Unlicensed Mobile Access (UMA) Dasun Weerasinghe School of Engineering and Mathematical Sciences City University London

Agenda What is UMA UMA Architecture Security in UMA Authentication Encryption EAP-AKA Authentication Future Work

What is UMA UMA allows to access the mobile voice and data services of the cellular network over a Wireless LAN Subscribers are enabled to roam and handover between cellular networks and wireless networks UMA Technology specification was published in September GPP approved the specification as “Generic Access to A/Gb interfaces” Pilot project by Nokia in Finland

What is UMA ( Contd..)

UMA Architecture Mobile devices access the Core Network through Unlicensed Mobile Access Network (UMAN). UMAN has 3 major entities Unlicensed wireless network IP access network UMA Network controller (UNC) UNC authorizes and authenticates the Mobile devices for accessing the Core Network

UMA Architecture ( Contd..)

UMA Security Authentication Authenticate MS with UNC to make secure tunnel Based GSM or UMTS credentials Protocol of authentication is IKEv2 GSM : EAP-SIM or UMTS : EAP-AKA Mutual Authentication of MS and Mobile Network Session Key Generation – IK and CK

UMA Security – EAP Authentication Steps in Authentication ( EAP ) MS establish a link with AP Determines the UNC to be connected Initiate the connection with UNC with IKE UNC connects with the local AAA

UMA Security - EAP Authentication (Contd..) Local AAA linked to the Home AAA EAP procedure is performed between MS and AAA UNC is a relay for EAP messages

EAP-AKA

EAP-AKA steps MS finds an AP MS finds the UNC-SGW and initiates the IKEv2 authentication procedure MS sends to NAI to UNC-SGW which contains IMSI UNC-SGW communicates with local AAA Local server determines the Home AAA by using the NAI. Routing path may include several AAA proxies Leading digits in NAI indicates the authentication procedure is EAP - AKA

EAP-AKA steps ( contd..) AAA requests the user profile and UMTS authentication vectors from HSS UMTS authentication vector consists with RAND, authentication part (AUTH), expected result, IK and CK AAA send the EAP Request/AKA Challenge to UNC-SGW with RAND, AUTH, MAC ( message authentication key ) and re-authentication identity. UNG-SGW forwards the EAP Request/AKA Challenge to MA

EAP-AKA steps ( contd..) MS runs the UMTS algorithm and verifies the AUTH. It computes the RES, IK, CK and calculates MAC using the generated IK and CK MS sends EAP Response/AKA Challenge with RES and MAC AAA verifies the received MAC and compares RES with XRES AAA sends IK and CK to UNC-SGW for the communication with MS UNC-SGW informs the successful authentication to MS

EAP-AKA Fast Re-Authentication Used to reduce the network load due to the authentication AAA server authenticates the user based on the keys derived by the last full authentication Re-authentication ID is generated by the AAA in the full authentication process

EAP-AKA Fast Re-Authentication (Contd..)

EAP-AKA Fast Re-Authentication Steps MS initiates the IKEv2 authentication procedure Re-Authentication identity is sent to the UNC-SGW UNC-SGW sends EAP Response/Identity to AAA with re-authentication Id AAA initiates a counter and sends EAP Request/AKA-Reauthentication message with counter value, MAC and re-authentication id for the next fast authentication. MS verifies the counter value and the MAC and send the EAP Response/AKA-Reauthentication with the same counter value and calculated MAC. AAA server verifies the counter value and MAC EAP success message is sent to MS

Encryption CK is generated during the authentication process Negotiated cryptographic algorithms are used.

Future Work Calls handing off between the cellular network and the wireless LAN with fast authentication process SSO from one UNC to another Introduce UNC to the Mobile Shopping Mall. UNC can be a web service. Introduce XML security to the communication between MS and UNC Authentication of the UNC to the network Some security holes in Fast authentication