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1、Thisextendedabstractappearsin:AdvancesinCryptology{ProceedingsofCRYPTO'02(August18-22,SantaBarbara,California,USA)M.YungEd.Springer-Verlag,LNCS2442,pages465{480.ThresholdRingSignaturesandApplicationstoAd-hocGroups(Extendedabstract)EmmanuelBresson1,JacquesStern1andMichaelSzydlo21Deptd'
2、informatique,Ecolenormalesuperieure,75230ParisCedex05,FrancefEmmanuel.Bresson,Jacques.Sterng@ens.fr2RSALaboratories,20CrosbyDrive,Bedford,MA01730,USAmszydlo@rsasecurity.comAbstract.Inthispaper,weinvestigatetherecentparadigmforgroupsignaturesproposedbyRivestetal.atAsiacrypt'01.We rsti
3、mproveontheirringsignatureparadigmbyshowingthatitholdsunderastrictlyweakerassumption,namelytherandomoraclemodelratherthantheidealcipher.Thenweprovideextensionstomakeringsignaturessuit-ableinpracticalsituations,suchasthresholdschemesorad-hocgroups.Finallyweproposeanecientschemeforthres
4、holdscenariosbasedonacombinatorialmethodandprovablysecureintherandomoraclemodel.1IntroductionInmanymulti-usercryptographicapplications,anonymityisrequiredtoensurethatinformationabouttheuserisnotrevealed.Typicalexamplesareelectronicvoting[4,14],digitallotteries[17,21],ore-cashapplicatio
5、ns[6,10].Intheseap-plicationsreleasingprivateinformationishighlyundesirableandmayresultinalarge nancialloss.Theconceptofgroupsignaturesintroducedin1991[11],allowsaregisteredmemberofaprede nedgrouptoproduceanonymoussig-naturesonbehalfofthegroup.However,thisanonymitycanberevokedbyanautho
6、rityifneeded.Theextratrapdoorinformationstoredbytheauthorityisusedtorevealtheidentityoftheactualsigner.Thismechanismprovidessomelevelofsecurityfornon-signingmembersincaseofdispute.Hence,groupsig-naturesareonlytheappropriatetoolwhenmembershaveagreedtocooperate.Thedistinctbutrelatedconce
7、ptofringsignaturehasrecentlybeenformalizedbyRivestetal[25].Thisconceptisofparticularinterestwhenthemembersdonotagreetocooperatesincetheschemerequiresneitheragroupmanager,norasetupprocedure,northeactionofanon-signingmember.Aringsignaturespeci esasetofpossiblesignersandaproofthatisinte
