Chainspace: A Sharded Smart Contracts Platform

WrittenBy:MustafaAl-Bassam,AlbertoSonnino,SheharBano,DaveHrycyszyn,andGeorgeDanezis

PresentedBy:AaronZhang

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign•  ImplementationandEvaluation•  Limitations• Conclusions

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign•  ImplementationandEvaluation•  Limitations• Conclusions

Modernblockchainsareveryslowwhensignificantvolumeisapplied.

Chainspace

• Chainspaceisadistributedledgerplatformforhigh-integrityandtransparentprocessingoftransactionswithinadecentralizedsystem.•  ItavoidsthehighlatencythatEthereumfacedbyshardingthecoinbase.•  Supportsanewformofprivacybyseparatingthecodethatexecutescommandsandthosethatcheckthecomputation.

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign•  ImplementationandEvaluation•  Limitations• Conclusions

•  ItemsthatholdstateinChainspace.

•  Refertotheobjectsasoandasetofobjectsaso∈O.

•  ObjectshaveanIDandaType.

•  Objectsareeitheractiveorinactive.

Objects

Contracts

•  Specialtypeofobjectthathasfunctionsanddataregardingitself.

• AnamespaceforObjectswithinChainspace.

• Refertocontractsasc

Procedures

• Whereanumberofobjectsareprocessedtogeneratesomeoutputofobjects.

•  c.p(~w,~r, lpar, spar)→ ~x, lret,sret

Checkers

•  Everycontracthasacheckerwhichrecievesaprocedureandthenchecksiftheprocedureisvalid.

•  c.v(p,~w,~r,lpar,~x,lret,dep)→{true,false}

• HonestShards• Ashardwherelessthan1/3rdofallnodesarenotcontrolledbyanattacker.

• DishonestShards• Ashardwheremorethan1/3rdorallnodesarecontrolledbyanattacker.

Chainspace supports Security Properties

•  Transparency•  EverynodeintheChainspacepublishesaMerkleTreetypeobjectwhichprovidesahistoryofchangestothatnodeitself.

•  Integrity•  Notwonodesintheshardcanhavethesamedata.

•  Encapsulation•  Shardscannotcommunicatewitheachother.

• Non-repudiation•  Ifafailurewouldallowthosetoaddinvalidtransactions,usingtheMerkleTreedata,onecanfindwherethatdatawasaddedandtakeaction.

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign•  ImplementationandEvaluation•  Limitations• Conclusions

• Transactionsareallcompiledinasequenceoftracesoftheproceduresthathavebeenusedtocreatethem.

Two Rules to Modify Nodes within Contracts

•  SequenceRule•  Thetracelistisonlyvalidifitsobjectsareinsequence

• CheckRule•  Onlytransactionsthatpassthecheckerforthecontractmaybeadded.

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign•  ImplementationandEvaluation•  Limitations• Conclusions

Directed Acrylic Graph

• Acombinationofobjects,procedures,andoutputsformaDirectedAcrylicGraphwhichcanbeusedtospeedupablockchain’sprocess.

• Auniqueidentifierisattributedtoeachandeverytraceintheobjectshistoryforquickindexing.

Security Theorem 1

Nosequenceofvalidtransactions,byapolynomialtimeconstrained

adversary,mayre-createanobjectwiththesameidentifierwithan

objectthathasalreadybeenactiveinthesystem.

ProofFortwoobjectstohavethesameID,theymusthavebewithinthesameshard,becreatedbythesameprocedure,andhavethesameinputs.Whenanobjectiscreatedwithatleastoneinput,theactiveinputobjectsareremovedfromthesetandnewnodescreatedwiththesameinputobjectcannotbeadded.

Audits

• PartialAudit•  Apartialauditissimplywhentheblockchainreturnsareplywhetherornotthetransactionhasbeenpassed

•  FullAudit•  Afullauditinvolvesreplayingalltransactionsfromthebeginningoftimesotheusercanunderstandthetracesthatledtothecurrenttransaction.

Security Theorem 2

IfacontractcappearsinanytracewithinatransactionT,thentheconcernednodessetΦ(T)willcontainnodesinashardmanaginganobjectOofatype

fromcontractc

Proof TransactionsTcannotbeplacedwithinanobjectOwithoutpassingthecheckerfunctionwhichonlyworksiftheobjectmatcheswiththesharditself.

S-BAC

•  ShardedByzantineAtomicCommit•  CombinationoftheByzantineAgreementandanAtomicCommit•  ByzantineAgreement

•  ensuresthatallhonestmembersofanodesideof3f+1willcometoanagreementdespitedishonestnodesofsizesmallerthanf.

•  AtomicCommit•  Ifonesharddeniesthecommit,allshardsdenythecommit.

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign• SystemandApplicationsSmartContracts•  ImplementationandEvaluation•  Limitations• Conclusions

Implementation

•  ImplementationinJava(Nodes)andPython(Contracts)

• Anodeismadeupoftwoparts•  Checker,checkstoseeiftheprocedurematcheswiththenode•  Core,whichcanaccessthetracestofindpreviousiterationsofthenodetocompare.

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign• SystemandApplicationsSmartContracts•  ImplementationandEvaluation•  Limitations• Conclusions

Limitations

• Ashardcanbetakenoverifmorethan1/3rdofitsnodesarecontrolledbyanattacker.• Nodesfromothershardscandetectmaliciousshardsbuttakenoaction.• Checkersforeachnodeisverycostlyintime.

Outline

•  Introduction• SystemOverview• TheChainspaceApplicationInterface• TheChainspaceSystemDesign• SystemandApplicationsSmartContracts•  ImplementationandEvaluation•  Limitations• Conclusions

Conclusion

• Chainspaceisanovelideaforexpeditingthetransactionsforacryptocurrencythathasalargeloadwhileincreasingprivacy.•  S-BACisanewwaythatcryptocurrenciescanauthenticatethemselves.

Questions?