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بسم الله الرحمن الرحیم
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2. Key Management in Group Communication
Mohammad Dakhilalian
Electrical and Computer Faculty,
Isfahan University of Technology (IUT)

3. Topics Introduction Key Management
Key Management in Group Communication
Centralized
Distributed
Decentralized

4. Introduction
Group communication: a means for providing multi-point to multi-point communication, by organizing processes in groups.
Efficiency: using minimum resources and hence saving bandwidth.

5. Examples Video conference Radar Tracking VPN On-line Chat
On-line playing
...

6. Introduction
Dynamic Group Communication has an active membership section,
Join
Leave
Merge
Partition

7. Is Security Important?

8. C I A Is Security Important?
Confidentiality
Integrity
Availability
Using Cryptography Algorithms as a trivial Solution. I C A

9. Topics Introduction Key Management
Key Management in Group Communication
Centralized
Distributed
Decentralized

10. Key Management Architecture
Secure Applications
Authorization, Access control, Non-repudiation …
Encryption, Authentication
Key Management

11. Key Management
Administration and use of the services of generation, registration, certification, distribution, installation and destruction of keying material.
The objective of key management is the secure administration and use of these management services and therefore the protection of keys is extremely important.

12. Definitions Key agreement Key confirmation Entity authentication
Key Distribution Centre (KDC)
Key Translation Centre (KTC)
Certification Authority (CA)

13. Key Management Techniques
Mechanisms using Symmetric Algorithms
Pre-shared key
Using KDC
Using KTC
Mechanisms using Asymmetric Algorithms
Certificate based (or using a TTP)
ID (Identity) based

14. Example (Pre-Shared key)
A , NA A B
B , {KB , NB , NA}KAB
A , {KA , NA , NB}KAB
K=g(KA ,KB)

15. Example (KDC) KDC = KA = KB Generates KAB A, B, N, {A,T}KA
{B,N,KAB}KA, {A,KAB}KB A B
{A,T}KAB, {A,KAB}KB
KAB
KAB

16. Example (KTC) KTC = KA = KB Translates KAB A, {KAB , B}KA {A,KAB}KB A

17. Example (Certificate)
B , N,CertB A B
CertA , [{N, KAB}PKB]SKA
PK : Public Key
SK : Secret Key

18. How ID Based works in practice Alice sends a Message to Bob
Key Server
Receives Private Key for 3
Requests private key, authenticates 2
Notes:
Alice encrypts with Bob’s ID, here address
No key lookup is required
Bob is not provisioned yet – ad hoc
In a PKI system, Bob generates key himself – In IBE no longer possible. Ig Bob could, so could everyone else
Instead bob goes to a key server
Only Key server can generate the key
Bob authenticates
Bob gets key decrypts
Alice encrypts with 1
Bob decrypts with Private Key 4

19. Topics Introduction Key Management
Key Management in Group Communication
Centralized
Distributed
Decentralized

20. Key Management in SGC (Secure Group Communication)
Establishment and maintenance of key (Group Key) between valid parties according to a security policy being enforced on the group.

21. … Simple Group Rekeying KDC
k = Group key
KDC
{k}k1 …
{k}k8
{k}k2 k1 k2 k3 k4 k5 k6 k7 k8
The cost of using the simple scheme in large groups is very high. u1 u2 u3 u4 u5 u6 u7 u8

22. Group Key Management Criteria
Scalability
Robustness
Anonymity
Dynamic
Forward, Backward Secrecy
Collusion
Transmission Efficiency
Computational Efficiency

23. Key Management Role
Providing member identification and authentication.
Access control.
Generation, distribution and installation of key material.

24. Different Approaches to Group Key Management.
Centralized
Distributed
Decentralized

25. Centralized group key management
The efficiency of protocols can be measured by:
Storage requirements.
Size of messages.
Backwards and forward secrecy.
Collusion

26. The solution has no forward secrecy
Example k1 k2 u1 u2 k3 k4 u3 u4 k5 k6 u5 u6 k7 k8 u7 u8
KDC
Broadcast {knew }kold
The solution has no forward secrecy

27. Example LKH (Logical key Hierarchy)u1 u2 u3 u4 u5 u6 u7 u8

28. LKH Join {k’}k’14 {k’}k58 {k’14}k12 {k’14}k’34 {k’34}k3 {k’34}k4 k k’u1 u2 u3 u4 u5 u6 u7 u8

29. LKH Leave {k’}k14 {k’}k’58 {k’56}k’56 {k’78}k78 {k’56}k6 k’ k k14 k’58u1 u2 u3 u4 u5 u6 u7 u8

30. Example OFT (One way Function Tree) Joink k’
k13
k’14
k58
k12
k34
k’34
k56
k78 k1 k2 k3 k4 k5 k6 k7 k8 u1 u2 u3 u4 u5 u6 u7 u8

31. OFT Leave k’ k k14 k’14 k58 k12 k34 k’4 k56 k78 k1 k2 k3 k3 k4 k5 k6u1 u2 u3 u4 u5 u6 u7 u8

32. Topics Introduction Key Management
Key Management in Group Communication
Centralized
Distributed
Decentralized

33. Distributed group key management
The efficiency of protocols can be measured by:
Number of rounds
Number of messages.
Processing during setup.

34. Example (CLIQUES): (Group Diffie-Helman Key Exchange)
K= gk1k2k3k4 k4
gk2k3k4 , gk1k3k4 ,gk1k2k4
Broadcast
gk1k2 ,gk1k3 , gk2k3 ,gk1k2k3
K= gk1k2k3k4
K= gk1k2k3k4
K= gk1k2k3k4
gk1
gk1 , gk2 ,gk1k2 k1 k2 k3 u1 u2 u3

35. Example(STR): k k14 k5 k13 k4 k12 k3 k1 k2 Blinding function u5 u4 u3

36. STR- Join k’ k
k’14 k5
sponsor
k13
k’4 k4 u5
k12 k3 u4 k1 k2 u3 u1 u2

37. STR -Leave k k’ k’14 k14 k5 k13 k4 k12 k’12 k3 k3 sponsor k1 k2 k’2 u5

38. TGDH join k k’ k14 k58 k’58 sponsor k12 k34 k56 k’7 k’78 k7 k1 k2 k3u1 u2 u3 u4 u5 u6 u7 u8

39. TGDH leave k k’ k14 k58 k’58 k12 k34 k56 k78 sponsor k1 k2 k3 k4 k’5u1 u2 u3 u4 u5 u6 u7 u8

40. Topics Introduction Key Management
Key Management in Group Communication
Centralized
Distributed
Decentralized

41. Decentralized group key management
The efficiency of protocols can be measured by:
Key independence.
Decentralized controller.
Local rekeying.
Rekeying per membership.
Type of communication.
Keys versus Data path

42. IOLUS hierarchy k4 k3
GSA3
GSA4 k1 k6
GSA1
GSA6 k2 k5
GSA2
GSA5

43. Intra-Domain Group Key Management Elements
All-KD-group k
DKD k
AKD 1 k
AKD 2 k
AKD 3
m m m
m m m
m m m k1 k2 k3
Local area group
Local area group
Local area group

44. Summary Definition of Group Communication (GC) and Secure GC(SGC)
Key Management with emphasis on Key Agreement
Type of Key Management Approach in Group Communication and their examples
(LKH,OFT,CLIQUES,STR,TGDH,IOLUS,IGKMP)

45. با تشکر از تمامی شرکت کنندگان در جلسه
با تشکر از تمامی شرکت کنندگان در جلسه