Proceed dings of the Asia-Pacific A Advanced N Network 20155 v. 40, p. 500-56. Networkk Research Workshop W htttp://dx.doi.oorg/10.7125//APAN.40.8 ISSN 222 27-3026 A Novel N Error E Correc C ction S Scheme in Quantum m Key Disttributio on (QK KD) Prrotocool Siao Ping Lee, L Chee Ky yun Ng and M Makhfudzah M Mokhtar Dep partment of Computer and Communicattion Systems Engineering, Faculty of En ngineering, Universiti U Putrra Malaysia, M Malaysia Emails: xquire_v@ho x otmail.com; mpnck@upm. m edu.my; fudzzah@upm.eduu.my antum key disstribution (QK KD) Abstract— Ideally, in any qua mmunication sy ystem, each sifted key is expectted to be receiv ved com witthout error. However H in prractice, due to o infeasibility of gen nerating pure single s photon and a device impa airment problem, som me of the sifted d key may experrience errors. This T results to the t inccrement of quan ntum bit error rate (QBER) th hat requires errror recconciliation forr correcting errror. The main concept in errror recconciliation is very much relateed to the capab bility of correctiing all errors while minimizing eavessdrop informatiion. The quantu um errror correcting code such as Hamming cod de which used in Wiinnow protocoll is found to bee more attractive. However the t Wiinnow protocol can only correct one error ou ut of seven bits. In thiis paper, a mo odified Hammin ng encoder/deccoder to impro ove Wiinnow protocol by correcting tw wo errors out of seven bits whiich leaads to reducing the QBER is presented. p Thiss design utilizess a paiir of forward and a reverse ord der syndromes for error patteern reccognition. A new w reconciliation n protocol has been b developed to enh hance the error correcting ca apability in BB B84 protocol. Itt is carrried out in a siimple structuree which can corrrect up to doub ble errroneous bits and d detect four errroneous bits for each seven bitts. IIndex Terms— — Cryptograp phy, Hammin ng code, errror corrrection, QKD D, reconciliation protocol, BB84 protoccol, Wiinnow Protocol. I. INTRO ODUCTION A of cryptograaphy are mosstly designed to h computationaal hardness asssumption and not n comply with witthstanding im mminent threat imposed by computationallly effficient device. Permitting su uperposition off binary states,, a quantum computter which execu utes operation on quantum bits b wn as qubits) is believed to o be capable of (coommonly know speeeding up ted dious computaations tremend dously once the t asssociated techn nologies are in place. Th hus, it rendeers staate-of-the-art asymmetric-key a y cryptograph hy compromissed andd endangers computation nally secure symmetric-k key cryyptography [1]. Thereforee, a vintagee technique of sym mmetric-key crryptography kn nown as one-tiime pad (OTP)) is heeeded as the ulttimate solution n because it has been proven to be information theoreticaally impreg gnable again nst 50 LGORITHMS cryptannalysis, if a pperfectly randoom secret keyy of infinite length is employed onnly once and nnever reused [1]-[4]. Owing mplementationn, it was not muuch attended to lackk of practical im until noow. As uunguarded dellivery of secreet key may jeopardize the plausibble scheme, qquantum key ddistribution (Q QKD) which escortss key through quantum chaannel using quuantum state encodinng, i.e., photoon polarizationn, is suggestedd to facilitate OTP inn order to set uup a secure com mmunication fo for secret key sharingg [5]. Having its security aascertained byy Heisenberg uncertaainty principle [6] and no-clooning theorem m of quantum mechannics, QKD guaarantees deliverry of key in succh a way that possiblle eavesdroppiing can be coonfidently deteected during error raate estimation [7]. The renow wned QKD prootocol, which has bbeen proven unconditionaally secure aagainst any eavesddropping and practically viable, was built upon inspiraation from quaantum realizattion of unforgeable bank notes [ 8] and promullgated by devellopers Charles Bennett and Brassard in 19984, typically kknown as Bennnett-Brassard Gilles B 1984 (B BB84) protocool [9]. In fact, the joint ventture between OTP annd QKD is connsistent with K Kerckhoffs's prinnciple which enunciaates that key’s secrecy shouldd be the one annd only pivot leveragging security oof a cryptosysttem [10]. How wever, errors attributted to imperfecctions in the phhysical implem mentation are prevaleent, with or without eaveesdropping. C Consequently, reconciiliation is vitall for secret keyy distillation, w which serves as pprerequisite ffor informattion-theoreticaally secure cryptoggraphy. Reconnciliation is ccarried out inn (noiseless) public yet authenticatted classical chhannel to correect undesired ween sender’s aand receiver's errors ssuch that discrrepancies betw secret key can be fixed for suuccessful enccryption and decryp tion respectiveely. It can be acccomplished bby employing either simple classiccal error corrrecting code oor advanced quantuum error correccting code [1]. Winnnow protocoll decreases tthe disclosuree of partial mation to eaveesdropper by ttaking advantage of both inform parity bbit and Hamm ming code for single-bit erroor correction. Neverttheless, the need of several iteratioons is still indispeensable becausse Winnow prrotocol tends to correct a block oof sifted secret key that is interspersed with tthree or more naccurately wh hile abandonin ng odd multiple biits of error in n multiple bits of error [11]. If convolution nal dettection of even codde takes the pllace of Hammiing code, the Winnow W protoccol cann correct any odd number of erroneous e bit(ss) with the loss of operational simpllicity [12]. Chaaracterized to allow a multiple-b bit errror correction, Bose-Chaudh huri-Hocquengh hen (BCH) co ode suiitably becomees a sound alternative a forr reconciliatio on. Noonetheless, its error e correcting g capability is rather limiting g if cloosely examineed [13]. Afterr all, there iss a very stron ng mootivation to dev velop a reconciiliation protoco ol that minimizzes pubblic communiccation between n legitimate com mmunicants wiith im mproved error co orrecting capab bility. Thus, th his paper is aim med to enhance reliab bility of QKD by proposing an efficient an nd ol that rectifiess errors in sing gle efffective reconciliation protoco passs with maxim mum of doublee-bit error correcting capabiliity intto BB84 protoccol. This design n utilizes a paiir of forward an nd revverse order syn ndromes for error pattern recognition. The neew recconciliation protocol has beeen developed and a evaluated in terrms of amountt of disclosed bit and quantu um bit error raate (QBER).. II. THE PROPOSED RECONCILIA ATION SYSTEM M ARCHITECTUR RE In the BB84 protocol p as sh hown in Fig. 1, 1 Alice sendss a m key through quantum chan nnel to Bob aft fter stream of random n state of each key element. The T key is firsttly reccording photon codded in bits then further enccoded in conju ugative quantu um staates, constituted by rectilineaar and diagonaal polarization of photon conventtionally. Map pping of bitt to respectiive polarization is indicated at the bottom of o Fig. 1. Bob otons and measure them using ga ackknowledge his receipt of pho stream of random m rectilinear an nd diagonal baases, independeent froom those of Alice. Wheneverr the photon staate is a subset of bassis of measurem ment, he gets correlated c resullt. His choices of bassis with corressponding measurement resultts, known as raaw keyy, are recorded d. After transfeerence of the random r key, Bob infforms Alice about a the streeam of basis being used for f meeasurement through (noiseleess) public yet y authenticatted claassical channel, which is accessible to passiv ve eavesdroppin ng sollely. Fig. 1. Schematics of the BB B84 protocol for id deal case. Alice notifies Bob which of his measuremeent is compatib ble d should have the photon staate witth the photonss delivered and dettected correctly y, enabling theem to disregard d those result th hat suscepttible to disruuptive measurrement. Afterr discarding anomallies in respectiive raw key, thhey deduce ideentical sifted keys inn secret, whichh can be used for cryptograpphic purpose. Obviouusly, their secret key is nnot predeterm mined but is developped in conjuncction of their raandom choicess, with an aid of guidded investigatioon [9]. Resuultantly, Bob’ss sifted key ssuffers from 225% [14] of QBER in respect to A Alice’s sifted kkey. Thus, afteer the sifting processs, reconciliaation is neecessitated too ascertain identic alness of the siifted keys pair.. Grueling prooofs of QKD’s wcase correspoonding noise securityy were presennted to show resistannt threshold [114],[15]. In thhe earliest atteempts, BB84 protocool was proven secure againstt all attacks peermissible by laws off quantum mecchanics wheneever the QBER R is less than 7.4% [[16] and up to 7.56% [17] inn two independdent research studiess. Once reconcciliation is initiated, error ddetection and correcttion make conccerted effort to mitigate inconnsistencies in the siffted keys paiir using interractive or noon-interactive protocool. An interaactive reconciiliation protoccol requires repetitiive exchange oof parity bit beetween Alice annd Bob via a two-waay communicaation channel too detect and coorrect errors. On thee contrary, a non-interactivve reconciliatiion protocol appliess concept off one-way soource coding with side inform mation to eliminnate the interaactivity betweeen Alice and wn in Fig. 2. Bob whhen performingg error correctiion [2], as show In a conceptual maanner, Alice’s sifted key is ffirst encoded into reespective syndrrome. The synndrome is thenn transmitted over a (noiseless) pubblic yet authennticated classicaal channel to Bob annd fed into a deecoder togetherr with his own sifted key to restoree Alice’s siftedd key with higgh probability. In this way, sifted kkey with flaw aat receiving endd is mended allegedly [12]. The noon-interactive reconciliationn protocol is a preferable techniqque since it caan catalyze effficiency of erroor correction and miinimize public communicatioon concomitanttly. At thhe beginning of Winnow prrotocol, after sshuffling the bits off sifted keys pair in the sam me way, Alice’’s and Bob’s string of sifted key are also diviided into bloccks and then subjectted to parity ccheck correspoondingly. Onee bit in each block iis then discardeed because of tthe parity check. After that, non-intteractive reconnciliation beginns. First of all, syndrome is calculaated and sent fr from Alice to B Bob, for each oof the blocks exhibitting odd resullt in preliminnary test. It iss noted that syndro me is primitiveely an indicatoor implying corrrectness of a receiveed codeword duuring error dettection, but herre is where it fits intoo reconciliationn. F Fig. 2. Source codding with side infoormation in reconciiliation. At reeceiving end, syndrome meaasurement is caarried out by Bob ussing received ssyndrome in taandem with hiis own sifted key’s syndrome too compute ddifference between their d asso ociated correctaable error patteern synndromes, and determine of his sifted key such that the most m probable error e can then be m independently y. Normally, th he assigned errror corrrected by him corrrecting code is Hamming code, c the firstt effective lineear bloock code inven nted to be able to correct onee bit of error in na vallid codeword. ode’s limited error correctin ng Confined by Hamming co cappability, this method m will hav ve a block of siffted key deducced by Bob that is interspersed with h three or more odd multiple bits b ous of error incompleetely corrected, i.e., only one of the erroneo bitts is corrected, not n corrected or o worse yet, wrrongly correcteed, cauusing an extraa erroneous bit. b Furthermo ore, this method cannnot detect even e multiple bits of errorr, leaving theem uncorrected. Hen nce, iterations that independeent of each oth her ning bits of siftted aree still a must during reconciliiation. Remain keyy in each block that equivaalent to redun ndancy bits off a Haamming code’s codeword, are also discarded d befo ore com mmencement of new rou und of recon nciliation. Som me errroneous bits that t fall amon ng the removeed bits are th hus disscarded withou ut undergoing error e correction n [11],[18]. H Hence, in our proposed reco onciliation prottocol, in order to dettect any Hamm ming (7, 4, 3) co odeword that iss interjected wiith up to two bits of error, codeworrds with weigh ht of two in eveery ndard array aree collectively gathered g as exttra cosset of the stan corrrectable error patterns associiated with respeective syndrom me. Reesultantly, there is a mix of single-bit and double-bit errror pattterns associatted with each non-zero syn ndrome. Witho out inttroducing addittional parameter which may be favorable for f possible eavesdropping, the sy yndrome measurement is do one d man nner for an atteempt to reconcile twiice in slightly distinctive possible errors in i the codewo ord such that two t set of errror pattterns in respecct to two set off syndromes are made availab ble forr matching an nalysis. Thus, a simple con ncept of logiccal reaasoning is feattured by analy yzing the codew word in forwaard andd reverse ordeers. It is utilizin ng an idea thaat the exact errror patttern should reemain the samee regardless off the direction in whhich analysis is performed, i.e., whether from the mo ost siggnificant bit (M MSB) toward th he least significcant bit (LSB) or vicce versa as sho own in Fig. 3. In I QKD appliccation, syndrom me in forward order is the syndrom me calculated when a block of fted key is anallyzed in forwaard order (MSB B LSB) while sift synndrome in reveerse order is th he syndrome caalculated when na bloock of sifted keey is analyzed in n reverse orderr (LSB MSB B). Fig. 3. Th he order of analysiss with respective syndrome. s Indeed syndrom me in forward order is the sy yndrome that has h beeen used in Winnow W protocol. The differrence between n a block ssyndrome of ssifted key deduuced by Alice and the one deduceed by Bob in foorward order aas well as reverrse order, are corresppondingly com mputed by Bob tto determine thhe associated error p atterns in bothh orders as show wn in Fig. 4. Itt can be seen that errror patterns associated witth non-zero ssyndrome in forwardd order are a coollection of coddewords with w weight of one or two in every cosett of the standarrd array duringg preparatory while error pattterns associateed with non-zeero syndrome stage, w in reveerse order are those of forw ward order but experienced straighht left right flippping. Such adjjustment is maade such that posteriior matching analysis and error correcttion can be perform med by Bob inn reference to cconventional foorward order. Wheneever syndrome measurement does not resuult in all-zero syndro mes in forwaard order and that of in reeverse order, mum occurrencee of two bits oof error in a block of sifted maxim key iss detected. O Otherwise, the differences are all-zero syndro mes, intimatinng that the blocck of sifted keyy is errorless. Matchiing analysis is tthen carried ouut to determine the identical error p attern associatted with differeence between ssyndromes in respecttive order, ruuling out irrellevant error ppatterns and pinpoinnting the exactt one for successsful error corrrection. The algorithm off proposed reeconciliation pprotocol that B84 protocol in single pass wiith maximum rectifiees errors of BB of douuble-bit error ccorrecting capaability is show wn in Fig. 5. First off all, the positiion of bits in A Alice’s and Boob’s string of sifted kkey is randomlly permuted viia folio interlaacement such that poossible sequennt errors are ddispersed at rrandom. The shuffleed strings of siifted key are ppartitioned by both parties into bloocks that compprise seven bitts out of the total bits each. Alice hhas syndrome oof the first blockk of sifted key calculated in both foorward and reveerse orders usinng her portion oof sifted key, and theen sent to Bobb via (noiseless) public yet aauthenticated classicaal channel. Meeanwhile, Bobb also has synddrome of the first bllock of sifted key calculatedd in both ordeers using his portionn of sifted key. Syndrome meeasurement is ccarried out by Bob ussing received ssyndromes in ttandem with hhis calculated syndro mes to compuute difference between theirr syndromes and dettermine associated error patteerns in both orders. The matching analyysis is carried oout by Bob to ddetermine the identic al error patteern associated with differennce between syndro mes in respecttive order. Thee conditional decision to be made bby Bob will bbe if there is a match of iddentical error patternn after performiing matching aanalysis, error correction is perform med by addingg his block of sifted key undder test with pinpoinnted error patteern bitwise usiing binary XO OR operation. Otherw wise, there is nnot a match of iidentical error pattern after perform ming matchingg analysis. Erroor correction is skipped and his bloock of siftedd key under test is discarrded with a notificaation sent to A Alice via the cclassical channnel such that correspponding blockk of her sifteed key is disscarded too. Proceddures are kept rrepeated for ennsuing blocks of sifted key before the last blockk is analyzed. F For all the blocks of sifted key thaat are successsfully reconciled, the fourthh bit in each block i s reserved while the rest are ddiscarded by booth parties on maintenance. accounnt of privacy m Fig. 4. The error patterrns associated with h difference betweeen syndromes in rrespective orders. Fig. 5. Flow of the pro oposed algorithm fo for reconciliation. Fig. 6. Reconciliiation and privacy maintenance utilizzing the proposedd algorithm. The reconciliaation and priv vacy maintenan nce utilizing the t prooposed protoccol is shown n through a self-explanato ory exaample in Fig. 6. 6 Remarkably,, a 7-bit block of o sifted key may m be interspersed with w three or fou ur bits of error,, but such a block onciliation in accordance a wiith willl be discardeed during reco fouurth step of thee proposed prottocol. III. PERFORMANC CE EVALUATIO ONS a for reeconciliation iss simulated usin ng The proposed algorithm MA ATLAB® softtware which su upports matrix x operations th hat aree fundamental to t error correcttion. The simulation is initiatted by generating tw wo strings of sifted key; on ne is errorless in nterjected with h sequent errors. refference while the other is in Booth strings un nderwent segm mentation, ran ndom shufflin ng, synndrome comp putation, mattching analyssis, appropriaate recconciliation, privacy p mainteenance and co ombination. The T sim mulation is repeeated using diffferent initial QB BER, i.e., QBE ER priior to reconciliation, and evalluated against final f QBER, i.e., QB BER right aftter reconciliattion, which iss the output of sim mulation. F Figure 7 show ws the simulation result in comparison c wiith Wiinnow protoco ol applying parrity check and Hamming cod de. Thhe line that corrresponds to Winnow W protoccol is plotted by b dirrectly applying g the data readiily available in n [18]. Length of sift fted key of abou ut 3000 bits and optimized block size are used in this simulation n. The final QB BER posts a rise in response to ols, inccrement of inittial QBER forr both reconcilliation protoco butt the percentag ges recorded fo or proposed alg gorithm are low wer thaan those of Wiinnow protoco ol. The differen nce is noticeab bly cleear for initial QBER Q ranging from f 4% to 11% %. It is due to the t cappability of the proposed algo orithm in correecting up to tw wo bitts of error in an erroneous 7-biit block of sifteed key, which iss a feaature not posssessed by Wiinnow protoco ol. Furthermorre, unlike the propossed algorithm, Winnow proto ocol is incapab ble d discarding thee erroneous blo ocks of sifted key k of identifying and ber of remainiing errors at the t whhich constitutes toward numb endd of reconciliaation in singlee pass. Hinging g on the limitted sinngle-bit error correcting c capaability, several iterations are in neeed for compleete reconciliation using Win nnow protocol in genneral. F Figure 8 show ws the simulation result in comparison c wiith im mproved Winn now protocol applying parrity check an nd connvolutional co ode. The line that correspo onds to Winno ow prootocol applyin ng convolution nal code is plo otted by directtly appplying the dataa readily availab ble in [12]. Len ngth of sifted key k of 100000 bits is used in theirr simulation in n which the daata preesented are av veraged valuess of 100 trials. The trend th hat corrresponds to proposed alg gorithm outpeerforms that of Wiinnow protoco ol applying con nvolutional, allthough any odd num mber of erron neous bit(s) in a block of siifted key can be corrrected via the improved Win nnow protocol. 55 Fig. 7.. Graph of final QB BER versus initiall QBER in referencce to Winnow protocol appllying parity check and Hamming codde. Fig. 8.. Graph of final QB BER versus initiall QBER in referencce to Winnow protocol applyiing parity check annd convolutional ccode. IV. CONCLUSSIONS The quuantum error ccorrecting codde such as Ham mming code which uused in Winnoow protocol is ffound to be moore attractive. Howevver, the Winnow w protocol cann only correct oone error out of seveen bits. In this paper, a new reconciliation protocol has been ddeveloped to ennhance the errror correcting capability in BB84 protocol. A ssingle pass reeconciliation pprotocol that capablee corrects up tto two bits of error in an errroneous 7-bit block oof sifted key has been pressented by appllying simple Hamm ming (7, 4, 3) coode. The syndrrome measurem ment is done twice iin slightly distiinctive mannerr such that twoo set of error patternns in respect to two set of synndromes are maade available for maatching analysiis. Thus, it is featured by aanalyzing the codewoord in forwardd and reverse orders where thhe exact error patternn should remaiin the same rregardless of tthe direction whetheer from the MS SB toward the L LSB or vice verrsa. With this new innterpretation oof Hamming code’s syndroome and an unpreccedented matchhing analysis, ooccurrence of tthree or four bits off error in the errroneous blockk of sifted keyy can also be fied by the propposed reconciliiation protocol. identifi REFER RENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [100] [11] [122] [13] [144] [15] [166] [177] [18] S. Loepp and W.K. W Wootters, “P Protecting Informaation: From Classiical Error Correction to Quantum Cry yptography,” in Cambridge C Universsity Press, New Yorrk, USA, 2006. G.V. Assche, “Q Quantum Cryptog graphy and Secret--Key Distillation,”” in Cambridge Uniiversity Press, New w York, USA, 200 06. C.E. Shannon, “Communication “ theory t of secrecy systems,” s Bell Systtem Technical Journ nal, pp. 656-715, 1948, 1 K. Schmeh, “Cryptography and d Public Key In nfrastructure on the Internet,” in Wiley, Bochum, Germ many, 2003. C.H.F. Fung, X. Ma, H.F. 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Chau, “Praactical Scheme to Share A Secret Key through An Up p to 27.6% Bit Erro or Rate Quantum Channel,” C Physica al Review A, vol. 66, no. 6,pp. 06030 02-1-060302-4, Deecember 2002. D. Mayers, “U Unconditional Seecurity in Quanttum Cryptograph hy,” Journal of the ACM, A vol. 48, no. 3, 3 pp. 351-406, 20 001. E. Biham, M. Boyer, B P.O. Boykiin, T. Mor and V.. Roychowdhury, “A Proof of the Security of Quan ntum Key Distrib bution,” Journal of Cryptology, voll. 19, no. 4, pp 381 1-439, October 200 06. F. Zhao, M. Fu, F. Wang, Y. Y Lu, C. Liao and S. Liu, “Errror Reconciliation for Practical Quantum Crypto ography,” Optik International Jo ournal for Light an nd Electron Optics, vol. 118, no. 10, pp. p 502-506, 2007. Siao Ping Lee received d his Bachelor of Engineeriing and Masster of Scien nce degrees majoring in Computer & Sy ystems fro om Communiication Universitii Putra Malaysia, Serdan ng, Selangor, Malaysia, in 2009 and 2013 h respectiveely. He was undertaking his research on optical communicatio ons specializeed in error corrrection coding. C Chee Kyun Ng received his Bachelor of E Engineering aand Master of Science ddegrees majooring in Coomputer & C Communicationn Systems from m Universiti P Putra Malayssia, Serdang,, Selangor, M Malaysia, in 19999 and 2002 respectively. H He has alsoo completed his PhD pprogramme iin 2007 m majoring in C Communicationns and Network Engineeering at thee same univversity. He iis currently undertaaking his ressearch on infformation com mmunication technollogy (ICT) tow wards ageing peeople. Since frrom his study program mmes, he has ppublished overr 100 papers in journals and in confferences. M Makhfudzah Mokhtar reeceived her B B.Eng. degree from thee Universiti K Kebangsaan Maalaysia in 20000. She started hher career inn education ffield at the D Department of Compputer and C Communicationn Systems E Engineering, F Faculty of Enggineering, Uniiversiti Putra M Malaysia as a tutor. In 2007, she compleeted her Ph.D. degree from m University oof Essex and served as a lecturer inn the same instiitution. Since 22001, she has been innvolved in optiical communiccation systems research and her ressearch interestss focus on chaannel coding, O Optical Code Divisioon Multiple Acccess and quanttum key distribbution. She is a mem mber of the Institute of E Electrical and Electronics Engineeers (IEEE) andd the Photonics Society undeer the IEEE. © 20015 by the authhors; licensee A Asia-Pacific Addvanced Netw work. This articcle is an open-aaccess article ddistributed undeer the teerms and condiitions of the Crreative Commoons Attribution n licensse (http://creattivecommons.oorg/licenses/byy/3.0/).