Decentralized key generation scheme for cellular-based heterogeneous wireless ad hoc networks

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. H.-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. H.-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. H.-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. • Node1: f(1,y) = 3+5y • Node2: f(2,y) = 5+8y • Node3: 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. • Node1& Node2: f(1,2) = f(2,1) = 13 • Node1& Node3: f(1,3) = f(3,1) = 18 • Node2& Node3: f(2,3) = f(3,2) = 29 Node3 f(2,3) = f(3,2) f(1,3) = f(3,1) f(3,y) f(2,y) Node2 f(1,y) Trust Server Node1 f(1,2) = f(2,1) H.-H. Ou

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. NG AHN2 PD2 AHN1 AHN3 PD1 H.-H. Ou

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. • Decentralized key generation scheme • Each PDi selects his polynomial function fi • Every PDi exchanges their fi with the neighbor PDs • Each PDi can obtains the group polynomial Pi by f • PDidistribute the polynomial Sj to his member AHNj, which the Sj is construct from Pi and AHNj’s ID. • Each AHNs just using the polynomial S with the ID of the another AHN to establish a pairwise key. PD2 PD1 PD3 PD4 H.-H. Ou

8. Procedures of the proposed • Group-based polynomial selection (PDs  PDs) • Exchange their polynomial f and establish the group polynomial g • 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 bypolynomial s • Group key establishment (AHNAHN) PD2 PD1 AHN2 AHN3 AHN1 AHN5 AHN4 H.-H. Ou

9. Procedures of the group-based polynomial selection • Each PDi independently generates a t-degree symmetric polynomial • fi(w, x, y, z) = fi(x, w, y, z) and fi(w, x, y, z) = fi(w, x, z, y) • Wixj = xjwiand ymzn = znym • w and x represent the AHNs • y and z denote the variables associated with PDs • Send fi(w, x, y, j)  PDj • The group polynomial Pi = H.-H. Ou

10. Procedures of the polynomial for MS • PDi AHNki • Ski(x,y) = Pi(ID(AHNki), x, y) = H.-H. Ou

11. Procedures of the pairwise key generation & Group key establishment • pairwise key generation • MSai • MSbi • Key = • Group key establishment • Peer-to peer communication • Group communication H.-H. Ou

12. Conclusions fj(w, x, y, i) fi(w, x, y, j) PDj PDi Skj(x,y) = Pj(ID(AHNki), x, y, j) Ski(x,y) = Pi(ID(AHNki), x, y, i) ADNb ADNa H.-H. Ou

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