1. A Server-aided Signature Scheme Based on Secret Sharing for Mobile Commerce Source: Journal of Computers, Vol.19, No.1, April 2008 Author: Chin-Ling Chen, Ling-Chun Liu, Gwoboa Horng Presenter: Chun-Yen Lee

2. Outline  Introduction  The Proposed Protocol Notation Negotiation Phase Authentication Phase  Comparison  Conclusions

3. Introduction

4. Outline  Introduction  The Proposed Protocol Notation Negotiation Phase Authentication Phase  Comparison  Conclusions

5. Outline  Introduction  The Proposed Protocol Notation Negotiation Phase Authentication Phase  Comparison  Conclusions

6. Notation  A :a mobile user.  B :the application server.  PS :a trusted proxy server.  a 0 : A random seed which is negotiated by a mobile user and trusted proxy server in advance.  m req :the request message.  M : the signed object.  ID x :X’s identity

7. Notation  P A : a pre-selected pseudonym of mobile user A  K : the symmetric session key.  PW i :the i th password.  (p x, q x ) : a pair of large prime numbers.  N X = p x q x, PK X, SK X

8. The Proposed Protocol Notation Negotiation Phase Authentication Phase

9. Negotiation Phase Mobile User (A)Trusted Proxy Server (PS) (PW 0,ID A ) A creates a register with the PS, and stores the (ID PS, SEED) 2.1 Compute 2.2 (ID A, Y A ) 3.1 Compute 3.2 (ID PS, Y PS )

10. Negotiation Phase Mobile User (A)Trusted Proxy Server (PS) 3.2 (ID PS, Y PS ) 4.1Compute 4.2(ID A, C 1 ) 5.1Compute Check the received PW 0 for i = 1 to n C 2 = E K (n, a 0, ID PS ) 5.2 (ID PS, C 2 ) 6.1 D K (C 2 )=(n, a 0, ID PS ) 6.Download (n, a 0, ID PS, K) to mobile device

11. The Proposed Protocol Notation Negotiation Phase Authentication Phase

12. Mobile User (A)Trusted Proxy Server (PS)Application Server (B)Mobile User (A)Trusted Proxy Server (PS) (M 1, X 1 )

13. Authentication Phase Mobile User (A)Trusted Proxy Server (PS) (M 1, X 1 )

14. Authentication Phase Mobile User (A)Trusted Proxy Server (PS)Application Server (B)Trusted Proxy Server (PS)Application Server (B) M 2, Sig π, Sig PS

15. Authentication Phase Trusted Proxy Server (PS)Application Server (B) Sig B

16. Outline  Introduction  The Proposed Protocol Notation Negotiation Phase Authentication Phase  Comparison  Conclusions

17. Computation comparison

18. Outline  Introduction  The Proposed Protocol Notation Negotiation Phase Authentication Phase  Comparison  Conclusions

19. Conclusions 1. 利用 verification 和 secret sharing 機制來達成 更好的安全性。 2. 透過此篇文章所提出的方法，解決 mobile devices 運算能力不足的問題。