1. Secure and efficient key management in mobile ad hoc networks Authors: Bing Wu, Jie Wu, Eduardo B. Fernandez, Mohammad Ilyas, and Spyros Magliveras Sources: Journal of Network and Computer Applications, 30(3), pp. 937-954, 2007. Reporter: Chun-Ta Li ( 李俊達 )

2. 2 22 Outline  Motivation  Secure and Efficient Key Management (SEKM)  Comments

3. 3 Motivation  Key management (PKI) CA (certificate authority) Secret sharing (distribute the central trust to multiple entities)

4. 4 Motivation  Secure and Efficient Key Management (SEKM) Share updating Certificate updating Certificate expiration/revocation

5. 5 Secure and Efficient Key Management  Notations  Structure of a certificate

6. 6 SEKM scheme (cont.)  Server group substructure snapshot in SEKM

7. 7 SEKM scheme (cont.)  Group creation {ID i, SEQ i, TTL, [h(ID i, SEQ i )] K i -1 ||(TTL) K i -1 } JoinServeReq Server node 1  14, 20 {ID 1, SEQ 1, TTL, [h(ID 1, SEQ 1 )] K 1 -1 ||(TTL) K 1 -1 } Forwarding node 20  9, 21 {ID 1, SEQ 1, TTL-1, [h(ID 1, SEQ 1 )] K 1 -1 ||(TTL-1) K 20 -1 } JoinServeReply

8. 8 SEKM scheme (cont.)  Server group mesh and table snapshot  Group maintenance (soft state) JoinServerRequest and JoinServerReply

9. 9 SEKM scheme (cont.)  Share updating (k, m) Selects k active servers to perform the share update phase Each active server i generates a (k-1)-degree polynomial Server i broadcasts the witness for polynomial coefficient and its hashed signature to the server group Each active server i computes a share for server j with S i  j =g i (j) mod p and sends {[S i  j ] K j } to the corresponding server j (1< j < k) Server j’s new share

10. 10 SEKM scheme (cont.)  Certificate updating k=3, node 1 receives a certificate updating request from regular node 14 or itself Regular node 14  1 CertUpdateReq m’ CertUpdateReq = {ID 14, SEQ 5, [h(m’)] K 14 -1 } Server node 1  20 (2 tickets) Server node 1, 16 and 22 produces a partial certificate for regular node 14 by computing Cert j=1,16,22  i=14 = (K 14 ) Sj*lj(0) mod p Server node 1 combines 3 partial certificates into one certificate by computing

11. 11 SEKM scheme (cont.)  Handling certificate expiration and revocation Expired certificate  off-line or in-person reconfiguration Certificate revocation  Refuse to issue certificates  Issues wrong partial certificates  Any misbehavior or malicious attacks Accusation (signature of initiator)  CRL (Certificate Revocation List)

12. 12 Comments  Group communications N1N2N3N4 N4 multicasts to the group The group key = g N1N2N3N4 Attacker intercepts the packets and multicasts to the group For N1, N2 and N3, the group key = g N1N2N3N4’ For N4, the group key = g N1N2N3N4 Signature

13. 13 Comments (cont.)  Solutions Group key validation process Symmetric encryption N1N2N3N4 E DH12 { } E DH23 { } E DH34 { } N1, N2 and N3 send E GK {IDi, T} to N4