美国国会研究服务部-NFT专题报告（英）

July20,2022sionalResearchServicehttps//R9SSUMMARYCongressionalResearchServiceNon-Non-FungibleTokens(NFTs)Non-fungibletokens(NFTs)havebecomepopularasuniqueandnon-interchangeableunitsofdatathatsignifyownershipofassociateddigitalitems,suchasimages,music,orvideos.Token“ownership”isrecordedandtrackedonablockchain(adigitaldatabasethatrecordsdataonadecentralizednetworkofcomputerswithouttheuseofacentralauthority).Inthefuture,supportersbelieveNFTswillbeusedasdigitalrepresentationsofphysicalitems,suchasadeedtoahouseortitletoacar.NFTsarecommonlyusedtorecordandrepresentownershipofanitem,verifyauthenticity,andenableexchange.However,theydonotnecessarilyreflectthelegalownershipofanassetorgrantcopyrighttoadigitalorphysicalitem.NFTownerspurchaseonlyR47189July2022schnalystinScienceandechnologyPolicytherighttotheNFT’sblockchainmetadataor“token,”nottheunderlyingasset,unlessotherwisespecifiedinexternalcontractsortermsandconditions.NFTssharemanysimilaritieswithcryptocurrencies,andtheyarecommonlyboughtandtradedusingcryptocurrency.BothNFTsandcryptocurrenciesarebuiltandtrackedonblockchains,andtheysharemuchofthesamecustomerandcommunitybase.However,cryptocurrenciesarefungible,meaninginterchangeable,whereasNFTsareuniqueandthereforenon-fungible.MostuserscreateandbuyNFTsondedicatedNFTmarketplaces.ForatypicalNFT,itiscreatedor“minted”onablockchain,auctionedofforsoldatafixedpriceonanNFTmarketplace,and“stored”inthebuyer’sdigitalwallet.Smartcontracts(self-executingcontractsorlinesofcomputercodeonablockchain)canminttherighttotheNFT’sblockchainmetadataor“token,”nottheunderlyingasset,unlessotherwisespecifiedinexternalcontractsortermsandconditions.EstimatesforthesizeoftheNFTmarketrangefromaround$17billiontoover$44billioninannualsales.Accordingtosomemarketanalyticcompanies,salesincreasedsubstantiallyin2021buthavedecreasedin2022.Somehigh-profileNFTshavesoldformillionsofdollars,whileonestudyfoundthat1%ofNFTssellforover$1,594andthatroughlythree-quartersofNFTsaresoldforlessthan$15.TheNFTmarketissimilarlystratifiedandconcentrated.Thetwolargestmarketplaces,OpenSeaandLooksRare,accountfornearlyallmonthlyNFTtradingvolume.Additionally,onestudyfoundthatthetop10%ofNFTbuyersandsellersmakeasmanytransactionsastheremaining90%.Thelatterstatisticmayreflecttheprevalenceofillicittradingpractices.Asof022,mostNFTsareusedtopurchasedigitalcollectibles,suchasdigitalartwork,orrepresentationsofotherdigitalitems.However,proponentsbelieveNFTswillfindwiderapplicationinotherfields,suchasrepresentingreal-worlditems;enablingdigitalidentitiesorgrantingexclusiveaccesstoevents,services,oronlinecommunities.NFTsmaybecomepopularinthesefieldsormayremainspecifictocertainmarkets.IfNFTsintheircurrentformbecomeobsolete,thetechnologyandcoreconceptsofdecentralization,uniquedigitalownership,andimmutabilitymaytakedifferentformsordevelopintoothernewtechnologies.Despitesubstantialmarketgrowthoverthepasttwoyears,NFTsarestillrelativelynascent.Intheircurrentform,NFTshaveimplicationsinavarietyofpolicyareas:Consumerprotection.ThereareanumberofriskstoconsumersintheNFTecosystem,andsomeNFTmarketplacesanddigitalwalletslackbasicfeaturestoprotectconsumersfromfraudandmisleadingordeceptivepractices.Financialregulation.DependingonthepurposeanduseofNFTs,someNFTsandNFTplatformsmayfallunderexistingfinancialregulatoryregimesanddefinitions.Copyrightandintellectualproperty.TherelationshipbetweenNFTsandthelegalownershipofdigitalorphysicalpropertyisunclear.SomeexistingregulationsmayimpactNFTmarkets.Energyandenvironmental.BothmintingandsellingNFTsrequiresubstantialamountsofenergy,whichhasraisedconcernsabouttheirenvironmentalimpact.DependingonhowNFTsdevelopinthefuture,Congressmayalsoconsiderpossibleprivacyorcontentmoderationconcerns.IfCongressdeterminesthatthereisaroleforthefederalgovernmentinregulatingNFTs,itmayconsideravarietyofoptionstoextendoversightoverNFTswhilefosteringinnovation.SinceNFTsareusedinarangeofindustriesandapplications,CongressmayconsiderwhethertotreatNFTsasaclassoftechnologyoraddressspecificNFTapplicationsincertainsectors.CongressmayalsoconsiderthedistinctionsbetweendifferenttypesofNFTsandtheirrespectivepurposesinthecontextofbroaderdecentralizedecosystemsandmarkets,suchascryptocurrenciesanddecentralizedfinance. Non-FungibleTokens(NFTs)CongressionalResearchServiceIntroduction 1NFTsOverview 2WhatAreNFTs? 2WhatDoesItMeantoOwnanNFT? 4HowDoNFTsUseBlockchainsandSmartContracts? 4Blockchains 4SmartContracts 5Off-ChainStorage 6HowAreNFTsStored? 6DigitalWallets 6NFTMarketplaces 7MarketplaceConcentration 8TransactionFees 9MarketplacePolicies 9HowElseAreNFTsUsed? 10Web3andMetaverse 10CampaignFundraising 11CongressionalIssues 12ConsumerProtection 12CopyrightandLegalOwnership 13FinancialRegulation 15Classification 15IllicitActivity 17EnergyandEnvironmentalImpacts 19PrivacyandContentModeration 20ConcludingObservations 21FiguresFigure1.ExampleNFTItem 3Figure2.NFTTransactionProcess 7TablesTable1.ExampleNFTMetadataRecordedonBlockchain 3ContactsAuthorInformation21 Non-FungibleTokens(NFTs)CongressionalResearchService1Non-fungibletokens(NFTs)areuniqueandnon-interchangeableunitsofdatathatcansignifyownershipofassociateddigitalitems,suchasimages,music,orvideos.SupportersbelieveNFTswillbeusedinthefuturetorepresentownershipofphysicalitems(e.g.,adeedtoacarortitletoahouse).Token“ownership”isrecordedandtrackedonablockchain,adigitaldatabasethatrecordsdataonadecentralizednetworkofcomputers.1NFTscanthemselvesbesoldortradedindigitalmarkets.However,ownershipofanNFTdoesnotnecessarilycorrespondtolegalownershiporgrantcopyrighttoadigitalorphysicalitem.NFTownerspurchaseonlytherighttotheNFT’sblockchainmetadataor“token,”nottheunderlyingitem,unlessotherwisespecified.In2014,thefirstNFTwascreatedaspartofanannualcollaborationeventforartistsandtechnologists.2Currently,NFTsarecreatedor“minted”onablockchain,auctionedoff,orsoldatafixedpriceinNFTmarketplaces(onlineexchangesforNFTs)and“stored”inabuyer’sdigitalwallet.3NFTsbeganasawayforartiststocontrol,sell,andearnroyaltiesondigitalartworks,buttheygainedmoremainstreampopularityafterthegrowthofNFT-basedgamesandmarketplacesin2017.4Theirusehasbecomeubiquitouswithindigitalcollectibleandartmarkets,withthetotalNFTmarketestimatedtobebetween$17billionand$40billionintransactionsin2021.5SomeproponentsassertthatNFTsmaketransactionsmoreefficientandsecure.Theypredictthattheirusewillexpandtoawidearrayofapplicationsbeyondthedigitalcollectiblesmarkets,suchasdigitalidentityauthentication,retailshopping,andrealestate.CriticsarguethatNFTsaresimplyspeculativeinvestments,providenoadditionalvalueoverexistingsystems,arepronetoillicitactivityandscams,andcontributetothe“financializationofeverything.”6IfCongressdeterminesthatregulatingNFTsisnecessary,itmayconsiderwhethertotreatNFTsasabroadtechnologyclassoraddressspecificNFTapplicationsinselectedsectors.CongressmayalsowishtoconsiderhowtobalancethedevelopmentofNFTapplicationswithanyappropriateconsumer,intellectualproperty,financial,andenvironmentalprotections.ThisreportprovidesanoverviewofNFTsandtheirtechnicalinfrastructure,includingtheuseofblockchainsandsmartcontracts(i.e.,self-executingcontractsontheblockchain).7Italsosurveys1Formoreinformationonblockchaintechnologies,seeCRSReportR47064,Blockchain:NovelProvenanceApplications,byKristenE.Busch;andCRSReportR45116,Blockchain:BackgroundandPolicyIssues,byChrisJaikaran.2In2014,AnilDashandKevinMcCoycreatedoneofthefirstNFTprojectsentitled“monetizedgraphics.”AnilDash,“NFTsWeren’tSupposedtoEndLikeThis,”TheAtlantic,April2,2021,/ideas/archive/2021/04/nfts-werent-supposed-end-like/618488/.3CRSInFocusIF12079,DigitalWalletsandSelectedPolicyIssues,byPaulTiernoandAndrewP.Scott.4CryptoKitties,createdin2017,isconsideredoneofthefirstpopularmainstreamNFTcollections.CryptoKittiesisavideogamedevelopedontheEthereumblockchaininwhichuserscancollect,breed,andtradedigitalcatNFTs.5EstimatesoftheexactsizeoftheNFTmarketvary.NonFandL’AtelierBNPParibas,“The2021NFTMarketReport:PresentedbyNonFungibleandL'AtelierBNPParibas,”March9,2022,/news/the-2021-nft-market-report-presented-by-nonfungible;AllysonVersprille,“NFTMarketSurpassed$40Billionin2021,NewEstimateShows,”Bloomberg,January6,2022,/news/articles/2022-01-06/nft-market-surpassed-40-billion-in-2021-new-estimate-shows.6SomecriticsbelieveNFTsandcryptocurrenciescontributetothe“financializationofeverything,”inwhichindividualswouldneedtoexchangetokensformostinteractionsandtransactions.7Formoreinformationonsmartcontracts,see“SmartContracts”sectioninthisreport. Non-FungibleTokens(NFTs)CongressionalResearchService2variousNFTapplicationsandmajorNFTmarketplaces.ThereportconcludeswithadiscussionofselectNFT-relatedissuesofpotentialcongressionalinterest.WhatAreNFTs?NFTsareoftencomparedtodigitalcertificatesofownership.8Thecertificate,intheformofdatarecordedonablockchain,signifiesownershipofanassociateddigitalitemnotcontainedinthedataitself.Ablockchainisadigitaldatabasethatrecordsdataonadecentralizednetworkofcomputerswithouttheuseofacentralauthority.9TherearetwopartstoanNFT(seeFigure1andTable1foranexample):NFTitem.ThedigitalitemassociatedwithanNFTisdescribedinanNFT’smetadata(seenextbullet).Theseitemsaretypicallystoredoff-chain,meaningtheitemisnotdirectlystoredonablockchain.10NFTmetadata(calledatoken).NFTmetadata11isstoredonablockchainandtypicallyincludesinformationidentifyingtheunderlyingNFTitem,itslocationonline,itsownership,andtransactioninformation.MostuserscreateandbuyNFTsondedicatedNFTmarketplaces.UserscanalsowritetheirowncodetodirectlyminttheirNFTstoablockchain.Ineithercase,theuseruploadsadigitalfileoftheitem,andthroughtheuseofsmartcontracts,theNFTis“minted”orrecordedonablockchain.NFTmetadatastoredonablockchainisanexampleofatoken—aunitofdatarecordedonablockchainthatcarriesvalue.12A“fungible”tokenisonethatisidenticalandinterchangeablewithanother.Forexample,cryptocurrenciesarefungibletokenssincetheunitsareinterchangeable(oneBitcoinforanotherBitcoin;oneEtherforanotherEther).NFTsare“non-fungible,”ornon-interchangeable,sinceeachtokentypicallyhasuniqueattributes(e.g.,anNFTtokenofonevideofileisnotinterchangeableforanNFTtokenofadifferentvideofile).However,multipleNFTscouldrepresentthesamedigitalorphysicalitem(e.g.,anartistmightsell40NFTsofthesameimage),althougheachNFT’smetadatawouldbeunique.overnmentAccountabilityOfficeScienceTechSpotlightNonFungibleTokensNFTsGAOJune14,2022,/products/gao-22-105990.9Formoreinformationonblockchaintechnologies,seeCRSReportR47064,Blockchain:NovelProvenanceApplications,byKristenE.Busch;andCRSReportR45116,Blockchain:BackgroundandPolicyIssues,byChrisJaikaran.Blockchainshavelimitedstoragespaceandhighnetworktraffic,sostoringanNFT’sunderlyingdigitalassetonablockchainmightbeexpensiveandinefficient.Instead,digitalassetsaretypicallystoredonaseparatehostedwebsiteoradecentralizedpeer-to-peerfilestoragesystem.11Metadataisadditionalinformationanddatathatcandescribe,contextualize,arrange,track,orenhanceotherdata.MurthaBacaetal.,IntroductiontoMetadata,3rded.(LosAngeles:GettyResearchInstitute,2016).12AnNFT’svalueisdeterminedbythewillingnessofpeopletopayforit.Thetokenisinherentlyvalueless(itissimplydatarecordedonablockchain),sothevalueofanyparticularNFTmayvarywidelyovertime. Non-FungibleTokens(NFTs)CongressionalResearchService3Figure1.ExampleNFTItemTable1.ExampleNFTMetadataRecordedonBlockchainCategoryiptionFTsh Non-FungibleTokens(NFTs)CongressionalResearchService4WhatDoesItMeantoOwnanNFT?“Owning”anon-fungibletokenreferstobeingidentifiedastheowneroftheNFTintheblockchainmetadataandhavingtherighttotransferthetokentosomeoneelse.Thetokenisoftenusedtosignifyownershipofanassociateddigitalorphysicalitem,enabledbyimmutableownershiprecordsonablockchain.However,theownershipmetadatarecordedinanNFTdoesnotnecessarilyrepresentthelegalownershiporgrantlegalcopyrighttoanassociateddigitalorphysicalitem.13LegalownershiprightsconveyedbyanNFTmaybespecifiedviaareferenceinthemetadatatoexternaltermsandconditionsorcontracts.14Despitetheselegallimitations,participantsoftenpurchaseNFTsasapurportedmeansfordigitalauthenticationandownershipverification.Sinceitisparticularlydifficulttoproveortransfertheownershipofuniquedigitalitems,supportersbelieveNFTsareanewmeansforenforcingdigitalscarcity.CopyrightandotherintellectualpropertyissuesforNFTsarefurtherdiscussedinthe“CongressionalIssues”sectionbelow.HowDoNFTsUseBlockchainsandSmartContracts?ainsNFTsare“minted”(i.e.,created)onblockchainnetworks.Datastoredonablockchainarecontinuallyshared,replicated,andsynchronizedacrossthenodesinanetwork—individualcomputersystemsorspecializedhardwarethatcommunicatewitheachotherandstoreandprocessinformation.15Thissystemenablestamper-resistantrecordkeepingwithoutacentralizedauthorityorintermediary.Onablockchainnetwork,aparticipantusesapublickeytoencryptdataandaprivatekeytodecryptthedata.16Participantscanalsosigntransactionswiththeirprivatekey,andotheruserscanverifythosesignatureswiththecorrespondingpublickey.Therearevariouskindsofblockchains.Mostsharesomecommoncharacteristics,includingdecentralization(i.e.,nocentralizedauthority),immutability(i.e.,theblockchainrecordsareunalterable),andpseudonymity(i.e.,users’real-worldidentitiesarenotdirectlydisplayed).UserstypicallymintNFTsonpublic,permissionlessblockchains,whichallowanynodeontheblockchainnetworktoreadandsubmittransactions.17AsmartcontractwillmintanNFTbyexecutinglinesofcodethataddtheNFTdatatotheblockchain.TheNFTmetadata,including13Formoreinformationonpropertyrights,ownership,andNFTs,seeJulietMoringielloandChristopherOdinet,“ThePropertyLawofTokens,”FloridaLawReview(forthcoming2022),November1,2021,/10.2139/ssrn.3928901.14FlorianIdelbergerandPeterMezei,“Non-FungibleTokens,”InternetPolicyReviewJournalonInternetRegulation,volnoAprilhttpspolicyreviewinfopdf/policyreview-2022-2-1660.pdf.Therearedifferenttypesofnodesonablockchainnetwork.Somenodesmaystoretheentiretyoronlypartsoftheblockchainrecords,whileotherspublishnewblocksorsimplypasstheirtransactionstoothernodes.Formoreinformation,seeCRSReportR47064,Blockchain:NovelProvenanceApplications,byKristenE.Busch.16Ausercanencrypthisorheridentityusingapublickeytoscrambledata,aswellasaprivatekey,whichisnecessarytoconducttransactionswiththepublickey.Eachkeyisageneratedthroughacryptographicalgorithm.“Publickeyencryptionorpublickeycryptography,isamethodofencryptingdatawithtwodifferentkeysandmakingoneofthekeysthepublickeyavailableforanyonetouse.Theotherkeyisknownastheprivatekey.Dataencryptedwiththepublickeycanonlybedecryptedwiththeprivatekey,anddataencryptedwiththeprivatekeycanonlybedecryptedwiththepublickey.”Cloudflare,“HowDoesPublicKeyEncryptionWork?PublicKeyCryptographyandSSL,”/learning/ssl/how-does-public-key-encryption-work/.Formoreinformationonthedifferenttypesofblockchain,suchaspublic,private,permissioned,andpermissionlessblockchains,seeCRSReportR47064,Blockchain:NovelProvenanceApplications,byKristenE.Busch. Non-FungibleTokens(NFTs)CongressionalResearchService5ownershipinformation,arethereforeaccessibletoallnodesoranyoneusingasearchableblockchainexplorer.18SomeNFTsareimmediatelymintedontheblockchainafterthecontentcreatoruploadsthefiletothemarketplace,whileothersarenotrecordedontheblockchainuntilaftersaleonamarketplace.MostNFTsaremintedontheEthereumblockchain.SomeNFTsaremintedonotherblockchains,suchasSolana,Flow,orCardano.MostNFTsarepurchasedwithEther(ETH,thecryptocurrencynativetotheEthereumnetwork)oranothercryptocurrency.PricechangesincryptocurrenciesoftenresultinchangesinNFTvaluations.sSmartcontractsareself-executingcontractsthatenabletheexchangeofmoney,property,orsomethingelseofvaluewithouttheservicesofathirdparty.19TheyarecommonlyusedtomintNFTs,transfertheirownership,orpayroyalties.Morespecifically,asmartcontractisacomputerprogram,orasetoflinesofcode,thatresidesataspecificaddressonablockchain.20Smartcontractsareautomaticallyexecutedbythecomputersintheblockchainnetworkifaspecificsetofconditionsaremetorthesmartcontractis“called.”Oncetheconditionsaremet(e.g.,thesmartcontractreceivesatransaction),thesmartcontractcodewillrunasprogrammedtoeithermintanNFT,transfertheNFT,payroyalties,orexecutesomeotherpredeterminedtransaction.21Allsmartcontractsrelyonexternaltransactionstotriggertheirfunctions.22MostusersminttheirNFTsviaamarketplace,whichmanagesthesmartcontractandback-endcodingtomintonablockchain.23Marketplacesarediscussedinthesection“NFTMarketplaces.”Ausercanalsowritehisorherowncodetocreateasmartcontractonablockchainandminttokensusingthesmartcontract.TocreateanNFT,asmartcontractmustincludecertaincodeandprogrammingcommandsthatfollowacceptedindustrystandards,suchasERC-721orERC-1155forEthereumNFTs.Thesestandardsallowwallets,marketplaces,andotherplatformstoworkwithanytokenthatconformstothestandard.24NFTsbuiltonotherblockchainsmayusedifferentstandardsorprotocols.Smartcontractcodeisvisibletoallblockchainparticipants,whichenableshackersorbadactorstosearchforbugsandsecurityvulnerabilitiestoexploit.AccordingtoEthereum’sown18Blockchainexplorerspulldatafromablockchain,suchasEthereumorBitcoin,anddisplayitinasearchabledatabasewhichcanbeaccessedbyanyonewithawebbrowser.EtherscanisapopularblockchainexplorerforEthereumcryptocurrencyandNFTtransactionsOtherexamplesincludePolygonscanforPolygontransactionsandExplorerforSolanatransactions.twascoinedinthemidsbycryptographerNickSzaboSeeNickSzaboSmartContractsBuildingBlocksforDigitalMarkets,”Extropy#16,1996,https://www.fon.hum.uva.nl/rob/Courses/InformationInSpeech/CDROM/Literature/LOTwinterschool2006//smart_contracts_2.html.20SincethemajorityofNFTsandsmartcontractsarebuiltonEthereum,seeEthereum,“IntroductiontoSmartContracts,”/en/developers/docs/smart-contracts/.21NickSzaboanalogizedsmartcontractsasdigitalvendingmachines.Giventherightinput(coins),theywilldispenseacertainoutputsodacansHoweverunlikevendingmachines,smartcontractscanautomatemanykindsofexchangeorcertaincommands.22Forexample,codeinthesmartcontractmaycreateacertainnumberoftokensandassignthemtoaparticularownerortransferownershipbetweenaddressesForexamplecodesee“AnatomyofSmartContracts,”Ethereum,/en/developers/docs/smart-contracts/anatomy/.23MitchellClark,“HowtoCreateanNFT—andWhyYouMayNotWantTo,”TheVerge,December8,2021,https///22809090/nft-create-opensea-rarible-cryptocurrency-ethereum-collectibles-how-to.24Ethereum,“HowtoMintanNFT(Part2/3ofNFTTutorialSeries),”/en/developers/tutorials/how-to-mint-an-nft/.CongressionalResearchService6developerspage,“smartcontractcodeusuallycannotbechangedtopatchsecurityflaws,assetsthathavebeenstolenfromsmartcontractsareirrecoverable,andstolenassetsareextremelydifficulttotrack.Thetotalofamountofvaluestolenorlostduetosmartcontractissuesiseasilyover$1B.”25Therealfigureofstolenfundsduetovulnerabilitiesinsmartcontractsmaybemuchhigher.26nStorageInmostcases,theunderlyingNFTitem,suchasajpegimageormp3audiofile,isstoredoff-chain,asblockchainshavelimitedstoragespaceandhighnetworktraffic.StoringanNFT’sunderlyingitemdirectlyonablockchainwouldtypicallybeexpensiveandinefficient.Instead,itemsaretypicallystoredseparatelyonanexternalhostingservice,suchasacentralizedserver(e.g.,aserverhostedbyOpenSea),adistributedfilesystem(e.g.,theInterplanetaryFileSystemorArweave),orcloudstorage(e.g.,AmazonWebServices).OnecommonmisconceptionisthatNFTsareimpervioustosecurityrisksasdataarerecordedonimmutableblockchains.However,theblockchainsecuresonlyNFTmetadata,nottheunderlyingasset.NFTmetadatastoreddirectlyontheblockchainareimmutable27(i.e.,tamper-proof),butdatastoredoff-chaincanbemanipulated.Ifoff-chainstoragesystemsgoofflineorarediscontinued,theNFTassetandanyoff-chainmetadatamaydisappear.Thisiscalled“linkrot,”becausefollowingabrokenlinkonablockchainwillreturnonlyanerrormessagestatingthatthefileattheprovidedaddresscannotbefound(a“404”error).28Inthissituation,theon-chainmetadatamaycontinuetosignifyownershipoftheNFT,buttheNFTassetitselfmaynolongerbeavailable.Typically,thisresultsintheNFTlosingvalue.HowAreNFTsStored?Adigitalwalletissoftwareorhardwaredesignedtostoreauser’scryptographicpublicandprivatekeys,whichmaycorrespondtoNFTs,cryptocurrencies,orotheridentifiersandcredentials.Digitalwalletscantakevariousforms.Web-basedwalletsareofteninstalledasbrowserextensionsormobileapplications.HardwarewalletsallowuserstostoretheirpublicandprivatekeysofflinewithoutaconnectiontotheInternettopreventhacking.29Manydigitalwalletscanbehacked,30anduserswholosetheirprivatekeysmayloseaccesstotheirfundsandtokens.25Ethereum,“SmartContractSecurity,”lastupdatedMarch23,2022,/en/developers/docs/smart-contracts/security/.26MacKenzieSigalos,“CryptoScammersTookaRecord$14Billionin2021,”CNBC,January6,2022,/2022/01/06/crypto-scammers-took-a-record-14-billion-in-2021-chainalysis.html.27Blockchaindataareimmutablebecauseofthehashingfunctionsu