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

5. 5 Basic assumptions and definitions  M: The plaintext sent by a source node  T stamp : system time synchronization  K C : 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  ID i : The unique identity of node i  Z i : An inverse of (ID i - 1) on modulo p-1  K i,j : A set of secret shadows  Λ i,j : A set of secret parameters corresponding to K i,j, Λ i,j = (g K i,j ) Z i mod p

6. 6 Two-tier authentication  First tier: cluster authentication Source node:  Step 1: generate T stamp  Step 2: generate MAC M = H(K C ; T stamp,M)  Step 3: generate the cluster signature MAC T = H(K C ;T stamp )  Step 4: generate encrypted message E KC (MAC M,T stamp,M)  Step 5: transmit the output packet PKT M = {MAC T,T stamp,E KC (MAC M,T stamp,M)}

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

8. = g a 1 +a 0 mod p = g a 0 mod p

9. 9 Two-tier authentication (cont.)  Second tier: individual authentication for a number of destination nodes (1 source + 2 destination) ID α (Source node) ID ω (destination node) ID ζ (destination node) 1. route discovery 2. generate a 0 and RAND α 3. find a 1 and a 2 on the function f 2 (x) = a 2 x 2 +a 1 x+a 0 mod (p-1) 4. generate Γ 1 and Γ 2 5. Authentication packet {Γ 1, Γ 2, RAND α } 6. compute the common session key K S = g a 0 mod p

10. 10 Two-tier authentication (cont.)  generation of K S = g a 0 mod p ID ω (destination node) 1.ω can compute 2.ω performs the computations as X 1 and X 2 together with the result of g Kα,ω 3.An approaching key AK is obtained by 4. inverse element d 5.The computation of, which is identical to the session key of K S

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

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