Transcript Document
Secure Authentication System for Public WLAN Roaming Yasuhiko Matsunaga Ana Sanz Merino Manish Shah Takashi Suzuki Randy Katz Agenda Single sign-on to confederated wireless networks with authentication adaptation Privacy information protection using policy engine Improve security of web-based WLAN authentication by binding 802.1x link level authentication Performance Measurement 2 Loose Trust Relationship in Current Public Wireless LAN Roaming WLAN Service Provider Strong Trust Weak Trust (ISPs, Card Companies) ID Provider WLAN Strong No Trust Service Trust Provider User Each WLAN system is isolated, deploys different authentication schemes Users have to maintain different ID and credentials 3 Challenges and Our Solutions Confederate service providers under different trust levels and with different authentication schemes to offer wider coverage Alleviate user burden of maintaining different identities and credentials per WLAN provider SSO Roaming with Authentication Adaptation Select proper authentication method and protect privacy of user information per WLAN provider Policy Engine Client Avoid theft of wireless service without assuming preshared secret between user and network L2/Web Compound Authentication 4 The Single Sign-on concept Single sign-on ID Provider Initial Sign-on Office (provider C) Street (provider B) Coffee shop (provider A) Confederation Single username and password Users authenticate only the first time Inter-system handover with minimal user intervention Each network may deploy its own authentication scheme 5 Single Sign-on Technology Currently two technologies clearly accepted by industry: RADIUS: Proxy-based authentication scheme Liberty Alliance: Redirect-based authentication scheme We adopted both of them for our implementation Need authentication adaptation framework 6 Authentication Adaptation Flow User Terminal (3)Select authentication method according to user’s preferences (1) Request authentication (2) Announce: - provider id - authentication methods - charging options - required user information (4) Submit: - selected authn. method - selected charging option - user information WLAN Service Provider (5) Authenticate the user 7 Client-side Policy Engine Control automatic submission of user authentication information according to communication context Context includes trust level of provider, cost, etc. Authentication/Authorization flow adaptation Switch between Proxy-based (Radius) and Redirect-based (Liberty-style) single sign on 8 Policy Engine Architecture End User Policy Check Engine Policy Repository Context Client Applet Auth Info. Repository Policy Enforcement Point Web Browser AAA Server Capability Policy EAP/ 802.1X WLAN provider 9 Security Threats of Web-based Authentication and Access Control Lack of cryptographic bindings causes several security vulnerabilities No Data Encryption ->Eavesdropping Rogue AP >DoS Web Server Gate-control (IP/MAC) No Message Integrity Check ->Message Alteration IP/MAC spoofing-> Theft of Service External Network 10 L2/Web Compound Authentication RADIUS/Web Server Client (1) 802.1x TLS guest authentication Access Point (3) Web Auth (with L2 session key digest) (2) Establish L2 Session Key (4)Firewall Control External Network • Prevent theft of service, eavesdropping, message alteration 11 • Don’t work for L2 DoS attack – out of scope WLAN Single Sign on Testbed Identity Provider Web Radius Server RADIUS Service Provider #1 Radius Web Portal Fire wall HTTPS Client MC External Network SOAP HTTPS Service Provider #2 Radius Web Fire wall Radius RADIUS Web 802.1x Client 12 Authentication Adaptation User Interface 13 Layer 2 Roaming User Interface 14 Delay Profile Evaluation (Units: sec) Proxy-based (RADIUS) Web Authentication Redirect-based (Liberty) Local Roaming Local Roaming 0.184 0.188 0.175 1.467 Policy Engine 0.318 Link Layer (802.1x) Authentication 0.124 Total 0.626 0.630 0.617 1.909 15 Conclusions 1. 2. 3. 4. 5. Secure public WLAN roaming made possible by accommodating multiple authentication scheme and ID providers with an adaptation framework Policy Engine reflects user authentication scheme preference and protects privacy of user information Compound L2/Web authentication ensures cryptographically-protected access Confirmed with prototype, measured performance shows reasonable delay for practical use Exploits industry-standard authentication architectures: Radius, Liberty alliance 16 backup Public Wireless LAN Service Model The network is ‘open’ to users without pre-shared secret User Category AAA Servers (1)Monthly/Prepaid Subscribers (2)One-time Users (3)NonSubscribers WLAN Infrastructure Services Premium Contents & External Network Access (Subscriber Pays) Free & Advertisement Contents (Hotspot Owner Pays) 18 802.1x/11i/WPA L2 Network Authentication and Access Control Conventional ‘Closed-style’ authentication: Only hosts with pre-shared key can access the network, Mainly for Corporate WLAN (1) Mutual TLS authentication with pre-shared key (2) Establish L2 session key dynamically (3) Only successfullydecrypted packets are forwarded External Network 19 L2/Web Authentication Comparison Support Pre-shared Secret Encryption Authentication Web-based 802.1x/WPA/11i Most public WLAN providers Not necessary (use credit-card authorization) None Corporate Networks SSL-protected Password EAP-TLS (certificatebased) Access Control IP/MAC address Accounting Fine-grained (only on 802 LAN/MANs) Necessary Per-station RC4, AES(802.11i) Cryptographic Only at boot time 20 Our Approach Compound L2/Web authentication to ensure users to have cryptographically-protected wireless LAN access Use 802.1x ‘guest’ authentication mode, embed L2 session key digest in web authentication At layer 2, do not assume pre-shared secret Digest embedding is necessary for avoiding race attack After Web authentication, user gets full access Otherwise, users have limited access to free contents L2 DoS protection is out of scope 21 Race Attack Scenario (Why L2 session key digest embedding is necessary) Malicious Client (MAC Spoofer) Legitimate Client L2 Auth AP RADIUS/Web Firewall Bind (MAC, MD5(K1) L2 Auth L2 Auth K1 K1 Web Auth+ MD5(K1) L2 Auth K2 K2 Bind (MAC, MD5(K2)) (L2 Session key verify NG) • Theft of service can be prevented by authentication binding 22 • L2 DoS attack is still possible Compound Authentication Testbed RADIUS/Web Server (1) 802.1x TLS guest authentication Client Access Point Cisco AIR-350 Xsupplicant 0.6 libwww-perl 5.6.9 (3) Web Auth (with L2 session key digest) (rejected) Attacker (2) Establish L2 Session Key FreeRADIUS 0.8.1 Apache 2.0.40 (4)Firewall Control External Network 23