电子现金系统设计代码 .pdf
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1、Department Of Computer Science University of Bristol Compact E-Cash Alireza Hajabbasgholi A.Hajabbasgholi.05bristol.ac.uk A dissertation submitted to the University of Bristol in accordance with the requirements of the degree of Bachelor of Science in the Faculty of Engineering 名师资料总结-精品资料欢迎下载-名师精心整
2、理-第 1 页,共 49 页 -2 Declaration A dissertation submitted to the University of Bristol in accordance with the requirements of the degree of Bachelor of Science in the Faculty of Engineering.It has not been submitted for any other degree or diploma of any examining body.Except where specifically acknowl
3、edged,it is all the work of the Author.Alireza Hajabbasgholi,April 2006名师资料总结-精品资料欢迎下载-名师精心整理-第 2 页,共 49 页 -AcknowledgementsFirstlyand foremostly,I would like to thank Professor Nigel Smart,who hasbeen the best tutorand supervisorone could wish for.As well as going out ofhis way to help me when di?c
4、ultiesarose,his moral supportkept me on therightpath.I am very gratefulfor havinghad his supervisionthroughoutmydegree.Secondly,I would like to thank Dr.TatsuakiOkamotoof NTTlabs,for hispromptassistance and recommendationson his paper.Finally,I wouldlike to thank all of the authorsmentionedin the re
5、ferencessectionof thisthesis.Completingthisthesis wouldhave notbeen possiblewithoutaccess to their previouswork(s).3名师资料总结-精品资料欢迎下载-名师精心整理-第 3 页,共 49 页 -AbstractE-cash or electronic cash has been the focus of?nancial cryptographerssince the 1980s.Every year,one or more E-Cash protocolsare presenteda
6、t majorcryptographyconferences aroundthe world.A goal common toall these schemes is to improveupon the e?ciencyof theirpredecessorswhile o?eringthe same level of anonymity.Buthow e?cientare theseprotocols?We aim to analyse this and other trends thatE-Cashhas seen sinceits conception.Originally,the a
7、nalysis method considered for this projectwas to verifythe e?ciencyand securityof the mostrecent protocolasan aid to our analysis.However,implementingthe most recent protocolsproves to be extremelytime-consuming.Therefore,our new strategy aimsto implementan older protocolthat has never been implemen
8、tedbefore.We shall also use it as a basis for a briefanalysisof some more recentschemes.We shall provide an implementationof one of the most in?uentialprotocolsin divisible,transferableand o?ineE-Cashs historyon whichmany other protocolsare based.We shall also provide the reader withabrief analysis
9、of the performanceof other importantprotocols,includingthe most recent paper presented at Eurocrypt05.This allows the readerto draw objectiveconclusions on the need for new schemes as well as thefutureof E-Cash.4名师资料总结-精品资料欢迎下载-名师精心整理-第 4 页,共 49 页 -Contents1Background71.1Introduction.71.1.1De?nition
10、and History.71.1.2Realisationsof E-Cash.91.2PreviousWork.91.2.1A Simple Protocol.91.2.2More AdvancedProtocols.121.3Our Contribution.131.4PreliminaryPreparations.142Analysis152.1TheoreticalDesign.152.1.1HierarchicalStructureTables.152.1.2Protocol1(Basic DivisibleUniversalElectronicCash).172.1.3Protoc
11、ol2(TransferableUniversalElectronicCash).212.1.4TheoreticalE?ciency.222.2Practicaldesign.242.2.1Protocols1 and 2(DivisibleUniversalElectronicCash).252.2.2PracticalE?ciency.282.2.3AlternativeApproaches.333ResultComparisons353.1Okamotos Second Scheme.353.2ProjectCAFE.363.3Brands Scheme.363.4CompactE-C
12、ash.364ConcludingRemarks374.1PotentialUses for Our E-Cash Implementation.374.2Futureof E-Cash.374.3FutureWork.384.4Final Words.385References406AppendixA:SelectedCodeSegments435名师资料总结-精品资料欢迎下载-名师精心整理-第 5 页,共 49 页 -Listof Figures1Basic E-Cash Circulation.72A More AdvancedExchange Protocol.113Hierarchi
13、calStructureTable.164Table.165The State of Table after Spending$18.246名师资料总结-精品资料欢迎下载-名师精心整理-第 6 页,共 49 页 -1Background1.1Introduction1.1.1De?nitionandHistoryE-Cash or as more generally known DigitalCash/Money1has been extensivelystudiedsince around25 years ago.E-Cash was inventedby DavidChaumetal 1,
14、2.Most E-Cash schemes are builtaround the core of Chaum sinventionof blindsignatures.Since its invention,E-Cash has received great attentionbycryptographersand a great deal of research has been undertakenin makingitmore secure and e?ciente.g.12,4,5,6,7,8,9,10,11.The main idea behind E-Cash is to rep
15、lace hard money by a series of binaryform of data.In its simplestform(Figure12),circulationof E-Cash is as follows33:1.A user obtains a wallet withsome money from her bank.2.The user then spends the money with a merchant.3.The merchantretrieves the money from the bank later.Figure1:Basic E-Cash Circ
16、ulationIt can be clearly seen thatthere are many securitythreatsassociated withthis model.We shall take a look at cryptographicallymore advanced protocolslater in this paper.Thereare two typesof E-Cashthathave so farbeen developed:onlineand o?ine.In the online scenario,we alreadyhave more securityas
17、 we havea Bank online who supervises transactions.However,in this paper,we aremainlyconcerned with the o?inescenario of E-Cash4.In the o?inescenario,weeliminatethe banks supervisionby introducingsome cryptographictechniques.1Fromnow on,we use the termE-Cashfor simplicityof use.2Source:cui.unige.ch/d
18、eriazm/Softs/ECash/images/ECash.PNG3Here,we are referringto the O?inemodeof E-Cash.4Fromnow on,by E-Cashwe are referringto the o?inescenariounlessstatedotherwise.7名师资料总结-精品资料欢迎下载-名师精心整理-第 7 页,共 49 页 -Thereason for our interestin theo?inescenario has arisenfrom the needfor physicalcash alike digitalm
19、oney as it o?ers anonymityand e?ciency(workuse,communicationslag and etc.).A complete E-Cash protocolmust satisfy the followingsix conditions12:1.Independence:As E-Cashis principallyin the form of data,its securitymust not depend on any physical conditions.2.Security:E-Cash is secure.I.e.it cannot b
20、e duplicated.3.Privacy:Also known as un-traceability;as withphysical cash,it must beanonymous;i.e.the bank cannot reveal the identityof the purchaserormerchantunless one of the twohas cheated.In a more secure context,even if the bank and merchantcollaborateto reveal the identityof anhonest purchaser
21、,thisshould not be possible,unless the purchaserhascheated.4.O?ineoperation:Transactionsbetween users and merchantsshouldbecompletedo?ine,i.e.the merchantdoes not need to establish a linktothe bank.5.Transferability:Just like real cash,E-Cashcan be transferredfrom oneholder to another.6.Divisibility
22、(multipledenominations):Althoughnot exactly physicalcashalike,divisibilitysimulatespossession of cash withdi?erentface values,i.e.if we have a walletof value S,we can dividethe walletintomanypieces such thatthe totalvalue of the small pieces equals S.The typicalplayers in a transactionare:1.A user U
23、:This is a customer who withdrawsa wallet from his/herbank.2.A bank :The bank is responsible for signing the money order and givingit to U.is also responsiblefor giving the paymentof the money to themerchantwho has received the money order.3.A merchantM:The merchantis essentiallythe same as the user
24、 in thesense thatthey can both hold digitalmoney.The only di?erence is thatthe merchant is the receiver of the money from U.Some protocolsintroducean extraentitycalled the“Trustedthirdparty”or“TTP”.A TTPis essentiallya supervisorthatcan trace all the coins of acheatinguser.However,thiscontradictswit
25、hthe anonymityprincipalof E-Cash.To a TTP,the user is known and therefore one must achieve the security8名师资料总结-精品资料欢迎下载-名师精心整理-第 8 页,共 49 页 -of a TTPwithouta TTP.Thishowever,does come at the cost of increasedspace complexityfor transactionsas a single coin is circulated.Thise?ect isdemonstratedin ou
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