1. A scalable and distributed multicast security protocol using a subgroup-key hierarchy
Source: Computers & Security, vol.23, pp , 2004
Author: Heba K. Aslan
Speaker: Yu-Wei Su

2. Outline
Introduction
Group Key
Proposed Protocol
Conclusions

3. Introduction Unicast to Multicast Group communication under security
Scalable
Goal

4. Group Key Join & Leave – backward secrecy & forward secrecy
Three classes of group key approaches

5. Group Key – Distributed approaches
Like Conference Key
Each group member contributes to generate the group key
Not scalable

6. Group Key – Centralized approaches
one central entity maintain the security of the group
Not scalable
LKH scheme C K2 K1 K3 K4 K5 K6 K7 U1 U2 U3 U4
Central entity
Symmetric Key
Group member

7. Centralized approaches – member join
C and U5 exchange K8
C generates K1-new, K3-new
C broadcast EK1(K1-new)
C broadcast EK3(K3-new)
C broadcast EK8(K1-new, K3-new)
K1-new K1 K2 K3
K3-new K4 K5 K6 K7 K8 U1 U2 U3 U4 U5

8. Centralized approaches – member leave
Delete K7
C Generates K1-new, K3-new
C broadcast EK6(K1-new, K3-new)
C broadcast Ek2(K1-new)
K1-new K1 K2
K3-new K3 K4 K5 K6 K7 U1 U2 U3 U4

9. Group Key – Distributed Subgroup approaches
Group Controller (GC) & Subgroup Controller (SC)
Iolus
scalable K3 GC
SC3
subgroup 1 K1 K2
SC1
SC2
subgroup 3
subgroup 2

10. Proposed Protocol – concept
KGC , KSC3
SC3 U1 U2 U3 U4 GC
KGC , KSC1
KGC , KSC2
subgroup 1
SC2 U1 U2 U3 U4
SC1 U1 U2 U3 U4
subgroup 3
subgroup 2

11. Proposed Protocol – Subgroup Hierarchy
SCi
KSCi(h,d)
h: heigh
d: number
Broadcast key
KSCi(0,1)
KSCi(0,1)
...
KSCi(1,1)
KSCi(1,2)
KSCi(1,d)
KSCi(h,1) U1

12. Proposed Protocol – Operations
Subgroup controller join
Message broadcast
Member join
Member leave

13. Subgroup controller joinGC
1. GC and SC4 Exchange KSC4
KSC4
SC4
2. GC Generates a KGC-new
KGC
3. broadcast EKGC(KGC-new)
and EKSC4(KGC-new)
KGC
KGC
SC3
SC1
SC2

14. Message broadcast GC GC generates a session KGC Key Kmess
SCi
KSCi(0,1) U1 U2 U3 U4
2. GC broadcast EKGC(Kmess)
3. Every SC DKGC(Kmess), and
then broadcast EKSCi(0,1)(Kmess)
subgroup i

15. Member join & leave in a subgroup
Just like LKH, page.7, page.8

16. Conclusions
Achieving Multicast & Unicast
Scalable