Threshold password authentication against guessing attacks in Ad hoc networks

1. Threshold password authentication against guessing attacks in Ad hoc networks Chai, Zhenchuan; Cao, Zhenfu; Lu, Rongxing Ad Hoc Networks Volume: 5, Issue: 7, September, 2007, pp. 1046-1054 97/09/24H.-H. Ou

2. Introduction • Password Authentication • Password or Verification Table • Secret Share • Smart Card • Threshold Password Authentication Scheme • (t, n) threshold password authentication H.-H. Ou

3. Requirements • The password or verification tables are not stored inside the server nodes. • The password can be chosen and changed freely by the owner. • The password cannot be revealed by the administrator of the server. • The length of a password must be appropriate for memorization. • The scheme can achieve mutual authentication • The system secret cannot be leaked even if some of the server nodes are compromised. • The availability of the system should not be affected even if some of the server nodes are unavailable. • No one can impersonate a legal user to login the server. • The scheme must resist the replay attack, modification attack and stolen-verifier. • The password cannot be broken by guessing attacks even if the mobile device is lost. H.-H. Ou

4. Basic concepts of the proposed • Hard problem assumptions • Hardness of inverting an one-way hash function • Hardness of discrete logarithm program • Hardness of computational Diffie-Hellman problem • Shamir’s secret sharing scheme • (t,n) secret sharing scheme • Select a large prime p(>x), and a random polynomial f(.) over Zp of degree t-1, satisfying f(0) = x. • Give xi = f(i) to Si, I = 1,…,n • When t servers cooperate, x = f(0) = , where is the Lagrange coefficients. H.-H. Ou

5. Notations H.-H. Ou

6. The proposed(1/3) • Set up process • Select a random polynomial f(.) over Zq of degree t-1, satisfying f(0)=x. • Compute f(i)=xi, then send xi to Si through a secure channel • Discard x • Registration phase Communication server H.-H. Ou

7. The proposed(2/3) • Login & authentication phase Communication server = h(ID)x = h(ID)rxi H.-H. Ou

8. The proposed(3/3) • Changing password • User can changed freely without registration again. (?) • Smart confirm the validity of PW by interacting with ζ • Replace βwithβ-h(PW)+h(PW*) mod p H.-H. Ou

9. Discussion • No password or verification table • Users could choose their own passwords, and can change their passwords without registration again. • Allows user to choose a short and memorable password, without worrying about subjecting to guessing attacks. • Administrator of server cannot know the password of the user. • Achieves mutual authentication • Even if an intruder break into up to t-1 server nodes, he cannot obtain any information about the system key x. • Even if n-t sever nodes are unavailable, the last t nodes can still provide service to user nodes. H.-H. Ou

10. Performance • Liao-Lee-Hwang’s scheme • Designed for single client/server applications • Comparison with ten existing smart card based schemes and only the proposed can against offline guessing attacks. Liao-Lee-Hwang’s scheme ? H.-H. Ou

11. comments • How to suitable the condition of Ad hoc networks? • The changing password process is must to contact with the ζ H.-H. Ou