LAAC: A Location-Aware Access Control Protocol

1. LAAC: A Location-Aware Access Control Protocol YounSun Cho, Lichun Bao and Michael T. Goodrich IWUAC 2006

2. Why Location-Based Access Control? • Previous user identity- based access control approaches cannot verify Physical location of the access requester, which plays an important role in determining access rights • Secure verification of location claims is required • Secure verification of location claims • Natural • No need to establish shared secrets in advance • Information about Location can strengthen access control policy • Not just which subject is accessing what object • Where the subject and object are located • Subject belongs to a location group as long as she can listen to one of the beacons in that group

3. Previous Works • Hardware dependency to determine location • GPS • Temper resistant device • Ultrasonic signals • Need central server • Expensive crypto and overhead • PKI, DH key exchange

4. Properties • No servers • No pre-registration • No expensive crypto • No expensive hardware (e.g. GPS) • Low communication/computation • Different from localization problem

5. Notation

6. Protocol Description • Each access point (APj)periodically broadcasts its nonce (rj) • Assume each APj knows other AP's nonces (rj) through a secure channel • A mobile station (MSi) collects nonces of the access points • MSi derives its location key (ki) by XOR-ing all the nonces of access points • MSi constructs its access request (ARi) using hash of ki and claims its location to its associated access point with it. • If MSi is located in the access-granted area, it can access to the resource • o/w, it cannot access it • This system is secure if each entity does not collude each other • Assume trust AP • not mutual authentication.

7. What is AP group ? G1 G3 G2 • Define three AP groups: • G1={AP1, AP2}, • G2={AP3, AP4}, • G3={AP1, AP4} • Each AP's group: • AP1 is in G1, G3 • AP2 is in G1 • AP3 is in G2 • AP4 is in G2,G3 Access-Granted Area

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9. Security Analysis • Insecure nonce combination • RNG with k=|nonce|  80 bits • Bogus location claim • zero-false positive with • Interval T < Speed of MS • cf. GPS error, sector error, etc.

10. Security Analysis (cont.) • Wormhole attack

11. Security Analysis (cont.) • Simple solution • Assume each mobile station has APs Certificates of each • Using AP's signature of BBM • Better solution? • Man-in-the-Middle Attack? • The Sybil attack

12. Efficiency Estimation • Various Hash Function Computation Times ( μseconds) based on the Crypto++ 5.2.1 benchmark tested on the AMD Opteron 1.6 GHz processor under Linux 2.4.21. • Let |nonce|= 80 bits and |ID|=8 bits and use 160-bit SHA-1 • Computation Time • Only 0.147 μseconds to compute access request of mobile station side • Communication Load • |BBM|  80 + 8 + 8*|L|*|N| bits of each access point • |AR| = 160 bits of each mobile station • Storage Requirement • For the mobile stations, there is no storage requirement

13. Simulation Result • Simulation condition • 23 MSs, 2 APs • 802.11 propagation and path-loss model in the free-space model without a routing protocol between mobile stations • Two access points broadcast beacons with nonces (r1, r2) 1000 times in every broadcasting interval  • False positive rate with various nonce sizes |r1| = |r2| = 4, 8, 16 bits of access points under T= =1 second of static mobile station model • False positive rate with various T=1, 2, 4, 8 seconds with  = 1 second T under |r1| = |r2| = 16 bits of randomly moving mobile station model

14. Application and Extension • HotSpot • Cyber Cafe, coffee shop, airport • Data encryption key as well as access control key • Location Tracking • Sensor network

15. Future Work • Scalability • Applicable to Sensor Network • LBS (Location Based Services) • Location Tracking • Location Privacy • Secure Data Aggregation

16. Conclusion • Easy • Simple • Cheap • Practical • Applicable

17. Q & A