1. KAIS T Scalable Key Management for Secure Multicast Communication in the Mobile Environment Jiannong Cao, Lin Liao, Guojun Wang Pervasive and Mobile Computing 2 (2006) 2007. 11. 8 Kim Pyung

2. Scalable Key Management for Secure Multicast Communication Introduction IP Multicast Saves a great deal of bandwidth Needs group key management in a scalable and secure manner Scalability Under the mobile Internet environment Frequent moving, joining and leaving, and the large size of a group 1-affects-N phenomenon ( re-keying message, # of enc/decryption ) Security Backward / forward confidentiality 2/15

3. System Model and Assumptions Scalable and Hierarchical key management(SHKM) S : multicast source F: forwarding node, subgroup manager CA : Centralized authority Scalable Key Management for Secure Multicast Communication 3/15

4. SHKM : Main idea Hierarchy by subgroup priority ordering F i » F j Initiation : RSA algorithm Randomly chosen TEKs by SGM The parameters for derivation of the lower group’s TEK from CA changing residue e j, related factor г ij Scalable Key Management for Secure Multicast Communication 4/15

5. SHKM : Key Generation SGM S i chooses the TEK k i CA gets (PK, SK) by RSA PK : public key E PK (k i ) D SK (k i ) changing residue : e i = k i 2 mod n ( n is secret ) if S j » S i, related factor : г ji = h(Z k j  e i mod P)  k i Scalable Key Management for Secure Multicast Communication SiCA 5/15

6. SHKM : Key Derivation TEK : k j requestsfor access S i parameters : e i, г ji E k j ( e i, г ji ) check S j » S i ? D k j ( e i, г ji ) TEK of S i : k i = h(Z k j  e i mod P)  г ji Scalable Key Management for Secure Multicast Communication SjCA 6/15

7. SHKM : Key Modification the relationship : S j » S l » S i key modification : k l  k l * e l * = ( k l *) 2 mod n г jl * = h(Z k j  e l * mod P)  k l * г li * = h(Z k l *  e i mod P)  k i Only direct successor and predecessor of S l Scalable Key Management for Secure Multicast Communication 7/15

8. SHKM : Protocol analysis Adding a new subgroup A new subgroup S i into an existing multicast group the changing residue e i, related factor г (CA) No re-keying message and No re-generation of a new TEK for whole group  Scalable vs Key Graph ? Backward confidentiality? S h » S i (new) » S j » S k » S l Scalable Key Management for Secure Multicast Communication 8/15

9. SHKM : Protocol analysis Deletion of a subgroup For the higher-priority subgroups Delete the changing residue e, related factor г (CA) No re-key message For the lower-priority subgroups New TEK for lower-priority subgroups New changing residue e, related factor г (CA) vs Centralized protocols ? - the cost transferred to CA Scalable Key Management for Secure Multicast Communication 9/15

10. SHKM : Protocol analysis Leaving of subgroup members Multiple leaving about h, (m i, m i+1, …, m i+h-1 ) in S l New TEK k l * for S l  new changing residue e l (CA) For the higher-priority subgroups New related factor г (CA) For the lower-priority subgroups New TEK for lower-priority subgroups New changing residue e, related factor г (CA) Scalable Key Management for Secure Multicast Communication 10/15

11. SHKM : Protocol analysis Joining of a new subgroup member New TEK k l * for S l  new changing residue e l (CA) For the higher-priority subgroups New related factor г (CA) For the lower-priority subgroups  backward confidentiality New related factor г (CA) Scalable Key Management for Secure Multicast Communication 11/15

12. SHKM : Protocol analysis Migration of member between subgroups First entry delayed re-keying + periodic (FEDRP) A TEK timer table for members residing outside the subgroup Leaving or timer expire  “Reset” A lower re-keying rate Scalable Key Management for Secure Multicast Communication 12/15

13. Attack Analysis Continuous attack (in Lin’ scheme) k i is exposed S j » S i г ji = Z k j  ID i mod P  k i k i = Z k j  ID i mod P  г ji k i *= Z k j  ID i mod P  г ji *  k i *=h( Z kj  e i * mod P )  г ji * Sibling attack S j » S i and S j » S l h( Z kj  e i * mod P ) = г ji *  k i h( Z kj  e l * mod P ) = г jl *  k l Scalable Key Management for Secure Multicast Communication 13/15

14. Evaluation n : # of group userss : # of groups t : # of ave successorsm : # of ave dir-successors r : related factor computatione : changing residue computation Scalable Key Management for Secure Multicast Communication 14/15

15. Conclusions No re-keying messages, but some reporting messages Reduced enc/dec cost compared with decentralized  transferred to CA The defense of malicious attacks Scalable Key Management for Secure Multicast Communication 15/15