An Extended Multi-Server-Based User Authentication and Key Agreement Scheme with User Anonymity

1. An Extended Multi-Server-Based User Authentication and Key Agreement Scheme with User Anonymity sPEAKER: Hong-JiWei Authors:Chun-Ta Li, Cheng-Chi Lee, Chi-Yao Weng and Chun-I Fan Date: 2013-05-10 KSII TRANSACTIONS ON INTERNET AND INFORMATION SYSTEMS VOL. 7, NO. 1, Jan 2013

2. Outline • Introduction • Review of Tsaur et al.’s Scheme • Weakness of Tsauret al.’s Scheme • Li et al.’s Scheme • Security Analysis • Conclusion

3. 1. Introduction (1/1) The Environment of Multi-Server Authentication User1 Server1 User2 Server2 User3 Server3 RC ……… ……… Useri-1 Serveri-1 Useri Serveri

4. 2. Review of Tsaur et al.'s Scheme (1/4)

5. 2. Review of Tsaur et al.'s Scheme (2/4)

6. 2. Review of Tsaur et al.'s Scheme (3/4) Registration Sj RC Ui Secure Channel Secure Channel Secure Channel

7. 2. Review of Tsaur et al.'s Scheme (4/4) Log-in and Session Key Agreement Phase Sj Ui

8. 3. Weaknesses of Tsaur et al.'s Scheme (1/2) Impersonation Attack Sj Ua

9. 3. Weaknesses of Tsaur et al.'s Scheme (2/2) Many Logged-In User’s Attack Sj Ui

10. 4. Li et al.'s Scheme (1/2) Registration Sj RC Ui Secure Channel Secure Channel Secure Channel Secure Channel

11. 4. Li et al.'s Scheme (2/2) Log-in and Session Key Agreement Phase Sj Ui

12. 5. Security Analysis (1/8) Resistance to Replay Attack Sj Ui

13. 5. Security Analysis (2/8) 12 Resistance to Impersonation Attack Sj Ui

14. 5. Security Analysis (3/8) 13 Resistance to Smart Card Lost Problem Sj Ui

15. 5. Security Analysis (4/8) 14 Resistance to Off-Line Password Guessing Attack Sj Ui PWi ?

16. 5. Security Analysis (5/8) 15 Resistance to Session Key Disclosure Attack Sj Ui

17. 5. Security Analysis (6/8) 16 Resistance to Stolen-Verifier Attack Sj Ui The attacker steals the verifier table

18. 5. Security Analysis (7/8) 17 Resistance to Many Logged-In User's Attack Sj Ui

19. 5. Security Analysis (8/8) 18 Anonymity Sj Ui

20. 5. Conclusions (1/2) This paper proposed a new user anonymously authentication scheme with key agreement for multi-server environments to overcome the weakness in Tsaur et al.'s scheme. Compared with other previous multi-server authentication schemes, our extended scheme has the following five advantages.

21. 5. Conclusions (2/2) 1. It provides secure user anonymity during log-in and session key agreement phase. 2. It provides a service period management for deleting users' accounts once users are stopped the service authority. 3. It does not need to maintain the password verification table stored at the server side. 4. It provides mutual authentication and session key agreement between login user and remote server. 5. It prevents impersonation attacks and many logged-in users' attacks.

22. Q & A Many thanks for your listening

23. Comment about Li et al.'s scheme 假設U1遺失了自己的智慧卡，且該卡被S1取得，則S1能夠藉由暴力破解的方式，來取得U1的密碼PW1，並偽冒U1與其他的Sj進行通訊(For j=2,3,…,n)。詳細的攻擊方式，如下所示。 步驟1: S1取得智慧卡內的 步驟2: S1計算 來取得 步驟3: S1計算 與 步驟4：若 ，則成功推算出U1擁有的v1 步驟5：S1計算 ，For j=2,3,...,n 步驟6: S1發送驗證訊息 ，來偽冒U1與其他Sj進行通訊(For j=2,3,…,nand k=1,2,…n)。