1. Yan (Lindsay) Sun and K. J. Ray Liu IEEE/ACM Transactions on Networking, Dec. 2007. Presented by Seo Bon Keun, 2008.

2. Group key management Multi-group key management Formalization Security requirements Hierarchical multi-group key management Key tree Integrated key graph generation Evaluation Conclusion

3. Group access control UserResource Documents Audio clips Movie clips

4. UserResource Drama Movie Animation DG : Data GroupSG : Service Group capability

5. Security requirements If a user leaves a group and joins other group, Forward secrecy cannot access the future content of the resources they leave Backward secrecy cannot access the previous content of the resources they join UserResource Forward secrecy Backward secrecy

6. K0K0 KeKe Key tree u1u1 K 00 u2u2 u3u3 K 01 u4u4 K0K0 K e’ KSKS u5u5 K 10 u6u6 u7u7 K 11 u8u8 K1K1 KDC knows : every keys User 1 knows : u 1, K 00, K 0, K e, K S K 10’ u6u6 K 11 K 1’ K 10’ K 1’ K e’ K S’ u 6 (K 10’ ) K 10’ (K 1’ ), K 11 (K 1’ ) K 1’ (K e’ ), K 0 (K e’ ) K e’ (K S’ ) Key Update Message

7. Integrated key graph K S1 K D3 u1u1 K0K0 u2u2 u3u3 K1K1 u4u4 u5u5 K2K2 u6u6 u7u7 K3K3 u8u8 K S2 SK 1 SK 2 u1u1 u2u2 u3u3 u4u4 u5u5 u6u6 u7u7 u8u8 DG 1 DG 3 DG 2 K S1 u1u1 K0K0 u1u1 SG1SG2 K D3 SK 3

8. Integrated key graph generation Generate subtree for each SG Generate subtree for each DG Merge two subtrees K S1 u1u1 K0K0 u2u2 u3u3 K1K1 u4u4 u5u5 K2K2 u6u6 u7u7 K3K3 u8u8 K S2 u1u1 u2u2 u3u3 u4u4 u5u5 u6u6 u7u7 u8u8 SG1SG2 DG 1 DG 3 DG 2

9. Integrated key graph generation Generate subtree for each SG Generate subtree for each DG Merge two subtrees u1u1 u2u2 u3u3 u4u4 u5u5 u6u6 u7u7 u8u8 SG1SG2 K D3 SK 3 K S1 K S2 K D2 SK 2 K S2 DG 1 DG 3 DG 2 K D1 SK 1 K S1

10. Integrated key graph generation Generate subtree for each SG Generate subtree for each DG Merge two subtrees K S1 K D3 u1u1 K0K0 u2u2 u3u3 K1K1 u4u4 u5u5 K2K2 u6u6 u7u7 K3K3 u8u8 K S2 SK 1 SK 2 SK 3 K D1 K D2

11. Storage overhead Rekey overhead Independent treeMulti-group tree Independent treeMulti-group tree d : tree depth / M : the number of trees / n : the number of users d : tree depth / j : the number of involved trees / n : the number of users

12. Simulation configuration Markov chain model

13. User Group size vs. Storage overhead KDC

14. User Group size vs. Rekey overhead KDC

15. Scalability Rekey overheadStorage overhead

16. A multi-group key management scheme that achieves hierarchical group access control Efficient w.r.t Storage overhead Communicational cost Scalability Evaluation Concrete by formalization Confusing denotations