P2PWNC Wireless Community Network

1. P2PWNCWireless Community Network CMSC 711: Computer Networks Yee Lin Tan Adam Phillippy

2. Introduction • Ubiquitous Internet access is a necessity • Email, web, VoIP, messaging, remote network access • Current state • Internet access far from ubiquitous • Required infrastructure not yet in place • Wireless Internet Service Providers (WISPs) • Coverage limited to selected hotspots • Wireless LAN (WLAN) • Deployed in homes, schools, airports, etc. • Idea • Why not unite all WLANs to provide ubiquitous access to the Internet?

3. Peer-to-Peer Wireless Network Confederation (P2PWNC) • Framework for uniting WLAN hotspots • Community of administrative domains that offer wireless internet access to each other’s users • P2P network of domain agents (DA)

4. Peer-to-Peer Wireless Network Confederation (P2PWNC) • Administrative Domain • Examples: • Residential hotspot with 1 access point • WISP with access points in many locations • Domain Agent (DA) • Each administrative domain maintains 1 DA • Physical node that represents the WLAN • Responsibilities: • Regulates wireless service provision and consumption • Eliminates need for roaming agreements

5. Peer-to-Peer Wireless Network Confederation (P2PWNC) • Simple accounting mechanism based on token-exchange • When roaming in another P2PWNC domain • To compensate for resources consumed, home DA transfers tokens to visited DA

6. P2PWNC Design • Based on reciprocity • Domains must provide resources to visitors • So that their own users can consume resources of other P2PWNC domains when roaming

7. Distinctive Characteristics • Open to all • No registration or central authority • Joining P2PWNC is similar to joining a file-sharing network • Free to use • No barrier to entry • Reciprocity drives the system • Autonomous domains • Each domain decides how much resources it wants to provide to visitors • Protects privacy • Identity and location privacy

8. P2P Systems • Communities of economic agents cooperating for mutual benefit without centralized control • Characteristics: • Makes use of otherwise underused resources • Agent autonomy • Scalability, fault-tolerance, reliability

9. P2PWNC as a P2P System • Underused resources • Residential hotspots typically operate only at a small percentage of maximum throughput • Cost-sharing • Distribute cost among participating administrative domains • High cost for a single provider to cover large areas • Hardware • Administration, operations, maintenance • Decentralized control • Distributed accounting to track who owes who and how much • Agent autonomy • Can dynamically adjust provisioning rates

10. Architectural Overview • Unique logical name for each DA • Can reuse DNS name • Registered users • Local users of a particular domain • Examples: • Residential hotspot: all household members • WISP: all subscribers • Roaming users • Visiting users from another domain

11. DA Modules • Name service • Maps logical P2PWNC domain names to IP addresses of DAs • Authentication • Maintains a database of registered users along with security credentials • Traffic-policing • Logs and shapes internet traffic • Allocates specific amounts of bandwidth to visitors • WLAN • Firewall, DHCP, DNS, access point control • Distributed accounting • Secure storage of accounting data

12. DA Modules (2) • Consumer-strategy • Home DA’s consumer-strategy is contacted when roaming user wants service • Decides if transaction should continue • Pays required tokens to visited DA’s provider-strategy module • Provider-strategy • Decides whether to provide service to visitor • Decides current service prices

13. DA Modules (3) • Privacy-enhancement • Protects identity privacy • Hides user name and home DA of roaming user from visited DA • Protects location privacy • Hides visited DA from home DA • Distributed Hash Table • Low-level module used by name service and distributed accounting

14. Security and Privacy Issues • Abuse by untrustworthy visitors • Illegal activities • Traffic logging by untrustworthy providers • Possible solution: tunneling through trusted gateway (e.g. home DA) • Identity privacy • Possible solution: create a new alias for every new connection? • Identity and location privacy • Possible solution: Mix network

15. Mix network Peer ‘A’ (mix 1) Peer ‘B’ (mix 2) Alias_X@B { MIX, C, { STOP, X }C }B Alias_X@C { STOP, X }C Alias_X@A { MIX, B, { MIX, C, { STOP, X }C }B }A Peer ‘P’ (provider) Peer ‘C’ (home) “My P2PWNC ID is Alias_X@A” Credentials include real ID and a mix chain encrypted using nested public-key encryptions X@C Idea credit: David ChaumSlide credit: George Polyzos

16. Economic Considerations • Optimal system parameters • Consumer/Provider strategies, token prices • Secure distributed accounting subsystem • Monitors peer contribution and consumption • Uses cryptographically secure tokens (cannot be forged) • Domain strategies • How to charge usage: • KBytes or hour, current congestions levels, identity of consumer • How to balance conflicting requirements: • Want best possible service for its own roaming users • Must provide service to visitors to earn tokens for use by roaming users • May affect service provided to its own local users

17. Economic Considerations (2) • Offline DAs • Problem • Roaming user requests service from visited DA • Visited DA unable to contact home DA • Possible Solution (decentralized version) • Home DA distributes token allowances to users • User pays without intervention of home DA • Token generation • How DAs first acquire tokens • Distributed banks generate tokens and distribute to new entrants

18. Economic Considerations (3) • Domain heterogeneity • Different in terms of: • Coverage size • Coverage location • Number of registered users • Problem: • Domains with few visitors, difficult to earn tokens • Possible solution: set high token prices • More general problem: • How to make sure a few domains don’t monopolize all tokens?

19. Summary of DA Responsibilities • Regulate prices for service • Make sure visitor traffic does not adversely affect traffic from registered users • Ensure best possible treatment for own (registered) users that are roaming

20. Business Models - Who can make a profit • Upstream ISPs that allow P2PWNC may be preferred by customers • “Pay-as-you-go” domains • Vendors can sell pre-paid cards containing P2PWNC user id and credentials • Virtual P2PWNC • Virtual DA obtains tokens from P2PWNC domains outside normal interaction model • Sells tokens in the form of pre-paid cards

21. Business Models – Who can make a profit (2) • P2PWNC domain aggregators • Host DA for multiple small WLANs • Similar to web hosting • Vendors of DA modules • Provide consumer-strategy and provider-strategy modules • Hotspot indexing engines • Tune DA parameters • Security and privacy enhancements

22. Operational Issues • Need more economic analysis and simulations • How P2PWNC and token-based incentive operate in real-world environment • Regulatory obstacles • Some ISPs prohibit sharing of broadband connections

23. P2PWNC Implementation • http://mm.aueb.gr/research/p2pwnc • GPL Licensed • AP: Linksys WRT54GS • Firmware • Client: QTEK 9100 • C and Java

24. Implementation Assumptions • Good • No central authority • Users may use unlimited, free IDs • User consumption is not homogeneous • Software can be modified/hacked • Teams (domains) will try and cheat • Teams will collude • Not so good • Team consumption is homogeneous • Team members trust each other • ISPs allow connection sharing

25. Teams, users, and receipts (IOUs) Team AP Team member

26. Receipt accounting C CONN RREQ RCPT RREQ CACK RREQ RCPT t0 w1 t0 w2 ? RCPT P R provider, team timestamp, weight t0 w2

27. R Centralized

28. Decentralized R R R

29. Decentralized • One receipt server per team • Gossiping protocol • Devices carry a sample of receipts • Consumers share receipts with providers • Adds overhead for verifying receipts • Incomplete view of the “receipt graph”

30. Receipt graph F E G G B B A I D D C C H H Does C owe H?

31. Maxflow decision • Probability of me granting you service What IOU What you owe me

32. Maxflow (bottle neck flow) F E G B A Min C-H cut I D C H

33. Abuse • Uncooperative teams • Evident from receipt graph • Other teams will stop providing service • DOS attacks • Centralized server is vulnerable • Decentralized servers have secret IPs • Teams do not communicate via Internet • Colluding teams…

34. Naive collusion F G X0 B X1 X2 I C H

35. Sophisticated collusion F G X1 B X0 X2 I X3 C H

36. Generalized Maxflow • Look for collusion hub X0 • Discount suspicious paths • Discount flow passing through vertices with a high sum of outgoing edge weights • Discount flow passing through many vertices • Assumes homogeneous team usage

37. Security • Team leader • Public/private keys for team identity • Signs member certificates • Team members • Public/private keys for member identity • All receipts are signed • Elliptic Curve Digital Signature Algorithm (ECDSA) • Signing faster than verification • Mobile devices have limited computing power • No central authority (decentralized)

38. Security

39. Simulation • Providers and consumers make decisions based on benefit-to-cost ratio • Evolutionary learning • Providing +cost, consuming +benefit • Simulate interaction across 500 rounds • 1 new team added per round • 300 total teams

40. Strategies • Switch to best strategy after each round • Most teams adopt cooperative strategies • After 500 rounds • 175 Reciprocative teams • 100 Unconditional cooperator teams • 20 Random cooperator teams • 5 Unconditional defector teams

41. Strategy

42. Questions • Will it work in the real world? • Sporadic usage • Receipt history flushing • Is it scalable? • Maxflow could get expensive • What about heterogeneous team usage? • Variable cost of bandwidth • Who is responsible for the AP’s traffic? • Will the RIAA believe it wasn’t you?

43. P2PWNC Publications • Initial idea • A Peer-to-Peer Approach to Wireless LAN Roaming. Efstathiou EC, Polyzos GC. ACM WMASH, 2003. • Implementation details • Stimulating Participation in Wireless Community Networks. Efstathiou EC, Frangoudis PA, Polyzos GC. IEEEINFOCOM, 2006.

44. Receipt repository

45. Collusion

46. Maxflow overhead

47. Cryptographic overhead

48. Real-World Example - FON • Largest WiFi community in the world • Idea • Members (aka Foneros) share wireless Internet access at home • In return, get free WiFi wherever there is a Fonero Access Point • Use Fonero login • How to become a member: • Buy a WiFi router (aka La Fonera) from FON

49. More about FON • 3 types of Foneros (members) • Linuses • People who share home WiFi to get free WiFi wherever there is a FON Access Point • Aliens • People who do not share their WiFi but want access to a FON Access Point • Charged $3 per day • Bills • Businesses who want to make money off their WiFi • Don’t want free roaming • Get 50% of money Aliens pay • Can advertise on their own personalized FON Access Point homepage