a hybrid user authentication protocol for mobile iptv service

A hybrid user authentication protocolfor mobile IPTV service

Soo-Cheol Kim & Sang-Soo Yeo & Sung Kwon Kim

Published online: 7 May 2011# Springer Science+Business Media, LLC 2011

Abstract IPTV, a technological convergence that combines communication and broad-casting technologies, delivers customized, interactive TV content and other multimediainformation over wired and wireless connections. Providing secure access to IPTV servicescalls for authentication, without proper and secure authentication mechanisms, anindividual impersonating a subscriber could steal a service. This paper proposes a newauthentication protocol to authenticate IPTV users. The authors based the proposedprotocol, a hybrid authentication protocol providing lightweight, personalized userauthentication, on RFID (radio-frequency identification) and USIM (Universal SubscriberIdentity Module) technologies. In the proposed protocol, USIM performs highlypersonalized authentication, and the authenticated subscriber’s RFID tags can have atemporary authority to execute authentication. These RFID tags become Agent Tagsauthorized to authenticate subscribers. Agent Tags identify and authenticate themselves toRFID readers in the set-top box, thus, simplifying the authentication process.

Keywords IPTV. RFID . Java Card . USIM . User authentication

1 Introduction

With increasing digitalization and diversity in media content, a technology designed to providerobust multimedia services over diverse access technologies has emerged to replace conventionalbroadcasting services, such as traditional radio frequency broadcast, satellite signal, and cabletelevision (CATV) formats. IPTV combines broadcast and telecommunication services and

Multimed Tools Appl (2013) 65:283–296DOI 10.1007/s11042-011-0810-5

S.-C. Kim : S. K. Kim (*)Division of Computer Science and Engineering, Chung-Ang University, Dong-Jak-gu,Seoul 156–756, Republic of Koreae-mail: [email protected]

S.-C. Kime-mail: [email protected]

S.-S. YeoDivision of Computer Engineering, Mokwon University, Daejeon, Republic of Koreae-mail: [email protected]

provides delivery of multimedia content using the architecture and networking methods of anIP-based network infrastructure, e.g., the Internet and broadband Internet access networks [6, 7].It offers interactive two-way television services as well as general Internet-based or web-basedmultimedia services. In particular, the widespread use of mobile devices has increased interestin mobile IPTV technology, enabling users to enjoy IPTV services anywhere and while on themove. Traditionally, IPTV has delivered high-quality TV content to fixed users on networks.Mobile IPTV, on the other hand, enables various mobile users (i.e., users with portable devicessuch as mobile phones, and PDAs.) to transmit and receive multimedia traffic through IP-basedwired and wireless networks. Providing a secure authentication mechanism to prevent illegalaccess represents one of the fundamental requirements for the use of IPTV services. As IPTVsystems provide the standard one-way broadcast service and the interactive on-demand service,traditionally employed protection schemes such as CAS (Conditional Access System) andDRM (Digital Rights Management) fail in IPTV environments. In addition, in mobile IPTV,new security issues regarding mobility and wireless characteristics. Thus, researchers considerdeveloping secure IPTV authentication mechanisms of great importance.

Furthermore, existing IPTV authentication schemes perform a set-top box (STB)-levelauthentication so that whole family members get the same service and access level to IPTVservices. Mobile IPTV, which generally provides personalized, tailored services forsubscribers, requires individual-level user authentication [1, 4].

Previous works on IPTV user authentication can be classified into three approaches–password-based, RFID-based, and USIM-based. Password-based user authentication is simpleand implementable solely with software, but it has disadvantages in terms of passwordmanagement overhead and the lack of personalized authentication. In the RFID-based approach,user authentication is performed through a set-top box that identifies RFID tags. This approach isimplementable with a relatively low cost and simple authentication process, but identifying userssimply via tags does not provide personalized authentication. In the USIM-based approach, userauthentication is performed via USIM embedded in mobile devices where user information issecurely stored. This approach supports personalized authentication, but its authenticationprocess is more complicated, compromising simplicity and ease of management. Moreover, theamount of data exchanged between terminals is large, causing server overhead.

This paper proposes a low-weight user authentication protocol adopting the concept ofAgent Tag. The proposed hybrid protocol combines RFID-based lightweight authenticationand enhanced personalized authentication based on Java Card, to make the most of meritsof both mechanisms. The proposed protocol simultaneously provides personalizedauthentication and a simplified authentication process, thereby enhancing the reliabilityand simplicity of user authentication. In addition, electric power consumption can belowered as the machine computation required for authentication is reduced.

The rest of the paper is organized as follows. Section 2 presents previous works on IPTVauthentication protocols and discusses their advantages and disadvantages. Section 3describes the user authentication protocol a hybrid authentication protocol providinglightweight, personalized user authentication, on RFID and USIM technologies, proposedin this paper. In Section 4, the proposed protocol is evaluated in terms of two aspects,performance and security. Finally conclusions are given in Section 5.

2 Related work

Secure access to IPTV services requires, authentication that identifies subscribers and legal users.Authentication becomes more challenging in the mobile IPTVenvironment where users/viewers

284 Multimed Tools Appl (2013) 65:283–296

request IPTV services anywhere and while on the move. Researchers have devoted considerablestudy to authentication protocols that enable users authentication by service providers beforeusers benefit from the requested services. The CAS, passwords, RFID, and Java Card includesome technologies used in previously proposed authentication protocols. This section describesexisting subscriber authentication schemes and their pros and cons.

Early pay TV used a CAS to operate service access management through subscriberauthentication. Content scrambling prevents unauthorized viewers from watching pay TV. WhileCAS-based schemes, offer good service security, difficulties remain in implementingauthentication based on information and in protecting the copyright of downloaded content [5,8, 11].

DRM-based schemes impose limitations on the usage of digital content and devices (i.e.,inhibiting uses of digital content by illegitimate users). While cost efficient as software-orientedschemes, their service/content security falls short of that of CAS-based schemes. In addition,billing for real-time broadcasting proves difficult in DRM-based schemes [10, 12, 13, 15].

An advantage of password authentication schemes based on subscriber credentials stored inthe STB includes ease of implementationwithout the need of hardware. However, they can onlyexploit limited personal information (user names and passwords). In addition, these schemessuffer from vulnerability to password guessing attacks, such as key-logging, sniffing, andphishing (i.e., the system identifies anyone who knows the username and password as a validuser). Hence, protection of personal credentials requires additional security mechanisms [3, 14].

In RFID-based authentication schemes, RFID readers attached to the STB read informationavailable in RFID tags, and the IPTV server authenticates subscribers based on the sensed taginformation. These easily implemented schemes also offer low communication overhead andhigh mobility, but require additional hardware (i.e., RFID readers and tags). Moreover,illegitimate users can access IPTV services due to lack of PIN-based authentication inRFID-based protocols [2].

USIM, used for 3G-and-beyond mobile networks, provides secure mutual authenticationbetween users and service providers. USIM can store rich subscriber information andauthentication information, so it can support highly personalized services as well as strongservice/content security. USIM-based schemes make use of Generic BootstrappingArchitecture (GBA) enabling user authentication. This enhances security but increasescomplexity. As a consequence, USIM-based authentication schemes have higher commu-nication and computational overhead than RFID-based or password-based authenticationschemes [9].

3 Proposed IPTV user authentication protocol

In this section, we propose a user-authentication protocol adopting the concept of Agent Tag.The proposed hybrid combines RFID-based lightweight authentication and enhancedpersonalized authentication based on Java Card to take advantage of merits of both mechanisms.

3.1 Architecture

Figure 1 shows the structure of the proposed Agent Tag-based user-authentication protocol.Four main parts make up the proposed system: User Equipment (USIM), Agent Tag (RFIDTag), STB, WAP (wireless application protocol) and IPTV Network. IPTV Networkindicates the conventional core network with multiple servers such as content servers andapplications servers.

Multimed Tools Appl (2013) 65:283–296 285

The proposed protocol uses the following abbreviations:

& User: An IPTV subscriber registers his/her family members, whose identificationinformation (mobile phone or RFID tag information) is stored in the STB. The STBrecognizes IPTV viewers via its user recognition device like RFID readers. Therecognized viewers connect to the IPTV service through a login at the terminal device.A viewer who has successfully logged in is called an “active user”.

& UE (User Equipment): Portable devices incorporating USIM, such as 3G mobilephones and PDAs. UE includes Identity Applet storing personal information, allowingpersonalized user authentication through UE. In addition, UE enables users to set acertain RFID tag as an Agent Tag.

& AS (Application Server): AS consists of an identifier management server and anauthentication server as the core of IPTV authentication mechanisms. AS receives andprocesses IPTV service requests from users. AS stores IPTV subscriber information anduses the stored subscriber information to authenticate service users. In the proposedprotocol, AS has an additional role that grants the privilege given to the Agent Tag andstores the information related to Agent Tag into a database.

& WPG (WAP Proxy Gateway): As a fundamental component of WAP-based wirelessInternet networks. To provide secure traffic, WAP supports the SSL (Secure SocketsLayer) security protocol for communications over wired networks and the WTLS(Wireless Transport Layer Security) protocol in a wireless communication environment.

Fig. 1 Agent Tag based IPTV service architecture


& RFID Reader: Part of the STB equipment that carries out the user’s request for IPTVservices. The STB’s RFID reader enables automatic authentication of users’ mobiledevices, thus simplifying the use of the devices. For example, implanted RFID readerequipment recognizes IPTV users within its range by capturing user from their RFIDtags. RFID Reader connects with the STB through the serial port or through a USBport. The STB has the plug-and-play function that automatically detects RFID Readerand loads the required driver.

& Agent Tag: Agent Tag, a standard RFID tag, has temporary authority to perform userauthentication as a substitute for UE. When registering an Agent Tag in a STB, a user cangive different kinds of authority conditions in terms of frequency, duration, programselection, and device selection. For example, an Agent Tag can perform user authenticationonly 10 times or only for one week (minute, day, week, month, year) or it can authenticateonly for certain programs (TV-14, TV-M, TV-PG) or for certain devices(Home TV, PDA,PC, laptop, mobile phone). Hence, an STB stores the authority information (Tag ID,remaining count for watching IPTV, remaining time for watching IPTV, accepted programlevel, accepted IPTV device) of the Agent Tag, as shown in Table 1.

In Table 1, Tag 101100 has the authority to watch TV-14 program 10 times fromtelevision device on the home. Tag 111000 has the authority to watch TV for 24 h on thePDA. Tag 100011 has the authority to watch all TV program 30 times for 7 days on alldevice. Tag 101010 has the authority to watch TV-PG program on personal computer. Tag100011 has the authority to watch TV-M program 5 times for 30 min on mobile phonedevice. As Table 1 shows, users can flexibly set various authorization conditions withregard to IPTV services using the proposed mechanism of the Agent Tag, which, in turn,leads to enhanced service scalability. For example, parents can create an Agent Tag for theirchildren to prevent them from exposure to certain media.

3.2 Definition of terms

The proposed IPTV authentication protocol consists of two stages: 1) user registration and2) user authentication. User registration signifies the process of registering informationabout those individuals subscribed to IPTV services. User authentication refers to theprocess of authenticating registered subscribers by the head end server.

This paper uses the terms and notations described in Table 2.

3.3 User registration

A user subscribes to an IPTV service and registers his or her personal information alongwith family member information. The information required for registration is the viewers’

Table 1 Example of agent tag data set in STB

Tag ID Remaining count Remaining time Accepted program Accepted device

101100 10 – TV-14 Home

111000 – 24 h – PDA

100011 30 7 day – –

101010 – – TV-PG PC

111100 5 30 min. TV-M Phone


profile (age, gender, address, job, etc.) and the mobile device information used to identifythe viewers. In the user registration phase, each user registers individually, and userauthentication follows via user’s mobile phone. When a user subscribes to an IPTV service,the user receives personal account information such as STB identifier and ID/password. TheIPTVoperator’s authentication server (AS) stores a key pair of the shared key (KS) betweenAS and user and of TID (session identifier). This TID is stored in the STB during the userregistration process, and it is also stored in the user’s terminal device (UE) if the userrequests this. Figure 2 shows the user registration process in our protocol.

Phase 1: Service registration request

• USER → AS: UE stores USIM information and sends a request for IPTV serviceregistration to AS.• AS: AS receives user’s request for IPTV service registration and registers theuser in the corresponding IPTV service list. The registered personal credentials,required credentials for the personalizing of authentication, include STB hardwareidentifier and user ID/password.

Phase 2: Service registration

• AS → USER, STB: AS sends the registration information (Info.User, Ks, TID) toUSER and to STB. UE and STB store the received information, respectively

Phase 3: User information update

• STB →USER: STB sends its update information to UE, and UE stores theupdate information.

3.4 User authentication

The user authentication phase determines the legitimacy of an IPTV subscriber servicerequestor. The proposed scheme has two types of user authentication: authentication viaUSIM and authentication via Agent Tag. When a strong personalized authentication isneeded or a re-authentication is required due to the expiration of temporary authority given

Notation Meaning

IDA Identifier of entity A

EX (M) Symmetric encryption of data M by using key x

DX (M) Symmetric decryption of data M by using key x

S(SX, M) Signature on data M by using key SXMACX(M) MAC on data M by using Key x

CertA X.509 certification of entity A

TID Session ID used between UE and AS

|| String concatenation function

h(M) Hash function of data M

RA Random number made by entity A

tX Time stamp made by entity A

ATA Authentication token of entity A

SKA Private key of entity A’s certificate

Table 2 Terms and notations


to an Agent Tag, USIM-based user authentication is performed. For other cases, lightweightauthentication based on an empowered Agent Tag is applied. Figures 3 and 4 providedetails of each type of user authentication.

1) USIM-based authentication

Phase 0: Pre-phase

• UE: UE acquires the information about RFID tags that will serve as an Agent Tag.UE sets the authentication conditions for each tag (allowed number of views, viewduration, allowed programs and devices).

Phase 1: Run identity applet

• UE → USIM: UE sends a request message to make USIM run Identity Applet• USIM → UE: USIM checks the request message sent from UE, and returns theUSIM identifier IDUSIM and a secret key KUSIM (shared between USIM and UE) to UE.UE stores the information sent from USIM.• UE → Applet: UE sends a message to Identity Applet to request the IPTVregistration information (i.e., STB hardware identifier and user ID/password).

Fig. 2 User registration process


• Applet → UE: Identity Applet returns the IPTV registration information to UE.

Phase 3: Authentication phase

• UE → AS: UE sends an authentication request message as in (1) to AS. Theauthentication request message contains TID and a time stamp tUE. The userinformation in the message is encrypted with KS for security, and a MAC algorithmis applied. The MAC value protects the message's data integrity as well as itsauthenticity.

fTID; t UE;EKS ðIDUEÞ;MACKS ðTID; tUE;EKS ðIDUEÞÞg ð1Þ

• AS → UE: Using the TID sent from UE, AS retrieves the corresponding master keyKS from the database. AS then decrypts DKs(IDUE) using the master key. With thedecrypted IDUE, AS verifies its legitimacy. When creating the certificate Cert for alegitimate subscriber, AS creates the authentication token ATAS and the authenticationresult code depending on if the authority to perform user authentication is delegated tothe user’s Agent Tags. AS signs the authentication token ATAS with AS’s private key,and then issues the certificate Cert. The signed authentication token is represented as S(ASSK, ATAS). Along with the signature, certificate CertAS, and time stamp, AS sends anacceptance message to UE so as to grant Agent Tag’s authority to execute userauthentication as in (2). If user authentication has failed, the message does not includethe signature S and the certificate CertAS.

fTID; t AS ; ½SðASSK ;ATASÞ;CertAS �;MACKS ðTID; tAS ; ½SðSKAS ;ATASÞ;CertAS �Þg ð2Þ

Fig. 3 USIM-based user authentication


Phase 4: Verification phase

• UE → Applet: UE verifies the integrity of the message sent from AS. If theintegrity check succeeds, Identity Applet stores the signature S(SKAS, ATAS) andSTB stores the information regarding Agent Tags.• Applet → UE: Identity Applet sends the result of storing the signature S (as inprevious step) to UE. IPTV user authentication based on USIM is completed.

2) Agent Tag-based authentication

Phase 0: Pre-phase

• Unlike USIM-based user authentication presented in Fig. 3, RFID tagsauthenticate subscribers. The authentication process in Fig. 4 begins when theauthentication procedures in Fig. 3 are completed and Agent Tags having thedelegated authority to authenticate the subscribers are granted by AS. Note thatSTB has stored the information about Agent Tags authorized by AS in USIM-based user authentication.

Phase 1: Scan-phase

• Reader → Agent Tag : RFID Reader attached to STB explores its surroundingsto check whether the authorized Agent Tags exist within its read range. Figure 4shows the simple manner of authentication, i.e., by simply verifying if the sensedRFID tags are one of the Agent Tags stored in STB. To initiate the process, theRFID Reader sends a message requesting tag information to nearby RFID tags,along with the random number Rr generated by RFID Reader and a time stamp tr.

Phase 2: Authentication phase

• Agent Tag → Reader : RFID Tag hashes the random number Rt generated by thetag, its tag ID IDtag, and the random number Rr and the time stamp tr sent from

Fig. 4 Agent Tag-based user authentication process


RFID Reader using a pre-shared secret key Kt, and sends the hashed result toRFID Reader as in (3).

fRt;Rr; tr; IDtag; hKt ðRt;Rr; tr; IDtagÞg ð3Þ

• Reader → STB : RFID Reader decrypts the information sent from RFID Tag andfinds the tag ID. RFID Reader sends the tag ID to STB to check if the tag is anAgent Tag.

Phase 3: Verification phase

• STB : STB compares the tag ID sent from RFID Reader with the IDs of theAgent Tags stored in the STB’s database. If a valid Agent Tag, it can execute userauthentications in connection with the authentication token obtained in USIM-based user authentication and its authorized conditions. Otherwise, the tag cannotconduct user authentication.• Agent Tag’s authority to validate the IPTV user’s authenticity has a timelimit. When it expires, this temporary authority given to an Agent Tag must bereacquired by completing the authentication steps in USIM-based userauthentication.

4 Evaluation of the proposed protocol

To implement the proposed protocol, the authors programmed the simulation system usingPython 2.6 in a Windows XP environment. This section evaluates the proposedauthentication protocol in terms of performance and security.

4.1 Performance analysis

Figure 5 shows the server’s computation delays according to the number of subscribers. Inconventional protocols, computation amounts in tags and the authentication server increase

Fig. 5 Server’s computation delays according to number of subscribers


by logN (N = number of subscribers) as the number of subscribers increases. On the otherhand, the proposed protocol utilizes Agent Tags to perform authentication and requires lesscomputation in the authentication server; thus, its increase rate in computation is lower thanconventional protocols.

Figure 6 shows the total amount of computation in the authentication server accordingto the degree to which Agent Tags participate in authentication. As USIM-basedauthentication increases, the total amount of computation increases. In the same sense, theoverall computational load decreases as Agent Tag based lightweight authenticationincreases.

4.2 Security analysis

1) Confidentiality

WPG uses secure channels having WTLS or SSL to transmit messages. To enhancesecurity, the proposed protocol employs the common key K and the hash functionmechanism. Encrypting sensitive user information using a secret key secures againstattacks. The common key KS shared by UE and AS is newly created whenever users requestservice. Hence, authentication cannot succeed even if an attacker has access to theinformation used in previous sessions. In RFID tag-based authentication, processing ofmessages uses the cryptographic hash function to prevent abuse by unauthorized users. Therandom numbers Rr and Rt, included in the hash function, guarantee the authenticity of themessages. The design of the hash function makes it difficult to reverse the process or, tofind a string that hashes to a given value. Thus, tag IDs remain protected even if attackersintercept the transmitted messages. In addition, tags generate their own random numbers, sothe proposed protocol maintains resiliency to man-in-the-middle attacks.

2) Integrity

The proposed protocol employs time stamps and the MAC algorithm to defend againstspoofing attacks. Time stamps and MACs endorse messages transmitted between USIM and ASand can detect any changes to the message content (forgery or modulation). AMAC for messageis newly created for each session, so attackers cannot find the shared common key K even if they

Fig. 6 Total amount of computation in the authentication server according to the degree to which AgentTags participate in authentication


have eavesdropped onmessages. Only UE andAS know the time stamps (Tue, and Tas) applied toMACs. Similarly, time stamps provide data integrity in Agent Tag-based authentications.

And if RFID tag is stolen by an adversary, all the information can be used by the adversary. Itmeans the RFID tag easily can be used for cheating or counterfeiting. In our scheme, wedesigned that an Agent Tag can take have a temporary authority to execute authentication.Therefore, in our scheme, IPTV service can be used by the adversary during limited times.

5 Conclusion

This paper proposed an authentication protocol that combines USIM-based personalizedauthentication and light-weight authentication using an Agent Tag-empowered temporarilyand conditionally to perform user authentication. User authentication using USIMsupported in the proposed protocol allows personalized identification that conventionalRFID-based authentication has lacked. Also, an Agent Tag has a certain level of authorityregarding user authentication so as to improve on limitations of USIM-based authenticationthat require a high level of computational resources. As a result, the proposed protocolachieves both reliability and simplicity of user authentication. The simplified authenticationprocess in the proposed protocol indicates a reduced use of computing resources and power,and the proposed scheme also contributes to Green Computing.

Acknowledgments This work was supported by Basic Science Research Programs through the NationalResearch Foundation of Korea (NRF) grand funded by the Korea government (MEST) (No.2010-0013121).

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Soo-Cheol Kim He received his master’s degrees in Computer Sciences & Engineering from Chung-AngUniversity, Seoul, Korea, in 2007. He is currently PH.D course at Department of Computer Science andEngineering, Graduate School, Chung-Ang University, Seoul, Korea. His areas of research interest areInformation security, Trust management, RFID system, and Multimedia Service.

Sang-Soo Yeo He received his master’s degree and doctorate in Computer Science & Engineering from Chung-Ang University, Seoul, Korea. He is currently a professor at the Division of Computer Engineering, MokwonUniversity, Korea. He is the Vice President of Future Technology Research Association International (FTRA) andVice President of Korea Information Technology Convergence Society. His areas of research interest are Security,Ubiquitous Computing, Multimedia Service, Embedded System, and Bioinformatics.


Sung Kwon Kim He received his bachelor’s degree from Seoul National University, Seoul, Korea, hismaster’s degree from Korea Advanced Institute of Science and Technology (KAIST), Korea, and his Ph.D.degree from University of Washington, Seattle, U.S.A. He is currently a professor at Department ofComputer Science and Engineering, Chung-Ang University, Seoul, Korea.


a hybrid user authentication protocol for mobile iptv service

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