted along with the smartphone ID and the server storesa copy of the counter of each authorized device. This counteris incremented, on the smartphone side, at every user access inthe house. In this way, when the server receives an authorizedsmartphone ID, if the counter of the message is equal to or lessthan the stored value, it does not allow the door opening.

A peculiar feature of the access control module is the useof an authentication method known as "Two-factorauthentication" (TFA) or “Strong authentication” [20]. It is anauthentication approach, which requires two of the followingthree authentication factors:

• Knowledge factor or "something the user knows" (e.g., password, PIN);

• Possession factor or "something the user has" (e.g.,smart card, mobile phone);

• Inherence factor or "something the user is" (e.g., biometric characteristic, such as a fingerprint).

In the proposed solution, the PIN represents the knowledgefactor, whereas the smartphone represents the possessionfactor.

V. A USE CASE: HOME AUTOMATION SYSTEM

The scenario used to validate the proposed and developedsystem architecture is a three-storey house, as shown in Fig. 7.The ground floor consists of a garage, which contains a lightcontrol. The first floor consists of two rooms: a bathroomcontaining an electrical loads control and a blind control, and aliving room containing a dimmer control and a light control.Finally, the second floor consists of a bedroom containing athermostat control. All devices are compliant with the KNXstandard.

Of course, the first step was dedicated to the configurationof all devices through the ETS software tool. Afterreproducing the building structure within the software andafter distributing the home automation devices in the rooms of

the house, we have set up their operating parameters, first ofall the addresses through which any external application canexploit their capabilities. Once the entire configuration wasdefined by using the ETS software, it was sent to each devicevia the KNX bus.

The second step was aimed at preparing the configurationfile for the Android App by using the Editor component. Inthis specific use case, the App screens hierarchy reflected thehome structure, with its floors and rooms, as can be observedin the screenshots reported in Fig. 8.a. This choice has allowedus to define the structure of the Android application by simplyimporting the information contained in the output file of theETS software. Afterwards, the JSON configuration file was

sent to the Android smartphone via secure email and it wasimported from the App at the first start. When the configuredApp was started, by clicking on the link representing the firstfloor and then on the bathroom link, the devices in that roomwere shown. In this way, we were able to immediately viewthe instantaneous power consumption of the electrical loadand the blind position. This is possible because, once enteredin the bathroom screen, the App sends a KNX message to the

Fig. 7. The home structure in the use case.



home automation system for each control on that screen.

These messages are used to interrogate the KNX implantabout the status of devices and therefore, once responsesreturn, they allow Android App to receive an up-to-date viewof the devices. This example helps to understand that anystatus change shown by the Android App is not due to the userinteraction with the graphical controls on the screen, but it isthe result of feedbacks received from the KNX system. TheFig. 8.b shows the value of the instantaneous powerconsumption detected by the power meter and the position ofthe blind. Leveraging this information, if the user detects anabnormal value of the instantaneous power consumption, hecan click the appropriate button in order to disable thecorresponding power line (Fig. 8.c). If so, the App sends a

KNX message to the actuator that manages the electrical load,asking for its disconnection.

VI. CONCLUSIONS AND FUTURE WORKS

In this work, a complete system able to manage a smarthome is designed and developed. In particular, a softwarecomponent (Editor) able to customize an Android App basingon the user requirements and the Android App itself have beenimplemented, as well as a further component able to guaranteean efficient and secure access control mechanism. The Editoris a Java application that the technician uses after the KNX

implant installation and it is characterized by high scalabilityand ease of use. The Android App provides a user-friendlyinterface through which the KNX implant could be easilycontrolled and managed. The Android App is also equippedwith an efficient system for controlling electrical loads, whichallows to increase the home security and the energy saving.

To evaluate the effectiveness of the proposed system, wealso presented a real use case through which all features of oursolution are successfully tested.

Future developments of the system are focusing on furtheruse of NFC technology in order to provide more smartservices, for example to increase the independence of elderlyor disabled people.

ACKNOWLEDGMENT

The authors thank GEWISS S.p.A. of Bergamo, ITALY,for their precious support.

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Fig. 8. a) Screenshot of the root screen; b) Instantaneous power

consumption of the electrical load; c) Electrical load disabled.



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The Use of NFC and Android Technologies to Enable a KNX-based Smart Home

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