1. KAIS T A Secure Group Key Management Scheme for Wireless Cellular Network Hwayoung Um and Edward J. Delp, ITNG’06 2007. 9. 5 Kim Pyung

2. A Secure Group Key Management Scheme for Wireless Cellular Network Contents Introduction Handoff schemes Location tracking Pre-positioned secret sharing Group key management Simulation and result Conclusion

3. A Secure Group Key Management Scheme for Wireless Cellular Network Introduction : Multicast protocols Growths with multimedia streaming over wireless networks Access control mechanism Session key(SK) “forward message secrecy” and “backward message secrecy” Tree-based key management schemes advantages when update and maintain the SK (computation, communication, storage) Performance issues Scalable no “1 affects n” Matching the key tree to the network topology reduces 33%~45% traffic

4. A Secure Group Key Management Scheme for Wireless Cellular Network Introduction The suggested scheme “The neighbors on the key tree are also physical neighbors” A pre-positioned secret sharing scheme

5. A Secure Group Key Management Scheme for Wireless Cellular Network Handoff Schemes Handoff schemes are based on the location of a user L_ADD : the beginning of handoff L_DROP : the termination of handoff Soft handoff(30% handoff area) L_ADD : the boundary of overlapping area L_DROP : the middle of two BSs Hard handoff The same with “joining after leaving”

6. A Secure Group Key Management Scheme for Wireless Cellular Network Location Tracking In Code Division Multiple Access(CDMA) The forward link transmission timing is synchronized within a μs (using self-synchronization, radio beacons, or GPS) The backward link transmission timing is based on the received timing derived from the first multipath component

7. A Secure Group Key Management Scheme for Wireless Cellular Network Pre-Positioned Secret Sharing(PSS) m-shares Lagrange interpolation Over the finite field GF(q) a 0 is the shared secret group key

8. A Secure Group Key Management Scheme for Wireless Cellular Network Pre-Positioned Secret Sharing(PSS) The pre-positioned shares share i, 1≤i≤m, i≠j  user group The activation share(AS) share j  key server

9. Joining a group {s 4-6 } k4-5 AS, {s 1-6,s 4-6 } k6 AS, {s 1-6 } k1-5 A Secure Group Key Management Scheme for Wireless Cellular Network Group Key Management M1 M3 M4 B1 G M6 B2 M2M5 Group manager Subgroup managers Users s 1-5 © AS  k 1-5 {s 1-6 } k1-5  s 1-6 s 1-5  s 1-6 s 4-5  s 4-6 s 1-6, s 4-6, s 6 s 4-5 © AS  k 4-5 {s 4-6 } k4-5  s 4-6

10. Leaving a group AS, {s 1-6 } k1-5,{s 4-6 } k4-5 AS, {s 1-5 } k1-3 A Secure Group Key Management Scheme for Wireless Cellular Network Group Key Management M1 M3 M4 B1 G M6 B2 M2M5 Group manager Subgroup managers Users s 1-3 © AS  k 1-3 {s 1-5 } k1-3  s 1-5 s 1-6  s 1-5 s 4-6  s 4-5 s 1-6  s 1-5 s 4 © AS  k 4 | s 5 © AS  k 5 {s 4-5 } k4  s 4-5 | {s 4-5 } k5  s 4-5 s 4-5 © AS  k 4-5 {s 1-5 } k4-5  s 1-5

11. Handoff AS, {s 5-6 } k5,{s 5-6 } k6 AS, {s 1-4 } k4 AS, {s 1-4 } k1-3 A Secure Group Key Management Scheme for Wireless Cellular Network Group Key Management M1 M3 M6 B1 G M4 B2 M2M5 Group manager Subgroup managers Users s 1-3  s 1-4 s 4-6  s 5-6 s 1-3 © AS  k 1-3 {s 1-4 } k1-3  s 1-5 s 4 © AS  k 4 {s 1-4 } k4  s 1-4 s 5 © AS  k 5 | s 6 © AS  k 6 {s 5-6 } k5  s 5-6 | {s 5-6 } k6  s 5-6 {s 1-6 } k1-4, {s 1-6 } k5-6 ?

12. A Secure Group Key Management Scheme for Wireless Cellular Network Cost Analysis Tree-based scheme vs Pre-positioned secret sharing d : the degree of the tree h : the height of the tree ( the length of the longest directed path) The group key tree is assumed full and balanced Comparison of TBC and PSS schemes : Storage cost TBCPSS # of keys held by serverdn/(d-1)- # of keys held by each memberh- # of share sets held by server-dn/(d-1) # of share sets held by each member-h

13. Comparison of TBC and PSS schemes : Communication cost Join Leave A Secure Group Key Management Scheme for Wireless Cellular Network Cost Analysis TBCPSS JoinO(log d (n))O(d log d (n)) and O(1) LeaveO(log d (n))O(d log d (n)) and O(1) Periodic rekeyingO(d)O(1)

14. A Secure Group Key Management Scheme for Wireless Cellular Network Cost Analysis TBC computation cost PSS computation cost ServerRequesting member Non-requesting member Join2(h-1)h-1d/(d-1) Leaved(h-1)0d/(d-1) Periodic rekeyingd11 ServerRequesting member Non-requesting member Join2(h-1)h-1d/(d-1) Leaved(h-1)0d/(d-1) Periodic rekeying000

15. A Secure Group Key Management Scheme for Wireless Cellular Network Simulations and Results Simulation Parameters ParameterValue # of MX1 # of BS16 # of MSUp to 100 per BS Call generationPoisson with λ (calls/sec) Call durationExponential with 1/μ (1/sec) User mobility0-1 km/h (walking) 2-5 km/h (running) 6-25 km/h (low speed vehicle) 25-100 km/h (high speed vehicle) Cell radius1 Km ServiceVoice, Data, Video L_ADD30% of BS coverage area L_DROPBoundary of BS

16. A Secure Group Key Management Scheme for Wireless Cellular Network Simulations and Results Number of key transaction 1 x (callgeneration) + 1 x (calltermination) + 2 x (# of Handoff) No call admission control(CAC) Call admission control(CAC)

17. A Secure Group Key Management Scheme for Wireless Cellular Network Conclusion New scheme the neighbors on the key tree – physical neighbors Pre-positioned secret sharing Simulation 3 - 8 handoff during a call duration Need of call admission control

18. A Secure Group Key Management Scheme for Wireless Cellular Network Time for Any questions? Thank you for listening !