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GSM Authentication
GSM Authentication
GSM Authentication
GSM Authentication
GSM Authentication
GSM Authentication
GSM Authentication
GSM Authentication
GSM Authentication
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GSM Authentication

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  • 1. An Ontology for Generic Wireless Authentication 1 Declaration Herewith, I declare that I have written this thesis myself and no other sources than listed in the references have been used. Asma Alazeib Stuttgart, 07.October.2005
  • 2. An Ontology for Generic Wireless Authentication 2 Acknowledgements I would like to thank first and foremost my supervisors in Alcatel SEL AG, Dr. Stephan Rupp and Andreas Diehl for all their help, support, follow ups and encouragement. I thank them for the weekly meetings held, for all the guidance and assistance and for all the times they were there whenever I needed advice and support. I would also like to thank Prof. Klaus Schünemann and Prof. Wolfgang Meyer for supervising me at the Hamburg University of Technology during my master thesis and for their help and support. Special thanks also goes to Franz Josef Banet and Matthias Duspiva who were always there to answer my questions, spent several hours clarifying my doubts, and whom supported me throughout my thesis. Never ending thanks also goes to the former Telematics group of Alcatel SEL AG, now the mm-lab company for being my entrance point in Alcatel and for making the company feel like home, for all the moral support, encouragement and for always being there for me in every case. Special thanks go to Lothar Krank, Ronald Prestin, Martin Geiger, Bernd Herrmann, Michael Meiser, Wolfgang Schäffer, Michael Koch, Horst Idler, Gerald Sander, Claus Hirdes, Andreas Streit and Sandra Steege. Warm wishes go to all my friends that I’ve encountered during my stay in Germany, each person has made a positive influence in my life and in very special and different ways. I thank them for the making me see life from other aspects and whom have greatly contributed to the person I am today. Last but not least, I would like to thank all my family members for believing in me and for their encouragement.
  • 3. An Ontology for Generic Wireless Authentication 3 Table of Contents Declaration......................................................................................................................................1 Acknowledgements........................................................................................................................2 1 Introduction...............................................................................................................................10 1.1 Restructuring Telecommunication Networks...............................................................12 1.1.1 Physical Consolidation of Subscriber Data ...........................................................13 1.1.2 Logical Consolidation of Subscriber Data .............................................................13 1.1.3 Harmonization of Interfaces....................................................................................13 2 Authentication in Wireless Networks ....................................................................................16 2.1 Security in wireless networks...........................................................................................16 2.2 Introduction to Authentication.......................................................................................17 2.3 Introduction to GSM networks ......................................................................................18 2.3.1 GSM Network Components....................................................................................19 2.3.1.1 Radio Subsystem ................................................................................................19 2.3.1.2 Base Station Subsystem.....................................................................................19 2.3.1.3 Network and Switching Subsystem.................................................................20 2.3.2 Visited Access/Core Network, Operator Home Network .................................21 2.3.3 Numbers and Identities ............................................................................................21 2.3.3.1 International Mobile Subscriber Identity .......................................................21 2.3.3.2 Mobile Subscriber Integrated Services Digital Network Number..............22 2.4 Security in GSM Networks..............................................................................................24 2.4.1 GSM Authentication .................................................................................................24 2.4.2 Security Algorithms in GSM....................................................................................26 2.4.2.1 A3 Algorithm......................................................................................................26 2.4.2.2 A5 Algorithm......................................................................................................27 2.4.2.3 A8 Algorithm......................................................................................................27 2.5 Introduction to UMTS networks....................................................................................28 2.5.1 UMTS Network Components .................................................................................29 2.5.1.1 User Equipment.................................................................................................29 2.5.1.2 UMTS Terrestrial Radio Access Network .....................................................29 2.5.1.3 Core Network.....................................................................................................30 2.6 Security in UMTS networks.............................................................................................31 2.6.1 UMTS Authentication ..............................................................................................32 2.6.1.1 UMTS Authentication Vector..........................................................................34
  • 4. An Ontology for Generic Wireless Authentication 4 2.6.1.2 USIM Authentication ........................................................................................36 2.6.2 Security Algorithms in UMTS .................................................................................37 2.7 Introduction into the Internet Protocol Multimedia Sub-System in UMTS networks....................................................................................................................................38 2.7.1 Identities in the IMS system.....................................................................................40 2.7.1.1 Private User Identities.......................................................................................40 2.7.1.2 Public User Identities ........................................................................................40 2.7.1.3 Public Service Identities....................................................................................41 2.8 Introduction to Wireless Local Area Networks............................................................42 2.9 Security in WLAN networks ...........................................................................................43 2.9.1 802.11 ..........................................................................................................................43 2.9.2 Wired Equivalent Privacy.........................................................................................43 2.9.3 Wi-Fi Protected Access ............................................................................................44 2.10 WLAN Security Architecture ........................................................................................44 2.10.1 802.1X .......................................................................................................................44 2.10.2 Authentication, Authorization and Accounting Server .....................................46 2.10.3 Certificate Based Authentication...........................................................................47 2.10.3.1 Public Key Infrastructure ...............................................................................47 2.10.4 Password Based Authentication............................................................................48 2.10.5 Extensible Authentication Protocol .....................................................................48 2.10.5.1 Lightweight Extensible Authentication Protocol........................................49 2.10.5.2 EAP Transport Layer Security.......................................................................49 2.10.5.3 Protected Extensible Authentication Protocol............................................50 2.10.5.4 EAP- Subscriber Identity Module.................................................................51 3 Ontologies and the Semantic Web.........................................................................................55 3.1 The Semantic Web ............................................................................................................55 3.2 Ontologies ..........................................................................................................................56 3.2.1 Origin ..........................................................................................................................56 3.2.2 Definition....................................................................................................................57 3.2.2.1 In Philosophy .....................................................................................................57 3.2.2.2 In Artificial Intelligence ....................................................................................57 3.2.3 Ontology Approaches...............................................................................................58 3.2.3.1 Description Logics.............................................................................................58 3.2.3.2 Frame-based .......................................................................................................58
  • 5. An Ontology for Generic Wireless Authentication 5 3.2.3.3 Predicate Logic...................................................................................................59 3.2.4 The Web Ontology Language..................................................................................59 3.2.4.1 OWL Lite ............................................................................................................60 3.2.4.2 OWL DL.............................................................................................................60 3.2.4.3 OWL Full ............................................................................................................61 3.2.5 OWL Language Constructs .....................................................................................61 3.2.5.1 Classes..................................................................................................................61 3.2.5.2 Properties ............................................................................................................62 3.2.5.3 Operators ............................................................................................................65 3.2.6 Ontology Tools..........................................................................................................66 3.2.6.1 Protégé.................................................................................................................66 3.2.6.2 RenamedABox and Concept Expression Reasoner Professional...............66 3.2.6.3 Graphical Visualization .....................................................................................67 3.2.7 Protégé-OWL Concepts ...........................................................................................67 3.2.8 Ontology Development............................................................................................68 3.2.8.1 Why Develop an Ontology ..............................................................................68 3.2.8.2 Steps in Developing an Ontology ...................................................................69 4 An Ontology for Generic Wireless Authentication.............................................................72 4.1 Class Overview ..................................................................................................................72 4.2 Ontology Classes and Subclasses....................................................................................73 4.2.1 The Algorithm class ..................................................................................................73 4.2.2 The AuthenticationMethod class ............................................................................74 4.2.3 The AuthenticationType class .................................................................................74 4.2.4 The Certificate class ..................................................................................................75 4.2.5 The CertificateComponent class .............................................................................75 4.2.6 The Code class ...........................................................................................................76 4.2.7 The DataBase class....................................................................................................76 4.2.8 The Identity class.......................................................................................................76 4.2.9 The Key class .............................................................................................................77 4.2.10 The Network class...................................................................................................78 4.2.11 The Number Class ..................................................................................................78 4.2.12 The Service class......................................................................................................79 4.2.13 The UserData class..................................................................................................80 4.2.14 The Subscriber class................................................................................................81
  • 6. An Ontology for Generic Wireless Authentication 6 4.3 Disjoint Classes..................................................................................................................81 4.3.1 The Algorithm class disjoints ..................................................................................82 4.3.2 The AuthenticationMethod class disjoints ............................................................82 4.3.2.1 The EAP-SIM subclass .....................................................................................82 4.3.2.2 The EAP-TLS subclass .....................................................................................83 4.3.2.3 The LEAP subclass ...........................................................................................83 4.3.2.4 The PEAP subclass ...........................................................................................83 4.3.3 The AuthenticationType class disjoints .................................................................84 4.3.3.1 The CertificateBased subclass ..........................................................................84 4.3.3.2 The ChallengeResponse subclass ....................................................................84 4.3.3.3 The MutualAuthentication subclass................................................................84 4.3.3.4 The NetworkAuthentication subclass.............................................................84 4.3.3.5 The PasswordBased subclass ...........................................................................84 4.3.3.6 The UserAuthentication subclass ....................................................................85 4.3.4 The Certificate class disjoints...................................................................................85 4.3.5 The CertificateComponent class disjoints .............................................................85 4.3.5.1 The IssuerName, SerialNumber, Signature, Subject, ValidFrom, ValidTo and PublicKey subclasses ..............................................................................................85 4.3.5.2 The SignatureAlgorithm subclass ....................................................................85 4.3.6 The Code class disjoints ...........................................................................................86 4.3.7 The Database class disjoints ....................................................................................86 4.3.8 The Identity class disjoints .......................................................................................86 4.3.9 The Key class disjoints..............................................................................................86 4.3.9.1 The DerivedKey subclass .................................................................................86 4.3.9.2 The GeneratedKey subclass .............................................................................86 4.3.9.3 The StaticKey subclass......................................................................................87 4.3.10 The Network class disjoints...................................................................................87 4.3.11 The Number class disjoints....................................................................................87 4.3.12 The Service class disjoints ......................................................................................87 4.3.12.1 The BasicService subclass...............................................................................87 4.3.12.2 The SupplementaryService subclass..............................................................87 4.3.12.3 The MultimediaService subclass....................................................................87 4.3.13 The UserData class disjoints..................................................................................88 4.4 Inconsistencies from Disjoint classes.............................................................................88
  • 7. An Ontology for Generic Wireless Authentication 7 4.5 Class Properties .................................................................................................................89 4.5.1 hasIdentity ↔ isIdentityOf .......................................................................................89 4.5.2 hasNetworkIdentity ↔ isNetworkIdentityOf.......................................................89 4.5.3 hasUserName ↔ isUserNameOf ...........................................................................89 4.5.4 hasAuthenticationMethod ↔ isAuthenticationMethodOf ..................................89 4.5.5 hasAuthenticationType ↔ isAuthenticationTypeOf ............................................90 4.5.6 hasCertificate ↔ isCertificateOf ..............................................................................90 4.5.7 hasPassword ↔ isPasswordOf .................................................................................90 4.5.8 hasBasicService ↔ isBasicServiceOf .......................................................................90 4.5.9 hasSupplementaryService ↔ isSupplementaryServiceOf .....................................90 4.5.10 hasDatabase ↔ isDatabaseOf ................................................................................90 4.5.11 hasChallenge ↔ isChallengeOf .............................................................................91 4.5.12 hasSecretKey ↔ isSecretKeyOf.............................................................................91 4.5.13 hasExpectedResponse ↔ isExpectedResponseOf .............................................91 4.5.14 hasTriplets ↔ isTripletsOf .....................................................................................91 4.5.15 hasInput ↔ isInputOf.............................................................................................91 4.5.16 hasOutput ↔ isOutputOf.......................................................................................91 4.5.17 hasNumber ↔ isNumberOf...................................................................................92 4.5.18 hasSubscriber ↔ isSubscriberOf ...........................................................................92 4.5.19 Stores ↔ isStoredIn .................................................................................................92 4.5.20 hasAlgorithm ↔ isAlgorithmOf ...........................................................................92 4.6 Identification of a new is-a relationship.........................................................................92 4.7 Initial ontology tests and reasoning................................................................................93
  • 8. An Ontology for Generic Wireless Authentication 8 4.8 Property Restrictions and Defining Classes ..................................................................94 4.8.1 Restrictions defining the f1 class.............................................................................94 4.8.2 Restrictions defining the EAP-SIM class...............................................................96 4.8.3 Restrictions defining the Subscriber class..............................................................98 4.8.4 Restrictions defining the IMSI class .......................................................................99 4.9 Asserted and Inferred Hierarchy.................................................................................. 101 5 Installation and Testing......................................................................................................... 102 5.1 Installation Guidelines................................................................................................... 102 5.2 Loading the Ontology ................................................................................................... 102 5.3 Encountered Problems.................................................................................................. 103 5.3.1 Enumerated Classes ............................................................................................... 103 5.3.2 Defining values for properties instead of individuals........................................ 104 5.3.3 allValuesFrom, someValuesFrom and Disjoint classes .................................... 105 5.3.4 Defining Cardinalities ............................................................................................ 106 6 Summary and Conclusions ................................................................................................... 107 6.1 Summary.......................................................................................................................... 107 6.2 Further research.............................................................................................................. 108 6.3 Areas of application ....................................................................................................... 109 References .................................................................................................................................. 110 Abbreviations............................................................................................................................. 116 Appendix A................................................................................................................................ 120 Appendix B ................................................................................................................................ 123
  • 9. An Ontology for Generic Wireless Authentication 9 Table of Figures Figure 1: Current status of telecommunication networks......................................................11 Figure 2: Distributed Subscriber Data ......................................................................................12 Figure 3: Physical and Logical Consolidation of Data............................................................14 Figure 4: GSM Network Architecture ......................................................................................18 Figure 5: IMSI Number Format ................................................................................................22 Figure 6: MSISDN Number Format.........................................................................................23 Figure 7: Authentication in GSM Networks............................................................................24 Figure 8: UMTS Network Architecture....................................................................................28 Figure 9: Authentication in UMTS Networks .........................................................................32 Figure 10: UMTS Authentication Vector .................................................................................34 Figure 11: USIM Authentication ...............................................................................................36 Figure 12: IMS Subsystem Architecture ...................................................................................38 Figure 13: WLAN Overview ......................................................................................................42 Figure 14: WLAN Security Architecture ..................................................................................44 Figure 15: EAP-SIM Architecture .............................................................................................51 Figure 16: EAP-SIM Authentication.........................................................................................53 Figure 17: Overview of Asserted Ontology Hierarchy...........................................................72 Figure 18: Disjoint Classes..........................................................................................................81 Figure 19: Incorrect disjoint definition - Inconsistent class ..................................................88 Figure 20: Ontology tests and reasoning results......................................................................93 Figure 21: f1 Class Restrictions..................................................................................................94 Figure 22: EAP-SIM Class Restrictions....................................................................................96 Figure 23: Subscriber Class Restrictions...................................................................................98 Figure 24: IMSI Class Restrictions ............................................................................................99 Figure 25: Asserted and Inferred Hierarchy.......................................................................... 101 Figure 26: Enumerated Classes and OWL-FULL Error..................................................... 104 Figure 27: Defining a value for an Object Property - OWL FULL Error ....................... 105 Figure 28: Integration of Future domains ............................................................................. 109
  • 10. An Ontology for Generic Wireless Authentication 10 1 Introduction The increase in network complexity in telecommunication systems has given rise to the need of restructuring telecommunication networks. Today networks are structured in such a way, that the introduction of new network elements and network services significantly increase the complexity of networks for network operators. Thus making it difficult to deploy and integrate new services and domains into existing networks, as well as complicating the maintenance and management of such networks. Examples for telecommunication networks are mobile and wireless networks. The original architecture for mobile networks was based on supporting the mobility of phone calls. The extension of such networks and the difficulty of maintaining such extensions were not put into consideration while designing these networks. Today several network domains exist in mobile and wireless networks. Each domain brings along with it new services, features and applications. And each domain requires the introduction of new network elements, thus further contributing to the complexity of networks. Each network element requires its own independent set of services, applications and subscriber data. As well as interfaces and protocols to communicate with each other. Subscriber data is required for the new network elements existing within the network, which is sometimes redundant across the different nodes. Each network node owns its own subscriber profile (data), which is sometimes replicated and distributed across the network. This complicates access to data and makes it impossible to obtain and maintain a complete profile of a specific network subscriber, since all data related to a subscriber is distributed along the network. Managing the network elements becomes difficult and operating expenses involved for network planning and maintenance of such networks also increases. Another problem that arises from the current architecture of networks today is the integration of several networks and domains (e.g. the integration of UMTS and WLAN networks). The current architecture was not designed to support the integration of new networks and services. The never-ending extensions of these networks will only make it impossible in the future to maintain such networks.
  • 11. An Ontology for Generic Wireless Authentication 11 The following points summarize the problems that arise from the way telecommunication networks are structured today: • Several domains • Several network elements within each domain • Inaccessible data due to vendor specific systems for the network elements • Separate set of subscriber data for each network element • Redundant subscriber data across the network elements • Several protocols and interfaces to communicate between the nodes • Increased complexity • Increased expenses The following figure illustrates the current status in telecommunication networks today: Node 3 Node 1 Node 3 Node 1 Domain 2 Domain 1 Node 4 Node 2 Node 4 Node 2 Node 3 Node 3 Node 1 Node 1 Domain 4 Domain 3 Node 4 Node 2 Node 4 Node 2 Figure 1: Current status of telecommunication networks For the purpose of this thesis the restructuring of the GSM, UMTS and WLAN domains are considered. In particular the authentication specific data related to a certain subscriber is modelled for the next generation profile register.
  • 12. An Ontology for Generic Wireless Authentication 12 1.1 Restructuring Telecommunication Networks Next Generation Networks (NGNs) are introduced in this thesis as a solution to the previously mentioned problems. The introduction of such networks reduces the complexity of current networks, but only to a certain extent. The concept behind a NGN is the separation of data from applications. Subscriber data is one of the most vital components of a network, and in today’s networks this data is not centrally accessible. Data today is not separated from the applications they belong to and this data is locally stored, distributed and inaccessible by other applications. Such an arrangement also causes the increase of operating and maintenance efforts and costs. A NGN solves these problems by providing a common storage for subscriber data , which is accessible to all applications. This common profile store is also referred to as the Next Generation Profile Register (NGPR). It simplifies data management and the interfaces needed for applications to access the data; it also enables the re-use of data among the various applications. The following figure illustrates the distribution of subscriber data among the three network domains: Figure 2: Distributed Subscriber Data
  • 13. An Ontology for Generic Wireless Authentication 13 Three approaches considered for the simplification of telecommunication networks today, and that complement each other are the following: • Physical Consolidation of Subscriber Data • Logical Consolidation of Subscriber Data • Harmonisation of Interfaces 1.1.1 Physical Consolidation of Subscriber Data Physical consolidation of data enables better data management, by storing data belonging to a subscriber in dedicated data servers. Data is stored in one physical location and the data servers can then be accessed via a common data interface. This process simplifies the integration of new application servers and network management, enables faster introduction of new services, and enables direct access to the data by different systems and applications. 1.1.2 Logical Consolidation of Subscriber Data Logical consolidation of subscriber data provides a common data model that provides meaning to subscriber data, and that describes this data. It solves the problem of the multiple independent subscriber sets of a certain subscriber, which are distributed across the network. It also associates subscriber data to the subscriber and provides the definition of data objects. The logical model can be used in conjunction with a common data interface. 1.1.3 Harmonization of Interfaces The number of interfaces and protocols needed to communicate between network nodes, increases with the increase of new network elements and new functions. This further complicates the integration of new services and functions within a network. A solution to this is to isolate interfaces from the applications and third party applications, and to provide a common standard interface, instead of several interfaces and protocols. The following figure illustrates the logical and physical consolidation of subscriber data for the three mentioned domains:
  • 14. An Ontology for Generic Wireless Authentication 14 WLAN Subscriber Data UMTS Subscriber Data Logical Consolidation GSM Subscriber Data of Data Physical Consolidation of Data Figure 3: Physical and Logical Consolidation of Data This thesis concentrates on the Logical Consolidation of Subscriber data, in specific authentication specific data for GSM, UMTS and WLAN networks. In order to create a logical model for subscriber data it is important to choose an appropriate modelling language for modelling the data stored in the subscriber profiles [61]. Relational models are not sufficient to describe the data for the logical model, the Unified Modelling Language (UML) focuses on the operational properties and run time data, the Extensible Markup Language (XML) and XML schema provide and define the structure of data, the Resource Description Framework (RDF) and RDF Schema define the data model for objects and the relationship between objects. It also provides a terminology for expressing classes and properties. The appropriate method evaluated for modelling the logical data was using the Semantic Web to provide meaning for the data. The most suitable language evaluated for the description of the data was the Web Ontology Language (OWL), which supports sharing and distribution of knowledge, a richer vocabulary for modelling and which focuses on the structural properties of a domain [49][52]. The thesis is organized in the following manner: this chapter provides an introduction to the thesis and the motivation behind the work performed. Chapter two provides an overview of GSM, UMTS and WLAN networks. The main focus of this chapter is the
  • 15. An Ontology for Generic Wireless Authentication 15 authentication procedures for each network. Chapter three describes the Semantic Web, ontologies (a knowledge based used to model the data), the Web Ontology Language and the tools needed to model an ontology. Chapter four describes the ontology created with the Protégé Tool. The ontology provides the definition of classes, the properties and the relationships between the classes. Chapter five describes the installation requirements needed to create the ontology, how the ontology can be loaded and a list of errors during testing the consistency of the ontology. The summary of the work achieved, the conclusions and open issues are described in Chapter 6.
  • 16. An Ontology for Generic Wireless Authentication 16 2 Authentication in Wireless Networks 2.1 Security in wireless networks Security has become an important issue in current mobile and wireless networks. As the security measures for such networks increase, the tools and techniques used to attack such networks also increases. Wireless communications security in simple terms, is the procedures or methods used for protecting the communication between certain entities. (An entity could be a user or a device requesting network access). Protection mechanisms are used to protect the entity from any third party attacks, such as impersonating an identity, revealing a specific identity, data-hijacking or data modification, eavesdropping and so forth. Dedicated technologies for securing data and communication are required in wireless networks, which vary according to the type of wireless technology deployed. Security in mobile and wireless networks covers various issues, from authentication of a user accessing a certain network, to data encryption and data integrity. Thus three major aspects are considered in securing wireless networks: [5] • Access control (Authentication) • Confidentiality • Anonymity [5] Authentication is used to prove the identity of a certain entity requesting access to a network. This is used so that the network operator is able to verify that the mobile subscriber in the case of GSM and UMTS networks is really who he/she claims to be. This reduces the possibility for mobile identity impersonation [6] [7]. Encryption is used to ensure the confidentiality of data. Data integrity guarantees that the data is not modified or destroyed in any way, thus sensitive signalling information and data are protected against eavesdropping attacks. Anonymity is another security aspect that protects user identity, making it hard to track the whereabouts of a certain user. Anonymity is achieved using temporary identities [6].
  • 17. An Ontology for Generic Wireless Authentication 17 The scope of this thesis only addresses the authentication procedures of mobile and wireless networks, specifically GSM, UMTS and WLAN networks. Other security aspects are not within this scope. 2.2 Introduction to Authentication Authentication is the process of uniquely proving an identity to a certain service, network or device and the verification of the given identity. Upon successful identity verification, access to certain services, networks or devices are granted. The kind of access and services granted depends on the privileges given to the specific entity requesting authentication. In the case the identity is not proven (unsuccessful authentication), no access is granted to the entity requesting access. The simple form of authentication is providing a user name and password, which is mainly the case in internet based authentication (e.g. email, online shopping, etc…) and in some wireless based networks. However, different types of authentication exist depending on the complexity of a certain system. Dedicated systems require a complex procedure of authentication involving the use of secret keys, tokens, certain credentials, digital certificates or signatures, complex algorithms and encryption methods and more [7] [8]. Several authentication methods exist, depending on the technology used and the type of information or services requiring access. In the following, the authentication procedures of GSM, UMTS and WLAN networks are discussed in detail.
  • 18. An Ontology for Generic Wireless Authentication 18 2.3 Introduction to GSM networks The Global System for Mobile Communication (GSM) is a second generation (2G) network and is the largest existing 2G network. Second generation refers to the fact that the system uses digital signals in contrast to first generation networks, where analogue signals were used [5]. The GSM network comprises of several network components that interact and function with each other. For the purpose of this thesis, only the components involved in the authentication process of GSM networks will be described and illustrated. The following figure illustrates a general overview of the GSM authentication specific network architecture. (All other elements not related to authentication are not illustrated or addressed): RSS NSS BSS BTS HLR AuC MS BSC MSC VLR Mobile Device Visited Access Network Visited Core Network Home Network Figure 4: GSM Network Architecture The GSM network comprises of three subsystems, namely the Radio Subsystem (RSS), the Network and Switching Subsystem (NSS) and the Operation Subsystem (OSS) [1] [4]. The OSS is not discussed in this thesis.
  • 19. An Ontology for Generic Wireless Authentication 19 2.3.1 GSM Network Components 2.3.1.1 Radio Subsystem The RSS [9] [4] deals with all the radio aspects of a network and is responsible for the following components it comprises: 2.3.1.1.1 Mobile Station The Mobile Station (MS) [3] [4] consists of two major components: 2.3.1.1.1.1 Mobile Equipment The Mobile Equipment (ME) is the actual mobile device a user uses to establish calls and other telephony services. The ME communicates with the radio channel and provides various services to the user of the mobile device. 2.3.1.1.1.2 Subscriber Identity Module The Subscriber Identity Module (SIM) [3] is located inside the ME and contains subscriber specific data. This data is used for identifying a subscriber to the network via the International Mobile Subscriber Identity (IMSI). Authentication specific data is also stored inside the SIM (e.g. algorithms, secret key), which are later used for key generation [4] [6]. Two security services are implemented for the SIM card. The first security mechanism for the SIM is access control, which controls a user from accessing the card and the information and services provided upon card access. This is provided via a secret Personal Identification Number (PIN), which the user has to enter before gaining access to the SIM. The second security mechanism provided is the network challenge and response mechanism described in section (2.4.1). 2.3.1.2 Base Station Subsystem The Base Station Subsystem (BSS) [1] [3] [4] is responsible for all radio functions and comprises of the Base Station Transceiver (BTS) and the Base Station Controller (BSC). These two components together support the radio interface. The responsibilities of the BSS are then assigned to the following two components:
  • 20. An Ontology for Generic Wireless Authentication 20 2.3.1.2.1 Base Transceiver Station The Base Transceiver Station (BTS) takes care of the communication with the mobile station, and is responsible for radio specific functions (sending and receiving) [4] 2.3.1.2.1 Base Station Controller The Base Station Controller (BSC) is responsible for the switching between several BTSs, and for the switching of radio channels. The BSC provides the necessary control functions and physical links between the Network Subsystem (NSS), via the Mobile Switching Center (MSC) and the BTS [1] [3] [4]. 2.3.1.3 Network and Switching Subsystem The NSS [3][4] comprises of the Mobile Switching Center (MSC), the Home Location Register (HLR) and the Visitor Location Register (VLR). The NSS provides switching services between GSM and external networks, and maintains the location registers needed to manage and administer subscribers. 2.3.1.3.1 Mobile Switching Center The Mobile Switching Center (MSC) is the switching node in the NSS that controls all MS connections. It provides telephony switching services to fixed and mobile networks. It links the NSS to the RSS via the BSC. Several BSCs can belong to a single MSC [1] [3] [4]. 2.3.1.3.2 Home Location Register The Home Location Register (HLR) is the main subscriber profile register, and contains all data related to a mobile subscriber. This data includes but is not limited to the following: the mobile subscriber’s identity, represented as the International Mobile Subscriber Identity (IMSI) (also stored in the SIM card), administrational information, service subscription and service specific data and location information [1] [2] [3] [4]. 2.3.1.3.3 Visitor Location Register The Visitor Location Register (VLR) is a subscriber profile containing temporary information, and is distributed in the network according to geographical locations. The VLR along with the MSC are responsible for handling mobile subscribers visiting an area
  • 21. An Ontology for Generic Wireless Authentication 21 outside their home network. Certain administrational data is replicated in the VLR from the HLR in order to provide service provisioning and call control. Information about the visiting subscriber is retrieved from the HLR and stored in the VLR as a temporary record [1] [2] [3] [4]. 2.3.1.3.4 Authentication Center) The Authentication Center (AuC) is a register that is logically part of the HLR. Authentication specific data for a given subscriber is stored in the AuC. It is responsible for storing the secret key of a subscriber (section 2.4.1). Other tasks of the AuC include the generation of authentication parameters needed for authentication and encryption, proving the identity of a subscriber and providing protection mechanisms for a subscriber’s SIM card [1] [3] [4]. 2.3.2 Visited Access/Core Network, Operator Home Network The Visited Access Network is the radio network accessed by the mobile station. Access is accomplished via the BSS. The Visited Core Network is the switching part of the network, and is a network other than the home network the subscriber is registered at. Visited Core Networks can be located at various national or international locations. The MSC and VLR reside at this network [6]. The Operator Home Network is the original network the mobile subscriber is registered at. The HLR and AuC reside in this network. 2.3.3 Numbers and Identities 2.3.3.1 International Mobile Subscriber Identity The International Mobile Subscriber Identity (IMSI) is a unique 15 digit identifier for a mobile subscriber. It is stored in the SIM card of the mobile station, and is assigned to a mobile subscriber at the time of subscription. It is used to identify a subscriber to a given network (i.e. GSM, UMTS networks). The main purpose of the IMSI is to allocate International Mobile Station Identities (INMSI) to stations. Mobile subscribers do not have access to this number or have any knowledge of it. Although this number is stored in the SIM card, it cannot be reached via a telephone call. Thus, the number is not made public.
  • 22. An Ontology for Generic Wireless Authentication 22 The IMSI is made up of three codes: • Mobile Country Code (MCC) • Mobile Network Code (MNC) – 2 digits • Mobile Station Identification Number (MSIN) – 10 digits o HLR-Number o Subscriber Number (SN) MCC MNC MSIN Figure 5: IMSI Number Format The Mobile Country Code is a three digit code, specifying a list of predefined mobile country codes that identify a mobile station in mobile networks. The MCC for Germany, for example is 262 and each country has its own respective MCC. The Mobile Network Code is the code, which identifies the home network of the mobile subscriber. E.g. in Germany the codes 01, 02 and 03 are used to identify the T-Mobile, Vodafone and E-Plus networks respectively. This code is 2 digits in Europe and 3 in North America. The Mobile Station Identification Number is a unique identifier, consisting of 10 digits that identify a mobile subscriber to the network. The MSIN consists of two parts, the first part represents the logical HLR address (HLR-Number) and consists of two digits and the second part is an identifier representing the subscriber number (SN) [2] [10] [11]. 2.3.3.2 Mobile Subscriber Integrated Services Digital Network Number The Mobile Subscriber Integrated Services Digital Network Number (MSISDN) is the mobile subscriber’s telephone number, which is associated with the IMSI. Several MSISDN numbers can be assigned to a single IMSI and are also stored on the SIM card. Together the IMSI and MSISDN are used for call setup and call routing. The MSISDN is made up of the following codes: • Country Code (CC)
  • 23. An Ontology for Generic Wireless Authentication 23 • National Destination Code (NDC) • Subscriber Number (SN) o HLR-Number (HLR#) o Individual Subscriber Number (ISN) CC NDC SN(HLR# + ISN) Figure 6: MSISDN Number Format The CC is consists of 1 – 3 digits and represents the code for the country. The NDC is consists of 2 – 3 digits and indicates the type of telephone number being called. In the case of mobile networks it indicates the code for the specific operator, E.g. 179 for the O2 network operator. The CC and the NDC together are used of routing purposes. The SN is a 10 digit number and consists of two parts; the HLR number representing the logical address of the HLR and the ISN, which is a number assigned to the subscriber [2] [10] [12].
  • 24. An Ontology for Generic Wireless Authentication 24 2.4 Security in GSM Networks As described in section 1.1, the security issue covers three main aspects: • Authentication • Confidentiality • Anonymity In GSM networks Authentication is achieved by a challenge-response type of authentication (described in section 2.4.1), and by the encryption of the radio channel, which also guarantees confidentiality. Anonymity is achieved by the use of temporary identities (i.e. the Temporary Mobile Subscriber Identity TMSI), which is a temporary identity assigned to the IMSI [5] [6]. Only the Authentication part will be described in this thesis. 2.4.1 GSM Authentication The following figure illustrates a general overview of the authentication procedure in GSM Networks: Figure 7: Authentication in GSM Networks
  • 25. An Ontology for Generic Wireless Authentication 25 GSM authentication is a challenge-response type of authentication. The mobile station initiates the authentication procedure, by issuing an authentication request. The home network generates a response and sends a challenge to the mobile station, in order to calculate the same response. If both responses generated from the home network and the mobile station match, then authentication is achieved, and access to the network is granted. Below a detailed description of the authentication procedure and the components involved in authentication are given. A new mobile subscriber is given a SIM card, in which relevant information about a subscriber is stored. The SIM card contains the necessary keys and algorithms needed for the authentication procedure, which enables a subscriber to connect to the home network. A secret key referred to as Ki is stored in the SIM card of the mobile subscriber, and in the Authentication Center of the home network of the mobile operator. This key remains secret and is never transmitted from the AuC or SIM card. The Ki is a unique 128-bit key. The whole authentication procedure depends on the privacy/secrecy of this key. The concept behind the challenge-response type of authentication is to prove that the secret key, stored in the SIM card of the mobile station is the same as the key stored in the AuC. The authentication procedure begins when a mobile station, requests access to the network. This is achieved via an authentication request, in which the mobile device sends out the IMSI as a request for authentication. The IMSI is broadcasted to a corresponding MSC, which in turn forwards this information to the HLR in the home network, and also the VLR in the visited network. The AuC is associated with the HLR, and is responsible for storing authentication specific parameters. After the reception of the IMSI by the AuC, a random number (RAND) is generated using the received IMSI and the stored secret key Ki. The RAND number is a 128-bit key, and represents the challenge to be sent to the SIM by the home network. The AuC and SIM card contain authentication algorithms, namely the A3 algorithm for authentication and the A8 algorithm for key generation (explained in section 1.4.1). With the help of these algorithms an Expected Response key (XRES), which is 32-bits long, and a Cipher key (Kc), 64-bits long are generated.
  • 26. An Ontology for Generic Wireless Authentication 26 The XRES is used to verify if the SIM can generate the same response, and is based on a symmetric mechanism. The Kc is used for encrypting calls between the mobile and base stations, and is a temporary session key. Upon generating these keys, the HLR sends out an authentication response known as triplets, which consists of the (RAND, XRES and Kc). The triplets are generated and stored in the VLR for each subscriber. The MSC then forwards the RAND number of the generated triplets to the mobile station. This RAND number is sent as a challenge to the mobile station, and challenges the mobile station to calculate the same response generated by the AuC. With the use of the A3 and A8 algorithms, the RAND number and Ki key are used to calculate the RES and a Kc. The RES is then forwarded to the MSC/VLR, and a comparison of RES and XRES is made. If both responses match, the authentication procedure is successful and the mobile station gains access to the network and its services. If, however the XRES and RES don’t match, then access is denied to the mobile station and the authentication procedure fails [5] [6] [15]. 2.4.2 Security Algorithms in GSM Three security algorithms exist in GSM networks, namely the A3 authentication algorithm, the A5 ciphering/deciphering algorithm and the A8 ciphering key generation algorithm. These three are used in order to provide different security features and techniques, including authentication and protection of the radio link, which guarantees privacy of calls and user data [13] [14] [15]. 2.4.2.1 A3 Algorithm The A3 algorithm is the authentication algorithm for GSM networks, and resides on the SIM card of the mobile subscriber, and on the HLR/AuC of the home network. The implementation of the A3 algorithm is network specific and depends on the network operator. The A3 algorithm is a non-recursive algorithm, meaning that the output generated from the input cannot be used to derive or guess the inputs. Thus, the output gives no indication about the input. The main purpose of this algorithm is to authenticate the identity of a mobile subscriber.
  • 27. An Ontology for Generic Wireless Authentication 27 The A3 algorithm generates the XRES on the network side and the RES on the mobile side. Both the XRES and RES are a 32-bit long key and are generated from Ki and RAND [13] [14] [15]. 2.4.2.2 A5 Algorithm The A5 algorithm is the ciphering/deciphering algorithm, and resides on the mobile station of a subscriber and on the BSS. The A5 algorithm is used for protecting data sent from the mobile station, and the BSS and vice-versa, this provides the privacy of data and calls. The Kc ensures that all calls are encrypted between the MS and the BSS. The A5 algorithm is a standardized algorithm, but this algorithm can only be obtained with a specific license from the GSM Association [5]. Although the A5 algorithm is standardized, its specification remains undisclosed [5] [13] [14] [15]. 2.4.2.3 A8 Algorithm The A8 algorithm is the ciphering key generation algorithm, as with the A3 algorithm it also resides on the SIM card and HLR/AuC. Its implementation is network specific and it is also a non-recursive algorithm. The A8 algorithm is used for generating the Kc, which is a session key and is used for encrypting voice and data traffic. The Kc is generated from the Ki and RAND and is 64- bits long [13] [14] [15].
  • 28. An Ontology for Generic Wireless Authentication 28 2.5 Introduction to UMTS networks The Universal Mobile Telecommunications System (UMTS) is one of the new third generation (3G) networks. 3G networks build on 2G networks with the General Packet Radio Service (GPRS) support, which are known as 2.5G networks. 2.5G networks support packet switching domains. A UMTS network also provides for inter-operability with a GSM network and is an extension of existing GSM networks [18]. UMTS networks support the circuit and packet switched domains, and are backward interoperable with GSM/GPRS networks [5][18] [19]. UMTS networks provide enhanced data transmission rates and a wider range of services, including multimedia and IP based services [5] [6] [16]. The following figure illustrates the UMTS network architecture, (only components related to authentication are illustrated): MS/UE Core Network Circuit Switched Domain BTS MS BSC MSC VLR BSS Packet Switched Domain UTRAN HLR AuC Node B UE RNC 3G SGSN RNS Mobile Device Visited Access Network Visited Core Network Home Network Figure 8: UMTS Network Architecture
  • 29. An Ontology for Generic Wireless Authentication 29 The UMTS network consists of the following components: [16] [17] [18] • User Equipment (UE) • UMTS Terrestrial Radio Access Network (UTRAN) • Core Network (CN) 2.5.1 UMTS Network Components 2.5.1.1 User Equipment The UE consists of the mobile device and the Universal Subscriber Identity Module (USIM) card. The UE separates between the user device functionality and the USIM functionality [16]. The USIM is similar in functionality to the SIM of the GSM network. The USIM is more enhanced in terms of security. The keys and algorithms used for authentication and encryption are stored on the USIM. Subscriber specific data and several identities are also stored on the USIM [15]. 2.5.1.2 UMTS Terrestrial Radio Access Network The UTRAN is the new access network for UMTS networks, which uses different multiple access methods than previous GSM networks [17]. It is responsible for network access procedures, mobility and resource allocation [4]. UTRAN is subdivided into individual Radio Network Subsystems (RNS), which consists of the following components [16] [17]: 2.5.1.2.1 Radio Network Controller The RNC is the controlling unit of the UTRAN and is responsible for communicating with the UE. It performs radio specific functions and maintains the connection to the CN for each UE. It functions like the BSC of GSM networks, and provides switching functions between other RNCs [16]. The RNC is connected to one or several Node Bs [17]. Two types of RNCs exist, namely Serving Radio Network Controllers (SRNC) and Drifting Radio Network Controllers (DRNC) [4] [18]. The SRNC is responsible for
  • 30. An Ontology for Generic Wireless Authentication 30 controlling the connection to the CN, while the DRNC is responsible for the connection to the UE and offers additional resources [4] [18]. 2.5.1.2.2 Node B Node-Bs are the base stations of the UMTS network, and several Node-Bs can be connected to one RNC. Each Node-B can serve one or several radio cells. A Node-B fulfils almost the same functionalities as a BTS in GSM networks [16]. A Node B is mainly responsible for the transmission and reception of data [17]. 2.5.1.3 Core Network The CN consists of two domains: the Circuit Switched (CS) domain, and the Packet Switched domain (PS). The CN in UMTS is an enhanced version of the GSM core network with GPRS. Each domain has its specific components. The CS domain includes the MSC and VLR as its components, and provides circuit switched functionalities such as calls and switching of calls. The PS domain includes the 3G Serving GPRS Support Node (SGSN) as its component, which is responsible for the delivery of data packets to and from the UE. The SGSN takes the role of the MSC/VLR of the CS domain. The PS domain provides IP-Based services. Components like the HLR and AuC are shared by both CS and PS domains [17] [18].
  • 31. An Ontology for Generic Wireless Authentication 31 2.6 Security in UMTS networks Security in UMTS networks is based and built on the existing GSM security mechanisms. However, UMTS has far more security mechanisms than in GSM, and is more enhanced in terms of security [6]. Robust security mechanisms of GSM networks have been adopted into UMTS networks. Compatibility with GSM networks is ensured in order to ease inter-working operations between the networks [21]. New security services have been introduced into UMTS networks as well as new domains. This required the introduction of new security mechanisms [5]. Some of the major security enhancements in UMTS networks are as follows: • Mutual Authentication; not only is the subscriber authenticated by the network, the subscriber can also authenticate the network. The subscriber can ensure that he/she is connecting to a trusted network. • Integrity Protection; enhanced algorithms and keys to ensure data integrity. • Network Security; security between and within different networks. • Secure Services and Applications; enhanced security features for services and applications [21]. • Interoperability and Roaming; standardized security features, enabling network to network interoperability and roaming [20].
  • 32. An Ontology for Generic Wireless Authentication 32 2.6.1 UMTS Authentication The following figure illustrates the authentication procedure in UMTS networks: IMSI IMSI Authentication Request Authentication Request UE MSC VLR SGSN HLR AuC USIM RAND K AUTN RAND K SQN (Quintets) RAND, AUTN, RAND, AUTN XRES, CK, IK Authentication Response RES SQN CK IK RES XRES AUTN CK IK RES = XRES User Equipment Serving Network Home Network Figure 9: Authentication in UMTS Networks UMTS authentication is based on a challenge-response type of authentication, similar to that of GSM networks. It is based on the existing GSM infrastructure and is built on GSM authentication and security mechanisms [5] [6]. UMTS authentication provides mutual authentication [5] [6], meaning that the network a certain subscriber is connecting to is authenticated. Details about the exact mutual authentication procedure are described below. The UE initiates the authentication procedure by sending an authentication request, which can be in the form of different subscriber identities: • The IMSI. • The Temporary Mobile Subscriber Identity (TMSI). This is a temporary identity, used instead of the IMSI in order to avoid the user’s identity from being continuously transferred via the network. • Packet-TMSI (P-TMSI), for the packet switched domain [5].
  • 33. An Ontology for Generic Wireless Authentication 33 These identities are also used in 2G GSM networks, apart from the P-TMSI, which is used in 2.5G networks. A permanent secret key (K) – 128 bits - resides in the USIM of the UE and in the AuC of the home network. As with GSM authentication, this key is never transmitted and is always kept secret. The user’s identity is verified by the Serving Network (SN) or the visited core network. Access to the network is granted by the SN if the verification procedure is successful. The SN forwards the authentication request (IMSI) to the HLR/AuC of the Home Network (HN). An authentication vector, called (Quintets) is generated as the authentication response and is returned back to the SN. Using the IMSI, the AuC then generates a Random Number (RAND) – 128 bits – and a Sequence Number (SQN) – 48 bits. This SQN is chosen in ascending order in order to later check the freshness of the SQN, and thus the freshness of the generated authentication vector sent to the USIM. The SQN and RAND number are then used, with the help of the f1, f2, f3, f4 and f5 functions/algorithms to generate the authentication vector. These functions are all non- recursive, and it is important to note that the output of one function cannot reveal any information about the input of another function [5]. The inputs for the authentication vector are the RAND, SQN and K, which is stored in the AuC. The authentication vector consists of the following keys: the Expected Response (XRES) generated using the f2 function and is 32 – 128 bits; the Cipher Key (CK) generated using the f3 function and is 128 bits; the Integrity Key (IK) generated using the f4 function an is 128 bits; the Authentication Token (AUTN), which is a concatenation of different keys (explained below) and is 128 bits. An authentication response is then sent out to the Serving Network in a form of quintets, this authentication response is made out of the following keys: (RAND, AUTN, XRES, CK and IK). The SN keeps a copy of the XRES to compare it with the RES that will be generated on the USIM. The SN sends a challenge to the USIM in the form of the RAND and the AUTN keys. This challenge is used in the USIM along with K as inputs for the authentication procedure on the USIM side. The generated output consists of the following keys; Response (RES) 32 – 128 bits, generated by the f2 function, the SQN 48 bits, the Cipher Key (CK) and the Integrity Key (IK), generated by the f3 and f4 functions respectively.
  • 34. An Ontology for Generic Wireless Authentication 34 The authentication procedure on the USIM starts upon the reception of RAND and AUTN. The importance of sending these two keys is for the mutual authentication process. The AUTN can only be computed by the AuC of the home network. Therefore, the UE is able to verify that it is connecting to a trusted network; a network that holds the same secret as the USIM (i.e. K) [19]. The RES is then forwarded to the SN, and is evaluated against the XRES response received from the Home Network. If both responses match then the UE is authenticated to access the network [5] [6] [19]. 2.6.1.1 UMTS Authentication Vector The following figure illustrates the authentication vector generated in the AuC. It is important to understand this authentication vector, in order to understand how UMTS performs mutual authentication. Up till now, only the UE has been authenticated to use the network, the second step of authentication is performed on the USIM side, where the UE checks whether it is connecting to a trusted network or not. Figure 10: UMTS Authentication Vector The generation of the authentication vector on the home network side begins with the reception of the IMSI (authentication request) from the UE. A fresh SQN and a RAND number are generated. SQN proves to the USIM that the generated authentication vector
  • 35. An Ontology for Generic Wireless Authentication 35 is fresh. Five one way functions (f1, f2, f3, f4 and f5) [5] are used for generating the authentication vector. The f1 and f2 functions/algorithms are message authentication functions. The input of the f1 function is the RAND, K, SQN and the Authentication and Management Field (AMF) a 16 bit key. The AMF is an operator-specific key, and is used for operator- specific functions in the authentication procedure. The output of the f1 function is the Message Authentication Code (MAC) a 64 bit key, which is an algorithm or a one way hash that computes bits and a secret key to generate a fixed-length of bits [20]. Its purpose is for verifying that the inputted bits have not been altered in some way or the other. The f3, f4 and f5 functions are key generating functions, which all take the RAND and K as inputs. The f2 function generates the XRES, and is used to compare the RES generated on the USIM side for subscriber authentication. The f3 and f4 functions generate the CK and IK keys respectively for ciphering and integrity protection purposes on the air interface. The f5 function generates an Anonymity Key (AK) 48 bit, which is used to conceal the generated sequence number SQN [5] [19].
  • 36. An Ontology for Generic Wireless Authentication 36 2.6.1.2 USIM Authentication The following figure illustrates the authentication procedure on the USIM of the UE: USIM K RAND f5 f2 f3 f4 AK RES CK IK SQN SQN + AK + f1 AMF AUTN XMAC MAC ? MAC = XMAC Figure 11: USIM Authentication The functions f1 – f5 are ordered in a different manner on the USIM as compared with the functions on the AuC. In USIM authentication the f5 function must generate outputs before the f1 function. The authentication procedure starts with the computation of the Anonymity Key (AK). This key is generated from the inputs of RAND and K using the f5 function, which is used to conceal the SQN preventing any leakage of user identity through the SQN. The functions f2, f3 and f4 take the RAND and K as inputs and generate RES, CK and IK respectively. The input of the f1 function is a bit more complicated; two keys from the AUTN namely SQN and AK are concatenated with the AK, which is generated from the f5 function in the following manner: SQN = (SQN ⊕ AK) ⊕ AK [19]. This SQN is then an input for the f1 function along with the AMF key. The f1 function generates the Expected MAC (XMAC) a 64 bit key as its output. This value (XMAC) is compared to the MAC of the AUTN key, which is a concatenation of the SQN, AK, AMF and MAC
  • 37. An Ontology for Generic Wireless Authentication 37 in the following way: AUTN = SQN ⊕ AK || AMF || MAC [19]. If both MACs match, authentication of the network is completed and the USIM verifies that it is connected to a trusted network [5] [19]. 2.6.2 Security Algorithms in UMTS The main algorithms in UMTS networks concerned with authentication are the f1, f1*, f2, f3, f4, f5 and f5* functions. These functions are operator-specific and only reside on the AuC of the home network and the USIM of the UE. Each of these functions is a one-way function. The functions are used for computing the authentication vector. The importance of these functions lies in that the output of one function cannot reveal any information about the other functions [5]. The f1 function is the network authentication function and is responsible for the generation of the MAC key on the network side and the XMAC key on the USIM side. The f1* function is the resynchronization message authentication function and is used for resynchronization purposes. The f2 function is the user authentication function and is responsible for the generation of the XRES key on the network side and the RES key on the USIM side. The f3 function is the CK derivation function. It generates the CK on both the network and USIM side. The f4 function is the IK derivation function. It generates the IK on both the network and USIM side. The f5 function is the AK derivation function for normal operation. The AK is generated using the f5 function on both the network and USIM side. The f5* function is the AK derivation function for resynchronization and is used for resynchronization purposes [5] [6].
  • 38. An Ontology for Generic Wireless Authentication 38 2.7 Introduction into the Internet Protocol Multimedia Sub-System in UMTS networks The IP Multimedia Sub-System (IMS) plays a major role in UMTS networks as of the UMTS release number 5 [5]. The IMS is an application layer, residing on top of the packet switched domain of the UMTS network. It is independent of the access network, and supports various types of networks and devices [5]. The main intention of the IMS is to provide multimedia services and applications to end users. IMS also supports roaming services for mobile networks [5] [23]. A multimedia service is a service that supports two or more kinds of multimedia services for telecommunication networks. Services can be for example, video and audio downloading and streaming, text messaging, web browsing, etc… [22] The following figure illustrates an overview of the IMS system architecture in mobile and fixed networks: Core Network PLMN / PSTN / GMSC ISDN Home IMS BTS MS BSC BSS MSC VLR HSS UTRAN I-CSCF S-CSCF Node B P-CSCF UE RNC SGSN RNS Visited IMS GGSN Fixed Access Networks / WLAN Figure 12: IMS Subsystem Architecture
  • 39. An Ontology for Generic Wireless Authentication 39 The IMS consists of the following components: • The Home Subscriber Server (HSS) • Proxy-Call Session Control Function (P-CSCF) • Interrogating-Call Session Control Function (I-CSCF) • Serving-Call Session Control Function (S-CSCF) • Gateway GRPS Support Node (GGSN); also supported in UMTS and 2.5G networks [22]. The HSS is the main database of the IMS network. The HLR and AuC are integrated into this database, and subscriber specific, location-related data and user identities are is stored in this database. The CSCF consists of three types that perform different functions within the network: The P-CSCF is the first contact point in the IMS. It is responsible for forwarding registration requests and responses, to and from the mobile device and the I-CSCF. The P-CSCF resides in the visited network, and is assigned to a terminal supporting IP Multimedia (E.g. mobile phone, laptop, computer, etc…). It is also responsible for the confidentiality and integrity of messages sent in the network. The I-CSCF is responsible for contacting the respective S-CSCF within the home network via the HSS. Its main task is the assignment of an S-CSCF, routing, and forwarding of requests and responses to the relevant S-CSCF. The S-CSCF is responsible for session control and session management. In addition, authentication and subscriber specific data are stored in the S-CSCF, which are retrieved from the HSS. The S-CSCF is assigned to an IMS terminal, and performs the authentication of an IMS user. Registration requests received by the S-CSCF are forwarded to the HSS [5] [22] [23]. The I-CSCF and S-CSCF reside in the home network of the IMS. The GGSN is a gateway between the IMS and UMTS networks, and represents the entrance point to the IMS system. The IMS supports the access of other networks like; Fixed Access Networks, Wireless Local Area Networks (WLAN), Public Land Mobile Networks (PLMN), Public Switched Telephone Networks (PSTN) and Integrated Services Digital Networks (ISDN). The
  • 40. An Ontology for Generic Wireless Authentication 40 latter three can be accessed by GSM networks via, the Gateway Mobile Switching Center (GMSC) [23]. Authentication in the IMS is performed, via the IMS Authentication and Key Agreement (AKA) mechanism, which is a challenge/response type of authentication and which is analogous to UMTS authentication. The IMS uses the IMS Subscriber Identity Module (ISIM), in the UE instead of the USIM and SIM in UMTS and GSM networks respectively [5]. 2.7.1 Identities in the IMS system Several identities exist in the IMS system, which are used to uniquely identify a user or a service of the IMS system. These identities are; Public User Identities, Private User Identities and Public Service Identities and are briefly described in the following: 2.7.1.1 Private User Identities Every user of an IMS system has one private user identity, used to identify the user of the IMS system. This identity is assigned by the home network, and it takes the form of a Network Access Identifier (NAI). An NAI is a standardized way to identify users to a network during authentication via a username or a username@realm. Private user identities are static, and are used to identify information related to a specific subscriber (subscriber and authentication information), which is stored in the HSS. Apart from the private user identity being stored in the HSS, it is also stored in the ISIM of the UE and also in the S-CSCF. The private user identity takes a similar function as that of the IMSI in GSM and UMTS networks. The private user identity is authenticated during user registration [23] [24] [25]. 2.7.1.2 Public User Identities One or more public user identities can be allocated to a user of an IMS system. A user should obtain at least one public user identity, which is also stored in the ISIM. This identifier is used for communication purposes with other IMS users. It is also used by external users to address a user. The public user identity takes the form of a telephone:URL number or a URL. Public user identities are used to identify information related to a specific subscriber within the HSS, but unlike private user identities, public user identities are not authenticated by the network. IMS terminals are tied to public user identities by the S-CSCF [24] [25].
  • 41. An Ontology for Generic Wireless Authentication 41 2.7.1.3 Public Service Identities Private and public user identities are used to identify users within an IMS system. However, public service identities are used for identifying the various services available to the IMS via application servers. Each public service identity is bound to a service of the IMS [24].
  • 42. An Ontology for Generic Wireless Authentication 42 2.8 Introduction to Wireless Local Area Networks A WLAN is a local area network that does not use wires to communicate between the stations, instead high frequency radio waves are used for communication. An example of WLAN networks is the 802.11 standard defined by the IEEE [26]. The following figure illustrates an overview of a WLAN network: Wireless Station 1 Target Network Access Point Wireless Station 2 Figure 13: WLAN Overview The main components involved in a WLAN network are the mobile station, which could be any mobile device (E.g. a laptop, Personal Digital Assistant (PDA)), the wireless Access Point (AP) that performs the task of a wired hub – the AP acts as an entry point to access the target network- , and some kind of authentication server performing, authentication and granting access to the network via the AP [8]. In the following the WLAN security architecture will be explained along with concepts relating to WLAN authentication.
  • 43. An Ontology for Generic Wireless Authentication 43 2.9 Security in WLAN networks 2.9.1 802.11 The 802.11 is a standard developed by the IEEE for wireless networks. The specification defines the interface between a wireless station, and an access point or another wireless station. The 802.11 also specifies how access to a WLAN is achieved or in other words how authentication of WLANs is implemented. Authentication in 802.11 networks is based on authenticating a wireless station rather than a user [29]. In order for a wireless station to connect to another station or access point, the initiating station must prove its identity, to the receiving wireless station or access point. This is achieved via various authentication methods, which depend on the type of authentication method deployed. The 802.11 is a family of standards, and several specifications of this standard exist,. Amongst these are; 802.11, 802.11a, 802.11b, 802.11g. Each specification differs from the other in the spectrums/multiplexing methods, transmission rates and bandwidths [27]. 2.9.2 Wired Equivalent Privacy The Wired Equivalent Privacy (WEP) key is used, between a wireless client, and an AP, in order to encrypt data being sent from the client to the AP, and to decrypt the same data on the AP. It is a standard defined by the IEEE 802.11 Working Group for data encryption. WEP keys are static keys, and are used as session keys, to enable communication of the client and the AP. If the client is not able to detect the AP’s WEP key, access to the network is blocked from the client. As the name implies, WEP was developed to be as secure as that of wired networks that is why it is termed as equivalent. This fact does not hold, since many flaws have been detected in this encryption scheme. Many enhancements have been made to WEP and it is deployed by several authentication methods [30].
  • 44. An Ontology for Generic Wireless Authentication 44 2.9.3 Wi-Fi Protected Access Wi-Fi Protected Access (WPA) is an enhancement over the vulnerable WEP encryption scheme. All flaws in WEP have been addressed in WPA. WPA provides authentication, key management and encryption mechanisms, to secure a wireless network [31]. 2.10 WLAN Security Architecture Unlike GSM and UMTS networks, security in WLAN networks is not standardized. WLANS are implementation specific, and depend on the technology deployed and chosen on the wireless devices and access points. Another issue to put into consideration when securing wireless networks is, how secure the network should be, and what are the costs of implementing such security, these factors influence the type of security mechanisms deployed. The following figure illustrates the general security architecture for a WLAN: Figure 14: WLAN Security Architecture 2.10.1 802.1X The 802.1X is an essential element in securing WLAN networks. It is a standard from the IEEE, and is used for port-based network access control. Authentication of wireless stations (e.g. laptop, access point) is performed via this standard, and is based on the EAP protocol [33]. The 802.1X is the authentication framework, and the EAP methods deployed are the authentication algorithms [29].
  • 45. An Ontology for Generic Wireless Authentication 45 Authentication methods in wireless networks must fulfil certain minimum requirements; amongst these requirements are the following: • Generation of session keys for authentication, confidentiality and integrity purposes. • Support for mutual authentication between client and access point, thus preventing rogue (impersonating) access points. • Protection against eavesdroppers and man in the middle attacks, this can be ensured using session keys for message authentication, data confidentiality and data integrity. • Protection against dictionary attacks [33]. Three components are involved in the 802.1X framework: • The client – the wireless station • The authenticator – the access point • The authentication server – the AAA server [cisco 2] The client initiates the connection procedure, by associating itself to the access point, and issuing an EAP Start Request. At this point, the access point blocks the communication between the client and the network, until the authentication procedure is completed, (i.e. until the client presents correct authentication data (user ID and password/certificate) and is verified). The access point requests the identity of the client, by issuing an EAP Request Identity message. The client replies to this message via an EAP Response message containing its identity. This information is forwarded to the AAA server. Authentication is achieved depending on the authentication method deployed. The access point, grants the client the right to access the network upon the reception of an accept message, unsuccessful authentication leads to a reject message. Keys (session key and broadcast keys) are derived when the client authenticates the authentication server [29]. The 802.1X, along with the EAP authentication methods provide centralized authentication and dynamic key generation and distribution. Authentication methods in
  • 46. An Ontology for Generic Wireless Authentication 46 WLAN can be of different types, the ones described in this chapter are password based and certificate based methods. 2.10.2 Authentication, Authorization and Accounting Server The basic purpose of an Authentication Authorization and Accounting (AAA) server is to control access to a wireless network. Authentication in wireless networks grants or denies a client the right to access a network, depending on the validity of credentials the client presents. This could be in the form of a user name and password, security tokens or digital certificates. Authorization specifies what rights a client is entitled to during the connection to the network. This includes but is not limited to session time, access to certain resources/groups, etc… Accounting is used for tracking a user, and for billing purposes. The user name and connection duration are stored for this purpose. Several types of authentication servers exist. The AAA server based on the Remote Authentication Dial In User Service (RADIUS) protocol is discussed in this thesis. Remote Authentication Dial In User Service (RADIUS) The Remote Authentication Dial In User Service (RADIUS) is a protocol, used for providing authentication, authorization and accounting services between an access point and an authentication server (a RADIUS server or any other kind of AAA server). It provides a central user database [35] that can be accessed by different servers, in order to authenticate users (validate credentials) as well as provide configuration information, such as the type of service to deliver to the user (authentication) and accounting services, based on the user’s usage of the network. A RADIUS server supports several methods for authentication (RFC 2138). In simple terms, a RADIUS server checks for the validity of a user, requesting access to a network. It authorizes the user to access the network, if the information stored in a database is verified [34].
  • 47. An Ontology for Generic Wireless Authentication 47 2.10.3 Certificate Based Authentication It is necessary to understand the underlying terminologies of certificates in order to understand certificate based authentication. 2.10.3.1 Public Key Infrastructure A Public Key Infrastructure (PKI) is an infrastructure composed of digital certificates, certifying authorities (CA), public keys and private keys. The concept behind a PKI is that parties/entities, trying to communicate with each other via the internet, can be verified and authenticated against who they really claim to be via authorizing and certifying authorities. Public and private keys are managed by a PKI. Public keys are signed and verified by trusted certifying authorities [36] [37]. 2.10.3.1.1 Digital Certificates A digital certificate is an electronic identity used to prove the identity of a certain party/entity. This certificate is approved by a certifying authority, and signed by the certifying authority’s private key. Access to certain resources can be obtained using digital certificates [38]. A certificate is obtained via a CA. A digital certificate consists of the following according to the X.509 standard: • A digital signature • Version • Serial Number • Signature Algorithm • Issuer Name • Validity period • Subject • Public key [39] 2.10.3.1.2 Certifying Authority A certifying authority is a trusted third party that issues digital certificates, and verifies the validity of public keys [39].
  • 48. An Ontology for Generic Wireless Authentication 48 2.10.3.1.3 Public Key A public key is a number belonging to a certain entity. This key is distributed among entities that interact with the entity owning this key. The public key is used for verifying a digital signature and is used for encryption [39]. 2.10.3.1.4 Private Key A private key is a number belonging to a certain entity and is not known to any other entity. The private key is used for computing signatures and decryption. Public and private keys exist in pairs and correspond to each other; a message can be decrypted by a private key upon the reception of a public key associated with that private key [39]. 2.10.3.1.5 Digital Signature A digital signature is a digital code, verifying that the sender is the one issuing the electronic message. The digital signature, also verifies that the contents of the electronic message have not been altered. 2.10.4 Password Based Authentication In password based authentication, the password is not directly transmitted to the access point from the client. Instead a password hash or secret key is generated from the password to protect it from being sniffed across the network. The secret key or password hash is calculated via a hash function, which provides a one way encryption of the password. The password is shared between the network and the client. The network calculates the password from the received secret key [29]. 2.10.5 Extensible Authentication Protocol Messages for the purpose of authentication, are sent from the wireless device to the authentication server via the Extensible Authentication Protocol (EAP), which is an envelope consisting of different types of authentication methods. EAP is a general authentication protocol, supporting various authentication procedures. Our concentration for this thesis will be EAP authentication methods for password and certificate based authentication [33].
  • 49. An Ontology for Generic Wireless Authentication 49 The EAP protocol defines several types of authentication methods, amongst them are the following: • Lightweight Extensible Authentication Protocol (LEAP) • Extensible Authentication Protocol – Transport Layer Security (EAP-TLS) • Protected Extensible Authentication Protocol (PEAP) • Extensible Authentication Protocol – Subscriber Identity Module (EAP-SIM) 2.10.5.1 Lightweight Extensible Authentication Protocol LEAP, is a password based authentication protocol that authenticates the user rather than the device. Authentication is performed according to the user name and password provided. No certificates are used in this type of authentication. Mutual authentication of the client and authentication server is performed in this protocol, which depends on the existence of a secret key, and the user’s password that is shared between the client and the network. An authentication challenge is sent to the client, from the authentication server. The client responds to the authentication challenge with the hashed password. The authentication server retrieves relevant authentication information, from a database to create a response to the authentication request. The response generated by the authentication server is then compared to the one received from the client. The client authenticates the authentication server in a similar fashion. A dynamic session key called WEP is generated upon successful authentication. Successful authentication ends with an EAP-Success method [28]. 2.10.5.2 EAP Transport Layer Security EAP TLS is a certificate based authentication method, and is based on the TLS protocol (RFC 2246), which is the present version of the Secure Socket Layer (SSL). SSL is used by web browsers to secure transactions within web applications [29]. In EAP-TLS, certificates are used on both the client and server side for authentication. The client authenticates the authentication server via a digital certificate, sent to the client by the authentication server, and checks for the validity of the certificate. The server in turn authenticates the client in a similar manner. Upon the reception of the EAP-Success
  • 50. An Ontology for Generic Wireless Authentication 50 message, the dynamic session keys are generated and network access is granted to the client [28]. 2.10.5.3 Protected Extensible Authentication Protocol The PEAP protocol is a hybrid of EAP-TLS and any other EAP authentication method. It is a certificate based authentication method. Server side authentication is performed via EAP-TLS and the use of digital certificates is employed. For client side authentication any EAP method can be deployed, which is transported via a secure TLS tunnel. Certificates are not required for client authentication in PEAP. As with the authentication of the server in EAP-TLS, PEAP performs the same procedure of requiring and verifying a digital certificate, from the authentication server. After verification of the server’s side certificate, an encrypted tunnel, between the client and the authentication server is created. The tunnel is a secure path, for authenticating the client via non-mutual EAP methods, like EAP-Message Digest 5 (EAP-MD5) or EAP-Challenge Handshake Authentication Protocol (EAP-CHAP) (RFC 2284, RFC 1994). Upon successful client authentication the EAP-Success message is sent and session keys are derived [28] [29].
  • 51. An Ontology for Generic Wireless Authentication 51 2.10.5.4 EAP- Subscriber Identity Module The following figure illustrates the general overview of a WLAN accessing a GSM/UMTS network via EAP-SIM: Figure 15: EAP-SIM Architecture EAP-SIM is an authentication method, designed to provide mutual authentication between a WLAN client and an AAA server, using the GSM network for accounting and billing purposes. It is especially useful in the case of hotspots, where a user of a WLAN network can easily gain access to the internet via a mobile phone. As the name implies, EAP-SIM uses the EAP framework and GSM system for authentication and encryption. It is based on the authentication procedure between the SIM card and mobile network’s AuC. Thus, EAP-SIM acts as a bridge between wireless and mobile networks, namely WLAN and GSM networks. For EAP-SIM, the wireless station requires a SIM reader, which could be in the form of a smart card, USB stick, PC access cards, etc… The overview scenario of an EAP-SIM protocol is that a wireless station, connected to a SIM card reader, requests access to a network via an AP. The AP forwards the request to an authentication server, which retrieves authentication data from an authentication
  • 52. An Ontology for Generic Wireless Authentication 52 center via a GSM gateway. The GSM gateway is responsible for translating requests from an authentication server into GSM syntax. After the retrieval of the authentication data, several messages are exchanged to and from the client and authentication server. Upon successful authentication, the client gains access to the network. Before successful authentication of the client and network, the communication ports are blocked from the client by the AP. The client is not able to send any messages to the network except for the authentication specific messages (EAP and EAP-SIM messages). After authentication is completed, the client is able to communicate with the network and the AP unblocks the ports from the client. The EAP-SIM mechanism is more secure than the stand alone GSM system for authentication, since it provides mutual authentication of the client and the network. Another factor is that client’s session key, is never transmitted via the radio interface with EAP-SIM, thus less data is exposed in comparison to GSM networks. EAP-SIM functions in a way that it retrieves several GSM triplets from the AuC, and combines them together in order to generate a session encryption key. This encryption key is more secure than the GSM counterpart. For the communication of the EAP-SIM between the client and the network, the EAP- SIM protocol and the EAP-SIM authenticator code are implemented on the client. The authenticator code is responsible for handling server side EAP-SIM messages, and is also responsible for communicating with the AuC. Messages sent from the AAA server to the AuC are translated into GSM specific messages [28]. EAP-AKA is used for 3G networks, namely UMTS networks and is similar in concept to EAP-SIM but with more enhanced security features. EAP-AKA is not addressed in this thesis.
  • 53. An Ontology for Generic Wireless Authentication 53 EAP-SIM Authentication The following figure illustrates WLAN authentication via the EAP-SIM protocol: Wireless Station Access Point AAA Server HLR AuC EAPOL Start EAP Request Network Identity EAP Identity EAP Identity Response Response 0<IMSI>@realm 0<IMSI>@realm EAP-SIM Start EAP-SIM Start EAP-SIM Start EAP-SIM Start Response Response (RAND) (RAND) Get GSM Triplets Calculate EAP-SIM EAP-SIM GSM Triplets MAC_RAND Challenge Challenge RAND, XRES, Kc RAND, MAC_RAND RAND, MAC_RAND MAC_RAND = Server Authenticated MAC_RAND Calculate Challenge Challenge Calculate XRES, Kc, Response Response MAC_XRES MAC_XRES MAC_XRES MAC_XRES MAC_XRES Client = Authenticated MAC_XRES EAP-Success Session Key Accept Session Key Broadcast Key Figure 16: EAP-SIM Authentication The EAP-SIM authentication procedure starts, when the client sends an EAP-over-LAN (EAPOL) Start message to the AP. This message informs the AP that the authentication procedure will be carried out via EAP. The AP responds to the EAPOL Start message, with an EAP Request Identity message, which requests the network identity of the user. This identity is forwarded from the client to the authentication server via the AP in the form of an EAP Identity Response. The user’s network identity takes the following syntax: 0 <IMSI>@<realm>, where IMSI represents the subscriber’s identity number and realm represents the network
  • 54. An Ontology for Generic Wireless Authentication 54 operator’s domain name. The network identity is used for WLAN authentication purposes. The authentication server determines the EAP type being used, and sends an EAP-SIM Start message to the client. The client responds via an EAP-SIM Start Response message that carries the RAND number generated from the SIM. After reception of the EAP- SIM Start Response message, the authentication server retrieves several GSM triplets from the AuC of the GSM network provider. A gateway is needed in order to translate the request from the AAA server’s syntax to GSM specific syntax. An EAP-SIM Challenge message is created from the RAND number, received from both the client’s SIM and the triplets from the GSM response. This challenge consists of the AuC’s RAND number and a Random Message Authentication Code (MAC_RAND), which is 160 bits long. A MAC_RAND number is calculated separately on the SIM card, and is compared to the one received from the authentication server in the EAP-SIM Challenge. If both MAC_RAND numbers are equal, the first step of mutual authentication is completed and the server is authenticated. Upon successful server authentication, the SIM generates the XRES and Kc for the respective RAND numbers received. Another number is also generated, which is the Expected MAC Response (MAC_XRES). The MAC_XRES is sent by the client to the authentication server as a response to the challenge sent. The authentication server separately calculates a MAC_XRES, and compares it to the one received from the SIM. If both MAC_XRES are equal, the second step of mutual authentication is completed and the client is authenticated to the server. Session encryption keys are generated on the SIM and authentication server. An Accept message is sent from the authentication server to the AP, along with an encapsulated EAP-Success message (which is sent to the client) and the client’s session key. The client’s session key, is sent to the client from the AP via a Broadcast key. Authentication at this stage is completed and the client is able to access the network [28].
  • 55. An Ontology for Generic Wireless Authentication 55 3 Ontologies and the Semantic Web 3.1 The Semantic Web “The Semantic Web is not a separate Web, but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation.” [40]. “The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. You can think of it as being an efficient way of representing data on the World Wide Web, or a globally linked database.” [41] The Semantic Web is used to express the meaning of content, to machines. It is used to provide machine readable content, on the web, to machines and processes. This content can be easily processed, and manipulated in a meaningful way. The current state of the Web today, only provides information accessible and understandable by humans. No semantics are expressed, or provided for the contents of the different web pages displayed. Thus, vital information cannot be used automatically, without manual insertion, or processing into some sort of application or database. As the first definition of the Semantic Web states, it is an extension of the current Web. This extension is in the form of three main components of the Semantic Web: • The Expression of Meaning • The Representation of Knowledge • The Collection of Information The meaning of content can be expressed, in order to enable machine readability, rather than just being used, for displaying content to humans, and which has no real value to processes or machines. Providing meaning to content enables the Web to be a resource, for processable data and information. Knowledge is represented in a structured way, which can be inferred according to various rules, thus enabling logical deduction and reasoning of data. This facilitates new information to be derived from existing information. The method of representing knowledge in such a way is called Knowledge Representation. Common meanings of information are collected in what is known as an ontology. The ontology can undergo inference rules, which can be used to reach common meanings
  • 56. An Ontology for Generic Wireless Authentication 56 among terms, and can be used for the creation of new meaning. The machine is able to read the ontology, and provide a user with more meaningful information [40]. Various languages and tools have been developed for the Semantic Web. The most popular are, the eXtensible Modelling Language (XML) – used to add arbitrary structure to documents without expressing the meaning of the structures, the Resource Description Framework (RDF) – used to express meaning and used to exchange knowledge on the Web, and the Web Ontology Language (OWL) – used for sharing and distributing knowledge. OWL is an ontology language, which supports knowledge management, and advanced Web searches [40] [42]. The ontologies section takes a deeper look into ontologies and explains ontologies in more detail. The most popular languages developed for the Semantic Web, and which are World Wide Web Consortium (W3C) recommendations are as follows: • XML and XML-Schema; provides structured syntax for documents (XML), restrict the structure of XML and extend it with dataypes (XML-Schema), but which also provide no semantic meaning for the documents. • RDF and RDF-Schema; using XML syntax provide a datamodel for objects and define the relationships between the datamodels (RDF). RDF-Schema provides a terminology to express RDF datamodels using classes and properties. • OWL; provides more terminology for expressing the relationships between the classes and properties. It provides more terminology for the description of classes and properties [51]. OWL differs from XML-Schema, in that it represents knowledge of a certain domain rather than just being a message format [52]. 3.2 Ontologies 3.2.1 Origin The term Ontology originates from philosophy and describes the nature of being in its different aspects. Ontology relates back to many years and has had a long history. Ontology in the field of metaphysics is the study, of existence and the relationships that relate to this existence. It attempts to answer questions like; what defines the nature of beings, what are its main characteristics/properties, what relationships exist among
  • 57. An Ontology for Generic Wireless Authentication 57 different beings, and how can they be defined, what are the main causes of being, what different entities exist in beings and what rules govern them, etc… Ontologies remained in the domain of philosophers, linguistics, librarians and knowledge representation researchers, until the recent adoption of the term in computer science and its usage in Artificial Intelligent (AI) research [43]. 3.2.2 Definition 3.2.2.1 In Philosophy “That department of the science of metaphysics, which investigates and explains the nature and essential properties and relations of all beings, as such, or the principles and causes of being” [44]. “A branch of metaphysics concerned with the nature and relations of being” [45]. “A particular theory about the nature of being or kinds of existence” [45]. 3.2.2.2 In Artificial Intelligence “A systematic arrangement of all the important categories of objects or concepts, which exist in some field of discourse, showing the relations between them. When complete, an ontology is a categorization of all the concepts in some field of knowledge, including the objects and all of the properties, relations, and functions needed to define the objects and specify their actions. A simplified ontology may contain only a hierarchical classification (a taxonomy) showing the type subsumption relations between concepts in the field of discourse. An ontology may be visualized as an abstract graph with nodes and labelled arcs representing the objects and relations” [47]. “An ontology defines a common vocabulary for researchers who need to share information in a domain. It includes machine-interpretable definitions of basic concepts in the domain and relations among them” [49]. “An Ontology is a formal, explicit specification of a shared conceptualization” [48]. Ontologies are designed for the purpose of knowledge sharing and re-use. An Ontology is formal if a machine is able to interpret its meaning. It is explicit if the ontology concepts and the constraints applied to the ontology are explicitly defined. It is a specification because it describes the concepts of a certain domain in an actual manner. It is a shared view or concept of a particular domain and finally, conceptualization refers to the fact that the ontology represents an abstract analysis/vision of a certain nature or reality. An important point to put into consideration when addressing ontologies, is that apart from ontologies defining information or data as formal semantics, which can be interpreted and processed by machines (machine-understandable). They also define real
  • 58. An Ontology for Generic Wireless Authentication 58 world semantics, which enables humans to understand the machine understandable content, thus permitting reuse and ontology sharing [46] [50]. 3.2.3 Ontology Approaches Ontologies can be expressed in various ways, and different approaches exist for defining concepts and the relations of concepts in a certain domain. A brief description between three approaches, namely Description Logics, Frame-based and Predicate Logic is given in the following: 3.2.3.1 Description Logics Description Logics, is a language based on logics and is used represent domain knowledge, based on logical representations of knowledge, and the reasoning of the described knowledge. A first step in representing a domain is the definition of concepts, related to and relevant for this domain. These concepts can be described, in terms of properties and restrictions that must be satisfied, in order for the concepts to belong to the described domain. Reasoning of the concepts, represented in the knowledge base (the ontology and its instances), is used to infer new information about the domain from the already existing knowledge. Description Logics also support the classification of concepts and individuals, which expresses the child and parent hierarchies amongst the defined concepts [50] [60]. 3.2.3.2 Frame-based Modelling in Frame based approaches, consists of classes and local class properties. It takes more of an object oriented approach in defining a domain. Frames (classes) describe an individual, or a set of individuals in a certain domain, thus representing knowledge of a concept in that domain. Properties of a class can be reused by other classes with other range values and value restrictions. Frames in a Frame-based system are interconnected and follow a hierarchy, such that the properties defined for parent frames, are inherited by those of the child frames. Properties can take specified values, or can be computed values [50] [59].
  • 59. An Ontology for Generic Wireless Authentication 59 An ontology in Frame-based systems, is made up of class definitions, and the connecting relationships between the classes and properties, functions, objects and relating axioms [50]. 3.2.3.3 Predicate Logic In Predicate Logic, the relationship(s) between subjects and objects are expressed. Predicate logic is based on predicates. A Predicate is an expression that expresses (a) relationship(s) between terms, e.g. the predicate “is a” in “GSM is a second generation network”. Thus, GSM is the subject and second generation network is the object. The most important elements in predicate logic are constants, predicates, variables, formulas and quantifiers. Constants are the names used in predicate logic, and represent the vocabulary used. Predicates as explained, define the relationships between terms. Variables represent terms, and are used as place holders for objects that represent individuals. Terms can also be objects and constants. Formulas form expressions that have meanings, which are a combination of individual terms. Quantifiers indicate the number of objects asserted to a predicate. Two types of quantifiers are, the universal quantifier that asserts a predicate to all objects, and the existential quantifier that asserts a predicate to some objects [58] [50]. Closed sentences are the result of combined terms that formulate expressions. A knowledge base in predicate logic is represented by a set of sentences [50]. 3.2.4 The Web Ontology Language Several ontology languages exist, which depend on the ontology approach being used, is a matter of preference, and also a matter of what purposes the ontology is used for. For the purpose of this thesis, the Web Ontology Language is chosen and is discussed in the following in detail. The Web Ontology Language (OWL) is a language, created specifically for designing, defining, creating and instantiating Web Ontologies. OWL is used for creating and describing classes, properties and their instances, as well as defining the relationships that exist between these classes and properties [52]. OWL is needed, and is used to provide machine-readable content to applications that need to process the content of the web rather than just display Web content. This in turn, facilitates greater machine interpretability of Web content, than that provided by
  • 60. An Ontology for Generic Wireless Authentication 60 other web languages (XML, XML-Schema, RDF and RDF-Schema). OWL is an extension of these technologies [51]. The use of OWL can be summarized into the three following points: • The description of a certain domain via the definition of classes and properties. • The definition of the relationships existing among these classes and properties. • The reasoning of the defined classes, properties and relationships, which prove the defined logic of the described domain, and verify its consistency [52]. OWL is divided into three sublanguages; OWL-Lite, OWL-DL and OWL Full, which differ from each other in the level of expressivity. Each sublanguage is an extension of its predecessor, and is designed according to what the required ontology should describe. Making a choice of which sublanguage to choose is based on the level of expressivity required for the ontology, and which best suits the needs of the ontology. OWL represents an important part of the Semantic Web. It allows the collection of information from distributed sources, by relating ontologies together. This enables web resources to be accessible to processes, via the description of the resource’s web content [52]. 3.2.4.1 OWL Lite Is the simplest form of OWL ontologies and provides simple classification support, and simple constraints [51]. 3.2.4.2 OWL DL OWL DL is based on Description Logics, as the abbreviations DL imply. With OWL DL full support of the OWL constructs is included. These constructs can only be expressed under certain restrictions. OWL DL supports reasoning mechanisms, thus inconsistencies of the described domain and concepts can be tested, in an ontology conforming to OWL DL. OWL DL represents an extension for OWL Lite, and provides better expressivity and maximum expressiveness, with the assurance that what is deducted from the ontology is computable [51].
  • 61. An Ontology for Generic Wireless Authentication 61 3.2.4.3 OWL Full OWL Full is an extension of OWL DL, and full support of the OWL constructs is given in OWL Full, without any restrictions. OWL Full provides for maximum expressiveness, but without any computational assurances. OWL Full provides some reasoning mechanisms, but complete reasoning for OWL Full is unlikely to be implemented. 3.2.5 OWL Language Constructs OWL is used to define classes, instances and properties, in addition to describing the relationships between the defined classes and properties. The basic language elements of OWL are built on these concepts, and the most important ones are described in the following [52]: 3.2.5.1 Classes A class represents a concept, which is represented by a name and a set of rules, or restrictions that qualify individuals to become members of the class. Individuals that share common characteristics (properties) can be grouped into one or several classes. Classes and individuals are, described by the properties assigned to the classes, and by the relationships existing among the properties of a class. Classes can be sub-classed, forming a hierarchy and a class may have several sub-classes. The subclass inherits its characteristics from the super or parent class, and it may have one or more parent class. Multiple inheritance is supported. Subclasses and instances of a class are, sometimes used interchangeably, and can be confused from the meaning. The main difference is that a subclass is used, to describe a subset of the class. Instances are used to state that the individual described, is an actual member of the class, and not a member that can be further characterized or subset. OWL Full supports classes and instances, while OWL DL does not [52]. 3.2.5.1.1 Enumerated Classes An Enumerated Class is a class that consists, of an enumerated number of individuals that belong to the class. Only the exact number of members that are specified in an enumerated class can be members of the defined class. Enumerated classes are described
  • 62. An Ontology for Generic Wireless Authentication 62 using the oneOf construct, the class consists of oneOf the enumerated members and nothing more [51] [52]. 3.2.5.1.2 Disjoint Classes Disjoint classes describe the difference between classes, and state that one class cannot have the same instance(s) as another class that it is disjoint with. This helps a reasoner in detecting inconsistencies between classes. What is an instance in class A cannot be an instance in class B, if both classes are declared as disjoint [51] [52]. 3.2.5.2 Properties Properties describe individuals that belong to a class. They define general and specialized facts about an individual. Relationships among individuals are defined using properties. The same property can be re-used by several classes. This is achieved by specifying rules, or restrictions for a particular individual. Therefore, the rules are specific to that particular individual, and are not a tied to the property. Applying restrictions to properties is a method, for defining the relationships between individuals of a class. As with classes, properties can have sub-properties that further classify or define the property, and that form a hierarchy of properties. A sub-property can have multiple properties as a parent, or super-property. Sub-properties inherit the super-property’s characteristics [52]. The two important types of properties in OWL are datatype properties and object properties: • datatype properties; define the relationship between instances of classes, RDF literals or XML Schema datatypes. • object properties; define the relationship between instances of two or more classes. 3.2.5.2.1 Property Domains and Ranges Domains and ranges can be defined for properties, which relate individuals of one class (the domain), to individuals of another class (the range), via a specific property. Domains specify the individuals the property can be applied to. A range limits the values a property can have, only the individuals specified in the range, can be values of the specified property.
  • 63. An Ontology for Generic Wireless Authentication 63 3.2.5.2.2 Property Characteristics Properties can be further specified, by assigning certain characteristics to a property. The following describes the characteristics that can be applied to a property in OWL [52]: 3.2.5.2.2.1 TransitiveProperty Transitive properties are properties, which relate one individual to another, via a common individual. E.g. considering two individuals (individual 1 and individual 2), are related to each other via a property, if a third individual (individual 3), is related to individual 2 via the same property, it can be deducted that individual 1 is also related to individual 3 via the same property. This is a transitive property [53]. 3.2.5.2.2.2 SymmetricProperty In symmetric properties, individual 1 is related to individual 2, via a property. And individual 2 is related to individual 1, via the same property [53]. 3.2.5.2.2.3 FunctionalProperty Functional properties can also be referred to as single valued properties, and are properties that can take only one individual as its value. If a functional property is applied to two individuals, it can be deducted that these two individuals, represent the same individual. The minimum cardinality allowed for a functional property is zero and the maximum cardinality is 1 [51] [53]. 3.2.5.2.2.4 InverseOf An inverse property relates individual 1 to individual 2, via a property and relates individual 2 to individual 1 via another property, which is its inverse property. A property can be the inverse of another property [51]. 3.2.5.2.2.5 InverseFunctionalProperty An inverse functional property, states that the inverse property is functional (i.e. has only one individual as its value) [51]. 3.2.5.2.3 Property Restrictions
  • 64. An Ontology for Generic Wireless Authentication 64 Property restrictions are, rules applied to properties, in order to specify which and how many individuals can belong to a certain class. A restriction is used, for describing an unknown class, which consists of individuals satisfying the restriction (e.g. individuals belonging to a certain group or that satisfy certain criteria). Property restrictions can be classified into quantifier restrictions; (existential quantifiers and universal quantifiers), hasValue restrictions and cardinality restrictions. These are addressed in the following [51] [53]: 3.2.5.2.3.1 Quantifier Restrictions Three parts make up a quantifier restriction; the first part is the type of quantifier (existential or universal), the second part is the property involved in assigning the restriction, and the third part is, the class from which values/individuals, are to be taken from, in order to create an anonymous class that satisfies the restriction (The creation of a group of values satisfying the condition). 3.2.5.2.3.2 Existential Quantifiers Existential restrictions (someValuesFrom) are assigned to a property, and denote that at least one individual of a class, associated with the restricted property belongs to an unknown class. This unknown class forms the values of the defined restriction. (E.g. the someValuesFrom restriction denotes that class A, has a set of individuals (at least one) from class B, because it fulfils the property A). In other words, there exists at least one kind of relationship between two or more classes [53]. 3.2.5.2.3.3 Universal Quantifiers Universal restrictions (allValuesFrom), as existential restrictions are assigned to a property, and denote that only individuals of a specific class associated with the restricted property belong to an unknown class, resulting from the property restriction. Individuals from other classes cannot belong to this unknown class. (E.g. the allValuesFrom denotes that class A can only have individuals from class B that fulfil the property A) [53]. 3.2.5.2.3.4 hasValue Restrictions The hasValue restriction relates individuals, from an unknown class to a specific individual. It states that the unknown class has a particular value, which is a specified individual [53].
  • 65. An Ontology for Generic Wireless Authentication 65 3.2.5.2.3.5 Cardinality Restrictions Cardinality is used, to specify the number the number of relationships that can be associated to a particular individual, via a specific property. In OWL minimum cardinality, maximum cardinality and cardinality, can be defined for properties, and which express the minimum, maximum and arbitrary number of occurrences respectively. Cardinality values start from 0 and are never negative values [53]. 3.2.5.3 Operators Operators are used to define the characteristics of a class. Logical combinations of classes can be performed with operators, such as; the intersection, union and complement of classes. New class definitions can be created with the use of operators [53]. 3.2.5.3.1 intersectionOf The intersectionOf operator performs a logical ‘AND’ operation, between two or more classes. It combines the features of the classes specified, into a new class. Individuals of the intersected classes become individuals of the new class [53]. 3.2.5.3.2 unionOf The unionOf operator performs a logical ‘OR’ operation between two or more classes, and combines either the characteristics of all the specified classes, or one of the classes into a new class. (E.g. if a union operation is performed for class A and class B, the resulting class would be the individuals, of class A and B, or would be either one of them) [53]. 3.2.5.3.3 complementOf The complementOf operator selects the individuals that do not belong to the specified class.
  • 66. An Ontology for Generic Wireless Authentication 66 3.2.6 Ontology Tools Several tools for editing and creating ontologies exist. For the purpose of this thesis, the Protégé tool with the Protégé OWL Plug-in were used as an ontology editor, the Racer tool as an ontology reasoner and the GraphViz tool as a tool to visualize the ontology. Descriptions of each tool are provided in the following: 3.2.6.1 Protégé Protégé was developed as a tool for developing ontologies. Apart from the development of ontologies, Protégé also supports the customization of data entry forms, and data entry. It is an open source tool, and provides a knowledge-base framework, based on Java and which can be extended, via customized Application Programming Interfaces (API) and Plugins. Extensions can provide different kinds of components, such as; graphs, tables, images, etc…as well as providing support for different storage formats, such as; XML, RDF(S), OWL and HTML [54]. The Protégé OWL Plug-in The Protégé OWL Plug-in is a complex extension of the Protégé tool, which is called Protégé Core. With Protégé OWL, it is possible to edit OWL ontologies and perform description logic reasoning, and OWL-related services (classification, consistency checking and ontology testing). Formats like RDF(S), OWL Lite, OWL DL, and OWL Full are supported by the Protégé OWL Plugin. Extensions that include custom tabs and widgets can be added. Protégé OWL provides a library of reusable components, and a very flexible architecture, which can be extended in various ways. Protégé OWL, becoming an architecture for the building of ontology based Semantic Web applications can be foreseen [55]. 3.2.6.2 RenamedABox and Concept Expression Reasoner Professional RenamedABox and Concept Expression Reasoner Professional (RacerPro) is a Description Logics reasoner, and knowledge representation system. It supports consistency checking (verifying the possibility of a class having instances and marking out
  • 67. An Ontology for Generic Wireless Authentication 67 inconsistent classes), and classification (inferring new concepts, classes, relations, etc… from the existing asserted concepts) [55] [56]. Inferred concepts correspond, to the deduction of new content and meaning from existing content (computed concepts). Asserted concepts are concepts which are defined in a certain domain, (manual definition of concepts). A knowledge base in description logics consists of, TBoxes (ontologies) that represent the knowledge of a certain domain, and ABoxes that represent the instances of the TBoxes domain knowledge. RacerPro can be used in many application fields, among them are the Semantic Web and Knowledge Engineering fields [56]. 3.2.6.3 Graphical Visualization GraphViz is an open source visualization software used for representing graphs. Structured information can be represented as graphs and diagrams. GraphViz takes graph descriptions from external sources in simple text languages like, XML for example to generate graphs and diagrams. GraphViz also supports manual editing of graphs, via test files or with the use of a graph editor [57]. GraphViz is used in Protégé for visualizing the ontology, in terms of its structured hierarchy (subclasses and superclasses). It also provides visualization for the asserted and inferred hierarchies of the ontology. 3.2.7 Protégé-OWL Concepts Protégé-OWL follows the OWL language constructs in the definition of an ontology, or knowledge base (which is basically an ontology with instances). A few additional points to understand, which are not part of the OWL construct are: • Asserted/Inferred Conditions/Hierarchy/Model • Necessary and Sufficient/Necessary Conditions An asserted condition/hierarchy/model is what is manually defined, while creating the ontology. Asserted models have not undergone any kind of logical classification or reasoning.
  • 68. An Ontology for Generic Wireless Authentication 68 An inferred condition/hierarchy/model is the asserted condition/hierarchy/model after reasoning has been performed (automatic computation of the assertions). New information is deducted according to logic in the inferred model, and also classification checking is performed. The results of information deduction and classification, is the information that is displayed in the inferred condition/hierarchy/model. While defining restrictions on classes, a differentiation between necessary conditions and necessary and sufficient conditions must be made. Necessary conditions relate to Primitive or Partial classes, while necessary and sufficient conditions relate to Defined or complete classes. Defined classes are classes that consist of at least one set of necessary and sufficient conditions. Necessary and sufficient conditions imply, that the necessary conditions defined, in order for an individual to qualify in being a member of a class, are not only necessary for class membership, but are also sufficient for the individuals, satisfying the conditions in becoming class members. Primitive classes are classes that consist of at least one set of necessary conditions. Necessary conditions imply that, certain conditions need to be satisfied, in order for an individual to become a member of the defined class. It does not imply, however, that any individual that satisfies the defined conditions must be an individual of the defined class [53]. 3.2.8 Ontology Development Two issues in ontology development are addressed in this thesis. The first, is the reasons why anyone would want to develop an ontology, and the second, is the steps involved in the development of an ontology, and what points should be put into consideration. 3.2.8.1 Why Develop an Ontology Several reasons exist to develop an ontology, some important reasons could be one of the following: • The sharing of common understandings. • The sharing of information structures. • The reuse of domain knowledge. • The analysis of domain knowledge.
  • 69. An Ontology for Generic Wireless Authentication 69 • The separation of domain knowledge and operational knowledge [49]. 3.2.8.2 Steps in Developing an Ontology The development of an ontology differs from the traditional object oriented development, in that object oriented modelling, is based on the operational properties of a class and its methods. Ontology modelling is based on the structural properties of a class [49]. There is no right or wrong way for the design and development of an ontology, different approaches can be used. This thesis concentrates on the following approach: The first point to consider while developing an ontology, is the domain the ontology is being developed for. A proper understanding of the intended domain should be performed, and the definition of the domain’s components, and the relationships that exist between these components should be clarified. An ontology defines concepts of the real world, which is a fact that should be put into consideration in ontology development. Therefore, the concepts defined in the ontology, must relate to the real concepts and relationships, in the real world domain. It must be clear what the ontology will be used for in order to decide the details of the ontology. Ontology development is an iterative process, and should be extensible and maintainable. The evaluation of an ontology should be performed after its initial design, and the testing, debugging and discussion of the concepts and relationships should also be carried out. This is performed, in order to determine whether the ontology actually describes the intended domain or not. Refinements of the ontology are then carried out, and the iterative process of ontology development continues throughout the ontology’s lifecycle. Ontology development includes the definition of the domain concept (classes) and the arrangement of these classes in a certain hierarchy. The definition of the properties, property values, and the definition of the relationships, existing amongst the concepts. The following lists and describes the steps that could be followed in developing an ontology: • The determination of the ontology’s scope and domain. • The re-usage of existing ontologies.
  • 70. An Ontology for Generic Wireless Authentication 70 • The enumeration of the ontology’s important terms • The definition of classes and its hierarchy. • The definition of class properties. • The description of property features. • The instantiation of class instances. In determining the scope and domain of an ontology, it is important to think of questions that will help in constructing the ontology, and defining its main concepts. The level of detail that the ontology should describe is also a critical issue to consider. Questions to consider could be: Q: What should the ontology describe? Q: Who will the ontology be useful for, and for what purposes? Q: What kinds of questions should the ontology be able to answer? The re-usage of ontologies could save a lot of effort, by just taking already existing ontologies and refining them, or extending them according to the intended use. The enumeration of terms is helpful in determining the contents of an ontology, e.g. the enumeration of the concepts the ontology will define, the concepts properties and characteristics, etc… Several approaches in defining the class hierarchy could be used, e.g. a top-down approach; which defines the most general terms first, and then goes down to specializing each term definition, a bottom-up approach; which defines the specific terms first and then goes up to the most general term definitions, or a combination of both approaches. After the definition of the concepts (classes of an ontology) further descriptions can be given to these concepts, by defining the properties of a concept, and its relationships to the other concepts in the ontology. More specialized descriptions can be applied to the properties. This is performed by describing what types of concepts can exist within another concept, the number of times a certain property can occur for a concept and so forth. The last step of the ontology development would be the instantiation of class instances. An instance is the value filled in for a certain property, of an individual belonging to a class [49].
  • 71. An Ontology for Generic Wireless Authentication 71 Ontologies can be classified and checked for consistency using a reasoner. RacerPro is one example for an ontology reasoner.
  • 72. An Ontology for Generic Wireless Authentication 72 4 An Ontology for Generic Wireless Authentication The Protégé 3.0 tool with the Protégé-OWL plugin, was used for the development of the Generic Wireless Authentication Ontology. RacerPro and several older versions of Racer were used, to classify and create the inferred hierarchy and check for consistencies in the ontology. For the visualization of the class hierarchy, the GraphViz tool was used along with the OWLViz plugin. 4.1 Class Overview The following figure illustrates a general overview of the ontology’s class hierarchy: Figure 17: Overview of Asserted Ontology Hierarchy The ontology consists of 14 main classes, which are divided into subclasses. The super class (not visualized here), is owl:thing which is part of the OWL language defined by the W3C. It represents the set that contains all individuals. All individuals in an ontology are subclasses of owl:thing [53].
  • 73. An Ontology for Generic Wireless Authentication 73 The main ontology classes are: the Algorithm class, the AuthenticationMethod class, the AuthenticationType class, the Certificate class, the CertificateComponent class, the Code class, the Database class, the Identity class, the Key class, the Network class, the Number class, the Service class, the UserData class and the Subscriber class. These classes are related to the description of authentication data stored in the profile registers for GSM, UMTS and WLAN networks and are explained in detail in the following section. 4.2 Ontology Classes and Subclasses Classes and subclasses describe an is-a relationship. An individual cannot be a subclass of a certain class if it does not fulfil the is-a relationship. E.g. an A3 algorithm is-a Algorithm, therefore the A3 individual is a subclass of the Algorithm class. 4.2.1 The Algorithm class The Algorithm class is the parent class of the authentication specific algorithms, used in GSM and UMTS networks. The Algorithm class contains the following subclasses: • A3 • A8 • f1 • f1_ (corresponds to f1*) • f2 • f3 • f4 • f5 • f5_ (corresponds to f5*) The A3 and A8 algorithms represent the authentication algorithms in GSM networks. The f1 - f5_ algorithms represent the UMTS network algorithms. Details about these algorithms can be found in sections (2.4.2 and 2.6.2). The Algorithm class is declared as disjoint from the other classes in the ontology, because an algorithm cannot be the same
  • 74. An Ontology for Generic Wireless Authentication 74 individual as any other class in the ontology. (E.g. an Algorithm cannot be a service or an identity). 4.2.2 The AuthenticationMethod class The AuthenticationMethod class is the parent class of the authentication types, used in WLAN networks. It describes some of the EAP authentication methods. The AuthenticationMethod class contains the following subclasses: • EAP-SIM • EAP-TLS • LEAP • PEAP The AuthenticationMethod class is declared disjoint from all of the classes in the ontology, except for the AuthenticationType class, because an authentication method can be both an authentication method and an authentication type. E.g. LEAP, which exists in the AuthenticationMethod class is a password based type of authentication method. The password based characteristic is a subclass of the AuthenticationType class, therefore, these two classes cannot be declared as disjoint. More details on the EAP authentication methods can be found in section (2.10.5.2 ). 4.2.3 The AuthenticationType class The AuthenticationType class describes the type of authentication an authentication method can be. The AuthenticationType class contains the following subclasses: • CertificateBased • ChallengeResponse • MutualAuthentication • NetworkAuthentication • PasswordBased • UserAuthentication
  • 75. An Ontology for Generic Wireless Authentication 75 Certificate based authentication is described in section (2.10.3), challenge response authentication is described in section (2.4.1), mutual authentication means that the type of authentication is performed on the network side as well as on the user side, network authentication means that only the network is authenticated, password based authentication is described in section (2.10.4), and user authentication means that only the user is authenticated. The AuthenticationType class is declared disjoint from all the classes in the ontology, except for the AuthenticationMethod class. An authentication type can be one type of authentication method. However, specific disjoints can be declared within the members of the AuthenticationType class. More on disjoints in section (4.3). 4.2.4 The Certificate class The Certificate class is an empty class that takes individuals of the CertificateComponent class as values. This is described in the following section. 4.2.5 The CertificateComponent class The CertificateComponent class describes the components that make out a digital certificate as described in section (2.10.3). The CertificateComponent class contains the following subclasses: • IssuerName • PublicKey • SerialNumber • Signature • SignatureAlgorithm • Subject • ValidFrom • ValidTo • Version
  • 76. An Ontology for Generic Wireless Authentication 76 4.2.6 The Code class The Code class describes the codes that are part of the IMSI and MSISDN. Details on the codes contained in the IMSI and MSISDN can be found in section (2.3.3). The Code class contains the following subclasses: • CountryCode • MobileCountryCode • MobileNetworkCode • NationalDestinationCode 4.2.7 The DataBase class The Database class describes the databases used by the GSM, UMTS, IMS and WLAN networks. Individuals of other classes are linked to subclasses of the database class, since several individuals are stored in the databases, defined as children of the database class. The DataBase class contains the following subclasses: • AuC • HLR • HSS • UserDatabase The AuC and HLR are also subclasses of the HSS class, and are later removed from the hierarchy in the inferred model. This will be discussed later on in this chapter. Details about the AuC, HLR, HSS and user database can be found in section (2.3.1.1 and 2.7). 4.2.8 The Identity class The Identity class describes the identities used in the GSM, UMTS, IMS and WLAN networks. The Identity class contains the following subclasses: • IMSI • NAI • PrivateUserIdentity
  • 77. An Ontology for Generic Wireless Authentication 77 • PublicServiceIdentity • PublicUserIdentity • UserNetworkIdentity • URL • Realm • IPAddress • UserName The UserNetworkIdentity is the identity used, to identify the user of a network to a network. The IPAddress and Realm are also used for identification purposes. Details about the IMSI, NAI, public service, private and public user identities are described in section (2.7.1). 4.2.9 The Key class The Key class is subdivided into three subclasses; the DerivedKey class, the GeneratedKey class and the StaticKey class, which are also sub-classed. The Key class describes the keys used, in the authentication process of the networks, and that are used for verification purposes. The DerivedKey class describes the keys that are derived from other keys, or that result of an algorithm computation. The GeneratedKey class contains the generated keys, like the RAND and SQN numbers. The StaticKey class, contains the keys that are static, and that are not created dynamically, like the secret key (Ki) of GSM and UMTS networks, or the public and private keys of a certificate. The DerivedKey class contains the following subclasses: • AK • AMF • AUTN • IK • Kc • MAC
  • 78. An Ontology for Generic Wireless Authentication 78 • MAC_RAND • MAC_XRES • RES • XMAC • XRES The GeneratedKey class contains the following subclasses: • RAND • SQN The StaticKey class contains the following subclasses: • Ki • PrivateKey • PublicKey 4.2.10 The Network class The Network class is the domain of the ontology modelling. All classes in the ontology correspond to one or more of the networks described in the network class. The Network class consists of the following subclasses: • GSM • IMS • UMTS • WLAN 4.2.11 The Number Class The Number class describes the numbers associated with the IMSI, IMSDN, and numbers associated to a public user identity. Details about these numbers can be found in section (2.3.3). The Number class contains the following subclasses: • HLRNumber
  • 79. An Ontology for Generic Wireless Authentication 79 • MSISDN • MobileSubscriberIdentificationNumber • SubscriberNumber • IndividualSubscriberNumber • FixedTelephoneNumber 4.2.12 The Service class Three types of services are distinguished in the Service class, namely; basic services, supplementary services, and multimedia services. The Service class describes the types of services available for a subscriber. Multimedia services are available for UMTS and WLAN networks and include several services like the Multimedia Messaging Service (MMS). The BasicService class contains the following subclasses: • SMS • Speech The SupplementaryService class contains the following subclasses: • CallBarring • CallDivert • CallWaiting • ConferenceCall • CustomerCareBilling • DataService The MutlimediaService subclass contains the following subclasses: • AudioDownload • AudioStream • MMS • VideoDownload
  • 80. An Ontology for Generic Wireless Authentication 80 • VideoStream • WebBrowsing 4.2.13 The UserData class The UserData class describes personal user data needed for a subscription to a mobile service (GSM, UMTS or WLAN). Information includes banking details, personal details (name, address, etc…). Session duration, also a subclass of the UserData class is used to record the duration of usage and is used for billing purposes in WLAN networks. The Password subclass of the UserData class is associated with the AuthenticationType class for password based authentication. The UserDataClass contains the following Subclasses: • AccountHolder • AccountNumber • BankCity • BankCode • BankCountry • City • Country • FirstName • HouseNumber • LastName • Password • PostalCode • SessionDuration • State • StreetName
  • 81. An Ontology for Generic Wireless Authentication 81 4.2.14 The Subscriber class The Subscriber class is an empty class that uses individuals of other classes as its values. E.g. using a property it can be used to describe that a subscriber is a subscriber of a certain service. 4.3 Disjoint Classes The following figure illustrates a snapshot of the Protégé-OWL tool, and the disjoint classes declared for the CertificateComponent class: Figure 18: Disjoint Classes In developing an ontology it is important to notice which classes should be declared as disjoint and which should not. Inconsistency errors occur, if classes that should logically not be disjoint, are declared as disjoint from each other. Disjointness means that one class cannot be the same as the other class, or have the same meaning. E.g. a Network is not a Database, therefore, the Network class must be declared as disjoint from the Database class, otherwise the reasoner understands that a Network is a Database.
  • 82. An Ontology for Generic Wireless Authentication 82 When a class is not disjoint it expresses an is-a relationship. E.g. An authentication method is-a authentication type. Disjointness can be applied to a class as a whole, or to parts of a class. Specifying that only part of the class is disjoint from another class, or vice-versa. A subclass inherits its disjointness to other classes, from its super class and cannot be disjoint from its super class. Logical errors occur in the ontology, when checking for consistency. An error is generated, if a subclass is declared as disjoint from its super class. The following section goes into detail about the disjointness of the classes in the ontology: 4.3.1 The Algorithm class disjoints The Algorithm class is disjoint from all the classes in the ontology, except for the SignatureAlgorithm subclass of the CertificateComponent class. A SignatureAlgorithm is also an Algorithm, it is not declared as disjoint from the Algorithm class for this reason. All subclasses of the Algorithm class, namely (A3, A8, f1, f1_, f2, f3, f4, f5 and f5_) are disjoint from each other, and are also disjoint from the SignatureAlgorithm class. An A3 algorithm is not an A8 algorithm, this case also holds for the other members of the class. A SignatureAlgorithm is not an A3 algorithm. 4.3.2 The AuthenticationMethod class disjoints The AuthenticationMethod class is disjoint from all classes in the ontology, except for the AuthenticationType class. An authentication method e.g. EAP-SIM is an authentication type e.g. ChallengeResponse type. 4.3.2.1 The EAP-SIM subclass The EAP-SIM subclass is disjoint from all its siblings (an EAP-SIM method is not an EAP-TLS method for example). It is also disjoint from the following subclasses of the AuthenticationType class; CertificateBased, PasswordBased, NetworkAuthentication and UserAuthentication. This is because EAP-SIM is neither a certificate based, password based, network authentication or user authentication type of authentication. What is meant by user and network authentication is that, the authentication method only authenticates the user, or only authenticates the network.
  • 83. An Ontology for Generic Wireless Authentication 83 EAP-SIM is not disjoint from the ChallengeResponse and MutualAuthentication classes, because EAP-SIM is a challenge response type of authentication method. It performs mutual authentication of the network and the user. 4.3.2.2 The EAP-TLS subclass The EAP-TLS subclass is disjoint from all its siblings (EAP-SIM, LEAP and PEAP). It is also disjoint from the PasswordBased, ChallengeRepsonse, and UserAuthentication subclasses of the AuthenticationType class. EAP-TLS does not perform any authentication, based on password, or challenge response mechanisms. It does not authenticate the user of a network. Classes that are not declared disjoint from the EAP-TLS class are; the CertificateBased, MutualAuthentication and NetworkAuthentication classes. EAP-TLS authentication is based on certificates. It performs mutual authentication of the network and user, and it also authenticates the network only in conjunction with the PEAP authentication method. 4.3.2.3 The LEAP subclass The LEAP subclass is disjoint from all its siblings, and is also disjoint from the CertificateBased and NetworkAuthentication subclasses of the AuthenticationType class. LEAP is a certificate based type of authentication, and it does not authenticate the network only (i.e. it provides mutual authentication of the client and network). The classes that are not disjoint from the LEAP class are; the ChallengeResponse, MutualAuthentication, PasswordBased and UserAuthentication classes. LEAP is a password based type of authentication. In this type of password based authentication, a challenge is sent in return for a response. This is performed in order to calculate the same secret, which enables a user to be authenticated. LEAP performs mutual authentication of the network and user, and also performs authentication of the user only in conjunction with PEAP authentication. 4.3.2.4 The PEAP subclass The PEAP subclass is disjoint from all its siblings (EAP-TLS, LEAP and EAP-SIM). It is not disjoint from any member of the AuthenticationType class, since the PEAP method is a certificate type of authentication method. It performs mutual authentication, it uses
  • 84. An Ontology for Generic Wireless Authentication 84 the EAP-TLS to authenticate the network, and any type of EAP method to authenticate the user. Network only authentication, user only authentication, password based authentication and challenge response type of authentication are supported by this class. 4.3.3 The AuthenticationType class disjoints The AuthenticationType class is disjoint from all the classes in the ontology, except for the AuthenticationMethod class. The concept behind the classes being disjoint from each other or not is the same as that for the AuthenticationMethod classes, except that it is in reverse order. 4.3.3.1 The CertificateBased subclass The CertificateBased subclass is disjoint from all its siblings, (a certificate based type of authentication is not a password based type of authentication or a challenge response type of authentication, etc…). It is also disjoint from the EAP-SIM and LEAP classes. The CertificateBased subclass is not disjoint from the EAP-TLS and PEAP classes. 4.3.3.2 The ChallengeResponse subclass The ChallengeResponse subclass is disjoint from all its siblings, (MutualAuthentication, CertificateBased, etc…). It is also disjoint from the EAP-TLS class. The ChallengeResponse subclass is not disjoint from the EAP-SIM, LEAP and PEAP classes. 4.3.3.3 The MutualAuthentication subclass The MutualAuthentication subclass is disjoint from all its siblings. It is not disjoint from any of the AuthenticationMethod subclasses, since all the authentication methods described in the AuthenticationMethod class perform mutual authentication. 4.3.3.4 The NetworkAuthentication subclass The NetworkAuthentication subclass is disjoint from all its siblings and from the EAP- SIM and LEAP classes. It is not disjoint from the PEAP and EAP-TLS classes, since these methods can perform authentication of only the network. 4.3.3.5 The PasswordBased subclass
  • 85. An Ontology for Generic Wireless Authentication 85 The PasswordBased subclass is disjoint from all its siblings, from the EAP-TLS, and EAP-SIM classes. It is not disjoint from the PEAP and LEAP classes, since password based authentication is what LEAP is based on, and PEAP can use an EAP password based method to authenticate the user. 4.3.3.6 The UserAuthentication subclass The UserAuthentication subclass is disjoint from all its siblings, from the EAP-TLS, and EAP-SIM authentication methods. It is not disjoint from the PEAP or LEAP classes, since these methods provide authentication of the user only, in conjunction with PEAP authentication. 4.3.4 The Certificate class disjoints The Certificate class is disjoint from all the classes in the ontology, since no other class in the ontology is-a Certificate. 4.3.5 The CertificateComponent class disjoints The CertificateComponent class is disjoint from all classes in the ontology, except for the Public Key subclass of the StaticKey subclass of the Key class. A public key is both a certificate component and a static key, therefore they are not declared as disjoint from each other. The PublicKey class has two super classes: the CertificateComponent class and the StaticKey class. 4.3.5.1 The IssuerName, SerialNumber, Signature, Subject, ValidFrom, ValidTo and PublicKey subclasses The IssuerName, SerialNumber, Signature, Subject, ValidFrom and ValidTo subclasses, are all disjoint from each other and their siblings. Nothing can be an issuer name and a serial number for example. These subclasses classes are also disjoint from the Algorithm class, since the algorithm class is not declared as disjoint from the CertificateComponent class. 4.3.5.2 The SignatureAlgorithm subclass The SignatureAlgorithm subclass is disjoint from all its siblings, and from the subclasses of the Algorithm class. Nothing can be a SignatureAlgorithm and a A3 algorithm.
  • 86. An Ontology for Generic Wireless Authentication 86 4.3.6 The Code class disjoints The Code class is disjoint from all the classes, except for the Number class. A code is-a number, therefore it is not declared as disjoint from the number class. The subclasses of the code class are all disjoint from each other, and also the subclasses of the number class are disjoint from the subclasses of the code class. E.g. The CountryCode subclass of the Code class is disjoint from the MSISDN subclass, of the number class, because a country code is not an MSISDN number. 4.3.7 The Database class disjoints The Database class is disjoint from all classes in the ontology, no class in the ontology, except for the subclasses of the class DataBase is-a database. The subclasses of the DataBase class are disjoint from each other. A HLR database is not a user database, an authentication database or a home subscriber server database. 4.3.8 The Identity class disjoints The Identity class is disjoint from all classes of the ontology, except for the UserData class. An identity can represent user data; therefore the classes are not disjoint from each other. The subclasses of the Identity class are all disjoint from each other e.g. an IMSI is not a NAI. Subclasses of the UserData class are also disjoint from the subclasses of the Identity class. A password for example is not a public user identity. 4.3.9 The Key class disjoints The Key class is disjoint from all the classes in the ontology, except for the PublicKey class of the CertificateComponent class. 4.3.9.1 The DerivedKey subclass The DerivedKey subclass is disjoint from all of its siblings, (GeneratedKey class and StaticKey class). The subclasses of the DerivedKey class are also disjoint from each other. 4.3.9.2 The GeneratedKey subclass The GeneratedKey class is disjoint from its siblings, (DerivedKey class and StaticKey class). The subclasses of the GeneratedKey class are also declared as disjoint from each other.
  • 87. An Ontology for Generic Wireless Authentication 87 4.3.9.3 The StaticKey subclass The StaticKey class, as the DerivedKey and GeneratedKey classes is disjoint from its siblings. The subclasses of the StaticKey class are also disjoint from each other. 4.3.10 The Network class disjoints The Network class is disjoint from all the classes in the ontology. A network is not any other type of concept declared in the ontology, therefore it must be declared as disjoint from all the other classes. 4.3.11 The Number class disjoints The Number class is disjoint from all the classes in the ontology, except for the Code class. A number is-a code and is therefore not declared as disjoint from the code class. The subclasses of the number class are all disjoint from each other, and the subclasses of the code class are also disjoint from the subclasses of the number class. 4.3.12 The Service class disjoints The Service class is disjoint from the other classes in the ontology. A Service is not any other type of concept defined in the ontology, therefore it is declared as disjoint. 4.3.12.1 The BasicService subclass The BasicService subclass is disjoint from the SupplementaryService subclass and its subclasses. Nothing can be both a BasicService and a SupplementaryService. 4.3.12.2 The SupplementaryService subclass The SupplementaryService subclass is disjoint from the BasicService subclass, for the same reason mentioned above. The subclasses of the Supplementary subclass are also disjoint from each other. E.g. the CallBarring and CallDivert subclasses are disjoint from each, other because a call barring service is not a call diverting service. 4.3.12.3 The MultimediaService subclass The MutilmediaService subclass also contains subclasses, which are all disjoint from each other. E.g. the VideoDownload and AudioDownload subclasses are disjoint from each other, because a video download service is not an audio download service.
  • 88. An Ontology for Generic Wireless Authentication 88 4.3.13 The UserData class disjoints The UserData class is disjoint from all classes of the ontology, except for the Identity class. User data can represent an Identity, therefore the UserData class and the Identity class are not disjoint from each other. Subclasses of the UserData class are disjoint from each other. Subclasses of the Identity class are also disjoint from the subclasses of the UserData class. 4.4 Inconsistencies from Disjoint classes Declaring classes as disjoint could result in reasoning errors that state that a class is inconsistent. For example, the following figure illustrates an inconsistency in the PublicKey class. Figure 19: Incorrect disjoint definition - Inconsistent class This inconsistency appeared because the Key and CertificateComponent class were declared as super classes of the PublicKey class. At the same time, the whole CertificateComponent class was declared as disjoint from the Key class.
  • 89. An Ontology for Generic Wireless Authentication 89 The solution to this problem was to make sure that the PublicKey class was not declared as disjoint in the Key class, and also in the CertificateComponent class. 4.5 Class Properties Properties link two individuals together, by describing a certain relationship between them. The Ontology consists of some of the following properties and inverse properties that describe how classes are related to each other: (Appendix A lists all the properties in the ontology) 4.5.1 hasIdentity ↔ isIdentityOf The hasIdentity property describes that an individual, has the value of another individual as its identity. The inverse property describes that an individual is an identity of another individual. 4.5.2 hasNetworkIdentity ↔ isNetworkIdentityOf The hasNetworkIdentity property describes that one individual or more, has the value of another individual or more as its network identity. The inverse property implies the same, but in reverse order (i.e. an individual is the network identity of another individual). 4.5.3 hasUserName ↔ isUserNameOf The hasUserName property describes that an individual, has the value of another individual as its user name. The inverse property describes that an individual is a user name of another individual. 4.5.4 hasAuthenticationMethod ↔ isAuthenticationMethodOf The hasAuthenticationMethod property describes that one or more individuals, are related to one or more other individuals via this property. It means that an individual has another individual, with an authentication method as it value via the hasAuthenticationMethod property. The inverse property implies that an individual is an authentication method of another individual.
  • 90. An Ontology for Generic Wireless Authentication 90 4.5.5 hasAuthenticationType ↔ isAuthenticationTypeOf The hasAuthenticationType property, describes that an individual, has the value of another individual as its authentication type. The inverse property, describes that an individual, is an authentication type of another individual. 4.5.6 hasCertificate ↔ isCertificateOf The hasCertificate property, describes that an individual, has the value of another individual as its certificate. The inverse property describes that an individual, is a certificate of another individual. 4.5.7 hasPassword ↔ isPasswordOf The hasPassword property, describes that an individual, has the value of another individual as its password. The inverse property, describes that an individual, is a password of another individual. 4.5.8 hasBasicService ↔ isBasicServiceOf The hasBasicService property, describes that an individual, has the value of another individual as its basic service. The inverse property, describes that an individual, is a basic service of another individual. 4.5.9 hasSupplementaryService ↔ isSupplementaryServiceOf The hasSupplementaryService property, describes that an individual, has the value of another individual as its supplementary service. The inverse property, describes that an individual, is a supplementary service of another individual. 4.5.10 hasDatabase ↔ isDatabaseOf The hasDatabase property, describes that an individual, has the value of another individual as its database. The inverse property, describes that an individual is a database of another individual.
  • 91. An Ontology for Generic Wireless Authentication 91 4.5.11 hasChallenge ↔ isChallengeOf The hasChallenge property, describes that an individual, has the value of another individual as its challenge. The inverse property, describes that an individual, is a challenge of another individual. 4.5.12 hasSecretKey ↔ isSecretKeyOf The hasSecretKey property, describes that an individual, has the value of another individual as its secret key. The inverse property, describes that an individual, is a secret key of another individual. 4.5.13 hasExpectedResponse ↔ isExpectedResponseOf The hasExpectedResponse property, describes that an individual, has the value of another individual as its expected response. The inverse property, describes that an individual, is an expected response of another individual. 4.5.14 hasTriplets ↔ isTripletsOf The hasTriplets property, describes that an individual, has the value of other individuals as its triplets. The inverse property, describes that individuals, are triplets of another individual. 4.5.15 hasInput ↔ isInputOf The hasInput property, describes that an individual, has the value of another individual as its input. The inverse property, describes that an individual, is an input of another individual. 4.5.16 hasOutput ↔ isOutputOf The hasOutput property, describes that an individual, has the value of another individual as its output. The inverse property, describes that an individual, is an output of another individual.
  • 92. An Ontology for Generic Wireless Authentication 92 4.5.17 hasNumber ↔ isNumberOf The hasNumber property, describes that an individual, has the value of another individual as its number. The inverse property, describes that an individual, is a number of another individual. 4.5.18 hasSubscriber ↔ isSubscriberOf The hasSubscriber property, describes that an individual, has the value of another individual as its subscriber. The inverse property, describes that an individual, is a subscriber of another individual. 4.5.19 Stores ↔ isStoredIn The Stores property, describes that an individual, stores the value of another individual. The inverse property, describes that an individual, is stored by another individual. 4.5.20 hasAlgorithm ↔ isAlgorithmOf The hasAlgorithm property, describes that an individual, has the value of another individual as its algorithm. The inverse property, describes that an individual, is an algorithm of another individual. 4.6 Identification of a new is-a relationship After the definition of the class properties, a new is-a relationship was identified. This relationship should have been expressed in a super class – subclass relationship. The NAI is an Identity, and belongs to the Identity class. However, the NAI is also a Private user Identity and must therefore be a subclass of the class PrivateUserIdentity. Thus NAI has two super classes, namely Identity and PrivateUserIdentity. The ontology process continues in this manner, with the identification of new concepts and new hierarchies. It is an iterative process.
  • 93. An Ontology for Generic Wireless Authentication 93 4.7 Initial ontology tests and reasoning Until this point, only the classes and properties of the ontology have been defined. Initial testing and reasoning of the ontology is performed, which checks whether the properties have been well defined and also checks for the consistencies between classes of the ontology. The following figures illustrate a list of errors generated from the ontology tests and from reasoning: Figure 20: Ontology tests and reasoning results The NAI is inconsistent due to the fact that it was identified and declared as a subclass of the PrivateUserIdentity and that it is still disjoint from its siblings. Removing the disjoint characteristic from the NAI makes the class consistent. Inconsistent classes are marked with a red circle around the class name.
  • 94. An Ontology for Generic Wireless Authentication 94 4.8 Property Restrictions and Defining Classes Classes are described and defined by creating restrictions on the defined properties. Properties restrict the individuals that belong to a specific class, thus enabling the description of the characteristics of a class. A class restriction takes the following form; (the class name (the restriction, the property, the filler)). The class name is the class that the restriction is defined for, the restriction can be either one of the following (an existential quantifier, a universal quantifier, a has value restriction, equal cardinality, minimum or equal cardinality and maximum or equal cardinality) the property is any property defined for the classes, and the filler can be a class and individual or instance of a class or a data type). The following, explains in detail some classes and how they are defined: 4.8.1 Restrictions defining the f1 class The following figure illustrates the conditions defined for the f1 class: Figure 21: f1 Class Restrictions
  • 95. An Ontology for Generic Wireless Authentication 95 The f1 class belongs to the Algorithm class, which means that f1 is an algorithm. The f1 algorithm has an AMF as its authentication management field, and all authentication management fields are AMF, this is described with the; f1(∀ hasAuthenticationManagementField AMF) expression. Where ∀, expresses a universal quantifier, and in this case means “only” (only AMF as an authentication management field). The hasAuthenticationManagementField is the property, and the AMF is a class, which is a subclass of the DerivedKey class. The f1 class, only has the XMAC key as its expected message authentication code; f1(∀ hasExpectedMessageAuthenticationCode XMAC). And only the MAC key as its message authentication code; f1(∀ hasMessageAuthenticationCode MAC). It only has the Ki Key as its secret key, only the RAND key as its random number, and only the SQN key as its sequence number; f1(∀ hasSecretKey Ki,, ∀ hasRandNumber RAND, (∀ hasSequenceNumber SQN). This relationship, can also be described as; f1(hasSecretKey (allValuesFrom Ki, hasRandNumber allValuesFrom RAND, hasSequenceNumber allValuesFrom SQN). The f1 class has only SQN “AND” AMF “AND” Ki “AND” RAND keys as its inputs, this is expressed by the following expression; f1(∀ hasInput SQN, ∀ hasInput AMF, ∀ hasInput Ki, ∀ hasInput RAND), or; f1(hasInput (allValuesFrom SQN, allValuesFrom AMF, allValuesFrom Ki, allValuesFrom RAND)). The f1 class is only an algorithm of the UMTS network, this is expressed as f1(∀ isAlgorithmOf UMTS), or; f1(isAlgorithmOf (allValuesFrom UMTS). The f1 class is stored in BOTH the AuC, and the HSS; f1(∀ isStoredIn AuC, ∀ isStoredIn HSS), or; f1(isStoredIn (allValuesFrom AuC, allValuesFromHSS). The output of the f1 class can be either the XMAC key or the MAC key, this is expressed by the following expression; f1(∃ hasOutput XMAC ⊔ MAC), or f1(someValuesFrom XMAC ⊔ MAC).
  • 96. An Ontology for Generic Wireless Authentication 96 4.8.2 Restrictions defining the EAP-SIM class The following figure illustrates the conditions defined for the EAP-SIM class: Figure 22: EAP-SIM Class Restrictions The EAP-SIM class belongs to the AuthenticationMethod class. This indicates that EAP- SIM is an authentication method. The EAP-SIM class has a challenge response and a mutual authentication type of authentication. This is expressed by; EAP-SIM(∀ hasAuthenticationType ChallengeRepsonse, ∀ hasAuthenticationType MutualAuthentication) or; EAP-SIM(hasAuthenticationType (allValuesFrom ChallengeRepsonse, allValuesFrom MutualAuthentication). The EAP-SIM class, has the RAND and MAC keys as its challenge, and the MAC_RAND and MAC_XRES keys as its challenge response, this is expressed by; EAP-SIM(∀ hasChallenge RAND, ∀ hasChallenge MAC) or EAP-SIM(hasChallenge (allValuesFrom RAND, allValuesFrom MAC)) and EAP-SIM(∀ hasChallengeResponse MAC_RAND, ∀ hasChallengeResponse MAC_XRES) or; EAP-
  • 97. An Ontology for Generic Wireless Authentication 97 SIM(hasChallengeResponse (allValuesFrom MAC_RAND, allValuesFrom MAC_XRES) respectively. The MAC_RAND, the random message authentication code and MAC_XRES, the expected response message authentication code, are described in the EAP-SIM class by EAP-SIM(∀ hasRandomMessageAuthenticationCode MAC_XRES) and EAP-SIM(∀ hasExpectedResponseMessageAuthenticationCode MAC_RAND) respectively. The UserNetworkIdentity is the network identity of an EAP-SIM method. This restriction is defined in the following way; EAP-SIM(∀ hasNetworkIdentity UserNetworkIdentity). The triplets (RAND “AND” Kc “AND” XRES) are the triplets used by the EAP-SIM method. This is expressed by; EAP-SIM (∀ hasTriplets RAND, ∀ hasTriplets Kc, ∀ hasTriplets XRES). The EAP-SIM method is an authentication method of BOTH GSM and WLAN networks; this is expressed by; EAP-SIM(∀ isAuthenticationMethodOf GSM, ∀ isAuthenticationMethodOf WLAN).
  • 98. An Ontology for Generic Wireless Authentication 98 4.8.3 Restrictions defining the Subscriber class The following figure illustrates the conditions defined for the Subscriber class: Figure 23: Subscriber Class Restrictions The Subscriber class only has individuals, as user data that belong to the UserData class. The UserData class contains all personal details of a user, e.g. first name, last name, address, country, etc…The following expression describes that the subscriber class only has UserData individuals, as its user data; Subscriber(∀ hasUserData UserData). A subscriber has a user name, IMSI and UserNetworkIdentity as identities. This is expressed by; Subscriber(∀ hasIdentity UserName, ∀ hasIdentity IMSI, ∀ hasIdentity UserNetworkIdentity). A subscriber has a public user identity; Subscriber(∀ hasPublicUserIdentity PublicUserIdentity), and a private user identity; Subscriber(∀ hasPrivateUserIdentity PrivateUserIdentity).
  • 99. An Ontology for Generic Wireless Authentication 99 A subscriber is subscribed to basic, supplementary and multimedia services; Subscriber(∀ isSubscribedTo BasicService, ∀ isSubscribedTo SupplementaryService, ∀ isSubscribedTo MultimediaService). A subscriber is a subscriber of GSM, UMTS and WLAN networks; Susbscriber(∀ isSubscriberOf UMTS, ∀ isSubscriberOf GSM, ∀ isSubscriberOf WLAN). 4.8.4 Restrictions defining the IMSI class The following figure illustrates the conditions defined for the IMSI class: Figure 24: IMSI Class Restrictions The IMSI class is a member of the Identity class, meaning that an IMSI is an identity. The IMSI has a mobile station ISDN number as its number; IMSI(∀ hasNumber MSISDN). The IMSI is made up of the following parts; the mobile station identification
  • 100. An Ontology for Generic Wireless Authentication 100 number, and the mobile network code and the mobile country code. This is expressed by IMSI(∀ hasPart MobileStationIdentificationNumber, ∀ hasPart MobileNetworkCode, ∀ hasPart MobileCountryCode). The IMSI is an identity of a subscriber and is part of a user network identity, this is expressed by; IMSI(∀ isIdentityOf Subscriber) and; IMSI(∀ isPartOf UserNetworkIdentity) respectively. The IMSI is stored in the HLR, AuC and the HSS, this is expressed by IMSI(∀ isStoredIn HLR, ∀ isStoredIn AuC, ∀ isStoredIn HSS).
  • 101. An Ontology for Generic Wireless Authentication 101 4.9 Asserted and Inferred Hierarchy An asserted hierarchy is a manually defined view of the ontology. When classifying an ontology with a resoner, the reasoner performs automatic computation of the defined ontology and creates an inferred hierarchy of the ontology. The following figure illustrates the asserted and inferred hierarchy in the ontology: Figure 25: Asserted and Inferred Hierarchy In the inferred hierarchy, the NAI is now the subclass of the PrivateUserIdentity class, this is because in the asserted hierarchy it was defined to be a child of both the PrivateUserIdentity, and the Identity class, which is a super class of the PrivateUserIdentity class. The changes are marked in blue in the inferred hierarchy.
  • 102. An Ontology for Generic Wireless Authentication 102 5 Installation and Testing 5.1 Installation Guidelines In order to create the ontology, an editor to edit ontologies was needed. The ontology editor used for this thesis was the Protégé Tool version 3.0 available from protégé.stanford.edu. The Racer tool was used for reasoning and classification of the ontology. Several versions of the racer tool exist; the current version is RacerPro available from www.racer- systems.com. For the purpose of this thesis the racer reasoner version 1.7.23 For the graph visualization of the ontology, the GraphViz tool and the OWL-Viz plug-in were used. GraphViz is available at http://www.graphviz.org/ and the OWL-Viz plug- in is a component of the Protégé OWL plug-in from protégé.stanford.edu. The installation of the Protégé tool is simple; after following the installation procedures that appear on the screen, the editing tool is ready for use. For visualization, the GraphViz Tool should be installed (follow screen instructions) and the OWL-Viz plugin should configured to be used, this is done in the Protégé editor by clicking on Project Configure… and selecting the OWL-Viz Tab, and clicking on the OK button. Racer is a .exe file, which should be run with Protégé or when classifying the ontology is required. RacerPro can only be used upon registration and upon obtaining a license. 5.2 Loading the Ontology Two types of files for the generic wireless authentication ontology, namely a file with an extension of .owl, which is the file described in the Web Ontology Language and a file with an extension of .pprj, which is the protégé project file. To load the .pprj file, simply click on File Open and choose the file from the appropriate directory. To load the .owl file, click on File Build New Project and then select the owl file from the appropriate directory.
  • 103. An Ontology for Generic Wireless Authentication 103 5.3 Encountered Problems The following describes some of the problems encountered while developing the ontology: 5.3.1 Enumerated Classes It was not possible to define an enumerated class. The complete ontology was inconsistent upon the execution of the reasoner. The reason for the inconsistent ontology was because of the definition of two enumerated classes as follows: The f1AuCInput class, which was an enumerated class containing the inputs of the f1 algorithm on the AuC side. And the f1USIMInput class, which was an enumerated class containing the inputs of the f1 algorithm on the USIM side. The intention of this was to define a union of the f1 algorithm inputs, which takes the value of either the enumerated class f1AuCInput class, or the enumerated class f1USIMInput. Upon classification of the ontology (the execution of the reasoner), the ontology was classified as an OWL-FULL ontology, and not as an OWL-DL ontology, therefore the whole ontology was classified as inconsistent.
  • 104. An Ontology for Generic Wireless Authentication 104 The following figure illustrates the generated error: Figure 26: Enumerated Classes and OWL-FULL Error The ontology became consistent again after the removal of the enumerated classes. 5.3.2 Defining values for properties instead of individuals A private user identity, consists of a user name, the “@” sign and the realm (username@realm). Restrictions for the PrivateUserIdentity class have been defined, to identify the parts belonging to a private user identity. The following expressions are some definitions of the PrivateUserIdentity class; PrivateUserIdentity(∀ hasPart UserName, ∀ hasPart Realm. When defining an additional restriction, stating that the “@” sign is also part of the PrivateUserIdentity as follows; PrivateUserIdentity(∀ hasPart “@”) an inconsistency in the ontology occurred. This inconsistency stated that the ontology was classified as an OWL-FULL ontology, and not as an OWL-DL ontology. The following figure illustrates the generated error:
  • 105. An Ontology for Generic Wireless Authentication 105 Figure 27: Defining a value for an Object Property - OWL FULL Error 5.3.3 allValuesFrom, someValuesFrom and Disjoint classes Several inconsistencies appeared in the ontology when trying to define classes with the someValuesFrom restriction. For example, an inconsistency occurred, when defining that the PEAP class has an authentication type that can be either password based, or challenge response based authentication types, using the someValuesFrom restriction. The expression was as follows; PEAP(∃ hasAuthenticationType (PasswordBased ⊔ ChallengeResponse)). This expression returned an inconsistency in the PEAP class. However, when using the allValuesFrom restriction for the password based and challenge response base classes, the PEAP class was no longer inconsistent. PEAP(∀ hasAuthenticationType PasswordBased, ∀ hasAuthenticationType ChallengeResponse).
  • 106. An Ontology for Generic Wireless Authentication 106 The same rule holds when trying to define that the f1 algorithm can be stored in either the AuC or the HSS. f1(∃ isStoredIn (AuC ⊔ HSS), this rule returns an inconsistency. Therefore, it was defined that the f1 algorithm is stored in BOTH the AuC and the HSS. This type of error also occurred, if classes were declared as disjoint from each other. When removing the disjointness of classes, it was possible to define some restrictions with the someValuesFrom restriction. An example of which is given; The A3 and f2 algorithms generate the responses XRES and RES on the AuC and USIM side respectively. When defining that the A3 algorithm takes either XRES, or RES as its output value, via the following expression; A3(∃ hasOutput XRES ⊔ RES) the A3 class was consistent. However, when defining the same rule for the f1 algorithm; f1(∃ hasOutput XRES ⊔ RES) an inconsistency in both the A3 and f1 algorithm classes arose. This was because the A3 and f1 algorithms were declared as disjoint from each other. When removing the disjointness of the A3 and f1 algorithm, the reasoner did not classify these classes as inconsistent. However, an A3 algorithm is not an f1 algorithm; therefore they must be defined as disjoint. 5.3.4 Defining Cardinalities Inconsistencies in the PrivateUserIdentity, PublicUserIdentity and PublicServiceIdentity classes occurred, when defining cardinalities for each class. The definition that a subscriber can have only one private user identity, and one or more public user identities, was not possible without returning any inconsistencies. The following rule was defined; Subscriber(= hasPrivateUserIdentity =1) and Subscriber(≥ hasPublicUserIdentity ≥ 1) this rule did not hold true. Another attempt, was to define that each multimedia service is assigned to exactly one public service identity, the following rule was defined; MultimediaService(= hasPublicServiceIdentity =1) this rule did not hold true as well, and resulted in an inconsistency.
  • 107. An Ontology for Generic Wireless Authentication 107 6 Summary and Conclusions 6.1 Summary This thesis addressed the issues of the current status in telecommunication networks today, and discussed an approach of how to better restructure telecommunication networks, in order to achieve less complexity and better data management. It also addressed the separation of data, from the applications and proposed a common view and understanding of physically and logically storing the data. In particular subscriber data, which today, is distributed among several network nodes, and is not accessible by all applications. Therefore, the Next Generation Profile Register was introduced as one method of restructuring telecommunication networks today. Providing a logical description of subscriber data was the motivation of this thesis. The domains concerned for modelling the subscriber data, were the authentication specific data of a certain subscriber in GSM, UMTS and WLAN networks. The analysis of GSM, UMTS and WLAN networks was performed, especially in terms of authentication, and in terms of what parameters of a subscriber is stored, and in which profile registers. In order to describe the data, it was also necessary to understand the relationships between subscriber data, stored in the registers. It was also necessary to provide a meaning for each term by defining rules. Evaluation of different modelling methods was also performed. The decision of describing the data in a semantic way was taken and in particular, using the OWL language, due to the way data can be logically described, related and shared among a particular domain. Therefore, the analysis of the Semantic Web, and the approaches used to describe data via the semantic web were also analysed. For the purpose of this thesis, the Web Ontology Language was chosen to describe the data using the Protégé Tool. The description of data was performed, by building an ontology, which is a knowledge base that describes data. The domain of GSM, UMTS and WLAN networks was broken down into classes and properties, each class representing a concept, and each property representing a link between the concepts. The definition of each class, was performed by
  • 108. An Ontology for Generic Wireless Authentication 108 defining restrictions for each class, indicating how classes are related to each other and which individuals can belong to a certain class. The ontology provides a logical description of the data, stored in profile registers of GSM, UMTS and WLAN networks in one logical view. Testing of the ontology was performed using a reasoning tool named Racer, which was used to classify the ontology, and to check for inconsistencies in the ontology. Using OWL to describe data provides better expressivity of data in comparison to other modelling techniques. It also enables the re-use and sharing of data among domains, and enables an easier translation of data between systems. This simplifies the complexity of managing data between systems in current networks today, and solves the problem of closed vendor specific systems. It also enables an easier integration of data from several other domains and for the integration of future networks. 6.2 Further research The ontology describes authentication specific data for GSM, UMTS and WLAN data. However, subscriber data stored in WLAN networks needs to be further analysed, further defined, and further described in the ontology. The relationships between the concepts also need to be verified from an external point of view, and several discussions upon the approach for defining the ontology from a domain expert point of view needs to be performed [49]. Description of other types of data, in the above mentioned domains also needs to be integrated into the ontology. E.g. data related to specific applications, location management, etc…
  • 109. An Ontology for Generic Wireless Authentication 109 The following figure illustrates the future view of the ontology with the integration of several other domains: CRM Billing Admin Ontology for Subscriber Data TTYPE WLAN Bluetooth GSM/UMTS Figure 28: Integration of Future domains Other domains other than the ones previously mentioned include Bluetooth networks, description and integration of TTYPE services, which describe the type of mobile device a subscriber has (the type of screen; color, black and white, size, etc…). This is used to determine what type of device a subscriber owns, in order to push multimedia services to the subscriber. Other domains include, but are not limited to administrational data, Customer Relationship Management (CRM) data, and Billing data. 6.3 Areas of application Ontologies are mainly used and widespread in the bio-medical sector, where several ontologies in this field have been developed, for the use of describing the human anatomy and biological terms. Several other ontologies have been defined, which include but are not limited to the following; ontologies for ethology, which describe the behaviour of animals [63], ontologies for describing mathematical terms, ontologies that describe the different parts of a camera, and also an ontology defined by the National Cancer Institute, which is an NCI Thesaurus. More examples of ontologies can be found in [64].
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  • 113. An Ontology for Generic Wireless Authentication 113 [34] Remote Authentication Dial In User Service (RADIUS), RFC 2138, C. Rigney Livingston, A. Rubens Merit, W. Simpson Daydreamer, S. Willens Livingston, The Internet Engineering Taskforce, http://www.ietf.org/rfc/rfc2138.txt, 9th September 2005. [35] Using RADIUS for WLAN Authentication, Part 1, Article, Lisa Phifer, http://www.wi-fiplanet.com/tutorials/article.php/3114511, 9th September 2005. [36] What is PKI?, Definition, webopedia, http://www.webopedia.com/TERM/P/PKI.html, 9th September 2005. [37] Definition of Public Key Infrastructure, Definition, M-Tech Information Technology Inc., http://mtechit.com/concepts/public_key_infrastructure.html, 9th September 2005. [38] Introduction to Digital Certificates, Tutorial, veriSign Australia Pty Ltd., http://www.verisign.com.au/repository/tutorial/digital/intro1.shtml, 9th September 2005. [39] X.509 Certificates and Certificate Revocation Lists (CRLs), Article, Sun Microsystems Inc., http://java.sun.com/j2se/1.3/docs/guide/security/cert3.html, 9th September 2005. [40] The Semantic Web, Article, Tim Berners Lee, James Hendler and Ora Lassila, Scientific American, May 17, 2001, http://www.scientificamerican.com/print_version.cfm?articleID=00048144-10D2- 1C70-84A9809EC588EF21, 12th September 2005. [41] The Semantic Web: An Introduction, Tutorial, Sean B. Palmer, http://infomesh.net/2001/swintro/, 12th September 2005. [42] Semantic Web, Overview, W3C, http://www.w3.org/2001/sw/, 12thSeptember 2005. [43] Ontologies Come of Age, Paper, Deborah L. McGuinness, Knowledge Systems Laboratory, Stanford University, CA., http://www.ksl.stanford.edu/people/dlm/papers/ontologies-come-of-age-mit-press- (with-citation).htm, 12th September 2005. [44] Ontology, Definition, Webster’s Revised Unabridged Dictionary (1913). [45] Ontology, Definition, Merriam – Webster Online Dictionary, http://www.m- w.com/cgi-bin/dictionary?book=Dictionary&va=Ontology&x=0&y=0, 12th September 2005.
  • 114. An Ontology for Generic Wireless Authentication 114 [46] Using Ontologies, Enabling Knowledge Sharing and Reuse on the Semantic Web, Technical Report, Jos de Bruijn, Digital Enterprise Research Institute, Austria, http://www.deri.at/publications/techpapers/documents/DERI-TR-2003-10-29.pdf, 12th September 2005. [47] Ontology, Definition, The Collaborative International Dictionary of English v.0.48, http://dict.diodesign.co.uk/index.pl, 12th September 2005. [48] A Translational Approach to Portable Ontology Specifications, Technical Report, Thomas R. Gruber, Knowledge Systems Laboratory, http://tomgruber.org/writing/ontolingua-kaj-1993.pdf, 12th September 2005. [49] Ontology Development 101: A Guide to Creating your First Ontology, Publication, Natalya F. Noy and Deborah L. McGuinness, Stanford University, Stanford CA., http://protege.stanford.edu/publications/ontology_development/ontology101-noy- mcguinness.html, 12th September 2005. [50] Dieter Fensel, Ontologies: A Silver Bullet for Knowledge Management and Electronic Commerce, Springer-Verlag Berlin Heidelberg 2004. [51] OWL Web Ontology Language Overview, Recommendation, Deborah McGuinness, Frank van Harmelen, W3C, http://www.w3.org/TR/owl-features/, 12th September 2005. [52] OWL Web Ontology Language Guide, Recommendation, Michael K. Smith, Chris Welty, Deborah L. McGuinness, W3C, http://www.w3.org/TR/owl-guide/, 12th September 2005. [53] A Practical Guide to Building OWL Ontologies Using the Protégé-OWL Plugin and CO-ODE Tools, Edition 1.0, Guide, Matthew Horridge, Holger Knublauch, Alan Rector, Robert Stevens, Chris Wroe, The University of Manchester, Stanford University, http://www.co-ode.org/resources/tutorials/ProtegeOWLTutorial.pdf, 12th September 2005. [54] Protégé Official Website, http://protege.stanford.edu/, 12th September 2005. [55] The Protégé OWL Plugin: An Open Development Environment for Semantic Web Applications, Publication, Holger Knublauch, Ray. W. Fergerson, Natalya F. Noy and Mark A. Musen, Stanford Medical Informatics, Stanford School of Medicine, Stanford – CA., http://protege.stanford.edu/plugins/owl/publications/ISWC2004-protege- owl.pdf, 12th September 2005. [56] RacerPro User’s Guide, Version 1.8, User Guide, Racer Systems GmbH & Co. KG, www.racer-systems.com, 12th September 2005.
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  • 116. An Ontology for Generic Wireless Authentication 116 Abbreviations 2G Second Generation Networks 2.5G Second and a half Generation Networks 3G Third Generation Networks 802.11 A WLAN network standard defined by the IEEE 802.1X Standard for securing WLAN networks defined by the IEEE A A3 An Authentication Algorithm in GSM Networks A5 A Ciphering/Deciphering Algorithm in GSM Networks A8 A Key Generation Algorithm in GSM Networks AAA Authentication Authorization and Accounting ABoxes Represent Instances of TBoxes AI Artificial Inteliigence AK Anonymity Key AKA Authentication and Key Agreement AMF Authentication Management Field AP Access Point API Application Programming Interface AuC Authentication Center AUTN Authentication Token B BSC Base Station Controller BSS Base Station Subsystem BTS Base Transceiver Station C CA Certifying Authority CC Country Code CK Cipher Key CN Core Network CRM Customer Relationship Management CS Circuit Switched ‘ D DL Description Logics DRNC Drifting Radio Network Controller E EAP Extensible Authentication Protocol EAP-AKA EAP-Authentication and Key Agreement EAP-CHAP EAP-Challenge Handshake Authentication Protocol
  • 117. An Ontology for Generic Wireless Authentication 117 EAP-MD5 EAP-Message Digest 5 EAP-OL EAP Over LAN EAP-SIM EAP-Subscriber Identity Module EAP-TLS EAP-Transport Layer Security F f1 – f5 UMTS Authentication Functions G GGSN Gateway GPRS Support Node GMSC Gateway Mobile Switching Center GPRS General Packet Radio Service GraphViz Graphical Visualization GSM Global System for Mobile Communication H HLR Home Location Register HLR-Number Logical HLR Address HSS Home Subscriber Server HTML Hypertext Markup Language I I-CSCF Interrogating Call Session Control Function ID Identification IEEE Institute of Electrical and Electronics Engineers IK Integrity Key INMSI International Mobile Station Identity IMS IP Multimedia Subsystem IMSI International Mobile Subscriber Identity IP Internet Protocol ISDN Integrated Services Digital Network ISIM IMS Subscriber Identity Module ISN Individual Subscriber Number K K Secret Key Kc Cipher Key Ki Secret Key L LEAP Lightweight Extensible Authentication Protocol M MAC Message Authentication Code
  • 118. An Ontology for Generic Wireless Authentication 118 MAC_RAND Random Message Authentication Code MAC_XRES Expected Message Authentication Code Response MCC Mobile Country Code ME Mobile Equipment MMS Multimedia Messaging Service MNC Mobile Network Code MS Mobile Station MSC Mobile Switching Center MSIN Mobile Station Identification Number MSISDN Mobile Station Integrated Services Digital Network Number N NAI Network Access Identifier NCI National Cancer Institute NDC National Destination Code NGN Next Generation Network NGPR Next Generation Profile Register Node B UMTS Base Station NSS Network Switching Subsystem O OSS Operation Subsystem OWL Web Ontology Language OWL-DL OWL- Description Logics OWL-Viz OWL-Visualization P PC Personal Computer P-CSCF Proxy Call Session Control Function PDA Personal Digital Assistant PEAP Protected Extensible Authentication Protocol PIN Personal Identification Number PKI Public Key Infrastructure PLMN Public Land Mobile Network PPRJ Protégé Project Extension PS Packet Switched PSTN Public Switched Telephone Network P-TMSI Packet-Temporary Mobile Subscriber Identity R RACER RenamedABox and Concept Expression Reasoner RacerPro RenamedABox and Concept Expression Reasoner Professional RADIUS Remote Authentication Dial-In User Service RAND Random Number RDF Resource Description Framework RES Response RNC Radio Network Controller
  • 119. An Ontology for Generic Wireless Authentication 119 RNS Radio Network Subsystem RSS Radio Subsystem S S-CSCF Serving Call Session Control Function SGSN Serving GPRS Support Node SIM Subscriber Identity Module SMS Simple Message Service SN Serving Network SN Subscriber Number SQN Sequence Number SRNC Serving Radio Network Controller SSL Secure Socket Layer T TBoxes Represents Ontologies TLS Transport Layer Security TMSI Temporary Mobile Subscriber Identity TTYPE Mobile Terminal Type U UML Unified Modelling Language UMTS Universal Mobile Telecommunication System URL Universal Resource Locator USB Universal Serial Bus USIM Universal Subscriber Identity Module UTRAN UMTS Terrestrial Radio Access Network V VLR Visitor Location Register W W3C World Wide Web Consortium WEP Wired Equivalent Privacy WLAN Wireless Network WPA Wi-Fi Protected Access X X.509 Standard for Digital Certificates XMAC Expected Message Authentication Code XML Extensible Modeling Language XRES Expected Response
  • 120. An Ontology for Generic Wireless Authentication 120 Appendix A Appendix A lists the classes and subclasses of the ontology Class Subclass Subclass of subclass Algorithm A3 n/a A8 F1 F1_ F2 F3 F4 F5 F5_ AuthenticationMethod EAP-SIM n/a EAP-TLS LEAP PEAP AuthenticationType CertificateBased n/a ChallengeResponse MutualAuthentication NetworkAuthentication PasswordBased UserAuthentication Certificate n/a n/a CertificateComponent IssuerName n/a PublicKey SerialNumber Signature SignatureAlgorithm Subject ValidFrom ValidTo Version Code CountryCode n/a MobileCountryCode MobileNetworkCode NationalDestinationCode Database AuC n/a HLR HSS UserDatabase Identity IMSI n/a NAI PrivateUserIdentity NAI PublicServiceIdentity n/a UserNetworkIdentity URL Realm
  • 121. An Ontology for Generic Wireless Authentication 121 IPAddress UserName Key DerivedKey AK AMF AUTN IK Kc MAC MAC_RAND MAC_XRES RES XMAC XRES GeneratedKey RAND SQN StaticKey Ki PrivateKey PublicKey Network GSM n/a IMS UMTS WLAN Number FixedTelephoneNumber n/a HLRNumber MSISDN MobileSubscriberIdentificatio nNumber SubscriberNumber IndividualSubscriberNumber Service BasicService SMS Speech MutlimediaService AudioDownload AudioStream MMS VideoDownload VideoStream WebBrowsing SupplementaryService CallBarring CallDivert CallWaiting ConferenceCall CustomerCareBilling DataService UserData AccountHolder n/a AccountNumber BankCity BankCode BankCountry City Country FirstName
  • 122. An Ontology for Generic Wireless Authentication 122 HouseNumber LastName Password PostalCode SessionDuration State StreetName Subscriber n/a n/a
  • 123. An Ontology for Generic Wireless Authentication 123 Appendix B The following appendix lists the properties and the inverse of each property if applicable: Property Inverse Property has Algorithm isAlgorithmOf hasAnonymityKey isAnonymityKeyOf hasAuthenticationManagementField isAuthenticationManagementFieldOf hasAuthenticationMethod isAuthenticationMethodOf hasAuthenticationType isAuthenticationTypeOf hasBasicService isBasicServiceOf hasCertificate isCertificateOf hasChallenge isChallengeOf hasChallengeResponse isChallengeResponseOf hasData isDataOf hasDatabase isDatabaseOf hasExpectedMessageAuthenticationCode isExpectedAuthenticationCodeOf hasExpectedResponse isExpectedResponseOf hasExpectedResponseMessageAuthenticati isExpectedResponseMessageAuthentication onCode CodeOf hasIdentity isIdentityOf hasInput isInputOf hasIntegrityKey isIntegrityKeyOf hasIssuerName isIssuerNameOf hasMessageAuthenticationCode isMessageAuthenticationCodeOf hasMultimediaService isMultimediaServiceOf hasNetworkIdentity isNetworkIdentityOf hasNumber isNumberOf hasOutput isOutputOf hasPart isPartOf hasPassword isPasswordOf hasPrivateUserIdentity isPrivateUserIdentityOf hasPublicKey isPublicKeyOf hasPublicServiceIdentity isPublicServiceIdentityOf hasPublicUserIdentity isPublicUserIdentityOf hasQuintets isQuintetsOf hasRandNumber isRandNumberOf hasRandomMessageAuthenticationCode isRandomMessageAuthenticationCodeOf hasResponse isResponseOf hasSecretKey isSecretKeyOf hasSequenceNumber isSequenceNumberOf hasSerialNumber isSerialNumberOf hasSessionKey isSessionKeyOf hasSignature isSignatureOf hasSignatureAlgoritm isSignatureAlgoritmOf hasSubject isSubjectOf hasSubscriber isSubscriberOf
  • 124. An Ontology for Generic Wireless Authentication 124 hasSupplementaryService isSupplementaryServiceOf hasTriplets isTripletsOf hasUserName isUserNameOf hasValidityFrom isValidityFromFieldOf hasValidityUntil isValdityToFieldOf hasVersion isVersionOf isAssociatedWith n/a isSubscribedTo n/a isStoredIn stores

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