"user manual"
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1. Share QR code InstaCircle Leave conversation MESSAGES PARTICIPANTS Navigation bar John Doe Received messages Message textbox Send message Figure A 2 Conversation Screen 18 A 5 Sharing the credentials In order to connect to a conversation one needs to know the network name and the pass word for the conversation These two parameters can be communicated orally or with other media The InstaCircle application provides two more sophisticated mechanisms to share these credentials This section will describe how to share the credentials after having created a network How to use them please see section A 6 QR code Once the conversation is set up the credentials for the conversation can be shared using a QR code by tapping on the according icon in the action bar on top of the conversation screen figure A 2 A new screen containing a QR code will be launched This QR code can now be captured of other devices or you can tap on the menu button usually on the bottom left on most devices which brings up a Share button From here you can share it as a picture for example sending it to a computer and display the code on an overhead projector NFC tag The credentials can also be written to a writable NFC tag Of course this feature is only available on NFC capable devices After tapping on the NFC share icon a dialog will pop up asking you to tap a writable NFC tag on the back of your device see figure A 3 Af2. Android API only offers only an unstable API for controlling this hotspot but it turns out to work quite well at least on Samsung devices 2 1 3 Near Field Communication NFC Near Field Communication 8 is an evolving technology which is designed for short range communication typically 4cm or less It has a wide range of applications for instance it can be used for sharing content electronic payments access control etc It is strongly related to the RFID technology which is also a standard for communication over short distances NFC is not suitable for exchanging a large amount of data it can be seen as an alternative for a QR code for example In this project NFC could be used for the handshaking process For example instead of entering a predefined PIN code the participants would just touch their mobile devices in order to enroll for the upcoming election or poll 2 2 Mobile Platforms In the past few years three platforms have proven to be the most successful of its kind The following sections give a short description of each one 2 2 1 Google Android The Android 1 platform of the internet company Google has evolved into the most common platform for mobile devices It has been built on top of a Linux Kernel The Android operating system is running on a wide range of devices from different manufacturers This is probably the main reason why this platform has evolved to the most widespread system used on mobile devices
3. will arrive It is used primarily in the area of multimedia streaming where the loss of a packet or a datagram in the case of UDP is not a big deal 2 6 Broadcast vs Unicast A state of the art computer network offers several ways of communicating with peers in the network among them broadcast one to many and unicast one to one When we evaluate the needs for this project the choice of a transmission protocol would clearly go to TCP as we clearly don t want to loose any messages There is one problem though with TCP which is that we can t broadcast messages Since the protocol is reliable the sender expects an acknowledgement from every recipient In a broadcast scenario this recipient is not clearly defined and therefore the protocol cannot run properly Hence TCP can be used for unicast communication only It would be possible to set up a network chat application with unicast when we go for a central messaging server which distributes all messages among all participants In this project we would like to avoid to depend on a central infrastructure which makes this topology a poor choice Another approach with TCP and unicast communication would be the sender sending each message explicitly to all participants This approach is inefficient though because for each message we need to open a connection to each participant in the network As an alternative to unicast we could have a look at broadcast Broadcast seems to be exactly what
4. all devices For the moment we restrict the implementation to the Google Android platform 2 Background and Related Work This section gives a short overview of the basic technologies which should be considered during this project 2 1 Wireless Communication Technologies At the time being there are mainly two standards which allow wireless device to device communication namely Bluetooth and Wi Fi IEEE 802 11g Another standard called NFC is currently appearing on the surface but it doesn t play a big role yet nowadays This section roughly explains the technologies which are used in mobile devices in order to communicate with each other 2 1 1 Bluetooth Being introduced in 1994 by Ericsson Bluetooth 7 evolved to a standard which is used in a wide range of devices for point to point communication over short distances Bluetooth is designed as an ad hoc protocol meaning both devices act as master and slave at the same time Although this seems like a perfectly suitable protocol it has a major drawback Blue tooth is designed for two device communication and therefore it is not offering a broadcast function which we need in our project 2 1 2 Wi Fi IEEE 802 11g Wi Fi 12 is a protocol that allows to establish an IP network wirelessly The communication protocol which is used is TCP IP and hence allows to use all the features of the TCP IP stack In ordinary Wi Fi setups the devices usually connect to a so called wireless a
5. on an overhead projector for example The main screen of InstaCircle offers an option to capture a QR code using the camera of the phone and instantly connect to the conversation afterwards The functionality for displaying and capturing the QR codes is implemented in a separate Android application called Barcode Scanner which has to be installed separately NFC Tag For NFC enabled devices InstaCircle also offers the possibility to share the configuration using a NFC Tag After configuring the network the user interface offers an option to write the configuration to a NFC tag which then can be passed through the participants The InstaCircle application automatically starts and connects immediately 13 Table 3 2 Devices for testing Model Form factor Android Version WLAN Camera NFC Samsung Galaxy S1 Smartphone 4 1 1 unofficial image yes yes no Samsung Galaxy S3 Smartphone 4 1 2 official image yes yes yes Samsung Galaxy Tab Tablet 4 0 4 official image yes yes no after tapping the NFC tag on the back of the device provided that the application is installed and NFC is enabled on the device 3 6 Testing Testing the functionality was quite a challenge because of limited availability of hardware The Android Software Development Kit SDK offers an emulator which can be used to run the developed code directly on the computer but due to the heavy dependency on the hardware this was not an option Finally the testing was done on
6. the application launch It is responsible for configuring the Android device in order to participate in a conversation e NetworkActiveActivity The NetworkActiveActivity is displayed during a con versation and keeps the user informed about incoming messages the participants and general network information It also offers the possibility to share the network config uration using a QR code or a NFC tag 9 e NetworkService The NetworkService implements an Android service It is respon sible to process incoming and outgoing messages The service runs in the background and is therefore able to handle messages even if the user is using other applications on the device It uses the local broadcasting infrastructure in order to communicate with the Activities e UDPBroadcastReceiver The UDPBroadcastReceiver is an implementation of a Java thread It allocates a UDP socket and waits for broadcast messages to arrive and passes them back to the NetworkService where they are being processed e TCPBroadcastReceiver The TCPBroadcastReceiver is an implementation of a Java thread It allocates a TCP server socket and waits for unicast messages to arrive and passes them back to the NetworkService where they are being processed e NetworkDbHelper This component acts as a gateway to the SQLite database and hosts methods to query and manipulate data records in the SQLite database of InstaCircle One big advantage of this architecture is that the user i
7. the credentials are different 3 4 Network Topologies InstaCircle offers the option to activate a Wi Fi hostspot on the Android device which then acts as a hub where the other participants can connect to This hotspot needs to be activated on one device only and can be used by the other participants as a communication hub It is only necessary to activate a hotspot if there is no other suitable wireless network in range though if there is a wireless network to which all the participants can connect it is probably the simpler option to connect all the devices to this network and use this hotspot as the communication hub 3 5 Exchanging the configuration In order to join an InstaCircle configuration there are basically two parameters which must be known e The WLAN SSID e The credential of the conversation All devices have to be configured to use these parameters The classic way of is of course just to connect to the according WLAN and type in the credential but this is quite painful and error prone In order to make this process a little simpler InstaCircle implements two alternative ways of sharing a configuration to other participants QR Code As soon as the network is configured the user interface provides an option which displays a QR code of the configuration This configuration contains the WLAN SSID and the credentials separating the two values by two pipe characters This QR code could also be sent to a computer and displayed
8. three Galaxy devices of the Samsung corporation Table 3 2 gives an overview of the testing equipment which was available in order to test the functionality of the software Moreover there was a writable NFC tag available which allowed to test the NFC functionality Since there was only one NFC capable device available the test could only be done by saving the configuration and then rejoining the same device into the conversation which is not a real life scenario 3 7 Documentation During this project three pieces of documentation have been created First of all this project report describes the technologies and methods which have been applied and gives information about the project structure To describe how to use the software a brief user manual can be found at the end of this document in the appendix Finally in order to make the code more readable there are comments in the code which included in the very common Javadoc style which is a standard of documenting the code when programming Java 4 Problems As most of the projects also this one turned out to bear some surprises and problems Reliable communication without master The assignment of building a communi cation infrastructure without a master doesn t seem to be hard at first It turns out that there are some obstacles such as time synchronization and the detection of missed messages These problems can be solved with some mechanisms for the most part but these solutions are
9. try to extract the name of the owner of the device and present it as a suggestion in the text box Feel free to change it if you don t like it This setting will be saved for more upcoming conversations You are now ready to connect to a network The principle of joining or creating a network is basically the same with the only difference that if you want to create a new chat you cannot use the credential sharing mechanisms such as QR code and NFC A 4 Creating a new conversation In order to create a new conversation you can just tap on the Wireless Network which you would like to use In the pop up you can specify the password which will be used for the 17 Rescan Networks InstaCircle 2 STP Connect using QR Code YOUR IDENTIFICATION John Doe Your Identification instacircl 6 Available Networks WPA secured network WPA secured network WPA secured network Create new network Create a new network Figure A 1 Start screen conversation You ll then be redirected to the conversation screen as shown in figure A 2 You also have the possibility to create your own network using the integrated hotspot of Android You can do that by tapping on Create new network In the opening pop up you ll have to specify the a name as well as a password for the new network After clicking on the button Create Network the hotspot will be activated and you will be redirected to the conversation screen as shown in figure A 2
10. we are looking for messages go to all participants in a network segment which is exactly what we want in a chat like application We have already discussed that TCP is not suited for broadcasting so we need to switch to UDP which in turn is not reliable As a compromise a hybrid setup could be built where the recipient of a message asks the sender using an unicast channel to resend the message when it has been detected as missing 3 Results The result of this project is an application called InstaCircle which is running on Android based mobile devices such as smartphones or tablet computers This application allows to connect multiple mobile devices to a network which allows the devices to exchange messages Messages can be exchanged in two fashions e Broadcast A message which is sent in broadcast mode will be sent to all participants in the network e Unicast A message which is sent in unicast mode is designated to a recipient meaning only this particular participant will receive this message The following sections give some more details about the architecture and techniques which have been used in this project 3 1 Architecture The Android platform offers a wide range of pre built components which allow to build applications which integrate themselves neatly into an Android device Most important ones are the following e Activities An Android activity basically represents a screen on a device It displays components su
11. Google offers a Java Software Development Kit for developing software on the Android Platform This SDK is available free of charge For software development an ordinary computer running either Windows Linux or Mac OS can be used 2 2 2 Apple iOS The second big player in the area of mobile devices is Apple with their iPhone iPod and iPad devices All these devices are running the iOS 2 operating system The programming language which is used for developing iOS applications is Objective C The integrated de velopment environment IDE which can be used for developing iOS applications is called XCode which comes for free with the newest version of the MacOS operating system 10 7 2 2 3 Microsoft Windows Phone 7 Microsoft recently launched its Windows Phone 7 14 platform which is supposed to evolve as a competitor to Apple and Google in the smartphone sector Microsoft proposes its rather proprietary programming languages Visual Basic and C for developing applications for Windows Phone 7 2 3 Sharing credentials The first application which should be built upon this platform is an ad hoc E Voting appli cation For performing an election a known set of potential voters must be defined In the ad hoc E Voting scenario assume that all the potential participants are physically in the same location Wireless communication is usually not strictly bound to physical locations Therefore an additional mechanism is needed to restrict the acc
12. InstaCircle A Location Bound Ad hoc Network for Android Devices Project Report Juerg Ritter rittj1 bfh ch Bern University of Applied Sciences Engineering and Information Technology Biel Switzerland January 16 2013 Abstract The E Voting group of the Bern University of Applied Sciences is planning to eval uate distributed E Voting systems for practical use The term distributed in that context means that there is no central server infrastructure involved in the voting pro cess The main application of such E Voting systems are polls with a low number of participants for example the board of directors in a company Since the whole imple mentation of such a system would exceed the time budget of this project it has been broken down to separate parts In virtually every E Voting protocol messages have to be exchanged between multiple parties To build up such a messaging platform was the main goal of this project During this project an application which allows to connect mobile devices such as smartphones or tablet computers has been built It allows par ticipants to easyily create an ad hoc network where messages can be exchanged among all participants In order to make the configuration of such a conversation a simple as possible the initiator can share his configuration using QR codes and NFC tags This allows participants to join a conversation without having to reconfigure their devices manually The communication is
13. ation gateway for other devices a failure of these gateway nodes has to be handled somehow which is not an easy task Furthermore the Android API which is going to be used in this project lacks of some functionality which is crucial for this kind of communication platform for example autoconnect without any user interaction The setup of such a mesh network would exceed the time budget of this project The implementation for such a network infrastructure would certainly be an interesting topic for an upcoming project 2 5 TCP vs UDP On top of IP Internet Protocol which is responsible for the addressing and routing in a network there are two well known concept of communicating within a network e TCP TCP Transmission Control Protocol 10 is probably the most widely used transmission protocol in the modern network world Simply speaking TCP adds a reliability layer on top of IP which assures the delivery of each single packet which is transmitted to a recipient The recipient has to acknowledge the arrival of every single packet If the sender doesn t get this acknowledgement it tries to resend the packet e UDP UDP User Datagram Protocol 11 is a protocol which allows unreliable communication within a network meaning the recipient doesn t have to acknowledge every received packet This reduces the footprint of the protocol and makes it a very efficient way of transmitting data of course without any guarantee that the content
14. based on network broadcasts within a network seg ment and therefore also location bound The application has been developed for the very popular Android platform In following projects the E Voting part itself can be built on top of this communication infrastructure 1 Introduction One of the research fields of the Bern University of Applied Sciences is the area of E Voting E Voting has become a big field of research in the past couple years Still there is no generic approach which meets all the criteria such as privacy transparency robustness etc which we want in E Voting The E Voting research group of the Bern University of Applied Sciences 3 tries to improve this situation with the following approaches e Develop new approaches and provide them to the community for review e Take existing approaches and evaluate them in terms of practicability These ap proaches are usually available as scientific papers The evaluation of these approaches is usually done by implementing them into a prototype level application to show that the approach actually works The E Voting group would like to start a new project whose goal is to implement an E Voting system for mobile devices such as smartphones or tablet computers The scenario would be that each voter uses his her own device for casting the vote The communication between the devices happens in a decentralized way ad hoc meaning there is no central server infrastructure This assures a
15. beacon Manipulation of sequence numbers The order in the conversation could be dis turbed if a participant is manipulating sequence numbers causing the other participants to ask for missing messages This could lead to a denial of service attack This problem is generally considered hard in TCP which is using a similar sequencing technique this flaw also exists Asynchronous clocks Since there is no central infrastructure there is also no reference 11 Table 3 1 Message Types Name Type number Stored Channel Description MSG_CONTENT 1 yes Broadcast Message type which trans Unicast fers conversation content MSG_JOIN 2 yes Broadcast Indicates a participant join ing into the conversation MSG LEAVE 3 yes Broadcast Indicates a participant leav ing the conversation MSG_RESENDREQ 4 no Unicast Used for asking a partici pant to resend messages MSG_RESENDRES 5 no Unicast Used to respond to a resend request Such a resend re sponse contains an array of the messages for which the requester asked MSG_WHOISTHERE 6 no Broadcast Can be used to discover who is around in the network this is mainly used after the join of a participant MSG_IAMHERE 7 no Unicast Response to the WHOIS THERE request It will be sent directly to the re quester containing the cur rent sequence number time which could be used as a reference for the conversation In order to deal with the fact that messages could be delivered with delays the ti
16. ccess point which handles all connections This wireless access point usually covers a certain physical area and let devices in that range connect to the network Using a hotspot to establish a wireless connection is not exactly an ad hoc setup There fore a substandard called Wi Fi Direct 13 has been introduced This standard allows to use the Wi Fi technology without having a hotspot Two or more devices can establish an ad hoc network with this technology Tablets and smartphones are not designed to act as a powerful Wi Fi access point The Wi Fi direct standard doesn t limit the number of con nected devices but it is surely not designed to serve more than 5 connected devices Behind the scenes Wi Fi direct acts as a low scale Wi Fi hotspot to which other devices can connect The connecting devices don t necessarily have to be Wi Fi direct capable The Android plat form provides an API which allows establish Wi Fi direct connections and exchange data over it has a major drawback at this point though During the handshake of two devices a confirmation pop up shows up asking to confirm the connection Unfortunately this is not very practical for the usability of our context As a third option Android offers a hotspot which can be activated on an Android device This can be done without having the user confirming each connection Other devices can discover and connect to this hotspot just as any other wireless network At this stage the 3
17. certain privacy There are theoretical approaches to realize decentralized elections For example in 2012 Hao Khader Ryan and Smyth 4 published an approach of a decentralized fair and robust E Voting system The time budget of this project is a 15 ECTS point project during the MSE studies at the Bern University of Applied Sciences This time budget doesn t allow to implement a fully fledged decentralized distributed E Voting system Therefore we split this project into several pieces In a first stage the communication infrastructure has to be implemented A system is required where users can build up an ad hoc network between multiple devices and exchange messages on this platform In a later stage E Voting protocols can be built on top of this infrastructure for example the HKRS12 4 system or any other system of this category Having said this the target of this fist stage project is stated as follows The goal of this project is to implement a communication platform where messages can be exchanged in an ad hoc network which is established between mobile devices No additional infrastruc ture wireless hotspots servers etc should be required In particular this communication platform has to provide the following features e Initialize an ad hoc network from a master device e Allow a group of physically present people to join their devices into the network e Send point to point messages to other devices e Send broadcast messages to
18. ch as buttons textboxes labels and other controls which allow the user to interact with the application In InstaCircle this technique has been used to implement the user interface e Services Services can be used for running code in the background meaning the user is using another application InstaCircle uses this technique for implementing handling the interface to the network and process incoming messages even if the InstaCircle user interface is in the background e Local Broadcasts Local broadcasts can be used in order to let components like activities services etc communicate with each other Example As soon as a message arrives and got processed by the service it notifies the user interface with a broadcast that a new message has been arrived The user interface can update the content accordingly if necessary e SQLite Database The Android platform tightly integrates the popular lightweight database SQLite which makes it easy to store relational data InstaCircle uses this feature for storing the conversations on the device 3 1 1 Software components Figure 3 1 gives an overview of the software components which have been implemented in InstaCircle and how they interact with each other UDPBroadcastReceiver f TCPBroadcastReceiver LocalBroadcastManager NetworkDbHelper SQLite Database Figure 3 1 Architecture e MainActivity The MainActivity implements the user interface which is displayed after
19. dwork for further projects with focus on distributed E Voting systems The Android application which has been built during this project allows users to simply connect their mobile devices to an ad hoc network where messages can be exchanged either in unicast or broadcast mode Exchanging simple messages over this platform is just the first stage of further more sophisticated applications which can be built on top of this platform Personally it was also a great experience to dive deeper into the Android platform from which I only had a very shallow knowledge at the beginning of this project Acknowledgments I would like to thank all the members of the E Voting group of the Bern University of Applied Sciences who contributed a great deal by giving valuable input in constructive discussions A special thanks goes to my advisor Prof Dr Rolf Haenni who provided me with valuable inputs and ideas Moreover I would like to thank Prof Reto Koenig for sharing his great expertise in developing software for Android which was helpful many times 16 A User Manual A 1 Prerequisites In order to run InstaCircle you need a Android device running at least Android 4 0 Ice Cream Sandwich It runs on smartphones as well as tablet computers In order to use the advanced credential sharing features you need the appropriate hardware i e a camera for reading the QR codes and NFC capability to use the NFC sharing functionality If you want to use the QR c
20. ess to the network An access credential of some sort has to be distributed using a separate communication channel which is bound to the physical location where all the participants are The following 3 approaches are considered as a solution for this problem 2 3 1 PIN Code The simplest way to control the access to the network is by defining a PIN code and commu nicate it to the allowed participants This communication should be done either acoustically or visually for example displaying it on a screen using an overhead projector All the par ticipants have to enter this PIN code on their devices in order to get access to the network This solution doesn t require any additional features of a phone and is therefore applicable for a wide range of mobile devices 2 3 2 QR codes or bar codes A bar code 6 is an optical machine readable representation of data It can be found on many products and is used to identify them quickly using an electronic device QR codes 9 are the newer version of bar codes While the data in bar codes is encoded using bars in a line QR codes are built up using filled or blank pixels on a two dimensional area One QR code can encode more data than the relatively old bar code Almost every modern mobile device contains a camera nowadays Using a software which is running on the mobile device a photographed bar or QR code can be found on the picture and the data can be extracted Using this technique a credentia
21. he big disadvantage of this approach is that mobile devices are not built to handle a large number of connections from other devices Hence this setup is only applicable for a small number of participants about 5 participants In order to solve that problem a number of approaches are available 2 4 1 Installation of a Wi Fi hotspot The limitation of the small number of participants using a software hotspot on a mobile device could be solved by installing an actual hotspot to which all devices are connecting The management of the participants would still be done on a participant s device since this is not a task of a classic wireless hotspot 2 4 2 Using an existing hotspot Many conference facilities are providing a WLAN infrastructure This infrastructure could be used to act as a communication hub The principle is the same as above only that we are using an existing infrastructure rather than bring our own 2 4 3 Building an ad hoc mesh network The most sophisticated approach would be to establish a self organizing mesh network which links all the devices together without having a central instance which manages all the con nections Using this configuration all devices can act as server and client at the same time Since the connection load is shared in this configuration the limitation of the small device number is removed Establishing a robust mesh network is not a simple task tough Since some devices are acting as a communic
22. it is readable and initiates the connecting process If the connect was successful you ll be redirected to the conversation screen figure A 2 NFC tag If you have a NFC capable device the only thing you need to do is tapping the NFC tag on the back of the device You should get this prepared NFC tag from the issuer of the conversation Make sure that NFC is enabled on your device it won t work otherwise In order to connect to a conversation using an NFC device it is not even necessary to launch the InstaCircle application manually Just tap the tag on the back of the device and InstaCircle immediately launches and initiates the connection process After a successful connect you ll find yourself in the conversation screen figure A 2 A 7 The conversation screen The conversation screen has three views which are accessible through the navigation tabs on top at the bottom of the action bar Messages In this tab you can see all the messages which have been exchanged so far during the conversation You can also see if other participants joined into the conversation or when participants leave the conversation This is indicated with a different icon and a different message text In this view you also see the messages which have been sent directly to you by another participant At the bottom of the screen there is a text field where you can compose and send your own broadcast messages Participants In this tab you can find a list of all invol
23. l for accessing the network could be encoded and provided to the participants in the physical realm for example by projecting it to a screen using a overhead projector or printing it out and pass along the paper 2 3 3 NFC Near Field Communication NFC can be used to communicate wirelessly over short dis tances The counterpart can either be another mobile device or a so called NFC tag which is a passive chip which usually has the size of coin For instance a NFC tag containing the conversation credentials could be passed to all participants As long as the tag doesn t leave the physical realm no one from outside the realm can join the network Since NFC is a relatively new technique not all mobile devices are NFC capable yet Chances are quite high that there are participants with devices that are not NFC capable Figure 2 1 NFC tag 2 4 Network Topologies A classical and simple Wi Fi network topology is a star topology meaning there is a central device which handles all the traffic which is flowing through the network Usually this central device is a Wi Fi hotspot Since we have the requirement that no infrastructure other than the mobile devices of the participants should be used we have to find another solution A simple solution is to replace the hotspot with a mobile device of a participant This device initializes a Wi Fi hotspot which is running on the device itself allowing other devices to connect to the network T
24. mestamp of the message has to be set already by the sender of the message This is no problem as long as the clocks of the participant s devices are in sync Otherwise it is possible that the timeline of the conversation is not quite accurate as all devices are using a different reference Clocks of modern smartphones are usually synchronized using the cellular network or a GPS signal which somewhat remediates this weakness 3 3 Security The goal of this project was to create a protected conversation meaning it shouldn t be possible for everyone to join in without knowing a credential Since we are not sure that in a particular wireless LAN are only devices of participants connected we need to secure the conversation with another technique Since we share a credential which is used for participation we can use that credential as a symmetric key The content of all messages are encrypted with this key using AES The android is shipped with the Bouncy Castle 5 12 security provider for Java so there is no need to install further software to use this feature Technically it would be possible to have multiple InstaCircle conversations running in the same network segment In this case broadcasts of both conversations would go to all devices in the network Multiple conversations are kept separate by just ignoring messages if the credential cannot be used for decrypting the message This ensures that conversations are kept separately as long as
25. not perfect It would probably be worth it to look at some sort of centralized messaging platform as an alternative 14 Figure 3 3 The device setup for testing The Wi Fi API of Android Generally speaking Android has a quite intuitive and well structured API for building applications The Wi Fi part of the API seems to make an exception here It is quite hard to understand the concept For example there is no universal way for handling the keys for the different encryption methods The lack of clear error messages made it hard to track down the problems so a lot of time went into building and troubleshooting the Wi Fi part of this application Homogenous devices for testing The application could only be tested on Samsung hardware it would have been interesting to test the software on other hardware as well Furthermore the NFC part could only be tested with one device because there was only one NFC capable device available 15 5 Future Work This project has already been realized with prospect to further project which will dive deeper into the world of decentralized E Voting systems such as the on provided by Hao et al 4 At the heart of virtually every E Voting system is a mechanism of exchanging messages among the participants and this project provides a platform to do so on Android devices At this stage these E Voting platforms can be built on top of this project 6 Conclusion With this project we lay the groun
26. nterface which presents the mes sages in this case the NetworkActiveActivity can be exchanged This comes in handy if this communication platform should be used for something else than a simple chat application 3 1 2 Data schema As already mentioned InstaCircle uses a relational data structure in order to store infor mation which accumulates during conversations Figure 3 2 shows the the simple relational data model which is used in this application There are three entities in the model A conversation which itself can have multiple participants Participants in turn can be the sender of multiple messages in the conversation 3 2 Messaging model A goal of this project is to keep the necessary infrastructure as minimal as possible so as already discussed in section 2 6 we need to think about implementing a protocol using broadcast and the unreliable UDP transmission protocol The solution applied in this project looks as follows Each message which contains conversation relevant content is assigned a sequence number by the sender and is then sent as a broadcast UDP datagram into the network All participants can pick up this message process it and store it into the database During the processing the recipient compares the sequence number of the received message with the sequence number it expects from this participant If this comparison succeeds the recipient knows that it got all the messages from this particular sender during this co
27. nversation In case the comparison fails there are missing messages from that sender In that case the recipient asks the sender to resend the missing messages using a unicast TCP channel 10 z INTEGER sender id INTEGERS message TEXT l message_type INTEGER l sequence number INTEGER l source ip address TEXT Pate j INTEGER EHS timestamp INTEGER 7 conversation id INTEGER eidentification TEXT ip address TEXT conversation l ostate INTEGER id INTEGER F 77 conversation key TEXT conversation_start INTEGER conversation end INTEGER conversation open INTEGER Figure 3 2 Data Model 3 2 1 Message types InstaCircle uses 7 different message types in order to communicate 3 of them hold commu nication relevant information the other 4 types are used to govern the message flow during the conversation Table 3 1 gives an overview of the message types used in InstaCircle 3 2 2 Weaknesses At the first sight this protocol seems to be straight forward has a couple of weaknesses though Currency Missing messages are only detected as soon as the following message arrives This problem could be solved by broadcasting a beacon containing the sequence number in a certain interval Using this technique the maximum delay each participant could get is the interval of the beacon The problem remains tough if a participant leaves unexpectedly between sending a message and the next
28. ode sharing functionality the application Barcode Scanner needs to be installed This application can be found on the Google Play platform A 2 Installation At this stage the InstaCircle is not available on the Google Play platform yet so it has to be installed manually As a first step the InstaCircle apk file needs to be transferred to the Android device either by downloading it over the wireless network or by transferring it by attaching the device using USB to a computer Second make sure that you allow the device to install software from unknown Sources i e not the Google Play store This option can be found here Settings Security Unknown Sources It is recommended to switch that option off after the installation Finally you can start the installation process by just tapping on the InstaCircle apk file in a file manager of your choice After the installation the application is available in your application browser and can be started If you want to use the QR code sharing functionality you also need to install the Barcode Scanner application which is available on the Google Play platform A 3 Start of InstaCircle Simply click on the InstaCircle Icon in your application browser in order to start InstaCircle It will lead you to the start screen as shown in figure A 1 The first thing you ll need to do is to specify an identification name for which will be used to identify you in the conversation InstaCircle will
29. ter having done that a dialog indicating the success of the write operation The newly written tag can now be passed along the participants who want to connect their devices Sharing with NFC Please tap a writeable NFC Tag on the back of your device Cancel Figure A 3 Writing NFC Tag A 6 Joining a conversation There are three possibilities to join into a conversation which will be explained in the fol lowing section Typing the password The process of connecting to a conversation using just the pass word is basically the same as creating a new conversation After tapping on the according 19 network in the start screen figure A 1 you ll just have to enter the password which has been given to you from the conversation issuer in the password dialog You ll be redirected to the conversation screen figure A 2 and you ll be able to exchange messages with the other participants QR code If your devices has a camera you can also use a QR code which is presented to you This QR code contains the SSID as well as the password for this conversation In order to initiate the capturing of the QR code just tap on the Connect using QR Code icon in the action bar on the top of your start screen figure A 1 On the new screen you ll see the picture as seen from your camera s perspective You ll now have to center the QR code in the clear area of the screen The software captures automatically the QR code as soon as
30. the application At this point you are no longer able to receive any messages of the conversation A 9 Rejoining the conversation After having left a conversation you can always rejoin a conversation just as you would connect for the first time In order to keep you updated The application will ask all other participants to resend you the messages which were exchanged during your absence Go back to main screen Alice Parker PARTICIPANT DETAILS Participant information Message textbox SEND MESSAGE TO PARTICIPANT Private message Tor Send message Alice qwertyu i al s1 al iE fg h1 Pr Iki fi gt zxcecvbnm a nz amp 1E Figure A 4 Participant Details 21 References 1 ANDROID Android http www android com 2013 Online accessed 12 January 2013 APPLE IOS Apple iOS http www apple com ios 2013 Online accessed 12 January 2013 BFH E VOTING Group E Voting Group http e voting bfh ch 2013 Online accessed 12 January 2013 F HAO D KHADER P Y A RYAN AND B SMYTH A Fair and Robust Voting System by Broadcast 2012 THE BOUNCY CASTLE PROJECT Bouncy Castle http www bouncycastle org 2013 Online accessed 12 January 2013 WIKIPEDIA Barcode Wikipedia The Free Encyclopedia http en wikipedia org wiki Barcode 2013 Online accessed 12 January 2013 Bluetooth Wikipedia The Free Encyclopedia http en wikipedia org wiki Bl
31. uetooth 2013 Online accessed 12 January 2013 Near field communication Wikipedia The Free Encyclopedia http en wikipedia org wiki Near_field_communication 2013 Online accessed 12 January 2013 9 QR code Wikipedia The Free Encyclopedia http en wikipedia org wiki QR_code 2013 Online accessed 12 January 2013 10 Transmission Control Protocol Wikipedia The Free Encyclopedia http en wikipedia org wiki Transmission_Control_Protocol 2013 Online accessed 12 January 2013 11 User Datagram Protocol Wikipedia The Free Encyclopedia http en 12 13 14 wikipedia org wiki User_Datagram_Protocol 2013 Online accessed 12 January 2013 Wi Fi Wikipedia The Free Encyclopedia http en wikipedia org wiki Wi Fi 2013 Online accessed 12 January 2013 Wi Fi direct Wikipedia The Free Encyclopedia http en wikipedia org wiki Wi Fi_Direct 2013 Online accessed 12 January 2013 WINDOWS PHONE Windows phone http www windowsphone com 2013 Online accessed 12 January 2013 22
32. ved participants of this con versation A participant can have the state active and inactive which is also indicated in this view A participant becomes inactive as soon as he she leaves the conversation When tapping on the participant a detail screen as displayed in figure A 4 will be launched where you can see further information IP address sequencing number etc of this particular conversation Further down there is a text field which can be used to compose messages which will only be seen by this particular participant unicast messages You can navigate back to the previous screen by tapping the back button of your device or just by clicking on the InstaCircle icon on the top left of the screen 20 Network Info In the last tab you can find information concerning the network config uration or you as a participant A 8 Leaving the conversation In order to leave a conversation it is not enough to just close the InstaCircle application Until you explicitly leave the conversation the application runs in the background and is able to receive messages even if the application is not visible on your screen If you want to leave the conversation you have to tap on the according icon on the top right of the conversation screen figure A 2 After having confirmed your leave in the following dialog you will be redirected back to the start screen where you can either initiate a new conversation connect to another conversation or just quit
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