1 Freeriders in P2P: Pricing Incentives Don Towsley UMass-Amherst collaborators: D. Figueiredo, J. Shapiro

2 Grand challenge Design economic mechanisms to provide incentives for increasing utility of network  Internet  ad hoc  overlays

3 Overlays  why?  to deploy new services/applications  to fine tune network for applications  instantiations  CDN  p2p  challenge  incentives for users to join and contribute services (freerider problem)  incentives for peering

4 Freerider problem  widely observed phenomenon  file sharing [e.g. Adar & Huberman Gnutella measuremets] Why should users participate – except when they need service?  solutions  reputations need reputation to get service providing reliable service yields reputation  payments need tokens to get service providing services yields tokens

5 G Anonymity problem  anonymity property  set of peers G  message initiator I  message from I appears to be from anyone in G  p2p implementation  message routed along random path through G  source routing vs. randomized forwarding  response routed along reverse path I

6 Onion routing  source based routing  packet encrypted by source in layers (onion)  each layer encrypted with public key of next node  encryption layer removed at each hop  install connection state in each hop  reverse path for responses

7 Onion routing example I C B D A R initiator recipient peer G Path = {C,B,D,C,R}

8 Pricing and anonymity  reputation mechanism  must know peer identities  won’t work for anonymity  pay to initiate messages  ante up at join  forward messages to earn money  payments in electronic cash to preserve anonymity  modified onion-routing protocol to control... who gets paid when they get paid how much they get paid

9 Payment system example NM peer... Bank

10 Research challenges  analysis  model?  equilibrium price?  sensitivity to user desires?  other anonymity protocols  crowds  approach tied to the “real” economy  simplifies bootstrapping (cash from outside)  alternate markets?

11 Research challenges  how to generate trust  central bank  can trust be distributed?  reputation-based solutions?  relationship to payment-based solutions?  hybrids? to deal with malicious users  other p2p apps?  ad hoc networks?  other networking applications

12 D.R. Figueiredo, J. Shapiro, D. Towsley "Incentives for Cooperation in Anonymity Systems" ftp://gaia.cs.umass.edu/Anon_Incentive_03. pdf

13 Payment System  use onion to embed payment  source inserts encrypted payment for each hop in path  node must forward message to get payment  key for payment is visible only to next hop  node cashes payment before forwarding response  ensure valid payment  off-line protocol can defer validation

14 Electronic cash  electronic cash  supports untraceable transactions  payer identity hidden from everyone  can prevent double payment  use onion to embed payment  source inserts encrypted payment for each hop  node must forward message to get payment  node cashes payment before forwarding response