class百度云100as

100100100GenuineUsersImposterswithoutstolenTokensImposterswithstolenTokensOriginalThresholdClearSeparation(ZeroEER)RelativeMatchCountDissimilarityScoresbetweenBiometricTemplatesCancelableBiometricSystemFig.
13.
Thestolen-tokenscenarioforcancelablebiometrics.
atenrollmentandauthentication,bydenition,two-factorauthenticationisyieldedwhichmayincreasethesecuritybutdoesnoteffecttheaccuracyofbiometricauthentication.
Asignicantincreaseofrecognitionratescanbecausedbyunpracticalassumptionsduringperformanceevaluations.
Ifuser-specictransformsareappliedtoachieveCBthesetrans-formshavetobeconsideredcompromisedduringinter-classcomparisons.
Otherwisebiometricsbecomesmeaninglessasthesystemcouldrelyonsecrettokensparameterswithoutanyrisk[102].
Secrettokens,beittransformparameters,randomnumbersoranykindofpasswordsareeasilycompromisedandmustnotbeconsideredsecure[1].
Thus,performanceevaluationsofapproachestoCBhavetobeperformedundertheso-called"stolen-tokenscenario"whereeachimpostorisinpossessionofvalidsecrettokens(thesameappliestoBCSsincasesecrettokensareapplied).
Fig.
13illustrateshowinter-classdistancesmaychangewithorwithoutconsideringthestolen-tokenscenario.
Ifdifferenttokensareappliedforeachsubjectaclearseparationofintra-classandinter-classdistributionsisachievedbyadoptinganewthreshold.
Incontrast,ifsecrettokensareconsideredcompromisedaccuracy2)RevocableBiotokens:Boultetal.
[149],[150]proposedcryptographicallysecurebiotokenswhichtheyappliedtofaceandngerprints.
Inordertoenhancesecurityinbiometricsystems,biotokens,whichtheyrefertoasBiotopeTM,areadoptedtoexistingrecognitionschemes(e.
g.
PCAforface).
Operationmode(seeFig.
15):eachmeasuredbiometricfeaturevistransformedviascalingandtranslationresultinginv=(vt)·s.
Thekeyideaistosplitvintoastablepartgtermedintegerandanunstablepartr.
Forfacebiometricstheauthorssuggesttosimplysplitrealfeaturevaluesintoanintegerpartandafractionalpart(e.
g.
15.
4issplittedinto15and0.
4).
Sincegisconsideredstable,anda"perfectmatching"isclaimedtobefeasibleatauthentication,comparisonscanbeperformedintheencrypteddomain.
Aone-waytransformofg,denotedbywisstoredasrstpartofthesecurebiometrictemplate.
Assecondpartofthetemplatetheunencodedrwhichhasbeenobscuredviathetransform,aswellassandtarestored.
Atauthenticationfeaturesaretransformedapplyingsandtontoaresidualregiondenedbyr.
Thentheunencryptedrisusedtocomputethelocaldistancewithina"window",whichisreferredtoasrobustdistancemeasure,toprovideaperfectmatchofw.
However,sinceaperfectmatchisrequiredonlyforanumber