Biometric Cryptographic Key Generation Based on City Block Distance

Transcription

1 Bometrc Cryptoraphc Key Geerato Based o Cty Block Dstace Xaqa W, Pepe Wa, KaqaWa, Yo X Bocompt Research Cetre BRC School of Compter Scece ad Techoloy Harb Isttte of Techoloy, Harb 5000, Cha {xqw, wpp, wakq, yx}@ht.ed.c Abstract Iformato secrty s becom creasly mportat or formato drve socety. Cryptoraphy s oe of the most effectve ways to ehace formato secrty. Bometrcs based cryptoraphc key eerato techqes, whch bometrc featres are sed to eerate cryptoraphc keys, have bee developed to overcome the shortaes of the tradtoal cryptoraphc methods. A essetal sse of bometrc cryptoraphc key eerato s to remove the varace betwee bometrc templates of ee sers. I prevos works, error correcto techqes are sed to elmate these varaces. However, these techqes ca oly be sed to remove errors Hamm metrc whereas may bometrc templates are real valed vectors ad caot se Hamm dstace to measre the smlarty, whch meas that the error correcto techqes ca ot be drectly sed to remove the varace betwee these bometrc templates. I ths paper, we proposed a ovel bometrc cryptoraphc framework based o cty block dstace. I the proposed framework, the real valed bometrc featre vector s frstly qatzed ad the ecoded to a bary str sch way that the cty block dstace betwee two featre vectors s coverted to Hamm dstace betwee two bary strs. After that, the error correcto techqes are sed to elmate the errors betwee the strs of the ee sers. Fally, the error free str s hashed to form a cryptoraphc key. The expermetal reslts codcted o face ad palmprt bometrcs demostrate the effectveess of the proposed framework.. Itrodcto Iformato secrty s becom a more ad more mportat sse owadays. Oe of the effectve soltos to ehace the formato secrty s to se of cryptoraphy. I cryptoraphc systems, the most crtcal sse s cpher key maaemet. There are some drawbacks to tradtoal cpher keys maaemet. For example, f the cpher key s too short or too smple, t s easy to be cracked. O the other had, f the key s lo ad complex, t s ot easy to be memorzed ad f t s stored somewhere t may be lost or stole. Bometrcs, as the heret ad qe characterstcs of hma bes, has a lo hstory be sed for detty recoto. Comb bometrcs wth cryptosystems cold overcome the shortaes of tradtoal cryptoraphc methods []. However, t s almost mpossble to drectly se a bometrc template as a cpher key sce the bometrc templates obtaed from the same ser at dfferet tmes are always vared, whereas the tradtoal cryptoraphc alorthms, sch as DES, AES ad RSA, reqre that the cpher keys sed for ecrypto ad decrypto shold be exactly detcal. Therefore, the essetal sse of the bometrc cryptoraphy s to elmate the varace betwee the bometrc templates of the ee ser. Bometrc templates have may types sch as the bary strs, featre pot sets ad featre vectors, etc. I prevos researches, dfferet methods have bee proposed to elmate the varace respect of dfferet types of bometrc templates. Davda et al. [] extracted a bary str from rs as a cpher key. I ecrypto phase, the athors compted the check bts of the bary str by s error correcto cod techqe ad stored the check bts. I decrypto phase, they cocateated a bary str whch s extracted from a clamer s rs wth the check bts ad decode t s error correcto decod techqe. The varace elmated ther method s measred by Hamm dstace. Hao et al. [3] proposed a two layer key eerato framework whch a bary key s bod wth a bary bometrc template that s extracted from rs. They stded the error patter the bometrc template ad leared that there are two types of errors bometrc template ad therefore employed two dfferet kds of error correcto techqes to correct each type of errors respectvely. Jels et al. [4, 5] proposed a method to elmate the varace betwee the featre sets. They desed a fzzy valt to lock the secret formato. Oly f the featres sed to lock the fzzy valt overlap eoh elemets of the featres sed to lock the fzzy valt, the secret formato ca be recovered. Clacy et al. [6] mplemeted a fzzy valt scheme based o ferprts. I ther expermet, a 69 bts key was derved bt the FRR s relatvely hh /09/$ IEEE

2 I ths paper, we wll cocetrate o cpher key eerato schemes based o real valed bometrc featre vector. Morose et al. [7, 8] proposed a harde password mechasm s key stroke dyamcs. The bometrc template of key stroke dyamcs s a real valed featre vector. If a featre s dstshable eoh, t wll be barzed to or 0. Otherwse, the featre wll be dscarded a mplct way. The bary str wll the be bod wth a tradtoal password throh a secret shar scheme. If all dstshable key stroke dyamc featres are close to the oe sed restrato, these featres wll be barzed to the same bary vales ad the password ca be recovered. I ther method, each featre s oly barzed to oe bt that ca ot provde eoh secrty. To overcome ths problem, Cha et al [9] proposed a method to barze each compoet of the bometrc featre vector to dfferet mber of bts. I ther method, the more dstshable a compoet s, the more bts ths compoet s barzed to. Each compoet s qatzed to a bary sbstr ad all of the sbstrs of the featre vector are cocateated to form the cryptoraphc key. Obvosly, oly whe all of the compoets are correctly barzed, the decrypto s sccessfl. As we kow that the vales of a bometrc template ca be dstrbed by ose easly, a promet ose may reatly affect oe or several compoets of the ee featre vector ad reslt errors whe these compoets are barzed s Cha s method, ad therefore the ee ser may fal to decrypt the secrete formato. To avod the effect of a sle b devato a ee ser s featre vector, ths paper proposes a ovel framework based o cty block dstace, whch cosder the sm of the devato of all compoets ad, therefore, ca redce the effect of a sle b devato the decrypto phase. The rest of ths paper s orazed as follows. Secto proposes the bometrc cryptoraphc framework based o cty block dstace. Secto 3 dscsses the qatzato ad cod of the bometrc featre vector. Secto 4 presets the key steps of the proposed framework. Secto 5 cotas the expermetal reslts ad aalyss ad Secto 6 provdes a coclso.. Proposed Framework The proposed framework s show Fre. There are two phases ths framework, the ecrypto ad decrypto phases... Ecrypto Phase I ecrypto phase, a featre vector s frstly extracted from a ser s bometrc trat by s some featre extracto method. The the featre vector s qatzed to a qatzato vector QV, ad at the same tme, some assstat data AD s also eerated ad kept, whch wll be sed to qatze the featre vector decrypto. After that, QV s coverted to a bary str BC ad BC s ecoded by s some error correcto techqe e.. BCH, ad keep the check bts CB whch wll be sed decrypto for correct errors. Fally, BC s coverted to a cryptoraphc key CK by s a hash fcto e.. MD5 ad sed to ecrypt a secret messae. Oly the ecrypted messae EM, AD ad CB are kept ad other formato s dscarded ths phase... Decrypto Phase a Ecrypto Phase. b Decrypto Phase. Fre : The proposed framework. I decrypto phase, a featre vector s extracted from a ser s bometrc s the same featre extracto method as sed ecrypto phase. The AD s sed to covert ths featre vector to a bary str BC. Cocateate BC wth CB ad decode t to et the corrected code CC s the same error correcto techqe. Fally, the corrected code CC s coverted to the decrypt key s the same hash fcto ad sed to decrypt the secret messae. Sce the proposed framework ams to elmate the varace of real valed featre vectors cty block dstace, we wll dscss detals the qatzato ad cod techqes whch ca covert the cty block dstace of featre vectors to Hamm dstace of bary strs the follow secto. 3. Qatzato ad Cod I a -dmeso space, a cty block dstace of two vectorsv ad V s defed as below:

3 D V, V = v v here v, v, =,, ad s the th =,,, compoet of V ad V respectvely. To covert the cty block dstace of V ad V.e. D V, V, to Hamm dstace, we frstly qatze each compoet of these featre vectors ad the ecode them to bary strs sch way that the Hamm dstace of the bary strs s the approxmato of the cty block dstace betwee V ad V. 3.. Qatzato I ths sbsecto, we se Cha s method [9] to qatze the featre vector. I ths method, the dstrbto of each compoet of all sers featre vectors,.e. lobal dstrbto, ad that of a certa ser s featre vectors,.e. ser dstrbto, are frstly compted. Geerally, the lobal dstrbto doma s mch larer tha the ser dstrbto doma. The the lobal dstrbto doma s eqally dvded to several tervals sch way that the ceter of oe terval locates where the mea of the ser dstrbto s ad the sze s decded by the stadard devato of the ser dstrbto. Let V = v, v,..., v be a featre vector. The process to qatze V cldes follow steps see Fre : For each compoet v, compt the mea ad varace of lobal dstrbto ad ser dstrbto by s the tra dataset, deoted as μ, δ ad μ, δ, respectvely. Compt the left ad rht bodares of v, deoted as L ad R, as follow: L = m μ K δ, μ K δ where R = max μ + K δ, μ + K δ 3 K ad K are costat parameters. K determes the sze of the whole qatzato doma ad K cotrols the sze of the qatzato tervals, deoted as step : step = K δ 4 3 Eqally dvd a doma whch covers the rae [ L, R ] to N tervals wth sze step : N = LS + RS + 5 LS = μ K δ L step 6 RS = R μ K δ step 7 where x s the operato to et larest teer whch s less tha x +. 4 Determ the left bodary LB ad the rht bodary RB of all the qatzato tervals as below: LB = μ K δ LS step 8 RB = μ + K δ + RS step 9 RB ad step for each compoet v are LB, stored as the assstat data AD. Us AD, we ca qatze ay featre vector. 3.. Cod I ths sbsecto, we ecode each qatzato terval wth a bary str to covert the qatzato dstace to Hamm dstace. For a featre vector V = v, v,..., v, we ecode t to a bary str wth AD the follow way: For each compoet v, compt the mber of qatzato tervals N : N RB LB step = 0 Eqally dvd the doma [ LB, RB ] to N tervals wth sze step, deoted as 0,,..., N from left to rht, ad lett j = j. 3 Decd the terval whch v belos to: where Fre : Qatzato ad Cod Illstrato. v LB step = ' x s the operato to et the smallest teer whch s ber tha x. ' s the qatz vale of v, that s

4 4 Ecod ' v ' N bts bary sbstr s a b whch the most left bts are s ad the rema bts are 0s. Obvosly, ' j' = ' j' = H b, b j 3 where H x, y s the Hamm dstace betwee Str x ad y. 5 Cocateat all of the sbstrs to form the fal bary str of V, B = b b... b. Fre shows a example of qatzato ad bary cod of a sle compoet, where N s 6. Let V = v, v,..., v, V = v, v,..., v,,, deote two featre vectors ad B b,b,... b,,,, B b, b,... b, =, = be ther correspod bary strs. Accord to Eq. ad 3, the cty block dstace betwee V ad V, D V, V ca be compted as follow: D V, V = = =, = H b = H B, B,,, b =, v, v, 4 From Eq. 4, the cty block dstace of two featre vectors D V, V has bee coverted to Hamm dstace of two bary strs. 4. Ecrypto ad Decrypto 4.. Ecrypto The lobal mea ad lobal stadard devato are compted s tra dataset before the ecrypto. Ad the crcal steps ecrypto phase are lsted as follow: A ser s bometrc trat s captred several tmes. For each sample, a featre vector s extracted. We compte the mea ad the stadard devato of each compoet of these featre vectors. Qatze the lobal featre dstrbto doma of each featre dmeso by s the method proposed secto III. LB, RB ad step of each compoet are stored as assstat data, AD. 3 Wth AD, ecode the mea of the ser s featre vectors to a bary str BC by s the bary cod scheme proposed secto III. 4 Employ a certa error correcto techqe e.. BCH to ecode BC, ad keep the check bts, CB. 5 Use a certa oe way hash fcto e.. MD5 to covert BC to a fxed leth bary str as the ecrypt key. 6 Ecrypt the messae s the key to obta the ecrypted messae, EM. The otpts of the ecrypt phase are AD, CB ad EM. 4.. Decrypto The decrypto procedre cldes the follow steps: A ser s bometrc trat s captred oce ad the featre vector s extracted. Ecode the featre vector s AD to a bary str, BC. 3 Cocateate BC wth CB, deoted by BC CB, ad decode BC CB s the error correcto techqe to obta a corrected code, CC. 4 Use the same hash fcto to covert CC to a fx leth bary str as the decrypt key. 5 Decrypt the EM s the key. 5. Expermetal Reslts ad Aalyss Or expermet s codcted o ORL face database [0] ad palmprt database respectvely. The face database cotas 400 samples of 40 sers wth each ser hav 0 samples. The featre vector s a 5-dmesoal real valed vector extracted by s a pealzed sbspace lear framework as proposed []. We selected radomly 50% bometrc templates from each ser for tra. That meas we se 5 featre vectors from the same ser ecrypto stae. The palmprt database cotas 000 samples of 00 sers. Each ser provded 0 samples. The palmprt template s a 56-dmesoal real valed vector whch s composed of the averae eery vales extracted by s a set of D Gabor flters. I bometrcs based system, the False Rejecto Rate FRR, ad False Acceptace Rate, FAR, are sally sed to evalate the performace of the system. The detecto error trade-off DET crve, whch s plot FAR aast FRR, s a effectve techqe to compare the performace of dfferet methods. I or expermets, K = 4. The DET crves of the proposed framework wth dfferet vales of K o face ad palmprt databases are show Fre 3 ad Fre 4, respectvely. For comparso, the DET crves of Cha s method [9] o the same databases are also plotted the correspod fres.

5 Fre 3: DET crves of face database. Fre 4: DET crves of palmprt database. As show Fre 3, all DET crves based o the proposed framework are der the crves of Cha s methods. Ad from Fre 4, most DET crves of the proposed framework are der the crve of Cha s method, whch meas that the proposed framework otperform Cha s method o both face ad palmprt datasets. The reaso s probably that or framework cosdered the dfferece of all compoets betwee the featre vectors whle Cha s method oly takes accot the maxmm dfferece of the compoets. 6. Coclso I bometrcs based cryptoraphc systems, the eerato of cpher key decrypto s based o the closeess of bometrc template to the oe sed ecrypto. I ths paper, we proposed a ovel framework based o the cty block dstace. I ths framework, the cty block dstace betwee two real valed featre vectors s coverted to Hamm dstace of two bary strs, ad the the error correct techqe are sed to remove the varace the ee template ad form the cpher key. Sce the cty block dstace s the sm of the dfferece of all compoets of the vectors, the proposed framework ca otperform the prevos oes whch oly cosder the maxmm dfferece the compoets. Ackowledemet Ths work was spported part by the Natral Scece Fodato of Cha NSFC der Cotract No ad , the Natoal Hh-Tech Research ad Developmet Pla of Cha 863 der Cotract No. 007AA0Z95, the Proram for New Cetry Excellet Talets Uversty der Cotract No. NCET ad NCET ad the Natral Scece Fodato of Heloja Provce of Cha der Cotract No. F Refereces [] U. Ulda, S. Pakat, ad S. Prabhakar, A. Ja. Bometrc cryptosystems: Isses ad challees. Proceeds of the IEEE, 96: , 004. [] G. Davda, Y. Frakel, ad B. Matt. O eabl secre applcatos throh off-le bometrc detfcato. IEEE Symposm Prvacy ad Secrty, 48-57, 998. [3] F. Hao, R. Aderso, ad J. Dama. Comb crypto wth bometrcs effectvely. IEEE Trasactos o Compters, 559:08-088, 006. [4] A. Jels, ad M. Sda. A fzzy valt scheme. Dess, Codes ad Cryptoraphy, 38: 37-57, 00. [5] A. Jles, ad M. Watteber. A fzzy commtmet scheme. ACM Coferece o Compter ad Commcato Secrty, 8-36, 999. [6] T. Clacy, N. Kyavash, ad D. L. Secre Smart Card-Based Ferprt Athetcato. ACM SIGMM workshop o Bometrcs Methods ad Applcato WBMA, 45-5, 003. [7] F. Morose, M. Reter, ad S. Wetzel. Password harde based o keystroke dyamcs. ACM Cof. Compter ad Commcatos Secrty, 73-8, 999. [8] F. Morose, M. Reter, Q. L, ad S. Wetzel. Cryptoraphc key eerato from voce. IEEE Symposm Prvacy ad Secrty, 0-3, 00. [9] Y. Cha, W. Zha, ad T. Che. Bometrcs-based cryptoraphc key eerato. I ICME, 03-06, 004. [0] ORL face database. /attarchve/facesatalace.html [] W. Zo, L. L, K. Wa, ad D. Zha. Spatally Smooth Sbspace Face Recoto Us LOG ad DOG Pealtes. Lectre Notes o Compter Scece, 55533: , 009.