Blockchain:Systems,SecurityandApplica8ons
Dr.Yuzhe(Richard)TangDepartmentofEECS,SyracuseUniversity
May10,2018
Outline
A. Introduc+on
B. What’sPublicBlockchain?– Externalviews– Internalviews
C. BlockchainModels,ProblemsandApplica8ons
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A.Introduc8on:Cryptocurrency
• Cryptocurrencyinthefield:– BitCoin,Ethereum,Litecoin,etc.
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CryptocurrencythatislikeUSDollars• Supportconven8onalmoneyflows:– Createmoneyinamint– Circulatemoneyamongownersthroughtransac+ons
• Securityunderthreats:– Threat1:Printfakemoney– Threat2:Doublespending(digitalcurrency)
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CryptocurrencythatisunlikeUSDollars• USdollarisfiatcurrencycontrolledbyautori8es– Issuedandprintedingov.mint– CirculatedwithmonitoringbyVisa
• Authoritymaynotbetrustworthy
• Cryptocurrencyremovescentralizedauthority.5/10/18 YuzheTang,SyracuseUniv. 5
KeyIdeasofCryptocurrency• Getridofauthoritybytrustdecentraliza+on
– Don’ttrustgov.andVisa,insteadtrusttheen8repopula8ononplanet.
• Makethenetworkopen-membershipandtransac8onhistorytransparent.– Transparency&open-membershiphelpsnetworkreachtheplanetscale.
• Automatetheen8reprocesswithincen+vecompa+bility.– Automa8onremoveslaborandreducescosts.– Paypeoplewhohelpmaintainthesystem.
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• Blockchainistheplacetorecordcryptocurrencytransac8ons.– BlockchainistheledgerforBitcoin
• Blockchainisthesystemmaterializingtheaboveideas.
Introduc8on:CryptocurrencyandBlockchain
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Outline
A. Introduc8on
B. What’sPublicBlockchain?– Externalviews– Internalviews
C. BlockchainModels,ProblemsandApplica8ons
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What’sBlockchain:Overview
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• Blockchainis…
What’sBlockchain:Overview
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• Blockchainis…1. Atransac8onstoragesystem
What’sBlockchain:Overview
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• Blockchainis…1. Atransac8onstoragesystem2. Acryptocurrencymine3. Aprogram-execu8onplacorm
What’sBlockchain:Overview
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• Blockchainis…1. Atransac8onstoragesystem2. Acryptocurrencymine3. Aprogram-execu8onplacorm4. Aconsensusprotocol5. Aproofsystem6. Manyotherthings
1.BlockchainasTransac8onStorage
• Interface:– sendTransac>on({from:account1,to:account2,value:amount})
– getTransac>on(txid)
• Scenario:– Getyourfirstbitcointhroughexchange/walletservice
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SecurityofTransac8onStorage
• Blockchainastransac8onstorage– Readabletothepublic(transparency)– Appendablebyhonestclientssendingvalidtransac8ons
– Oncecommieed,cannotbemodified(immutability)
• Transac8onvalidity:Nodoublespending– AgerAlicepaysBobcoinX,Alicecan’tspendcoinX.
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InternalofTransac8onStorage
• Add-transac8onflow– Recentlysenttxsbroadcastandbufferedinmemorypools.
– Pendingtxsarevalidated• Ensuringnodouble-spending
– AppendtxstoBlockchain• Validatedtxsaregroupedtoblocks• Blocksareappendedtotheblockchain.
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InternalofTransac8onStorage
• Transac8onsformaDAG– Hashpointer:Representspendingrela8onshipbtwntxs
• Transac8onDAG(100GB)isstoredintheBlockchainnetwork.
• Blocks(32MB)arechainedandreplicatedintheBlockchainnetwork.
• Immutabilityisensuredby– Securityofhash(collisionresistance)– Blocksarereplicated.
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2.BlockchainasaMine
• Likegoldmine,theBlockchainwillgivevaluables(inBitcoins)topeoplewhoputeffortsin.
• Scenarios:Youpurchasesomehardwareandrunsome(non-sense)computa8ons– Withsomeprobability,yourcomputa8onwillberewardedinBitCoin
– Theprobabilitydependsonhowpowerfulyourhardwareisandhowmanyothersarecompe8ng
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2.BlockchainasaMine
• HowlikelyitistogetBitCointhru.mining?– Howbigisyourbudget?• Constantcapital:buymachines,Variablecapital:electricityconsump8on
– Whoyouareupagainst(racingtowinthereward)?• State-levelminers,bitcoinfarm,datacenters
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Security:SybilAeackResilience
• Open-membershipnetwork:anyonecanjoin• Honestmajorityminers:Securityassump8on• Sybilaeack– Anindividualcancreatealargenumberofminerstobecomeandcontrolthemajorityofnetwork.
• Mining:MakeithardtodoSybilaeack.– Havingaminerwinconsumesresources.– Havingmanyminerswinconsumessomanyresourcesthatan(adversarial)individualcannotafford.
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3.BlockchainasProgram-Execu8onPlacorm
• Programminginterface:Smartcontract– Smart-contractprogramisanexecutablerunningontheBlockchainnetwork
– Examples:
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3.BlockchainasProgram-Execu8onPlacorm
• Commonuseofsmartcontract:– Decision-makinglogic(IFTTT)
• Whentosendtx,whocanspendthetx– Generalprogram(Turingcompletelanguageonchain)
• Applica8on:Stock-exchange– Alicewilltrade10sharesfor$10,000whenthestockpriceisbelow$1000.• (BitCoincanrepresentboth$10Kandsharesasdigitalgoods)
Acknowledge:Prof.AriJuels5/10/18 YuzheTang,SyracuseUniv. 21
Security:UnstoppableExecu8on• Securityproper8es:– Autonomouslyexecuted,unstoppable– Transac8onfairness:
• IfIpaidyou,tobefair,Ineedtoreceiveyourgoods.• Replacetheroleofconven8onalbanksinasupplychain.
• Internally,itisensuredby– Replicatedexecu8on– Honestmajority
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Outline
A. Introduc8on
B. What’sPublicBlockchain?– Externalviews– Internalviews
C. BlockchainModels,ProblemsandApplica8ons
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Internal-MechanismOverview
1. BlockchainisaP2Pnetworkoftwolayers– Clientssend/readtransac8ons– Minersmaintaintransac8onstorage
2. Minersrunadd-txlogic1. Broadcastpendingtxs2. Validatetxs3. Appendvalidatedtxsto
Blockchain
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Outline
A. Introduc8on
B. What’sPublicBlockchain?– Externalviews– Internalviews
C. BlockchainModels,ProblemsandApplica+ons
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Alterna8veBlockchainModels
• Private/Permissionedblockchain– QuorumfromJPMorganChase,HyperledgerfromIBM
– Runsinaconsor8umofminers(closednetwork)• Privacy-preservingBlockchain– zCash/zeroCash:encryptedtransac8ons
• Theyfeature:closed-membership,privatetransac8ons,privatecontractstate.
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BigProblemsofBlockchainToday• Energyconsump8onbyPoW
• Scalability– boundedbyblocksizeandminingrate.
• Compu8ngpowercentraliza+on– Miningpool
• Cyber-crimethroughcryptocurrency
• Privacyleakagethru.sidechannels
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BlockchainApplica8onsBeyondBitcoins
• DNSservers– Blockstack
• Personalkeymanagment– Keybase.io,
• Iden8tymanagement– Interna8onaltravellingandCanadianbordercontrol
• ServicediscoveryinVMWare• Incen8vizedfitness
– FryEgg• Streamlinedincidentrepor8ng
– BikeBlockchain
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What’sNext?• OnlineBlockchainLabsatSyracuseUniv.:
– heps://goo.gl/hFmfQc
• SEEDworkshopinMay,2018inSyracuse,NY– Aneduca8onworkshopforcollegeandhigh-schoolteachers
– hep://www.cis.syr.edu/~wedu/seed/workshop.html
• Blockchaincourse– CIS600&FIN600:BlockchainandCryptocurrencies(inFall,2018,atSU)• hep://tristartom.github.io/docs/syl-4600.pdf• Otheronlinematerials
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Q/A
Contact: Yuzhe (Richard) Tang Assistant Professor Dept. of EECS Syracuse University [email protected] ecs.syr.edu/faculty/yuzhe
Thankyou!
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