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Off-line Karma

Off-line Karma. A Decentralized Currency for P2P and Grid Applications. Overview. Peer-to-peer systems Application example P2P Applications Related work Our approach For static networks For dynamic networks Conclusions. [ Castro et al ’02 ]

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Off-line Karma

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  1. Off-line Karma A Decentralized Currency for P2P and Grid Applications

  2. Overview • Peer-to-peer systems • Application example • P2P Applications • Related work • Our approach • For static networks • For dynamic networks • Conclusions Flavio Garcia - SOS Group - Off-line Karma

  3. [Castro et al ’02] “Secure routing for structured Peer-to-Peer overlay networks” Id, m Peer-to-peer networks CA Flavio Garcia - SOS Group - Off-line Karma

  4. Application Example f(x) x x x f(x) S Flavio Garcia - SOS Group - Off-line Karma

  5. Free riding problem Donations P2P Applications • Seti@home • Folding@home • Distributed.net • Napster • Gnutella • Kazaa • eDonkey Flavio Garcia - SOS Group - Off-line Karma

  6. Related Work • Generic Payment Schemes • Rivest and Shamir’s “Pay World” • Rivest’s “Electronic lottery” • Rivest and Shamir’s “Micromint” • Multi-payment schemes based on public key signatures • P2P Specific • The POPCORN project • MojoNation • KARMA • PPay Flavio Garcia - SOS Group - Off-line Karma

  7. Objectives: • ScalabilityTransaction cost should be independent of the size of the network. • No centralized controlThe system should not rely on one or several central, nodes and should not require any hierarchy. • Load BalanceThe overhead of the protocol is, in average, equally distributed over the peers. • AvailabilityTwo Karma users should be able to make transactions even when users are joining or leaving. • Double-spending detection For every double spent coin, a fraudulent user should be blacklisted Flavio Garcia - SOS Group - Off-line Karma

  8. The Threat Model Flavio Garcia - SOS Group - Off-line Karma

  9. The Threat Model Flavio Garcia - SOS Group - Off-line Karma

  10. Off-line Karma for Static Networks • Minting • Spending • Re-minting Flavio Garcia - SOS Group - Off-line Karma

  11. Flavio Garcia - SOS Group - Off-line Karma

  12. Spending k0 U0 k1 U1 ? k2 U2 k3b k3a U3a U3b k4b k4a U4a U4b Flavio Garcia - SOS Group - Off-line Karma

  13. Re-minting • Check for fraud in DB • Coin expires • |R| = r • Remint set for k is always the same DB Flavio Garcia - SOS Group - Off-line Karma

  14. Flavio Garcia - SOS Group - Off-line Karma

  15. Dynamic Networks • Minting still works. • Spending still works. • Reminting has a problem: • Some reminter may be off-line. • Remint set depends on density. • While verifying users do not know the state of the network at re-mint time. • Adversary has more freedom. Flavio Garcia - SOS Group - Off-line Karma

  16. Fixing re-minting for dynamic networks DB Flavio Garcia - SOS Group - Off-line Karma

  17. adv. pick r nodes make c faulty How large should r be? Flavio Garcia - SOS Group - Off-line Karma

  18. Early double-spending detection Flavio Garcia - SOS Group - Off-line Karma

  19. Conclusions - Disadvantages • Public key crypto involved. • Users need to be on-line periodically. • Coin grow. • Re-minting is an expensive operation. Flavio Garcia - SOS Group - Off-line Karma

  20. Conclusions - Advantages • We have developed a secure and fully distributed currency. • We provide a non-repudiable blacklisting mechanism. • The message complexity is two for spending and O( s) for re-minting. • Possible early double-spending detection. Flavio Garcia - SOS Group - Off-line Karma

  21. THE END Flavio Garcia - SOS Group - Off-line Karma

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