Data Integrity and Network Security in Wireless LAN/3G Integrated Networks

Transcription

1 Data Integrity and Network Security in Wireless LAN/3G Integrated Networks International Workshop on Internet Security and Management 2004 Sendai, Japan, Jan. 29, 2004 Abbas Jamalipour a.jamalipour The University of Sydney Australia

2 Contents 1. Mobile Internet and the Wireless LAN 2. Integrated Network Architecture 3. Security Arrangements 4. Concluding Remarks 2

3 Mobile Internet and the Wireless LAN 1

4 Wireless local area networks! Wireless LAN is becoming increasingly popular! Mobile users typical demands of information access is characterized by heavy data files and applications; W-LAN can provide mobility and speed at the same time! In major structured hot spots such as airports and rail stations, the mobile radio infrastructure support of data communications seems to be inadequate and expensive! For office users, mobility, simple and low-cost network scalability, and high-speed access are advantageous factors! For home users, advantages of mobility without new wiring and at the same time high-speed access are the key issues " W-LAN provides network flexibility: No infrastructure (ad hoc), single-cell network (BSS), or cellular topology (ESS) " Use of unlicensed spectrum reduces the user s cost 4

5 Mobile Internet using W-LANW! Simple structure and cost-efficient equipment involved in W-LAN can easily extend the fixed Internet into the mobile environment! Mobility is supported but in a limited scale; more than that is neither logically feasible nor economically efficient! Data integrity, user and network security, and billing methods are not sufficiently supported by current standards! Can be done (as it is undergoing) but this will add the complexity and cost of the network, resulting in lighter image of original advantages of W-LAN! Traffic is loosely controlled through multiple access scheme; more traffic requires better traffic management and licensed spectrum, adding the cost and network complexity! Co-located W-LANs could interferer each other easily 5

6 Mobile Internet using cellular networks! 2.5G/3G cellular systems will provide some infrastructure for the mobile Internet service, but not necessarily sufficient! Cellular deployment timetable was not fast enough! Cellular data rate growth does not follow the rapid increase in new applications bandwidth demand! Cellular tariffs are not easily reducible! Cellular radio access will remain the limiting factor in competing speed with wired network! Compatibility and roaming issues between IP networks and cellular systems are not necessarily resolved within cellularonly implementations! Need for hybrid networks 6

7 Hybrid networks! To support new and existing mobile Internet applications! Horizontal communication among existing access technology! cellular, cordless, W-LAN, short-range connectivity, wired! On a common platform to complement services of each other! Connected through a common, flexible, seamless IP-based core network (questionable but promising)! An advanced media access technology that connects the core network to different access technologies! Global roaming and inter-working between different access technologies both horizontal (intra-system) and vertical (inter-system) handover! Seamless, transparent service negotiation including mobility, security, quality (data rate, delay, dropping probability, etc) 7

8 Vision of a hybrid network cdmaone Private IP Network cdma2000 Core Global Internet Wireless LAN GSM ADSL IP Core Network Inter-Network Access Technology cdma2000 Access Network Satellite Backbone DECT GPRS/UMTS Core UMTS Access Network PSTN/ISDN 8

9 Short- and long-term solutions! Long-term solutions! Merging IP and cellular networks at core and access sides! Reducing dissimilarities in management of the two systems! Improving radio access technology! Global interconnection of cellular and IP networks! Short-term solutions! Use of available infrastructures and try to accommodate simple systems within individual cellular networks! Push of IP-oriented applications into cellular services! Gradual decrease in traffic load from non-ip services! Blend all traffic data into one mixed-type! All, in order to be prepared for longer-term solutions 9

10 Integrated Network Architecture 2

11 Wireless LAN! W-LAN: The most accessible network to start with the short-term solutions! Much higher speed than 3G systems: Mbps and above compared with 300 Kbps 2 Mbps! Close relation with the legacy wired IP networks (basically an extension)! Use of unlicensed spectrum and low-cost equipments that may enable low end-user tariffs too! Already deployed in major hot-spots and is rapidly expanding; easily deployable anywhere! Potential integrating elements in its architecture with cellular 3G systems! Advantage of huge research work undergoing toward its standardization and regulation, access control, and security 11

12 W-LAN and 3GPP! 3GPP has already started the initiative for cellular- Wireless LAN internetworking architecture.! To be included in the 3GPP Release 6 specifications! Issues that need to be considered:! Integrating a highly-standardized system such as UMTS with a loosely standardized network; i.e. the W-LAN! Standardize the W-LAN network architecture or its radio interface? Maybe not; keep it undefined! Integrating a multi-service network such as UMTS with mainly IP-service network of W-LAN! Whether the W-LAN should be administrated by the UMTS operator or treated just as a foreign network! User data routing and access to available services! UMTS CN versus IP backbone 12

13 W-LAN architecture AAA interface AAA server/ proxy External IP networks interfaces Users database Billing IP backbone network DHCP HTTP server DNS IP interface Gateway NT LAN bus Access Router Layer 2 distribution network W-LAN Extended Service Set (ESS) Access Point 1 Access Point 2 Mobile Nodes Mobile Nodes 13

14 W-LAN general architecture! DHCP to facilitate the W-LAN terminal IP address! DNS to resolve Internet fully equipped domain name (FQDN) addresses into IP addresses! Gateway NT (network address and port translation) to external networks (Internet)! Using W-LAN private-space IP address and enabling services offered by external networks at the same time! HTTP server for local application-level services! Billing system for accounting! Access point: A layer 2 bridge between and the Ethernet! Security: using WEP, IEEE x/802.11i, RADIUS 14

15 User subscription! 3GPP! A heavily worked area for all subscriber s charging and billing systems using SIM/USIM smart cards! User database kept at home subscriber servers (HSS) for IP and other packet services over the packet-switched CN! Establishment of global roaming among 3G operators! Overall, not to compromise such a high-level of security just for a new interworking domain! Concluded that! The W-LAN needs to reuse the 3GPP subscription system! Equipping a W-LAN terminal with SIM/USIM! Making the AAA signaling a roaming case, where all subscription services will be provided by the 3GPP HSS 15

16 Authentication and authorization! 3GPP! Use of (U)SIM card for subscriber authentication for network access and for secret key agreement used for encryption and integrity protection! Use of a challenge and response algorithm for key management and authentication in GSM/GPRS; and an advanced version in UMTS! Wireless LAN integrated network! Utilizing the new IEEE i for authentication, access control and key agreement functions, especially the extensible authentication protocol (E) based on RADIUS! Use of E-SIM: mainly using SIM s key agreement algorithm! Use of E-AKA: encapsulation UMTS authentication and key agreement (AKA) within E 16

17 Integration options! Use of W-LAN as a Peer Network! Really an inclusion not integration! Connecting W-LAN and cellular systems independently to the IP core network! Tight Coupling! Accommodating W-LAN tightly inside cellular core network! Achieving virtual high-speed at the end-user level! Loose Coupling! Take advantage of both IP core network and cellular core network without getting virtual (imaginary) high-speed! Better option to get the two network really integrated! Obviously with adding more overall complexity V.K. Varma, S. Ramesh, K.D. Wong and J.A. Friedhoffer, Mobility management in integrated UMTS/WLAN networks, IEEE International Conference on Communications (ICC 03), vol. 2, pp , May. 17

18 Integration options MS Node B RNC MS Node B Iu-ps UMTS CN SGSN Tight Coupling HSS BG AAA GGSN/ HA AGW /HA b AAA /HLR b GW SGSN Peer Network MS MS Core IP Network b GW GSN Loose Coupling CN MS 18

19 Peer Network MS Node B RNC Node B I u-ps UMTS CN HSS AAA MS SGSN GGSN/ HA BG MS b AAA/ HLR GW AGW/ HA Core IP Network MS b GW CN! Operation by a same or different UMTS W-LAN operators! Use of Mobile IP for mobility management among peer networks! Inclusion of a HA functionality and a AAA server inside UMTS CN for supporting mobility among UMTS and non-umts networks! Multiple ESSs are connected via an access gateway to IP CN 19

20 Peer Network! Authentication to UMTS and other peer networks! To UMTS: through a HLR emulator (HLR ) in W-LAN! W-LAN: appearing as a foreign UMTS network! To other peer networks: through an AAA server and HA! Roaming from UMTS to W-LAN, MS! Associates with an access point! Performs AAA functions with the local AAA server which interacts with the AAA server in UMTS home! Obtains a CoA and sends a binding update! Interaction of HA with HSS in UMTS CN to update location! Similar procedure for roaming from W-LAN to UMTS 20

21 Tight coupling MS Node B RNC UMTS CN HSS AAA Node B I u -ps SGSN GGSN/ HA MS BG MS b GW SGSN Core IP Network CN! W-LAN emulates either a RNC or a SGSN (shown as SGSN )! W-LAN is deployed either by UMTS or an independent operator! Mobility between two networks means an inter-sgsn RA update! With the same GGSN, IP address will be assigned from the same pool: mobility results in no change in IP address! All signaling and data traffic and the user location are maintained by the home subscriber server (HSS) 21

22 Tight coupling! This coupling allows independent W-LAN operators! SGSN emulator meets the UMTS CN at G p interface! Simple architecture and procedure! Use of UMTS mobility management! To roam into a W-LAN high-speed network, an MS! Associates with an access point! Enters into an inter-sgsn routing area update with SGSN! Connects to the UMTS CN via SGSN! Moving within W-LAN ESS follows the W-LAN MM procedure! Signal strength, bandwidth measurement, etc may be used to select between the two networks when both are available 22

23 Loose coupling MS MS Node B Node B RNC I u-ps UMTS CN SGSN HSS BG AAA GGSN/ HA signaling MS b GW GSN data Core IP Network MS b GW CN! A master/slave architecture: UMTS: Master, W-LAN: Slave! Connection of several W-LAN ESSs via individual GWs to a combined SGSN/GGSN emulator (GSN )! Possible deployment of W-LAN by UMTS or independent operator: W-LAN is a visiting network to the UMTS CN 23

24 Loose coupling! Different routing areas for UMTS and W-LAN! Different sets of IP address domains! Simplifying GGSN in forwarding packets from GSN! Different handling of signaling and data traffics! Signaling goes to UMTS CN; directly (same operator) or indirectly (different operators)! Data traffic goes to IP core directly! Mobility management is more complex than in tight coupling as a user has a different IP address when roaming from one network to another 24

25 Loose coupling! While in UMTS! Performing Attach and PDP context activation! Following GPRS mobility management for moving around! Roaming to W-LAN! Associating with an access point! Acquiring an IP address from the W-LAN domain! Attaching to GSN similar to UMTS attach! Authentication with UMTS by GSN (via old SGSN)! Updating MS location and canceling it in HSS! Exchanging packets directly through IP core network! DNS or SIP could be used to identify the MS within the IP network; ongoing research! Similar procedure when roaming to UMTS 25

26 Other issues in W-LAN/3G W interworking! Mobility management! Roaming between W-LAN and cellular networks! Criteria for roaming! data rate, signal strength, traffic load, application, user preference, network preference, handheld device type,! Timing for roaming! Frequency for roaming! QoS guarantee issues after roaming! Device auto-detection and auto-configuration! Network administration! One administrator or more for! AAA! Billing! Customer care 26

27 Interworking scenarios! Only common billing and customer care! With no internetworking still this may be possible! To have same AAA functions as defined by 3GPP! This requires AAA procedures to be adopted in W-LAN too! To have UMTS-specific services in W-LAN! More internetworking is needed so that either a gateway to those service is emulated or they are accessed directly! Service continuity is maintained! We can restrict the type of services to be maintained continuously based on QoS availability (e.g. voice delay)! Seamless service across two networks! Access even to the UMTS circuit-switched services from the W-LAN 27

28 Security Arrangements 3

29 Security requirements! Requirements! The integrated system should not compromise 3G security! Use of UMTS authentication and key agreement (AKA)! AKA challenge-response procedure is network independent and may be run over other transport mechanisms! E.g., E-over-LAN supported by IEEE ! The home network in the integrated system should be always the 3GPP home! The serving network should support E-AKA! AAA node to handle transport of E! UMTS AKA relies on the terminal s smartcard! USIM application runs the UMTS AKA cryptographic algorithm! W-LAN terminal should be able to access USIM! Not necessarily have a smartcard reader; can be accessed via host system 29

30 Security elements! Authentication! No problem as the integrated network still uses UMTS AKA procedure! Confidentiality! Use of symmetric key encryption to protect disclosure of user and system data by passive attacks! Integrity! Use of (symmetric) keyed cryptographic checksum function to protect data modifications by active attacks! Functions are called message authentication codes (MAC); per message authentication 30

31 Security on the air! Assumptions: Access network supports confidentiality and integrity services over the air! Problem for W-LAN due to its weak WEP method! Use of new IEEE i specification! Use of interim solutions such as Wi-Fi protected access (WPA)! Based on Temporal Key Integrity Protocol (TKIP) of i! W-LAN access points must be also protected against dedicated attacks that aim to get access to session keys! Possible solution is to extend the W-LAN integrity and confidentiality services to the access server (similar to UMTS where data connections are protected between UE and RNC! To solve the problem of confidentiality and integrity services over the air, we must go beyond the usual link-layer security mechanisms (e.g., create an IPSec tunnel between UE and the network) 31

32 Security standards! Security architecture of the integrated system is directly modeled in the UMTS security architecture! UMTS access security: based on one-pass mutual entity authentication scheme between USIM and serving network! AKA procedure provides authentication and generation of 128-bit session keys for confidentiality and integrity protection! AKA procedure implementation! Cryptographic functions are implemented in USIM and HSS; depend only on HE operator! AKA successful outcome! The USIM and network will be mutually authenticated! They will get common key materials 32

33 UMTS AKA procedure! AKA procedure consists of two phases! Phase 1: Transfer of authentication vectors (AV) from home environment (HE) to the serving network (SN)! Not available in the interworking version of AKA; AKA is globally executed from the HE toward the USIM! Phase 2: Execution of AKA procedure by the SN User Serving Network (SN) Home Environment (HE) User Equipment (UE) Access Point () Radio Network Controller I u Interface Serving Network (SN) Home Subscriber Server (HSS) USIM MS Node B RNC SGSN/VLR HLR/AuC AV transport over M One-Pass Challenge/Response G. M. Koien and T. Haslestad, Security aspects of 3G-WLAN interworking, IEEE Communications Mag., pp , Nov. 33

34 Challenge/Response mechanism! If the AKA fails, either during challenge from network or response from USIM, a resynchronization procedure will be required USIM Challenge (RAND, AUTN) Network Valid AV presents Authenticate the network; if not ok proceed with failure Check sequence number in AUTN; if not ok resynchronize Compute response: RES Generate key material Response (RES) Failure (resync or MAC failure) Reject (cause) Verify (authenticate) USIM; if not ok proceed with reject 34

35 Security architecture (loose coupling)! Rather simple architecture using AAA and E! To execute UMTS AKA from 3G home domain toward W-LAN UE! AAA architecture, RADIUS and/or Diameter protocols are used to bridge 3GPP and W-LAN access networks! E-AKA allows execution of UMTS AKA over W-LAN Visited Network Home Network W-LAN access network UE Network access server 3GPP AAA proxy 3GPP AAA W r W r W x Home subscriber server Internet 35

36 Extensible authentication protocol (E)! A key element in security architecture of the integrated system! Provides a generic peer-to-peer based request-response transaction for authentication dialogs! Supports multiple authentication mechanisms! Does not provide authentication itself but supports existing authentication methods through specialized E methods! Using a negotiation sequence where the authenticator asks information on which authentication method to use! The main authentication method supported is E-AKA, but always a backend authentication server can help authenticator for unsupported authentication methods! Runs directly over link layer (no need for IP)! Has its own flow control mechanisms! Can remove duplicate messages! Can retransmits lost messages! Runs over different link layer protocols including the IEEE W-LAN link layer 36

37 Concluding Remarks 4

38 Concluding remarks! A hybrid W-LAN/cellular network takes the advantages of wide area coverage of the cellular systems and high-bandwidth and low-cost equipment of the W-LAN! The three integrated architectures look good, but is there any other option?! The three architectures use one of available mobility management techniques: GPRS/UMTS, W-LAN, MIP, SIP; are there any better option for MM in hybrid networks?! While authentication and authorization are handled through different combination of available methods (AAA, W-LAN, GPRS/UMTS, HLR, etc), are those techniques sufficient?! Radio access security! Network access security 38

39 Further reading! 3GPP, 3GPP System to Wireless Local Area Network (WLAN) Interworking; System Description, Tech. rep. 3GPP TS v1.10.0, May! 3GPP, Feasibility Study on 3GPP System to Wireless Local Area Network (WLAN) Interworking, Tech. rep. 3GPP TR v6.1.0, Dec. 2002! K. Ahmavaara, H. Haverinen, and R. Pichna, Interworking Architecture Between 3GPP and WLAN Systems, IEEE Communications Mag., pp , Nov.! A.K. Salkintzis, C. Fors, and R. Pazhyannur, WLAN-GPRS Integration for Next-generation Mobile Data Networks, IEEE Wireless Communications, vol. 9, no. 5, pp , Oct. 2002! A. Doufexi, E. Tameh, A. Nix and S. Armour, Hotspot Wireless LANs to Enhance the Performance of 3G and Beyond Cellular Networks, IEEE Communications Magazine, vol. 41, no. 7, pp , July! B. Sarikaya and T. Ozugur, Dormant Mode Operation Support for Roaming from WLAN to UMTS, IEEE International Conference on Communications (ICC '03), vol. 2, pp , May! Shiao-Li Tsao and Chin-Ching Lin, VGSN: A Gateway Approach to Interconnect UMTS/WLAN Networks, The 13 th IEEE Int. Symposium on Personal, Indoor and Mobile Radio Communications, vol. 1, pp , Sept. 2002! ETSI, Requirements and Architectures for Interworking Between HIPERLAN/3 and 3 rd Generation Cellular Systems, Tech. rep. ETSI TR v1.1.1, Aug. 2001! G. M. Koien and T. Haslestad, Security Aspects of 3G-WLAN Interworking, IEEE Communications Mag., pp , Nov. 39