A Proposal of One-Time Biometric Authentication

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1 A Proposal of Oe-Time Biometric Autheticatio Yoshifumi Ueshige* *Istitute of Systems & Iformatio Techologies/ KYUSHU Fukuoka City, Fukuoka Pref., JAPAN Kouichi Sakurai*+ +The Graduate School of Iformatio Sciece ad Electrical Egieerig, Kyushu Uiversity Fukuoka City, Fukuoka Pref., JAPAN Abstract - I biometric autheticatio, feature iformatio of each erolled perso s biometric iformatio is erolled as templates. Secure databases or ati-tampered devices store the templates i geeral. The biometric iformatio, however, is irreplaceable iformatio, whe it is compromised. Thereby, oe must give a special attetio to protectio of such iformatio. O the other hads, icreasig iteret ecoomical services causes a motivatio of implemetig olie biometric autheticatio. We propose a ovel protectio techique for the biometric iformatio, especially the feature iformatio ad the templates. The poit of our proposal is that the extracted features ad the erolled templates are trasformed by oe-time trasformatio that is geerated i each autheticatio. The trasformed features ad templates travel through isecure commuicatio lie like the iteret, ad they are used i matchig process. This techique causes security agaist eavesdroppig ad replay attacks o the iteret, because the trasmitted feature iformatio ad the templates are differet every time. Keywords: biometric autheticatio, oe-time, template protectio, oliear trasform, securety 1 Itroductio 1.1 Backgroud Biometric autheticatio is well kow with both of kowledge-based autheticatio like passwords, ad possessio-based autheticatio like cards (magetic cards, IC cards, etc.). Because the biological features (figerprit, vei, iris, facial image, voice, etc.) are uique for each perso, productio of the biometric techiques is ecouraged. I facts, facilities for fiace ad immigratio authorities [1] have already itroduced the biometric autheticatio i may coutries. I additio, some products of persoal computers iclude the biometric autheticatio systems. The biometrics rapidly prevails i society like this. I these examples, the biometric systems are applied i closed eviromets, however, there are fervet social demad about the biometric systems applied to the autheticatio o iteret services such as iteret bakig, electrical govermet, approval i compay, etc. O the other hads, the biometric system causes some privacy issues. That is, i some cases, sigificat privacy iformatio like a medical history is compromised from the biometric iformatio which is icludig biometric raw data acquired from biometric sesor devices, the feature iformatio extracted from the correspodig biometric raw data, ad erolled templates. For example, oe ca kow a perso s diabetes from retia data. Whe biometric autheticatio system as show i figure 1 leaks erolled biometric templates, these templates are uable to re-eroll, because the correspodig biometric data is irreplaceable. This poit is seriously differet from the same situatio of password system ad public-key ecryptio. I the case that ecrypted data is trasmitted o each lie coectig betwee ay processes i figure 1, oe eeds the maagemet of the ecryptio (ad decryptio) keys amog the biometric autheticatio systems. Furthermore, if oe biometric autheticatio system cosists of distributed equipmets, the cost of the key maagemet becomes expesive. I additio, it is possible for adversaries to perform replay attack by usig ecrypted biometric iformatio eavesdropped. Therefore, we eed to protect the biometric iformatio strictly. I this viewpoit, Ratha et al.[2] ad Tulys et al.[3], [4] proposed some protectio techiques as biometric template protectio techiques. Next subsectio, we will briefly itroduce them. 1.2 Related Work We ca roughly classify the cocepts of template protectio ito followig two categories: 1) Geometrical trasformatio or irreversible mappig trasforms the erolled templates ito straied templates separately [2]. 2) Oe-way fuctio with helper data trasforms the erolled templates ito some correspodig uique parameter [3], [4]. Accordig to the former cocept, the biometric templates are blockwise scrambled, or geometrically distorted like morphig as show i figure 2. I this figure, the umber i the cells deotes idices of the sub blocks. The stars i these sub blocks deote the poits of features. It is difficult for ay adversaries to extract the iformatio of erolled templates from the trasformed templates. Thus, the ref [2] states oe ca protect the erolled templates. Because this method, however, causes decrease of the template quality i

2 Capture Feature Extractio Erolmet Autheticatio matchig process, we are ot able to expect high accuracy of autheticatio. I latter oe [3], [4], the framework is show i figure 3. We eroll both of a oe-way fuctio F(.) ad correctio term amed helper data W so that the fuctio F(.) geerate same values whe extracted feature Y for verificatio are close origial templates X. That is, erollmet data cosists of F(.), F(X) ad W. I verificatio, a user calculates F(Y) with helper data W. If F(X)=F(Y), the user is autheticated. This scheme has a characteristic, of which X or Y does ot directly travel through ope etworks. Because this scheme is the autheticatio by usig output of F(.) with W, this scheme has o compatibility with popular biometric autheticatio systems as show i figure 1. Furthermore, autheticatio accuracy seems to rely o the value W susceptibly. 1.3 Our cotributio Template Storage Matchig Judgmet Figure 1. Basic model of biometric autheticatio system I this paper, we propose a ovel compatible scheme with the popular biometric systems. Our mai idea is biometric autheticatio by usig oe-time characteristics. That is, commuicated data of the features ad the templates is differet every autheticatio sessio for eve uique perso, as show i oe-time password [9]. This scheme has followig properties: 1) The extracted features ad the erolled templates are trasformed by a commo oliear fuctio, ad matchig is doe by usig the trasformed features ad the trasformed templates i order to esure the oetime feature. 2) Our scheme eeds o cocer about compromisig the trasformed iformatio i the commuicatio through arbitrary lies, because of chageable autheticatio data for each autheticatio sessio. I every sessio, some TTP geerates the commo fuctio by usig a autheticatio sessio with a time-stamp ad some credetial. The geeratig algorithm of the fuctio esures oe-time characteristic of it. I this paper, we suppose the geeratig algorithm exists, we discuss the privacy protectio ad the biometric autheticatio scheme. If this requiremet is satisfied, eve though eavesdroppers X Ec. Erollmet S W F F(S) Autheticatio Database W V F(V) F(S) Y Dec. F Matchig Figure 3. Biometric autheticatio with oe way fuctio ad helper data collect commuicatio data betwee the biometric autheticatio processes, they caot obtai the erolled templates ad the extracted features. Whe they moitor some perso s etire autheticatio, they obtai oly trasformed data which has o correlatio with other autheticatio sessios. A autheticatio server which performs matchig process obtai the trasformed data that are the trasformed template, ad the trasformed features. We ca expect the oe-time characteristic of the trasform causes high security of biometrics from the view of privacy protectio. I this work, we call this trasform oe-time trasform (OTT). I the rest, sectio 2 describes what iformatio should be protected i the biometric autheticatio. I sectio 3, we propose a defiitio of OTT, cosideratio of geeratig OTT, ad autheticatio protocol. Sectio 4 gives a discussio of security i proposed scheme. Fially, sectio 5 cocludes this paper. 2 Problems i this work Figure 2. Trasform of template by scramblig blockwise Biometric autheticatio has two flows of processig, that is, erollmet ad autheticatio. Erollmet process is performed through the broke arrow lies i figure 1. Sesor device acquires a user s biometric raw data. Next step is feature extractio of the biometric raw data. The obtaied features are erolled as templates i the database. O the other hads, there are autheticatio processes alog straight arrow lies i figure 1. I the autheticatio, capture process ad feature extractio process are i commo with erollmet. The matchig process performs

3 Iteret Database of Templates Time Stamp Process of Time stamp Fuctio Geerator Geeratig OTT Database of Templates Applyig OTT Cliet Acquisitio Feature Extractio Autheticatio Matchig Judgemet Cliet Acquisitio Feature Extractio Iteret Autheticatio Matchig Figure 4. The server autheticatio model o the iteret applicatio Applyig OTT Judgemet compariso betwee the extracted features ad the erolled templates. The judgmet process evaluates the matchig result (matchig score) ad calls the user accept or reject referrig autheticatio policy. Whe we apply this biometric autheticatio to iteret services, we must cosider a part or all of the above five processes are icluded i separate etities distributed i iteret. Because the biometrics o the iteret services requires commuicatio of the autheticatio iformatio like the feature iformatio, the template iformatio, the autheticatio results etc. betwee the five processes through the iteret. Sice the iteret is ot secure agaist eavesdroppig, substitutio, ad impersoatio, we must appreciate that isufficiet security for the above iformatio compromises the user s biometric iformatio as oe of persoal iformatio. Because biometric iformatio is irreplaceable i geeral, the user is uable to re-eroll to the biometric autheticatio system [5]. I additio, eve if eavesdroppers obtaied oly ecrypted biometric iformatio, their replay attacks ca meace the biometric system. Thereby, protectio of the biometric iformatio from these risks is oe of the sigificat problems i the biometric autheticatio as a problem of privacy protectio. I the rest of this paper, we otice protectio of the feature iformatio ad the template iformatio i the server autheticatio model as show i figure 4. This model seems to be a practical implemetatio as a remote biometric autheticatio. I this model, we must save the features ad the templates as persoal iformatio from adversaries. 3 Proposals oe-time trasform I this work, we propose the biometric autheticatio so that iformatio trasformed by a chageable commo fuctio, OTT is used as commuicatio data o the iteret. The OTT is oliear fuctio ad chages every Figure 5. Proposed framework (The sever autheticatio model) autheticatio sessio i order to prevet predictio of the fuctios by adversaries. A third trusted party geerates the OTTs as show i figure 5. I this paper, we apply the OTT to the feature iformatio ad the template iformatio. Eve if our proposal eeds ew etities for geeratig the OTTs, it is easy to exted the curret popular biometric system because oly software of applicatio of OTT is added to the system. We call our biometric autheticatio oe-time biometric autheticatio (OTBA). Followig subsectios precisely explai the OTBA i server autheticatio model. 3.1 Requiremets of the autheticatio system usig OTT For costructio of the OTBA system, we suppose five etities which are cliet, autheticatio server, database storig templates, fuctio geerator of OTT, ad time-stamp server as show i figure 5. I figure 5, the fuctio geerator ad the time-stamp server are TTP. Requiremet of the fuctio geerator is followigs: Algorithm ad iput values for geeratig the OTT is opeed. I order to give time depedecy to fuctio geerator, the iput values are autheticatio sessio with time-stamp data siged by time-stamp server ad secret value of fuctio geerator. 3.2 Requiremets of the OTT fuctios The goals of applicatio of the OTT fuctio are to protect erolled origial templates ad to prevet replay attacks by usig dishoest acquiremet data of trasformed iformatio by OTT. For achievemet of the goals, the OTTs eed to satisfy the followig coditios:

4 Y : Recursively trasformed poits by OTT at time t 1, sessio a 1 : Recursively trasformed poits by OTT at time t 2, sessio a 2, ( t1 t 2 ) Because orbits of poits recursively mapped by this fuctio are strogly deped o the parameters a, b, ad iitial poits (see figure 6), we expect the mapped poits do ot imply the iformatio of iitial poits if a ad b are securely protected. That is, it may be possible to costruct the OTTs by geeratig ad protectig the parameters of the OTTs. I additio, if these parameters are chageable at each geeratio of OTTs, eve though adversaries obtai data of the idetical user s autheticatio sessios, the adversaries caot kow eve the idetity. For example of Heo s mappig, we ca represet geeratig the parameters a ad b at fuctio geerator as followig: O Coordiate of oe feature poit or template Figure 6 Image of OTT X a= f ( H b= g( H, t, t, s), s) where H, t c, ad s deote hash value of sessio, time from the time-stamp data of the sessio, secret value, respectively. Fuctio f ad g eed to be oe-way fuctios. C C (2) 1) Oe-to-oe fuctio I the methods [3], ad [4], the origial templates ad features are trasformed ito a differet space which has o direct relatioship with a space of these iformatio. Therefore, the method [3] ad [4] become low similarity to the curret biometric systems. This poit receives our attetio. I our method, the origial templates ad features are trasformed ito same space i order to keep the similarity at the matchig process. 2) Difficulty of predictio It is extremely difficult for ay adversary to guess the origial templates ad features from the trasformed iformatio. 3) Preservatio of distace This meas that matchig process ca evaluate the distace betwee the trasformed feature ad the correspodig trasformed template by usig optimal distace fuctio. Because OTTs are oliear mappig, OTTs may be cotractive or expasile, locally. However, it is ecessary to desig OTTs so that every OTT trasforms relative feature ad template ito close poits. We aticipate satisfyig the above coditios may be difficult. We, however, expect a cadidate of the OTTs is chaos mappig such as Heo s mappig: x t+ 1 = 1 axt + by y = x t+ 1 2 t y (1) 3.3 Protocols of the biometric autheticatio usig oe-time trasforms We propose a autheticatio protocol usig OTT. I the rest, (a) - (p) deote umeral otatios show i figure 7. 1) Processes from (a) to (c) deote egotiatio for begiig the autheticatio. After these steps, the cliet ad the autheticatio server share the autheticatio sessio 2) I (d), fuctio geerator receives requests of geeratig OTT with the sessio from both of the cliet ad the autheticatio server. Process (e) is a verificatio cocerig validity of the autheticatio sessio. 3) I (f) ad (g), the fuctio geerator obtais timestamped data of the above sessio. The timestamped data is used for a parameter of OTT geeratio ad a evidece of the sessio performed. 4) About process (h), please refer the discussio i subsectio 3.1 ad ) I (i), the fuctio geerator seds the geerated OTT to both of the cliet ad the database of erolled templates. 6) I order to ed the geeratio process, the fuctio geerator seds sigal of the ed to the autheticatio server i process (l). 7) I j) ad k), the cliet ad the database apply the OTT to the feature data ad the correspodig template data, respectively. Because of commo OTT used, the trasformed data are used i matchig process as is. For example, we ca deote formally as followig equatio: o ftr = F ( ftr) (3), where F(x),, ad ftr deote the OTT, the umber of iteratio, ad the coordiate of the features,

5 Cliet Time Stamp Fuctio Geerator Database of Templates Autheticatio (a) Request of Autheticatio Sessio (b) Start of Autheticatio Sessio (c) Cofirmatio of the start (d) Autheticatio Sessio (d) Autheticatio Sessio (e) Verificatio of the received data from Cliet ad Autheticatio (f) Autheticatio Sessio (i) OTT (g) Time Stamp data of iformatio received i step (f) (h) Geeratig OTT (i) OTT (j) Applyig OTT to feature data (k) Applyig OTT to template data (l) Sig of fiishig geeratio of OTT (m) Request of OTT feature data () Request of OTT template data (o) OTT Template data (p) OTT Feature data Figure 7. Protocol of startig autheticatio sessio to sedig oe-time trasformed features ad oe-time trasformed template respectively. We ca describe the trasform of the templates as followig: o tpl = F (tpl) (4), where tpl deotes the coordiate of the templates. 8) I ()-(q) the autheticatio server obtais the trasformed data of templates ad features. After the above protocols fiished, the autheticatio server performs matchig process ad judgmet process. 9) I matchig process, the autheticatio server calculates distace betwee the set of trasformed features ad oe of the trasformed templates. For a example of distace fuctio, we ca fid the Hausdorff distace [6]: H ( Tpl, Ftr ) = max{ max tpl Tpl ftr Ftr max ftr Ftr tpl Tpl mi { d( tpl mi { d( tpl, ftr, ftr )}} )}, (5), where Tpl, Ftr deote the set of OTT templates ad oe of the OTT features. Fuctio d(.) deotes distace fuctio betwee two poits. We should choose the optimal distace fuctio depedig upo OTT. 10) The autheticatio server calculates the matchig score based o H(Tpl,Ftr ). I judgmet process, the autheticatio server decides accept or reject by comparig H(Tpl,Ftr ) with the correspodig threshold. 4 Argumet of Security of OTBA We discuss the security of the above proposal. First, we metio the security of the framework of the OTBA. If adversaries success to steal this value s stored i the fuctio geerator, they ca become impostor of the fuctio geerator. After that, the fuctio geerator loses trust from other etities i figure 5. However, eve if adversaries hijack the fuctio geerator, because it receives o persoal iformatio, of course icludig the

6 origial template ad the extracted feature, the takeover does ot threate the user s privacy. The we cosider the case of a malicious autheticatio server collects iformatio. I this framework, it receives trasformed features ad templates. As aforemetioed, they imply o iformatio before trasform. Furthermore, the malicious sever caot kow the correspodig OTT. Hece, the malicious server obtais o iformatio about origial templates ad extracted features. Next, we cosider security of the iformatio trasformed by OTT agaist hill-climbig attack [7], [8], replay attack, collusio attack. Hill-climbig attack uses of replied matchig score i order to make a fake. Whe the applicatio server seds the matchig score to cliet (adversary) i figure 5, the adversary trasforms feature data selected from database which the adversary costructs. The adversary seds the trasformed features to the autheticatio server. Because this system chages the calculatio algorithm of matchig score ad threshold for it accordig to selected distace fuctio d(.), it is difficult for the adversary to improve the fake from the replied matchig score. Therefore, the probability of the adversary s success o the OTBA becomes less tha covetioal biometric autheticatio like figure 4. I geeral, replay attack is impossible, if previously obtaied iformatio is ot reusable. Whe adversaries eavesdrop o the commuicatio betwee the cliet ad the autheticatio server, they obtai oly trasformed features which are ot reusable. Hece, o adversary successes replay attack o the OTBA. If the adversaries ca liste to the commuicatio from the fuctio geerator, they obtai the iformatio of OTT. Whe they reuse this iformatio, the cliet ad the database ca detect replay attack by verifyig the differece amog the iformatio of OTT used i former autheticatio sessios. Two cases of collusio attack establish possibly. The oe of case is that the cliet cospires with the fuctio geerator. I this case, the cliet ca obtai ot oly OTT but also iformatio of evaluatio fuctio. Hece, adversaries who ca perform ormal hill-climbig attack success the collusio attack. The other oe is that the autheticatio server stads i with the fuctio geerator. The maer of attack is same as the above oe. 5 Coclusios I this paper, we poited out the problems of the curret studies of the template protectio. As a coutermeasure, we proposed the OTBA to protect the biometric templates ad the extracted features. The mai cocept of the OTBA is that stole biometric iformatio is ot reusable by chageable trasform, OTT every autheticatio for eve same perso. We described recursive trasform as a cadidate of OTT. As a result, we obtaied the view of the security of the OTBA agaist hill-climbig attack ad replay attack durig the fuctio geerator keeps security. This paper described oly cocept of the OTBA. As future works, we should study optimal fuctio of the OTTs, ad practical geeratig algorithm of the OTTs. I additio, we should research formal aalysis of iformatio theoretic security ad time of calculatio i the OTBA. Ackowledgemet This research was supported by Strategic Iteratioal Cooperative Program, Japa Sciece ad Techology Agecy (JST). Refereces [1] ISO/JTC1/SC17/WG3/TF1 for ICAO-NTWG, Supplemet 9303, Iteratioal Civil Aviatio Orgaizatio (ICAO), (URL: mrtd/dowload/documets/ftt_supplemet%20to%20 Doc% pdf) [2] N. K. Ratha, J. H. Coell, R. M. Bolle, "Ehacig Security ad Privacy i Biometric-based Autheticatio Systems", IBM Systems Joural, Vol. 40, No. 3, pp , [3] P. Tulys, J. Goselig, Capacity ad Example of Template-Protectig Biometric Autheticatio Systems, ECCV Workshop BioAW, o. 77, pp , [4] J.-P. Liartz, P. Tuyls New Shieldig Fuctios to Ehace Privacy ad Prevet Misuse of Biometric Templates, AVBPA 2003, pp , [5] P. Reid, Biometrics for Network Security, Pretice Hall, [6] M. F. Barsley, Fractals Everywhere secod editio, Academic Press Professioal, [7] C. Soutar, Biometric System Security, Secure No. 5, pp , 2002 (URL: pdf/secure_5/46_techo_4.pdf) [8] A. Dimovski, D. Gilogoroski, Geeratig highly oliear Boolea fuctio usig a geetic algorithm, 1st Balka Coferece o Iformatics, 2003 [9] PKCS #11 v2.20 Amedmet 1, PKCS #11 mechaisms for Oe-Time Password Tokes, RSA Security Ic. (URL: ftp://ftp.rsasecurity.com/pub/pkcs/ pkcs-11/v2-20/pkcs-11v2-20a1.pdf)