IEICE TRANS. ??, VOL.Exx–??, NO.xx XXXX 200x1

LETTEREnhancing Credibility of Location Based Service using MultipleSensing Technologies

Kyusuk HAN†, Nonmember, Kwangjo KIM†, and Taeshik SHON††, Members

SUMMARY Recent Location Based Services (LBS) extend not only in-formation services such as car navigation services, but supporting variousapplications such as augmented reality and emergency services in ubiq-uitous computing environments. However location based services in theubiquitous computing environment bring several security issues such aslocation privacy and forgery. While the privacy of the location based ser-vice is considered as the important security issue, security against locationforgery is less considered. In this paper, we propose improved Han et al.’sprotocol [1] that provides more lightweight computation. Our proposedmodel also improves the credibility of LBS by deploying multiple locationsensing technologies.key words: Ubiquitous Computing, context-awareness, Location BasedService, privacy, authentication, credibility

1. Introduction

Location based service (LBS) is a service using a user’s lo-cation information that is sensed by location sensing tech-nologies, and widely deployed in the ubiquitous computingenvironment. Wider deployment of LBS invoke the concernof security problems such as privacy and location forgery.

While many studies such as [2][3][4][5] focused on theprivacy problem in LBS, less interests are given to prevent-ing location forgery. Han et al. [1] proposed authenticationprotocols that provides both credibility and privacy to LBS,and only few studies such as [6] are done since then.

However, the concerning of credibility of the locationinformation is becoming more important in wider applica-tions of LBS, it is important to provide the credible solutionfor preventing location forgery.

Therefore, our motivation is to provide more reliablesolution that provides privacy and credibility of locationbased service. Although Han et al. [1] showed basic loca-tion authentication protocol, that was difficult to be imple-mented for ubiquitous environments due to deployed PKIthat needs quite heavy computation. In this paper, we im-prove Han et al.’s protocol [1] by substituting the publickey based computation to symmetric key based computa-tion. Our improved protocol deploys two different types oflocation sensing technologies.

The paper is organized as follows: We categorize LBS

Manuscript received November 1, 2010.Manuscript revised March 4, 2011.†The authors are with Korea Advanced Institute of Science and

Technology, Daejeon, Korea; e-mail:hankyusuk, kkj@kaist.ac.kr.††The author is with Division of Information and Computer

Engineering, College of Information Technology, Ajou Uni-versity, Suwon 443-749, Korea, Corresponding author; e-mail:tsshon@ajou.ac.kr

DOI: 10.1587/trans.E0.??.1

Antenna

Satellite

Antenna

Antenna

GPS(LLC)

Mobile Network(non-LLC)

Fig. 1 Example Scenario: Car Navigation Service using GPS (LLC) andmobile network (non-LLC)

model using two different sensing technologies and locationsensing architecture in Section 2 . We propose our improvedprotocols in Section 3, and analyze our protocols in Section4. We conclude our paper in Section 5.

2. Location Sensing Technologies

2.1 Location Sensing Methods

We focus ourselves on the capability of localized locationcomputation (LLC). By the characteristic of LLC, variouslocation-sensing technologies can be divided into two cat-egories; LLC and non-LLC that depending on recognitionwithout the capability of LLC. Using LLC, the object beinglocated actually computes its own position. GPS and Cricket[7] are typical examples. In contrast, the methods that do notuse LLC require the located object to periodically broadcast,respond with, or otherwise emit telemetry to allow the exter-nal infrastructure to locate it. Currently, most systems suchas SpotON [8] have recognition capability. Location servicevia mobile network is also considered as non-LLC. Figure 1shows the location sensing using LLC and non-LLC.

In the case of LLC, users privacy is easily guaranteedsince user computes own location for himself. However, arisk exist that a malicious user can forge the information. Onthe contrast, non-LLC has potential threat that the privacymay not be guaranteed since the infrastructure knows thelocation with recognition.

Copyright c⃝ 200x The Institute of Electronics, Information and Communication Engineers

2IEICE TRANS. ??, VOL.Exx–??, NO.xx XXXX 200x

2.2 Location Service Architecture

A location service architecture for protecting location pri-vacy is defined by The Geopriv Working Group [9][10]. Thearchitecture consists of four main components; a locationgenerator, a location server, a rule holder and a locationrecipient. By user ownership, four possible architecturesare defined as User-controlled model, user-mediated model,third-party model, and hybrid model. User-controlled modelhas the capability of LLC. And, in the User-mediated model,the user does not control the location generators, which cantherefore be inside-out or outside-in location systems, butinstead the user owns and controls only the rule holder andlocation server. Also, in the third-party model user cannotcontrol the location generators, the rule holder and locationserver. Hybrid model combines user controlled model andthird-party model.

2.3 Security Requirements

We use security requirements for the location informationdefined in [1] as follows:

Privacy An attacker cannot know a clients location duringcommunications of LBS.

Prevention from over-collection A service provider shouldknow only sufficient location information of the client.

Authentication The service provider can verify whether aclients location it correct.

Unforgeability An attacker cannot forge a clients location.Also, The client cannot forge own location.

Resistance to Replay-attack When a clients location isauthenticated and used for the service, the location can-not be used again.

Preventing over-collection of location information isan important requirement for location privacy. For exam-ple, in the DRM scenario, the distributer only need to knowwhether the request of the purchase is from the inside of thenational boundary. It shall not be allowed that the distributerrequires more specific information like city and street.

The whole security considerations from the communi-cation in the location based service are not our considera-tion; Authentication of entities, confidentiality of commonmessages, temper resistance of a location generator and alocation server, and so on [11].

3. Improved Location Authentication and Privacy Pro-tocol

In this section, we show our improved scheme for authen-tication and privacy of location information. We adopt theservice architecture defined in [1]. Our model comprisesthree entities, a user U, a service provider S P, and a trustedoperator OP. U wants to prove his current location to S P,while S P needs to verify Us location information LU . OPhas an important role similar to a trusted authority of PKI.

The similar model is introduced in [12] that multiple OPsonly share the secret and U directly communicates with S P.Our protocol deploys two different types of location sensingtechnologies, while we do not define specific location sens-ing methods. We show the improved location authenticationand privacy protocol in following section.

3.1 Protocol Description

We assume that U knows IDOP and IDS P. The protocolmainly has four parts as below.

P.1 U request authentication of his location LU to OP inorder to get a service from S P.

P.2 OP generates credit of LU for U.P.3 U request service to S P by proving LU .P.4 S P verifies U’s location, LU .

Table 1 shows notations used in the paper. Detailed proto-cols are as followings.

Table 1 NotationsNotation Description

A||B sequence of A and BA→B : M A sends M to B

KU Symmetric key shared between U and OPKS P Symmetric key shared between OP and S P

eK (M) Encrypt M using a key KMACK (M) Message authentication code of M using KLU A user Us location information

REQ authentication request messageIDU Identity of a user UIDOP Identity of an operator OPIDS P Identity of a service provider S PTS OP Timestamp generated by OPROP Random nonce generated by OPCRT Credit of user’s locationS EN Encrypted message for sendingRT N Encrypted message fore receiving

P.1 a) U self-generates LU using LLC based de-vice such as GPS, and S EN0

U , where S EN0U =

eKU (REQ||IDS P||LU). U also generates M0U , where

M0U = MACKU (IDU ||IDOP||S EN0

U).b) After that U sends S EN0

U and M0U to OP.

U → OP : S EN0U ||M0

U

P.2 a) After verifying M0U and decrypting S EN0

U , OP findsa key KS P shared with S P, and also verifies LU usingnon-LLC. The number ‘1’ in RT N or S EN denotes thatthe parameter is decrypted or verified by U. The num-ber ‘2’ is for S P, and ‘0’ is for OP.b) OP randomly selects ROP and generates CRTS P andCRTU , where CRTS P = MACKS P (IDU ||LU ||ROP), andCRTU = MACKU (IDU ||LU ||CRTS P) respectively.c) OP then generates RT N1

U , RT N2S P, M2

OP and M1OP

sends them to U, whereRT N1

U = eKU (CRTS P||CRTU ||ROP||HU ||TS OP),RT N2

S P = eKS P (ROP||HS P||TS OP),

LETTER3

M2OP = MACKS P (IDU ||RT N2

S P), andM1

OP = MACKU (RT N1U ||S EN1

U ||RT N2S P||M2

S P).

OP→ U : RT N1U ||RT N2

S P||M2OP||M1

OP

HU = h(KS P||ROP||TS OP), and HS P = h(KU ||ROP||TS OP),where h(m) denotes hash of m.

P.3 a) After verifying M1OP and decrypting RT N1

U , U findsCRTS P, CRTU , ROP, HU and TS OP.b) U then verifies CRTU , and then generates T KU ,where T KU = h(HU ||HS P).c) After that, U generates S EN2

U and M2U , and sends

them to S P, where S EN2U = eT KU (CRTS P||LU) and

M2U = MACT KU (IDU ||IDS P||S EN2

U).

U → S P : RT N2S P||S EN2

U ||M2U ||M2

OP

Remaining part (P.4) is operated by S P.

P.4 a) After verifying M2OP, S P decrypts RT N2

U and re-trieves ROP and TS OP.b) S P also generates T KU , decrypts S EN2

U , and thenretrieves CRTS P and LU .c) After verifying CRTS P, S P authenticates LU .

4. Design Analysis

We analyze that our protocol holds security requirements asfollows:

Privacy AdversaryA cannot know Us location LU withoutKU or KS P. Also, U cannot know KS P from T KU and viseversa. The success probability ofA relies on the strength ofencryption schemes.

Prevention of Over-Collecting S P only receive LU fromU, and verification information from OP. OP identifies lo-cation of U, and generates CRTS P for S P that needs loca-tion. Since each S P may need proper level of location in-formation and the accuracy of each location sensing tech-nologies is different, we can use civic addresses for locationinformation.

There are two common ways to identify the location ofan object, either through geospatial coordinates or civic ad-dresses. Geospatial coordinates indicate longitude, latitude,and altitude, while civic addresses indicate a street address.6 divisions of civil addresses are defined as national subdi-vision, county, city, city division, neighborhood, group ofstreets below the neighborhood level in [5].

Fig 2 shows the example of services. In case of deliveryservices, very accurate information is required. By contrast,only country information is sufficient to verify users for on-line stores that sell digital contents. Thus, when U has veryaccurate information from GPS, U convert it to civic addressand sends only proper level of information to S P. OP alsogenerates CRTS P with such level.

Delivery Service

National

subdivisionCountry City

City

DivisionNeighborhood Street

Appstore

Fig. 2 Example Scenario: Car Navigation Service using GPS (LLC) andmobile network (non-LLC)

Authentication S P verifies U’s LU from CRTS P. Althougha malicious U sends LU to other user UA, S P can checkLU from UA is invalid. Since CRTS P is infeasible by UA

without KS P . Computational infeasibility of hash functionis well known property.

Unforgeability AdversaryA fails to forge LU without key.The success probability of UA cheating S P is 1/2n for themessage length n.

Replay-attack by User The protocol prevents U’s mali-cious trial of reusing LU by timestamp TS OP. S P verifiesLU by CRTS P. Since ROP is updated in each session, mali-cious trail by U fails.

5. Conclusion

The credibility of location information is one of critical is-sues in ubiquitous computing environments. We believe thatthe proposed model is an applicable solution for the issue.In this paper, we presented improved location authentica-tion and privacy protocol proposed in [1]. The distinguishedpoints are the location information is generated by multi-ple sensors: LLC and non-LLC , and the protocol is fullybased on symmetric key based cryptosystem for supportingmassive interaction. In future work, we will concentrate onthe research to improve the accuracy of a location sensingservice by combining multiple sensors.

References

[1] K. Han and K. Kim, “Enhancing privacy and authentication for loca-tion based service using trusted authority,” The 2nd Joint Workshopon Information Security, 2007.

[2] S. Gajparia, C.J. Mitchell, and C.Y. Yeun, “The location informationpreference authority: supporting user privacy in location based ser-vices,,” In the 8th IFIP TC-6 TC-11 Conference on Communicationsand Multimedia Security, Cumbria, UK, pp.15–18, 2004.

[3] J. Al-muhtadi, A. Ranganathan, R. Campbell, and M.D. Mickunas,“A flexible, privacy-preserving authentication framework for ubiqui-tous computing environments,” In In Proceedings of IWSAEC 2002,pp.771–776, 2002.

[4] A. Novobilski, “Pervasive/invasive computing; two sides of thelocation-enabled coin,” In PDPTA ’02: Proceedings of the Interna-tional Conference on Parallel and Distributed Processing Techniquesand Applications, CSREA Press, pp.1063–1067, 2002.

[5] Dynamic host configuration protocol (DHCPv4 and DHCPv6) op-tion for civic addresses configuration information. RFC 4776.

[6] W. Luo and U. Hengartner, “Proving your location without giving upyour privacy,” HotMobile 2010, Annapolis, Maryland, USA, 2010.

[7] N.B. Priyantha, A. Chakraborty, and H. Balakrishnan, “The Cricketlocation-support system,” In MobiCom ’00: Proceedings of the 6th

4IEICE TRANS. ??, VOL.Exx–??, NO.xx XXXX 200x

annual international conference on Mobile computing and network-ing, New York, NY, USA. ACM., pp.32–43, 2000.

[8] J. Hightower, C. Vakili, G. Borriello, and R. Want, “Design and cali-bration of the spoton ad-hoc location sensing system,” August 2001.

[9] A.R. Beresford, “Location privacy in ubiquitous computing,” tech.rep., Technical Report No 612, UCAM-CL-TR-612, ISSN 1476-2986, University of Cambridge, 2005.

[10] J.R. Cuellar, J.B. Morris, D.K. Mulligan, J. Peterson, and J. Polk,Geopriv requirements, RFC3693, 2004.

[11] A. Corradi, R. Montanari, and D. Tibaldi, “Context-based accesscontrol for ubiquitous service provisioning,” In Proceedings of the28th Annual Interna- tional Computer Software and ApplicationsConference (COMPSAC’04)., 2004.

[12] C. Delakouridis, L. Kazatzopoulos, G.F. Marias, and P. Georgiadis,“Share the secret: Enabling location privacy in ubiquitous envi-ronments,” LOCATION AND CONTEXT-AWARENESS LectureNotes in Computer Science, vol.3479/2005, pp.289–305, 2005.