Freeriders in P2P: Pricing Incentives

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Freeriders in P2P Pricing Incentives

• Don Towsley
• UMass-Amherst

collaborators D. Figueiredo, J. Shapiro
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Grand challenge

• Design economic mechanisms to provide incentives
  for increasing utility of network
• Internet
• ad hoc
• overlays

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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

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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

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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
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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

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Onion routing example
peer
peer
C
A
R
initiator
I
recipient
Path C,B,D,C,R
B
D
peer
peer
G
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Pricing and anonymity

• reputation mechanism
• must know peer identities
• wont 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

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Payment system example
peer
peer
. . .
. . .
N
M
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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?

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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

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

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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

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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