Peer-to-Peer Systems. Winter semester 2014 Jun.-Prof. Dr.-Ing. Kalman Graffi Heinrich Heine University Düsseldorf

Transcription

1 Peer-to-Peer Systems Winter semester 2014 Jun.-Prof. Dr.-Ing. Kalman Graffi Heinrich Heine University Düsseldorf

2 Peer-to-Peer Systems Chapter 13 Online Social Networks Introduction to Online Social Networks Safebook P2P Framework for Social Networks This slide set is partially based on the lecture Peer-to-Peer Networks" of Prof. Dr. Thorsten Strufe at TU Darmstadt

3 Facebook, Twitter & Co. (Online Social Networks) Online Social Networks (Social Networking Services) web-based services that allow individuals to construct a public or semi-public profile within a bounded system, articulate a list of other users with whom they share a connection, and view and traverse their list of connections and those made by others within the system. Is this really all? the communication of participants through message exchange, commenting on the profiles of others (or previous interactions, e.g. in recommendations), which merely is a message exchange with the aim to annotate the addressed profile, and the wealth of applications (starting from simple ``poking'' mechanisms to a variety of ``gift'' and ``likeness'' applications for interactions between users) Source1: Boyd et al.: Social Network Sites Source2: Cutillo et al.: Privacy Preserving Social Networking through Decentralization 3

4 Online Social Networks Simplified, walled-garden version of the Web : Easy to set-up pages ( profiles ) of individuals ( and companies ) Links reflecting real-world relations between individuals Possibility to share user generated content including messaging Guest book / Wall (asynchronous broadcast) (asynchronous unicast) Chat (~ synchronous unicast) Collaborative applications / games Different target audience / application domain Private and personal OSN Public and professional OSN (business-oriented) 4

5 Target Audience and Domain Professional business services Private and personal services Niche/tailored services Micro blogging : Twitter Business trips and meeting service: Dopplr, TripIT Location-based achievement systems: foursquare, gowalla Slide based on lecture slides of Prof. Dr. Thorsten Strufe, TU Darmstadt, Peer -to-peer Networks, WS

6 Why Bother? 6

7 Goals and Motivations of Users and Providers Users want Storing / searching for content Profiles, friend lists, Pictures, shared Wall editing, User to user interaction Chatting, VoIP, Games Security Access control on their data Secure, confidential communication à Fun! System providers want High profit Many users Personalized advertisements Low operational costs For servers, electricity, cooling For personnel, legal issues Controlled Quality of Service To attract and keep users Providing reliable, high quality services à Money! 7

8 Security Objectives in OSNs Availability Of data and services Robust against censorship But you do not want to have childporn profile pictures Prevent from seizure or hijacking of identities Privacy / Confidentiality Users want to define access control rights on Personal information Communication traces Possibility to hide any data about any user Integrity Protect user data from unauthorized modification and tampering Ensure the link between OSN accounts and people 8

9 Generalized Architectural Model of SNS Distributed Environment Main SNS centralized Additional 3rd party application servers 9

10 Centrally hosted SNS Web-based solution Centrally hosted data Benefits for the provider Data used for marketing Issues Costs / scalability Trust in provider You cannot delete your account, only deactivate (Facebook) Limited application scope No real user-to-user interaction Wide community focus Must share information with the world Although only meant for family» Google+ addresses this with circles 10

11 Quest to Decentralize Issues of centralized architectures Centralized control Centralized data storage Full, centralized access to data Single Point of Failure ( and the legendary twitter whale) Taking back the web Breaking out of the walled gardens (again, cf. AOL) Re-democratizing the web Distribute the services! 11

12 Peer-to-Peer Systems Online Social Networks Decentralized Approaches for OSN This slide set is partially based on the lecture Peer-to-Peer Networks" of Prof. Dr. Thorsten Strufe at TU Darmstadt

13 Plethora P2P / Decentralized Social Services Free and open source software Diaspora, BuddyPress, CrabGrass, Cobs, DaisyChain, Diki, Elgg, FETHR, GNUNet, Gossple, Jappix, Lorea, Mycella, Movim, PeerScape, Pinax, StatusNet Academia Friend-of-a-Friend, FriendStore, HelloWorld, LifeSocial, LotusNet (Likir), PeerSon, Safebook, SocialCircle, Tribler, vis-à-vis, wuala, LifeSocial Focus on systems that implement social networking and publication functions Provide running software or a comprehensive protocol / system description Actually are decentralized 13

14 Decentralized Social Networking Approaches Centralized Idea: host your own OSN Social networks: BuddyPress, CrabGrass Federation of webservers Idea: link (private) webservers via standard protocols Social networks: Diaspora, Hello World Network, Fethr (Twitter), Diki 14

15 Decentralized Social Networking Approaches Centralized index, Storage on clients Idea: server manages index of users, storage of users is used Social networks: Daisychain, COBS, Gossple P2P-based social networks Idea: client devices form p2p network to store and find data Social networks: LibreSocial Motivated through: CPU power & bandwidth grow Privacy - awareness 15

16 1.2 Decentralized Social Networking Approaches Centralized Idea: host your own OSN Social networks: BuddyPress, CrabGrass Federation of (private) webservers Idea: link (private) webservers via standard protocols (FOAF, XMPP, PSYC) Social networks: Diaspora, Hello World Network, Fethr (Twitter), Diki Centralized index, storage on clients Idea: server manages index of users, storage of users is used Social networks: Daisychain, COBS, Gossple P2P applications with social aspects Idea: add to traditional p2p applications social aspects Social networks: Tribler, Wuala P2P-based social networks 16

17 Some Words on these Solutions Friend-of-a-Friend Data-centric, similar to yellow pages Federation of private webservers Store your data on your own / trusted friends webserver BUT: do you have a webserver? No real user-user interaction HelloWorld Network Won a startup prize Not existent anymore Diaspora Great marketing, $ for a promise Buggy and bad code Similar to Friend-of-a-Friend Now ~ users 17

18 Challenges for P2P OSN Let s use P2P to increase privacy in OSN! How could we proceed? Which challenges are we about to encounter? Performance Properties: P2P à filesharing! OSN: small, short lived objects Extreme heterogeneity (friends, uploaded content, resources) User behaviour / sessions (diurnal patterns, session- and inter session times) Incentives Mobile users vs. p2p / recursive routing, etc Security How can we guarantee availability? How do you search for somebody? Key management!? Identification services (we don t want fake accounts!) 18

19 Requirements for a (DHT-based) OSN Functionality Like Facebook Extendible through apps / plugins Different to typical p2p applications à Platform to host a wide set of applications General platform Core functionality as a basis Communication patterns? Extendible out of the box App-functionality, app-market? Data access patterns Read: Independent whether friends are online Write: create new content Update: update previous data Consistently for all copies of the data Delete: securely remove data Community-enforced deletion of illegal content 19

20 Requirements for a (DHT-based) OSN Suitable distributed data structures Security Supporting a wide range of apps Heterogeneous peer capacities and data access patterns Root of trust, user authentication Confidential, integer, auth. communication Access control: read/write/delete rights How to address attackers? Controlled Quality of Service Guarantees on system behavior? Response time, availability Self-adaptive behavior Several hands-on challenges How to implement Various search mechanisms Bootstrapping, NAT-handling An extendible graphical user interface 20

21 Peer-to-Peer Systems Online Social Networks Safebook This slide set is partially based on the lecture Peer-to-Peer Networks" of Jun.-Prof. Dr. Thorsten Strufe at TU Darmstadt

22 Safebook Developed at Eurecom & TU- Darmstadt Main idea: Use only friends in overlay Social topology Results in some security Main issue: Performance Requires large friend base per user 22

23 Design Principles Decentralization - P2P architecture Cooperation enforcement - Friends cooperate Leveraging existing Trust - Social trust trusted link - Friend = neighbor Privacy - Simple anonymous routing - Based on trusted links - Group Encryption 23

24 Architecture 3 Trusted ID System ID Management Contrast 1 Matryoshka Data storage Cooperation Communication with privacy 2 Peer- to- peer dht Lookup Different views of the network 24

25 Network View Social network overlay Trusted ID user id Peer to peer node id ip address 25

26 User i s Matryoshka Entry nodes Outer shell k e a Trust relabonship for i c s friend Inner shell i c d j b i s node d friend of c c friend of i d friend of i l f Trust relabonship for c User i s friends: store i s encrypted profile data End to end privacy based on hop by hop trust 26

27 Finding it, using P2P: a looks for b a e a b s profile req. DHT hash(b s afribute) e d c b s outer shell nodes b s profile d c b k f b s outer shell: h(b), e h(b), f lookup a looks for b s entry nodes k provides b s outer shell nodes data request a sends profile data request to a b s entry node Data reply One of b s inner shell nodes answers 27

28 Role of P2P system x Hop- by- hop trust User 1 u Node Privacy Hide requester s id Hide ids identities Hide requests statistics Integrity No msg forging No id manipulation H(User2) List of entrypoints Availability No DOS P2P system Tradeoff y Entrypoint z Performance Low Delays Lookup key redundancy v Mirror User 2 User2 s Matryoshka 28

29 Evaluation of the scheme (1) Privacy Friendship relations hidden through Matryoshkas Untraceability through pseudonymity and anonymous routing Cloning prevention Dos prevention Access control Availability ID management Key management Data replication at friends nodes 29

30 Performance - Reachability Number of contacts in the inner shell 80 to 250+ contacts required to be reachable at 90% with 3 or 4 hops 30% online probability (Skype data) Too many contacts? 30

31 Performance Reachability Incr. Spanning Ratio Number of contacts in the inner shell 30% online probability (Skype data) 15 to 25 contacts required to be reachable at 90% with 3 or 4 hops 31

32 Performance - Delay Further 1 st Lookup Lookups delay delay CDF CDF for a for 4 shell a 4 shell matryoshka matryoshka (*) (*) 90 th percentile: 90 th percentile: 5,42 s 13,49 s Total data lookup Bme: T dl = T DHT + T Mat Median: Median: 1,73 s 8,04 s Further lookups: T DHT =0 thanks to caching Average: 9,17 2,71 s Time [ms] (*) Data computed by applying the Monte Carlo sampling technique on single hop delay measurements and on delay measurement for a successful DHT key lookup in KAD (Biersack..) 32

33 Summary on Safebook P2P topology matches social topology Social storage, security through trust relations Some critical remarks Performance may be an issue Onion routing of messages Delay: median 1.73s, average 2.71s à in real life probably more Bandwidth: Retrieval of a 100kb picture à generates a multitude of load + delay Bootstrapping problems How to handle users with only few friends? Where to store data if friends are offline? Security issues Do you trust your friends? Conclusion Very interesting attempt, hopefully successful soon 2012: Sold to a startup 33