1. Privacy-Preserving P2P Data Sharing with OneSwarm -Piggy

2. Outline Overview Related Works Data Sharing with OneSwarm Protocol Design Security Analysis Evaluation

3. Overview P2P file sharing is efficient and common Most P2P application allow third parties to monitor users behaviour Privacy -the protection of information from unauthorized disclosure Attackers can get some privacy information by observing user behaviour ex: using BitTorrent to download security patch

4. Related Works BitTorrent A common P2P file sharing protocol with high efficiency but without privacy protection Tor Uses onion routing techniques to anonymize request via a set of relay nodes Freenet Uses an anonymous P2P publishing system

5. Data Sharing with OneSwarm An exmaple

6. Data Sharing with OneSwarm Public distribution Everyone in the network can download file freely All data need not be private Serves as a fully backwards compatible BitTorrent client

7. Data Sharing with OneSwarm With permission Only users with permission can download files Uses persistent identities to define per-file permission Allows all permitted users to recognize one another and engage in swarming downlod

8. Data Sharing with OneSwarm Without attribution Depends on obscuring attribution of source and/or destination Instead of directly advertise data, it uses privacy- preserving keyword search Data is relayed through unknown number of intermediaries Apprpriate for sensitive material

9. Protocol Design Two major tasks Defining and maintaining the overlay topology Locating and transferring data objects Topology Define overlay links by exchanging public keys Peers are either trusted or untrusted

10. Protocol Design Transport The mesh defined by the web of trust among users is ued to locate and transfer data Inspired by existing P2P swarming systems e.g., BitTorrent Restrics direct communication to a small number of persistent contacts Locates distant data source by flooding through the overlay Data transfers occur over the reverse search path Obscuring the identities of sender and receiver when sharing data without attribution

11. Protocol Design Linking Peers with Trust relationships 1024 bit RSA public/private key pair, public key serves as its identity (persistent) among its peers Key exchange Discover and exchange over local area network Piggy-back on existing social network e.g., Google Talk By email invitations

12. Protocol Design Managing Groups and Trusted Peers Private Community Server Maintains a list of registered users Provides authorized subscibers with a current set of public keys Public Community Server Allows new users to easily obtain a set of untrusted peers

13. Protocol Design Identity and Connectivity Long-term identities are linked to transient IP and port number via DHT DHT entries are encrypted with public key ID->{IP, Port} Various key exchange + DHT => overlay mesh

14. Protocol Design Naming and Locating Data Between connected peers => exchange file list Naming 160 bit SHA-1 hash of name and content Low order 6 bit => file ID in search message Congestion Aware Search Tradeoff between overhead and performance Shortest path Management of propagation of searches

15. Protocol Design Naming and Locating Data Congestion Aware Search Search message don’t have time-to-live Maintaining a set of rotating Bloom filter and forward search message if the forwarder had idle cpacity and hasnot yet forwrded it Forward to untrusted peer probabilistically Delay 150ms before forwarding Terminate with search cancel message

16. Protocol Design Naming and Locating Data Path Setup Search message matched => search reply (delayed) Search identifier Path identifier

17. Protocol Design Swarming Data Transfer Keep alive message refresh path Tunnels BitTorrent traffic through overlay paths Dicover new path by periodically flooding search message Enhance load balance and efficiency

18. Protocol Design Incentives Client maintain tansfer statistics for each peer Retain tic-for-tac in BitTorrent Contention => weight decided by ratio of contribution and net consumption Forwarding is sum to 0

19. Security Analysis Goal Improve privacy by allowing users to control information disclosure Resistent to the disclosure of user behaviour to an attacker with control over a limited # of overlay nodes

20. Security Analysis Attacks and Defenses Persistent peering relationship limit monitoring power Heterogeneity of trust relationship foils timing attacks Lack of source routing limits correlation attacks Constrained reandomness frustrates statistical attacks Network dynamics limit value of historical data

21. Security Analysis Timming Attacks

22. Security Analysis Collusion Attacks

23. Evaluation Overlay structure

24. Evaluation Multiple-path Transfer

25. Evaluation Comparison with existing systems

26. Evaluation Overhead

27. Evaluation Utilization

28. Conclusion Strength Data collected from real world Weakness Not well organized