1. Self proxy signature scheme IJCSNS International Journal of Computer Science and Network Security,VOL.7 No.2,Februry 2007 Author:Young-seol Kim,Jik Hyun Chang Presenter: 紀汶承

2. outline Introduction Preliminaries Description of a self proxy signature scheme Analysis Conclusion

3. outline Introduction Preliminaries Description of a self proxy signature scheme Analysis Conclusion

4. Introduction 基於一個人同一時間必須著手許多工作， 需要同時有很多把 key pair 去簽章不同 的工作。 必須有一把 legal key 去產生其他的 key pair 。

5. outline Introduction Preliminaries Description of a self proxy signature scheme Analysis Conclusion

6. Preliminaries Assumption:  Discrete Logarithm (DL)assumption Definition:  Setup  Proxy delegation  Self proxy signature generation  Self proxy signature verification

7. Preliminaries(cont.) Definition:  Unforgeability  Undeniability  Distinguishability  Verifiability

8. outline Introduction Preliminaries Description of a self proxy signature scheme Analysis Conclusion

9. Descripyion of a self proxy signature scheme Signer Alice 擁有 original signing private/public key pair(x a,y a ) Generate temporary self proxy signature private/public key pair (x p, y p )  Chooses,compute  Compute  Alice publish y t.

10. Descripyion of a self proxy signature scheme(cont.) Signing  Alice choose compute  Send (m,(r’,s’),r,m w ) to verifier Bob.

11. Descripyion of a self proxy signature scheme(cont.) Verification  Recover y p  Check the equation:  If holds, accept (r’,s’)

12. outline Introduction Preliminaries Description of a self proxy signature scheme Analysis Conclusion

13. Analysis 滿足 Unforgeability,  假定 Cindy 是攻擊者,  in first way, 計算出 self proxy private key x p. but 要 從 y p 求出 x p 是困難的 (DLP)  Second way, 偽造有效的 proxy signature (r’,s’),in  y p, m, p is publish, (r’,s’) is unknown. But s’ is an exponent. Therefore, it’s a DLP.  因此攻擊者要偽造有效的 self proxy signature 是 困難的.

14. Analysis(cont.) 滿足 Undeniability  在驗證的式子中，包含 y a 。因此當 verification accept. signer 無法否認有效的 message 和 signature.

15. Analysis(cont.) 滿足 Distinguishability  當 self proxy signature 被驗證, the signer’s public key and identity are used in the verification phase.  因此我們可以分辨出此為 self proxy signature not a normal signature.

16. Analysis(cont.) 滿足 Verifiability  當 self proxy signature 被驗證, the signer’s public key and identity are used in the verification phase.  有這些 public information, 任何人都可以 recover y p.  因此，所有人都可以做驗證.

17. outline Introduction Preliminaries Description of a self proxy signature scheme Analysis Conclusion

18. 在 paper 中，實現一個新的 proxy signature 的方法. 可以同時的使用多把 temporary private/public keys 去完成不同的工作. 且滿足一些安全性議題.