Post on 01-Apr-2015
Unlicensed Mobile Access (UMA)
Dasun Weerasinghe
School of Engineering and Mathematical Sciences
City University
London
Agenda
What is UMA
UMA Architecture
Security in UMAAuthentication
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 2004
3GPP 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 CKMS sends EAP Response/AKA Challenge with RES and MACAAA verifies the received MAC and compares RES with XRESAAA sends IK and CK to UNC-SGW for the communication with MSUNC-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 StepsMS initiates the IKEv2 authentication procedure
Re-Authentication identity is sent to the UNC-SGWUNC-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 MACEAP 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 processSSO 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 UNCAuthentication of the UNC to the networkSome security holes in Fast authentication