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1、Off-lineKarma:ADecentralizedCurrencyforStaticPeer-to-peerandGridNetworksFlavioD.GarciaJaap-HenkHoepmanNijmegenInstituteforComputingandInformationSciences(NIII)RadboudUniversityNijmegenP.O.Box9010,6500GLNijmegen,theNetherlandsflaviog,jhh@cs.ru.nl23rdNovember2004AbstractPeer-to-peer(P2P)an
2、dgridsystemsallowtheiruserstoexchangeinformationandshareresourcesinauniformandreliablemanner.Inanidealworld,usersmakeroughlyasmuchresourcesavailableastheyuse.Inreality,thisisnotalwaysthecase,andsomekindofcurrencyorbarter(calledkarma)isneededthatcanbeexchangedforresourcestolimitabuse.Previ
3、ousproposalsforsuchsystemshavenottakenthedecentralisedandnon-hierarchicalnatureofP2Pandgridsystemsintoaccount.Wepresentacompletelydecentralised,off-linekarmaimplementationforP2Pandgridsystems,thatdetectsdoublespendingandothertypesoffraudundervaryingadversarialscenarios.Thesystemisbasedont
4、racingthespendingpatternofcoins,anddistributingthenormallycentralroleofabankoverapredetermined,butrandom,selectionofnodes.1IntroductionPeer-to-peer(aka.P2P)networkslikeBitTorrent[Coh03]andGnutella[Kir],andgridsys-temslikeXGridaredistributedsystemswithoutcentralisedcontrolorhierarchicalorg
5、anisation.Giventhisatstructure,thesesystemsscaleverywellwhenthenumberofnodesincreases.Scalabilityisimportant,giventhefactthattheInternetisstillgrowingexponentiallyandmorepeoplehavepermanentInternetconnections.Currentapplicationsofthesesystemsincludebutarenotlimitedto:lesharing,redundant
6、storage,distributedcomputations,dataperpetuation,P2Pe-mail,P2Pwebcacheandanonymity.Gridsystemshavebeendevelopedasaresponsetothefactthatcomputerresourcesareusuallyverybadlydistributedintimeandspace,andalmostallofthemarewastedmostofthetime.CPUcyclesaremaybethebestexampleofthis.Mostofthecomp
7、utersintheworldareidlemostofthetime,withonlyoccasionalperiodsofhighload.Then,itseemsnaturaltomakeId:karma-inc.tex,v1.42004/11/2311:54:57jhhExp1resourcesavailablewhenidle,andtobeabletouseotherusersresourcesinreturnwhenneeded.Inanidealgridsystem,thewholeInternetconst
