Two-tier authentication for cluster and individual sets in mobile ad hoc networks

1. Two-tier authentication for cluster and individual sets in mobile ad hoc networks Authors: Yuh-Ren Tsai and Shiuh-Jeng Wang Sources: Computer Networks, article in press Reporter: Chun-Ta Li (李俊達)

2. Outline • Introduction • Basic assumptions and definitions • Two-tier authentication • First tier: cluster authentication • Second tier: individual authentication for unicast • Second tier: individual authentication for a number of destination nodes • Second tier: route authentication for the same pair of nodes • Comments

3. Introduction • Motivation • Routing security in mobile ad hoc networks (session key) • prevent internal and external attacks (black holes, impersonation) • prevent routing table overflows • prevent energy consumption attacks • Two-tier authentication scheme for cluster and individual sets in MANETs • Source-initiated on-demand driven protocol • Hash function and MAC concept in first tier (group) • Secret sharing technology in second tier (individual)

4. Routing path discovery Authentication and Confirmation packets for user authentication Introduction (cont.)

5. Basic assumptions and definitions • M: The plaintext sent by a source node • Tstamp: system time synchronization • KC: A common secret key hold by all nodes • A symmetric cryptosystem • H(.): A collision-free hash function • p, g: A large prime number and a generator • IDi: The unique identity of node i • Zi: An inverse of (IDi - 1) on modulo p-1 • Ki,j: A set of secret shadows • Λi,j: A set of secret parameters corresponding to Ki,j, Λi,j = (gKi,j)Zi mod p

6. Two-tier authentication • First tier: cluster authentication • Source node: • Step 1: generate Tstamp • Step 2: generate MACM = H(KC; Tstamp,M) • Step 3: generate the cluster signature MACT = H(KC;Tstamp) • Step 4: generate encrypted message EKC(MACM,Tstamp,M) • Step 5: transmit the output packet PKTM = {MACT,Tstamp,EKC(MACM,Tstamp,M)}

7. Two-tier authentication (cont.) • Second tier: individual authentication for unicast

8. = ga1+a0 mod p = ga0 mod p

9. Two-tier authentication (cont.) • Second tier: individual authentication for a number of destination nodes (1 source + 2 destination) 1. route discovery IDω (destination node) IDα (Source node) IDζ (destination node) 2. generate a0 and RANDα 3. find a1 and a2 on the function f2(x) = a2x2+a1x+a0 mod (p-1) 6. compute the common session key KS = ga0 mod p 5. Authentication packet {Γ1, Γ2, RANDα} 4. generate Γ1 and Γ2

10. 5.The computation of , which is identical to the session key of KS Two-tier authentication (cont.) • generation of KS = ga0 mod p IDω (destination node) 1.ω can compute 2.ω performs the computations as X1 and X2 together with the result of gKα,ω 3.An approaching key AK is obtained by 4. inverse element d

11. Two-tier authentication (cont.) • Second tier: route authentication for the same pair of nodes

12. Comments • Authentication message • The concept of conference key • Renewal of secret shadow