1. Inter-Domain Identity-Based Authenticated Key Agreement Protocols from Weil Pairing Authors: Hong-bin Tasi, Yun-Peng Chiu and Chin-Laung Lei From:ISC2006 Presented: 魏聲尊

2. Outline Introduction Preliminaries The Proposed Protocol Conclusions

3. Introduction A key agreement protocol that provides mutual key authentication is called an authenticated key agreement protocol. Communicating parties using pairing to establish a share secret must require a globally agreed P in distinct domain. This may need vast cost of parameter update and cause another problem. So they proposed a new protocol that is more scalable and practical.

4. Introduction TA 1 TA 2 TA n TTP Alice A globally agreed P Bob TTP: trusted third party TA: trusted authority

5. Preliminaries A pairing is a computable bilinear map between an additive group,, and a multiplicative group. and are of prime order q. The Weil pairing is a map which satisfies the following three properties: –Bilinear: If –Non-degenerate: There exist a generator such that –Computable: If, one can compute in polynomial time

6. Preliminaries The security of this protocol relies on the hardness of the co-bilinear Diffie-Hellman problem, which is assumed to be a hard problem derived from Diffie-Hellman problem.

7. TA 1 TA 2 TA n Alice The Proposed Protocol Bob Ephemeral private key: a Ephemeral private key: b TA: Trusted Authorities H 1 :0,1*  G 1

8. The Proposed Protocol Then Alice and Bob have their shared session key is where is a key derivation function.

9. Conclusions They argue that from a practical point of view, a globally agreed P leave key update a heavy burden. Besides, the different accomplished time may cause parties in different domains unable to establish a share secret key. To solve these problem, they propose an inter- domain ID-AK protocol through pairings without the requirement of using identical generator.