1. Decentralized key generation scheme for cellular- based heterogeneous wireless ad hoc networks ► Gupta, Ananya; Mukherjee, Anindo; Xie, Bin; Agrawal, Dharma P. ► Journal of Parallel and Distributed Computing Volume: 67, Issue: 9, September, 2007, pp. 981-991 97/09/12 H.-H. Ou

2. Introduction (1/2)  Cause  The key generation programs on the traditional MANET.  No prior trust relationships among ad hoc nodes due to absence of any centralized authority. In a mobile environment, it is difficult to identify an MS.  Opinion  Integration of MANET with cellular network  It enables availability of a trustable infrastructure (i.e., BS) so that validation of MS’s identify is feasible before any actual key generation.  Prerequisite  A dual-mode mobile station (MS)  variety of mediums (e.g., Bluetooth, Infrared, Wi-Fi)  Infrastructure-based (cellular, access point) networks.  Proposal  Support cellular system with a cellular-based mobile ad hoc network (MANET).  Flexible peer-to-peer communication between two MSs by utilizing a high-speed interface without passing through the BS.  Releases the traffic load in cellular wireless systems. 2008/9/122H.-H. Ou

3. Introduction (2/2)  The challenges  Multiple BSs  The MS may be associated with several BSs.  Secured channel  Maintain a secured channel between any pair of MSs in the MANET with minimal intervention of the BSs.  Scalability of key generation and distribution  Logically segregates the key management/distribution entities and group memberships.  Group key management infrastructure  MANET members may join or leave at any time. 2008/9/123H.-H. Ou

4. The features of the proposed  Decentralized key generation scheme  Using a cellular backbone for initial key setup and distribution  The BS only distributes a piece of keying material (i.e., a polynomial) to each MS so that every pair of MSs can compute the shared key between them, rather than directly managing the key with an intensive interaction.  Every pair of MSs, with the ability to calculate a shared symmetric key as required by using secure symmetric polynomial.  Symmetric polynomial key generating scheme in a hierarchical and distributed manner for communication in a MANET. 2008/9/124H.-H. Ou

5. Polynomial-based conference key  Polynomial-based conference key  A trust server selects a polynomial function f(x,y), which satisfies the property f(x,y) = f(y,x), and keeps it secretly.  Ex: f(x,y) = 1+2(x+y)+3xy  The trust server securely transmits the f(i,y) to the corresponding node i.  Node 1 : f(1,y) = 3+5y  Node 2 : f(2,y) = 5+8y  Node 3 : f(3,y) = 7+11y  When two of the nodes initiate the communication, each node just using the ID of the another node to establish a pairwise key.  Node 1 & Node 2 : f(1,2) = f(2,1) = 13  Node 1 & Node 3 : f(1,3) = f(3,1) = 18  Node 2 & Node 3 : f(2,3) = f(3,2) = 29 2008/9/125H.-H. Ou f(3,y) f(1,y) f(2,y) f(1,3) = f(3,1) f(2,3) = f(3,2) f(1,2) = f(2,1) Node3 Node1 Node2 Trust Server

6. The Terms of the proposed  NG (Node group) ： The group of MSs in a local MANET with the same polynomial distributors and derives its keying material from these leaders.  AHN (Ad Hoc node) ： An MS that belongs to an NG.  PD (Polynomial distributer) ： A BS that acts as a polynomial supplier to an NG. 2008/9/126H.-H. Ou PD 1 NG AHN 1 AHN 2 AHN 3 PD 2

7. Concept of the proposed  Polynomial-based conference key  A polynomial function f(w, x, y, z), which satisfies the property f(w, x, y, z) = f(x, w, y, z) and f(w, x, y, z) = f(w, x, z, y)  w&x represent the AHNs’ ID, and y&z represent the PDs’ ID. 2008/9/127H.-H. Ou PD 4 PD 2 PD 3 PD 1  Decentralized key generation scheme  Each PD i selects his polynomial function f i  Every PD i exchanges their f i with the neighbor PDs  Each PD i can obtains the group polynomial P i by f  PD i distribute the polynomial S j to his member AHN j, which the S j is construct from Pi and AHN j ’s ID.  Each AHNs just using the polynomial S with the ID of the another AHN to establish a pairwise key.

8. Procedures of the proposed  Group-based polynomial selection (PDs  PDs)  Exchange their polynomial f and establish the group polynomial g 2008/9/128H.-H. Ou PD 1 AHN 1 AHN 2 AHN 3 PD 2 AHN 5 AHN 4  Polynomial for AHN (PD  AHN)  Generate the user polynomial s from the group polynomial g, and distribute to AHNs.  Pairwise key generation (AHN)  Calculate the pairwise key with the communication AHN by polynomial s  Group key establishment (AHN  AHN)

9. Procedures of the group-based polynomial selection  Each PD i independently generates a t-degree symmetric polynomial   f i (w, x, y, z) = f i (x, w, y, z) and f i (w, x, y, z) = f i (w, x, z, y)  W i x j = x j w i and y m z n = z n y m  w and x represent the AHNs  y and z denote the variables associated with PDs  Send f i (w, x, y, j)  PD j  The group polynomial P i = 2008/9/129H.-H. Ou

10. Procedures of the polynomial for MS  PD i  AHN ki  S ki (x,y) = P i (ID(AHN ki ), x, y) = 2008/9/1210H.-H. Ou

11. Procedures of the pairwise key generation & Group key establishment  pairwise key generation  MS ai   MS bi   Key =  Group key establishment  Peer-to peer communication  Group communication 2008/9/1211H.-H. Ou

12. Conclusions 2008/9/1212H.-H. Ou ADN a ADN b PD i PD j f i (w, x, y, j) f j (w, x, y, i) S ki (x,y) = P i (ID(AHN ki ), x, y, i) S kj (x,y) = P j (ID(AHN ki ), x, y, j)

13. Comments  Symbol disorder (MS, ADH, BS, PD…) and unclear definition.  Decentralized??  Distributed (PDs) + Decentralized (ADNs)  Revocation?  Multi-group?  Join or leave 2008/9/1213H.-H. Ou