1. Accelerating Key Establishment Protocols for Mobile Communication Source: Lecture Notes in Computer Science, 1999, Volume 1587/1999, 51-63pp. Author: Seungwon Lee ,Seong-Min Hong ,Hyunsoo Yoon ,Yookun Cho Presenter:林志鴻

2. Outline • Introduction • Keyestablishment protocols in mobile • Sever-aided secret computation

3. Introduction • Secure channel between base station and mobile station • Public-key cryptosystem and secret-key cryptosystem • Secret-key cryptosystem • Key management • More dangerous than Public-key cryptosystem

4. Introduction (cont.) • Key establishment protocols • Beller et. al. – MSR (Modular Square Root) + Diffie-Hellman • Beller and Yacobi – ElGamal • Aziz and Diffie’s protocol • In this paper – SASC (sever-aided secret compution)

5. Outline • Introduction • Key establishment protocols in mobile • Sever-aided secret computation

6. Key establishment protocols in mobile • MSR+DH: Beller et. al. Step1: B ,NB ,PKB ,Cert(B) Step2: B: base M: mobile

7. Key establishment protocols in mobile • Beller and Yacobi’s protocol Step1: B ,NB ,PKB ,Cert(B) Step2: B: base M: mobile Step3: {NB}x

8. Key establishment protocols in mobile • Aziz and Diffie’s protocol Step1: Cert(M) ,NM,alg_list Step2: B: base M: mobile Step3:

9. Outline • Introduction • Key establishment protocols in mobile • Sever-aided secret computation

10. Sever-aided secret computation • Slitting-based techniques • Decomposition of secret s into several pieces ,( Beguin and Quisquater’s ) • Blinding-based techniques • Using a random number to blind the secret s

11. Sever-aided secret computation • Adaptation of SASC Mobile Station Base Station 1、Modified_secrets 2、Pseudo-signing(/decryption) With modified_secrets 3、Pseudo-signed_messages (/pseudo-decrypted_messages, Hash_value of the plaintext) 4、Postcalculation & verification

12. Heavy operations at mobile station side

13. Acceleration of improved BY scheme • 目標︰加快gr mod p • 隨機選取m個x與b滿足 並將b傳給base station • base計算 ,for 0 ≦i≦m-1 • mobile 計算

14. Performance Analysis