1. Efficient verifier-based key agreement protocol for three parties without server’s public key Source: Applied Mathematics and Computation 167 (2005)996-1003 Author: Sung-Woon Lee, Hyun-Sung Kim, Kee- Young Yoo Presenter: Li-Tzu Chang

2. Outline Introduction Efficient verifier-based key agreement protocol for three-parties Security analysis Conclusions

3. Introduction Three-party password table trusted server password A password B session key

4. Outline Introduction Efficient verifier-based key agreement protocol for three-parties Security analysis Conclusions

5. Preliminaries

6. Proposed protocol Register AASB (v A ) (v B ) v A, v B (password table)

7. Proposed protocol AASB (A,X A ) (A,X A,B,X B ) (X B ) (X SB ) (X SA )

8. Proposed protocol AASB (X SA ) (X SB ) (A,X A,B,X B,X SA, X SB ) (v AS ) (v BS )

9. Proposed protocol AASB (v SA ) (v SB )

10. Outline Introduction Efficient verifier-based key agreement protocol for three-parties Security analysis Conclusions

11. Security analysis AS 可透過 v AS 、 v BS 確認 Alice 和 Bob 的合法身份 且確定收到訊息； Alice 和 Bob 可透過 v SA 、 v SB 認證 AS 的深份和收到訊息 Attackers can’t directly compute the passwords or the session key Against attackers masquerade clients or server Using ‘ ⊕ ‘ operation to against password guessing attack

12. Outline Introduction Efficient verifier-based key agreement protocol for three-parties Security analysis Conclusions

13. proposed a new verifier-based key agreement protocol for three-parties, which does not require servers public key but requires each client only to remember a memorable password.