Confidential peer-to-peer file-sharing using social-network sites

Confidential peer-to-peer file-sharing usingsocial-network sitesMaarten FonvilleFaculty of Electrical Engineering, Mathematics and Computer ScienceUniversity of Twente, the Netherlandsmaarten.fonville@gmail.comABSTRACTSocial networking sites and peer-to-peer systems are twoconcepts that are being applied in our daily life. This papercombines the strong characteristics of these two concepts:using the social-network sites to provide access controlto available data and the peer-to-peer system to distributethis available data. In particular, this paper combinesthe fine-grained access control that social-networksites offer and efficient file-sharing throughput of peer-topeersystems. An architecture is proposed that uses andenhances the features provided by the Facebook social networkand by the OneSwarm file-sharing system.KeywordsPeer-to-Peer, File-sharing, Social-Network1. INTRODUCTIONCurrent peer-to-peer file-sharing systems like Bittorrentare an efficient way to share large amounts of data. Butthose systems are not designed for sharing confidentialdata, since the access and sharing process often cannotbe controlled [6].Social-network sites already have effective ways for controllingaccess to confidential data but users are often notable to share large files and are dependent on a centralserver.So both systems have strong and weak characteristics butexactly the opposite ones. The challenge is trying to combinethese systems keeping only their strong propertieswhich could give a boost to social-network sites and peerto-peertechnology. Such a combined system will enableusers to share large files, like movies of their holidays, withselected friends and family in an easy way. It will integratewith their regular social-network site activities andwill not require the knowledge to have, for example, theirownserversoftwareorhaveanalways-oncomputerandinternet connection.The target of this research is about combining the strengthsof both systems into a system where a user can use a socialnetworksite for controlling access to its confidential dataand use peer-to-peer technology for the actual sharing. Wewill index the possibilities of such a system, whether it isPermission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copiesare not made or distributed for profit or commercial advantage and thatcopies bear this notice and the full citation on the first page. To copy otherwise,or republish, to post on servers or to redistribute to lists, requiresprior specific permission and/or a fee.13th Twente Student Conference on IT June 21, 2010, Enschede, TheNetherlandsCopyright 2010, University of Twente, Faculty of Electrical Engineering,Mathematics and Computer Science.Figure 1. System that combines social networkingand file sharing.feasible and how this could be implemented. A simple exampleof the kind of system we would like to accomplishis shown in figure 1. In this figure the shown social networkingusers are members of certain groups or are friendsof a user. They share files with each other (the files theywould have access to are shown in the folder). “PublicFiles” are shared with all relations of the users, thus witheveryone in their group with a friendship connection. The“Company Files” or “Family Files” represent files associatedwith the company and family groups, respectively.These files are only shared with those that are memberof the relevant group. The sharing of the data is doneusing the peer-to-peer technology, but the access control,authentication and relation management is done by usingsocial-networking features.The main research question that is answered by this paperis:• Can we combine the strong characteristics of peerto-peersystems and social-network sites?The sub research questions are:• What are the possibilities to control the file-sharingprocess in current peer-to-peer file-sharing systemsusing social features?• What are the possibilities to share large amounts ofdata on social-network or otherwise socially awaresites?• What are the requirements for a combined system toenable confidential peer-to-peer file-sharing systemusing a social-network site?• Is it possible to actually combine these systems andhow could this be done?

To index the possibilities of controlling the file-sharing processin current file-sharing systems and the sharing of largeamounts of data on social-network sites, we will do a combinedresearch study. A literature study is used to answerthe first three research questions. The fourth question isanswered by specifying and designing the desired architecture.This paper is organized as follows. In section two,the first sub question is answered, by studying currentpeer-to-peer file-sharing systems. Section three discussesdata-sharing on social-network sites and answers the researchquestion two. Section four lists the requirementsfor the desired combined system and answers the third researchquestion. The proposed architecture is describedin section five, where also the answer to the last researchquestion is provided. Section six concludes and providesrecommendations for future activities.2. SOCIAL-NETWORK FEATURES IN CUR-RENT PEER-TO-PEER FILE-SHARINGSYSTEMSVarious researchers try to improve current peer-to-peersystems. Challenges are often effective and efficient searching[38], reducing free-riding [14] and bootstrapping overlaysand managing those [21]. So some of our requirementshave already been studied in other papers or solved withincurrent peer-to-peer file-sharing applications.2.1 Friends as peersAt the moment there are several systems or studies thattry to embed a social layer within peer-to-peer systemssince there is a theoretical base that this can improve performance[13].MazeOne of those systems is Maze [7]. Maze builds an overlay intheir peer-to-peer file-sharing network based on the interestof the user. The software has algorithms to automaticallyand dynamically detect these interests. With theseinterests it groups users together into so-called ‘friend’groups. The identity of a friend is checked the first timeand confirmed via a central server (Ticket Grand Server)so that friends can be kept for a longer time, even if, forexample, their IP address does change. The idea is thatall the friends of a client also keep each other’s status, sothat if the central server goes down for some time, the networkcan still function because friends can give each otherconnection details of their friends and vouch for their identity.If a user wants to search for a certain file, it sends thesearch requests to its friends. Those friends answer to therequest with matching files and give connection details oftheir own friends who also do have this file, to help thesearching party download from more sources, resulting ina faster download.Epidemic-Style management of Semantic OverlaysIn the Epidemic-Style Management of Semantic Overlays[34] study at the Vrije Universiteit Amsterdam a neighbourmechanism is proposed in which clients would becomeneighbours, based on a calculated proximity. If aclient would introduce a new file to the peer-to-peer network,they would ‘gossip’ this to their neighbours, whowould gossip it to theirs until a certain distance. This gossipingconcept proved to be a very efficient way of findingthe needed files and peers. High hit ratios were achievedwhen the user wanted to request a file and his client alreadyhad heard of this file via the gossip, even when relativelysmall gossip broadcast distances are used.TRIBLERAnother system masking certain peers as friends is TRI-BLER [28]. TRIBLER is based on Bittorrent for the actualfile-sharing, but adds another dimension with socialnetworkingto it. The clients are de-anonymized by a permanentidentity, which can be checked by a challenge andresponse system, and users rate their favorite files. Basedon these favourite files, users get so called ‘taste buddies’assigned with whom they form a group and they can explicitlyadd some of their real life friends. These groups,friends and a small number of random peers, exchangewitheachotheronaregularintervalalistofthese‘befriended’peers and a list of their favourite files. In thisway the network can keep updating itself with, for example,proper ‘taste buddy’ matches and suggestions to usersfor files to download. Due to the fact that the systemcreates groups with non-anonymous peers with which theuser shares interests, an altruistic behaviour is encouraged.This gives peers an incentive to take part in collaborativedownloading, speeding up the download process for otherusers.OneSwarmAnother system using Bittorent technology for file-sharingand using friendship between peers is OneSwarm [19]. One-Swarm is completely backwards compatible with Bittorrent,but gives the possibility for new features. A One-Swarm user creates an identity at a central ‘CommunityServer’ which manages a ‘swarm’. Since such an identity isnot exchanged between the community, servers of swarmsand community servers are not connected with each other,it is possible to have disjunct swarms. In the swarm theuser has a permanent identity which can be checked witha key system and keys can be exchanged via other systemslike Google Talk [16]. The identity has a list of friends thatare peers trusted by the user. OneSwarm gives the possibilityto connect, like the original Bittorrent system, toany peer. But it also gives the user the choice to connectonly to trusted peers and ask, if necessary, these peers toretrieve a download for the user. This enables the userto still download from peers that are not his friends, andstill does not have to exchange data with untrusted peers.OneSwarm has certain mechanisms build in which can obfuscatethe downloading and uploading via peers and thefollowed route. This can be by adding, for example, randomintervals with the trusted download chain to preventtracking of the original source [27].A simple overview of the current authentication and filesharingis shown in figure 2.2.2 Access control and authenticationPeer-to-peer systems were till now mostly developed withjust sharing files as fast and efficiently as possible in mind.Connections would be between random peers, often in amore or less anonymous way and not excluding any peersat all, even if they were maybe not trustworthy. Some listslike Peerguardian [20] did exist, which were only createdto prevent certain users from being tracked by corporationstrying to enforce copyright legislation. There was nofocus at all on using peer-to-peer systems for small privatesharing in the form of sharing certain files with onlya selected public.The by far most popular peer-to-peer system at the momentis Bittorrent [4], which has no form of access controlin the protocol at all. But there do exist some Bittorrentcommunities where trackers would only allow connectionsfrom users from a registered IP address. This is to createa small and exclusive community, which can enforce good

Figure 2. Simple representation of current authenticationand file-sharing in OneSwarm, taken from[19] and slightly modified.sharing ratio’s and eliminate free-riding [3]. This accesscontrol is an all-or-nothing approach. The user has accessto all files tracked or no access to any file at all. Alsothe implementation is not straightforward. Manual linkshave to be made between a service for logging in (a webserver for example) and the tracker service on the serverside. And meanwhile at the client side the user has to login with, for example, a browser on the web page beforebeing able to use his torrent application to connect to thetracker.There also exists an advanced piece of middleware calledAuthenticatr [31]. Authenticatr can connect to socialnetworksites to retrieve a list of friends and their networklocation. Next, it creates extra layers in the network whichare an overlay of a network of friends based on the definedrelationships in these social-networks. This enables anyapplication which runs on top of this middleware to berestricted to communicating with friends only. Thus, if apeer-to-peer application is developed that runs on top ofthis, it can be restricted to only have access to a file in acertain layer.At the moment the only application that can share onlycertain files with certain other users is OneSwarm. In thisapplication the user can select within the application itselfper file if it wants to share it unlimited or with a certaindefined set of users. But there is no possibility to userelationship rules or external data sets for applying this tofiles in a simple way. However, there is a current weaknessin the system as described in the OneSwarm paper [19].The visibility of files is done by keeping a certain hashsecret. If an attacker can guess this hash, the files will stillbe downloadable. The details of such a possible attack aredescribed very extensively in the paper of the OneSwarmdevelopers.3. CURRENT DATA SHARING WITH SO-CIAL CONTEXTMost internet users do want to interact with friends whileon-line, to exchange messages and pictures or to collaborate[22]. At the moment there are social-network sites toexchange these messages or to upload photos, which givegranular control over sharing these things with friends. Tocollaborate, people often have to share files like documentswith each other, for this certain tools and sites have beendeveloped. Both types of systems are considered. And wewill discuss which features they offer and which they lackto share files within a social context.3.1 Social-network sitesAll social-network sites give their users the possibility toshare text information, such as status updates or commentswith each other and often called ‘posts’, since thisis their core functionality [5]. These ‘posts’ can have, forexample, web links to information that can be found somewhereelse on the internet, like a YouTube video. In allmajor social-networks one cannot control per post whocan see and read theme. Often if one can define a groupof people who are allowed to see his or her posts, it willbe applied to all posts and not to a single one. If weblinks are posted, they are usually not hosted on the socialnetwork itself. So there is in general no possibility to useany authentication means to detect whether such a weblink is actually opened by a party that is authorized to doso or not.Most major social-networking sites like Facebook [11] andMySpace [24] also allow the sharing of pictures by its users.Those are uploaded to the central server of the socialnetworksite and the user can often control in detail whichfriends are allowed to see which picture and which onesnot. Often a very effective interface is available for definingcertain groups and rules to simplify this process. Somesocial-network sites also allow this for videos, but no otherfile types are allowed.Up to date is Facebook in number of users by far thelargest social-network [37]. Part of its popularity is creditedto the unique possibility of ‘Facebook Applications’[12]. Applications allow third party developers to interactwith Facebook, taking advantage of the authentication,relationship and access control management. Two FacebookApplications have been developed for data-sharingbetween users, like the ‘My Documents’ Facebook Application[1] and the ‘SMEStorage’ Facebook Application [2].Both applications run on a central server, which hosts theFacebook Application itself. The user actually uploadsthe file first to this central server and later other users candownload this file from the central server. Since a centralserver is used for the storage, there is often a file sizelimit enforced and the central server is the bottleneck inthe file distribution which can negatively influence performance.This makes that these kind of solutions can beused to easily share a data document, but their applicationon sharing a personal movie can be difficult. Also anapplication exists that integrates with the Azureus BittorrentClient [18]. The application has only a little amountof features. In short, it only shows a status on the user’sFacebook page whether its Azureus Client is on-line andwhich files it is sharing at each moment.Other major social-network sites, such as LinkedIn or MySpaceand others as listed in [37], are not able to provide allthe features offered currently by Facebook. So there is nosupport for features where third-parties are offering somekind of data sharing features on those sites.The conclusion is that apparently there are no social-networksites that offer currently proper integration with peer-topeerfile-sharing. While, if they would offer such a service,

enabling users to combine the strengths of peer-to-peerand social-network sites to share large files with selectedfriends, an advantage for the users could be gained.3.2 Data-sharing with applications & websitesThere do exist some applications and websites that offerthe feature of sharing data. These services can be split upin websites designed to handle uploads for sharing withother people and tools to synchronise your own files overmultiple computers.A very typical example of an uploading website is Rapid-Share [32]. These kind of web sites offer the user the possibilityto upload, via an applet or directly via the browser,a single file. This single file is not allowed to be too large,so that their server’s resources are not becoming too restrained.Because they have a central-server approachwhere everything is stored, it is difficult for them to handlehuge amounts of large files, in hard disk space and inbandwidth. To further restrict the amount of downloadingand to prevent their servers from overloading, thereis a limit for every IP address on the data that can bedownloaded every day. Moreover, before the downloadweb link is shown to the user, a waiting delay of aroundtwo minutes is used. Their business model is to removethese restrictions for registered users who pay a certainamount of money every month. Enabling them to investin their servers and bandwidth with the funds these paidusers generate. After the user has uploaded a file, he orshe will get an unique link to the download page of thisfile. Theuserisincontrolofwhohegivesthislinktoby, for example, e-mail or publicly posting it on an internetforum. The only security support that is offered isanonymity. As long as other users are not able to guessthis unique web link, they cannot download the file. Assoon as they have this web link, they have full access.A typical example of the synchronization tool type sharingis Dropbox [9]. Dropbox enables the user to automaticallysynchronize files between his or her computers. Thisis done by installing their client on these computers andcreating an account with their service. If the user changesa file on one computer, the client monitors this changedfile and uploads it to Dropbox server, to the user’s account.The other computers regularly poll the user’s accountat the Dropbox server to check for updated files andif they find updated files, they download these automatically.The sharing can be done by setting extra Dropboxonlyattributes on a file. Within these attributes the usercan choose for sharing a file with another Dropbox user(of which they will manually have to enter the accountname) or can even share files publicly. If the user doeschoose for the publicly accessible link, a RapidShare-likeservice can be created by a unique link that points to theshared file. When the user does choose the possibility forsharing only with another user, then this other user willsee this file in a special folder. Such special folders are alsoshown for all other users sharing files with the user. Dropboxhas the same capacity issues as RapidShare, becausethey also use a fully central server approach. Normally,the amount of data that can be stored by an account islimited. Moreover, paid upgrades are offered.Clearly both systems have weak points in their centralserver based approach. And especially the upload sites donot give any control over the access to the files. The currentsystems cannot fulfill the requirements we are lookingfor.4. REQUIREMENTSThis section describes requirements that have to be supportedby the desired combined solution.4.1 Integration with current systemsOur first demand will be that the new proposed architecturewill be simple and straightforward to use, easy toimplement and integrate with current peer-to-peer solutionsand current social-network sites. It is important toemphasize that we don’t want to create another socialnetworksite, but we want users to be able to use theircurrent social-networks. Sharing of files and other datainformation must be as easy as sharing, for example, pictureswith the social-network site.For the peer-to-peer downloading we should try to incorporatecurrent peer-to-peer technology, so that currentclients can be adopted to our new architecture with smallchanges, and that new advancements in peer-to-peer caneasily be integrated in our proposed architecture.4.2 Detailed control of sharingThe new architecture should implement one of the mainfeatures most social-network sites offer: controlling whatis shared with whom [5]. Most social-network sites offerthis feature, for example, when uploading pictures. Theuser can control in detail who is allowed to view them.The new architecture should incorporate this in the samemanner for sharing files, with logical rules differentiatingrelations as a (1) single friend, (2) all friends, (3) friend offriends, (4) certain networks or simply (5) everyone [36].4.3 Trusted sharingThe new architecture shall use the identity of the users inthe process of access control, instead of using the conceptof anonymous peers. We actually want that our proposedarchitecture uses the relations between users to improvethe operation of peer-to-peer system. We want that ourusers should be able to use only trusted connections withothers users, knowing who their peers are and having themauthenticated by e.g., a chain of trust [23]. By puttingusers in the context of their social group we are willing toreduce free-riding and encourage altruistic behaviour [28].This should be able to reduce the amount of malware andfake files on the network [33].Thus the proposed system must be able to authenticateusers and support a chain of trust.4.4 Proper scalingThe new architecture must not have major regressions incomparison with current peer-to-peer networks. The networkshould scale at least as well as current systems. Thatmeans as well with non-popular (e.g. scarcity of peers), aspopular (e.g. overloaded trackers [33]) files.The system must be able to deliver the files to the userswho wish to download them and must support an acceptabledownload speed.5. PROPOSED ARCHITECTUREThis section describes the architecture that should be designedin such a way that the requirements specified inthe previous section are satisfied. The proposed architectureis combining that capabilities and features providedby selected social network sites and the peer-to-peer filesharing systems.5.1 Chosen current technologies

Figure 4. A Simple overview of the Facebook Applicationarchitecture. Taken from [30]Figure 3. The current privacy and access controlas offered by Facebook for pictures.To meet the requirements presented in the previous sectionit is important to select one social network system andone peer-to-peer sharing system described in section three.When analysing the integration with a social-network, Facebookseems to be by far the best choice. The amountof registered users is a couple of times larger then anyrunner-up with more than 400,000 [10] . Moreover, Facebookis one of the few social-networks that provides anAPI (Application Programming Interface) that gives thepossibility to deeply integrate with the user-interface ofsocial-network website. Also a very convenient aspect isthat 70% of the current Facebook users is already usingthird-party ‘Facebook Applications’ and will probably notbe finding any trouble with adding, authorizing and usinga new Facebook Application [10].Facebook also offers fine-grained settings for access control.Thus detailed control of sharing is possible with reusingtheir interface of which an example is given in figure3. Facebook also offers so called ‘Facebook Networks’and ‘Friend Lists’ features. Both features allow users toassociate certain friends and relationships with a group.Facebook users can become members of a ‘Facebook Network’if they have an approved e-mail address of a certaindomain that is associated with a ‘Facebook Network’. Anexample is that only people with @(*.)utwente.nl e-mailaddresses are eligible to become member of the ‘Universityof Twente’ ‘Facebook Network’. The ‘Friend Lists’ are definedby Facebook users themselves, an example would beadding all colleagues from work to one list. A friend canbe member of multiple networks, multiple lists or none atall.Implementing a Facebook Application will demand a centralserver (or servers, the load can be balanced of course)running a web server to serve the users of the applicationthe web pages for the application and a database tokeep necessary information stored. Also a scripting languagewill have to be used on the web pages to be ableto communicate with Facebook. There is a wide choice oflanguages that can be chosen from for this [12]. A simpleoverview of how a Facebook Application does communicatewith Facebook itself and the user is shown in 4.From the peer-to-peer protocols, Bittorrent, with the One-Swarm extensions added, is the preferred choice. Bittorrenthas proven to be a very good and efficient way fordistributing files. OneSwarm uses and enhances Bittorrentwith security and access control features.Since OneSwarm is based on the Azureus Bittorrent Client,which is written in Java, OneSwarm is available for everymajor platform and can also be distributed as applets infor example a browser, giving it a lot of flexibility for theusers as a client. Also the interface of OneSwarm is at themoment already web based, making the integration withother web based services easier.5.2 ArchitectureNow we will describe the overview and functionality of ourproposed architecture for sharing data with peer-to-peeron social-network sites based on OneSwarm and Facebook.5.2.1 OverviewWe will approach the social-network within OneSwarmas one ‘Community Server’, whose role with the One-Swarm process was described in section two. The FacebookApplication server will be connected to the One-Swarm server populating the relationship data with theinformation from Facebook. This will be done througha database where the information is stored. At the momentOneSwarm has already support for defining groups.When integrating with Facebook, we will make the Facebook‘Networks’ and the Facebook ‘Friend Lists’ groupswithin OneSwarm.OneSwarm offers the choice between several back ends forits database. A new back end has to be written that willimplement a kind of middleware that will store part of thedata in an own database and can communicate with Facebookin, for example, FQL (Facebook Query Language)to retrieve relationship information.Figure 5. A basic overview of the proposed architecture.The user can start the OneSwarm client easily with for exampleJava Web Start [25]. This would give the user thepossibility to choose between starting the client automaticallyduring boot if preferred, or to let it be started automaticallywhen opening the Facebook Application pagein the web browser. The client will run in the background

Figure 6. An example of suggestions the FacebookApplication could give on the Facebook homepage.to perform the actual peer-to-peer sharing. This way thesharing can be active even when not having the FacebookApplication web page itself opened, making the availabilityof peers higher.The user can easily control the client via the FacebookApplication page in the web browser, see figure 5. Thiscan be done in a similar way as in Facebook. A user logsin on Facebook and opens the Facebook Application page.The user receives a web interface build up by this FacebookApplication and its own local client. The FacebookApplication stores relevant information for the CommunityServer or itself in a database. The Community Serverdoes communicate and authenticates the clients that theruns on the local computer of the users and retrieves necessary(relationship) information from the database. Sointegration in the Facebook website can be achieved properlyand deliver a consistent interface with the rest of thewebsite. This enables users to easily adopt the applicationas any other feature they are used to on Facebook.The client will have the ability to share files with otherusers. The process of file sharing is accomplished usingthe OneSwarm peer-to-peer system. This process can beset up in the background. The client can see their own(completed) downloads. They can check which files theirfriends share and provide web links to download these inthe background on the peer-to-peer system. The systemmay suggest even some popular downloads. An exampleof how this could look like is given in figure 6.The proposed architecture will combine the architecturesand features provided by the OneSwarm and Facebooksystems. The supported features are: (1) Access controland authentication, (2) Creating and Uploading, (3)Searching, (4) Downloading. In particular, the “Accesscontrol and authentication” and “Creating and Uploading”,features are enhanced versions of the similar featuresdeveloped by Facebook. The proposed architecture usesenhanced versions of the following features developed byOneSwarm: “Searching” and “Downloading”.The protocol used by the OneSwarm to communicate itsCommunity Server has to be enhanced in order to supportthe advanced Facebook Application features that will bedescribed in the following subsections. This should berelatively easy since the OneSwarm protocol is specifiedusing XML (Extensible Markup Language).We should also extend the security of the file-sharing, sincean attacker could guess a specific hash that is used forsharing files with a private group. It is described as weaknessin the current OneSwarm system by the developersthemselves. We propose generating a private and publicencryption key combination for shared files to tackle thisFigure 7. Enhancement of the encryption mechanism.problem. This would be the most straightforward, sincewe have to restrict access to unique sets of files.Since the access restrictions can vary for each set of files,thekeyshavetobegeneratedforeachset. Anexchangeofthe necessary keys to decrypt to authorized parties wouldenable those to actually decrypt the files. A technologylike PGP (Pretty Good Privacy) [15] which can be used toencrypt and decrypt files can be used. Other asymmetricencryption technologies, generating a public and privatekey pair, can also be used. A key will be generated perset of files and the decryption key will be uploaded tothe Community Server. The Community Server can thenprovide the decryption key only to the authorized clients(since those are authenticated and identified by the CommunityServer) according to the sharing rule-set as definedfor the file. This way physically being able to downloadthe data after successfully guessing the hash will still disablethe use of this data. The chosen technology for thekey pair does not influence the Community Server sinceit only has to store the key itself, which is small and normallyin text form. The encryption technology can bechosen by the clients itself, as long as the other client withwhom they exchange the files also supports this technologyand the chosen encryption technology is known bythe decrypting client. An overview of the extension forthe earlier overview is given in figure 7. The user’s clientencrypts the files and sends encrypted data via the peer-topeersystem. A key is uploaded to the Community Serverwhich stores this key in the database. The key can bedownloaded by clients that are authorized to do so.5.2.2 Access control and AuthenticationThe main operation of this feature is the same as the onespecified and used by the Facebook system. This subsectiondiscusses the main enhancements on Facebook fromthe point of view of access control and authentication.The first time the user wants to utilize the file-sharing featureit will have to add the Facebook Application to itsFacebook profile, see figure 8. This is an easy step thatmost Facebook users are used to do. Users can invite theirfriends to also add the Facebook Application, giving the

Figure 9. An example of a download request.Figure 8. A simple overview of the access controland authentication process.application the possibility to increase its user base quickly.After the Facebook Application has been added, the userwill receive the installation for the OneSwarm Java client.The client is written in Java and can be installed as, forexample, a Java Web Start Application. If the user subsequentlylogs in at the same web page, the web page shouldcheck for the client application, start it if necessary and,if it is not installed, offer installation of the client again.When the client is started for the first time by the user,the client will generate an asymmetric encryption key pairused for OneSwarm authentication. The key is publishedto the server, by our extended OneSwarm protocol, whichwill store it in the database with a reference to the FacebookAccount. This database can be accessed later bythe Community Server to identify the user when using theapplication. A user can have multiple clients installed, allwith different keys. This capability is useful when the useris using, for example, more than one machine. All of thosekeys are connected to the user’s Facebook identity and areavailable as peers in the peer-to-peer file-sharing process.When trying to download a file the client retrieves a list ofpeers from the Community Server, containing users withwhom they have a relationship on Facebook, with theirthen on-line clients and authentication keys. For large‘Facebook Networks’ a choice could be to only return asubset of users instead of all.5.2.3 SearchingThe main operation of this feature is the same as the onespecified and used by the OneSwarm system. This subsectiondiscusses the main enhancements on OneSwarm fromthe point of view of searching information.OneSwarm itself allows searching on the network by meansof ‘flooding’. The search query is performed on neighbouringpeers, who will further continue the search request.Thus, searching can be done using the OneSwarm protocolused for searching. Of course the interface for thesearching feature needs to be be presented via the FacebookApplication web page itself. This interface can bedesigned in the same way as the design of a default Face-book search feature.Because most users are not interested in selecting randomlyfrom available files, but often interested in files theyself noticed of via their friends that have shared interestsor having a common relationship to the file (like a vacationvideo where the user also took part in). With this wepropose a feature that might reduce the amount of searchingneeded. We can analyze the files users are sharingand measure their popularity. These suggestions for theuser can be adjusted to the popularity of the user’s friendswithin the social network. Every user can get its own optimizedset of what is considered popular and of courseonly ‘popular’ things are shown for files that are actuallyallowed to be discovered and downloaded by the user.A Facebook user has a so called Facebook ‘Wall’. This isa user’s own web page on Facebook where a user him orherself or a friend can post short text messages, pictures,web links and links to other Facebook pages. Other userscan respond to these posts with comments. Our FacebookApplication should offer the possibility to explicitly postabout files. In this way a user can update their friendsabout files they consider relevant, just like they can do atthe moment for, for example, pictures. Their friends dosee an aggregation of their friends’ posts in their Facebook‘News’ feed. This ‘News’ feed is a Facebook feature thatautomatically highlights the more interesting posts of auser’s friends.Users can invite their friends to download a certain filevia the Facebook ‘Requests’ system. This is a direct privatemessage between Facebook users in which a link canbe embedded. Such a link is able to let the user takean action within Facebook Application directly. A ‘FacebookRequest’ our application could offer is, for example,‘Download this file now’. In this way one user sends a linksuggesting to download a file directly to one of its friends.If this friend does click the link, the downloading wouldstart directly within the Facebook Application. An exampleof how this feature could look like is given in figure9.5.2.4 Creating & UploadingThe main operation of this feature is the same as the onespecified and used by the Facebook system. This subsectiondiscusses the main enhancements on Facebook fromthe point of view of creating and uploading information.When the user opens the Facebook Application web page,it will see the web interface of the client embedded in theweb page of the Facebook Application itself, see figure

10. On this web page there is the possibility to ‘upload’new files. Note that actually the new file is not uploadedbut it is shared, since no physical upload to the centralserver takes place. Files can be selected via a dialog to beshared. When files have been selected, the client generatesan asymmetrical encryption key that will be used for thesecure sharing. Next step for the user will be selectingwith whom the files have to be shared. For this a defaultFacebook sharing control interface can be used. After theselection of these sharing rules they will be saved on theserver and retrieved by the local client. One part of theencryption key will be uploaded to the Community Server,for decryption by authorized clients later on, and the metadataof the files, for indexing by the server to be used in,for example, measuring the popularity of a file. A simpleoverview of this encryption process is displayed in figure10.Figure 10. A simple overview of the creating &uploading process.5.2.5 DownloadingThe main operation of this feature is the same as the onespecified and used by the OneSwarm system. This subsectiondiscusses the main enhancements on OneSwarm fromthe point of view of downloading information.When user has found a file via the one of the methodsas described in the “Searching” section, the actual downloadingbegins. For this to happen, the user clicks a linkthat is actually presented by the client application andalso handled by the client. The client will start the download.The user will see a web page with an overview ofhis downloads and can see the progress as presented by itsclient. An example of this is given in figure 11.The downloading is done with the standard OneSwarmprotocol which is based on Bittorrent [8]. In the One-Swarm protocol, the client first downloads the metadata inwhich it can find a list of block hashes needed to downloadthe actual blocks of data. In the Bittorrent protocol thismetadata is normally stored in ‘.torrent’ files, but thoseare not used in the OneSwarm protocol. More detailedinformation about differences between the OneSwarm andBittorrent protocol can be found in the OneSwarm paper[19].Next, instead of contacting the other peers via a directconnection, as is in the Bittorrent protocol, OneSwarmtunnels the traffic through overlay paths created over thetrusted links [19]. Such an overlay path is interpreted as apeer within the Bittorrent implementation that the One-Swarm client is based on. So different paths can actuallyconnect to the same endpoint, but are considered separatepeers within the application. An overview of this isgiven in figure 12. All clients are authenticated with theOneSwarm Community Server, which enables them to authorizeconnections with friends. The user is trying todownload a file that Friend C is also trying to download.Since they are friends they can also exchange file-parts betweeneach other. The user is also friend with Friend Aand Friend B, which are both friends with a client that isnot a friend of the user. Still the user can download thefile with a path over Friend A and B. Both are in fact locatedat the same endpoint, but the user’s client does notknowthat.FriendCisalsoafriendwithFriendBandisalso using the path over Friend B to download the file.Since the downloading is done with (an extended) Bittorrentprotocol, it shares its features with it. So are thefiles split in blocks. The blocks are hashed, and blocks aredownloaded from different peers. Advanced tricks of theoriginal client (Azureus) of OneSwarm allow the detectionof congestion, which proves to be a very effective systemfor avoiding the congestion of single paths and shifting toalternative paths when needed. Also peer sharing incentivepolicies implemented by the Bittorrent protocol like‘tit-for-tat’ [8] are used. ‘Tit-for-tat’ is a mechanism thatmotivates a peer to upload to peers that also upload toitself. This gives peers an incentive to upload as muchas possible to increase their own download speed. Thisshould reduce the so-called ‘free-riding’ of clients, whichdo not upload and only download. The ‘tit-for-tat’ sharingmechanism is even more effective in OneSwarm than inthe usual Bittorrent protocol, because within OneSwarmthe peer’s identity is persistent, as where in Bittorrent it isused for only one session, and previous and future downloadsdo also count in the sharing file ratio.After the downloading of the file, the client should checkwith the Community Server for a public encryption key todecrypt the file. If the user is actually authorized to seethe file, the server does hand the key over to the client,enabling the user to use the contents of the file.5.3 DiscussionOur proposed architecture is based on the earlier definedrequirements. Full integration with current systems wouldbe achieved. The proposed user interface that integrateswith Facebook appears as any other typical Facebook Applicationto the user. Room for improvement would bethat social-network sites like Facebook, but also otherFigure 11. An example of the download overviewweb page.

Figure 12. An overview of a user’s client downloadingvia peer-to-peer (P2P).sites, would embed the installation of the new FacebookApplication via the existing social networking web sites.This would remove the step for users having to add andauthorize the proposed new Facebook Application. Alsothe social-network sites that do not offer support for anythird-party applications, which are all with the exceptionof Facebook, could offer this peer-to-peer file-sharing service.The proposed client integrates with current peer-to-peertechnology based on OneSwarm & Bittorrent. A vastamount of Bittorrent clients could easily be extended justlike OneSwarm to work with our architecture. A nice featurewould be that the download services of the clientwould already be offered by, for example, the browser oroperating system. In that case the website only has tointeract with this client service and does not have to bebothered with checking if the client software is running onthe user’s computer. Such a service for a browser couldprobably be compared with the newer geo-location featuresin HTML5 [35], where the browser is able to gatherdata from a local service [17] or application and hand itover to the website.The proposed architecture gives fine-grained control to theuser about who is able to access which files. The currentweakness in the system is the attack as was described bythe developers of OneSwarm. The current solution thatencrypts the file with a private key and handing the publickey over to authorized downloading parties does takecare of this problem, but might introduce a dependencyon requiring complexity and capabilities. A better solutionwould be to take care of this weakness somehow inthe sharing system itself.The proposed architecture gives the user the possibility toonly use trusted web links. The proposed client of the userwill only exchange data directly with known and trustedpeers, but still it has the possibility to access files that areshared by peers they do not trust themselves but have achain of trust with. Since actual sharing always appearsto be with direct friends within the social-network, freeridingcan probably be reduced to a minimum since usersare aware of their social group.The proposed architecture would scale quite well. Accordingto the research done in TRIBLER [28] by crawling asocial-network site, users of social-network sites have onaverage around 250 friends and 9.000 friends-of-friends.Facebook has next to other social-network sites also the‘Networks’ feature that people are often a member of.Which means that an average user has a lot of trustedpeers to connect to, and via these peers a lot of differentpeers can be reached too. The creators of OneSwarmdid crawl last.fm [19], which a social-network site focusedon music by aggregating all songs played by their users.Last.fm is a much less dense network than Facebook, buteven there the researchers did find out that most usersare connected within seven steps from other users andreal disjunct groups are almost non existent. Thus Facebook,with a much higher amount of users, maintainedrelationships and the existence of ‘Networks’, will give theusersalwaysapossibilityofapathtothedatatheywant.Also it is considered that at least some interests are sharedwith friends which greatly increases the probabilities thatfriends already have the requested files. In [13] they wereable to achieve 65% hits by just optimizing the overlay ofpeers. The scaling on the central server for the FacebookApplication and Community server will also do fine. Thereare at the moment already some very popular FacebookApplications with millions of users, and those are scalableeven while running sometimes heavy applications. Our applicationwon’t be that heavy since a lot of the web pageswill be rendered by Facebook itself and the local client.And within the file-sharing process and PGP key distributionthe server is sending only little amounts of (control)data. The scaling of the peer-to-peer process is, accordingto the OneSwarm study over the trusted paths, also quiteeffective. It might not be as effective as not using paths,but could outperform [19] Bittorrent on an anonymizernetwork, which uses a random set of peers as proxy toanonymize connections to end-points, like Tor [29].6. CONCLUSIONS & FUTURE WORKTo conclude our research we will look back at our subquestions. We did find out that possibilities to control thefile-sharing in current peer-to-peer applications with socialfeatures is quite limited. Though quite some systemswith friends as peers were developed only one system didcombine this successfully with access control. This is One-Swarm.Social-network sites or otherwise social aware sites did notoffer any peer-to-peer file-sharing at the moment. Onlycentral server based solutions were available, often limitingusers in their possibilities to share easily large files.We made a list of requirements for a combined system,this list was composed of:• Integration with current systems• Detailed control of sharing• Trusted sharing• Proper scalingWe researched whether it was possible at all to combinepeer-to-peer file-sharing systems and social-network sitesfulfilling these requirements, which did lead us to the answerof our main research question.This question was “Can we combine the strong characteristicsof peer-to-peer systems and social-network sites?”and can be answered positively. In our study we found outthat it is possible to combine both systems into a systemthat gives users the possibility to share large amounts ofpossibly confidential data in an effective way that can beaccessed and authenticated using a social-network site.Future work would include actually building this system.For this, the OneSwarm software should be expanded tointegrate with the friends system with Facebook. Contacthas been established by the author of this paper with theOneSwarm developers. From this communication could

e deduced that the integration of OneSwarm with a socialnetworking site such as Facebook, is received by theOneSwarm developers as positive. In order to realize thisintegration, also a detailed protocol has to be specifiedthat interconnects the new client and the new FacebookApplication. Moreover, the the new Facebook Applicationwill have to be specified in detail and programmed.Other future work could be related to a study on definingwhether the proposed architecture and features could alsobe applied for new concepts in the area of peer-to-peersocial-networks [23] like PeerSoN [26]. This is a kind ofsocial-network that stores all its information in a peer-topeermanner, removing the need of storing all data on onecentral server.7. REFERENCES[1] My Documents. Facebook Application, March 2010.Retrieved March 23, 2010, fromhttp://www.facebook.com/apps/application.php?id=8256642130.[2] SMEStorage -File Sharing. Facebook Application,March 2010. 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