1. A novel and efficient unlinkable secret handshakes scheme Author: Hai Huang and Zhenfu Cao (PR China) Source: IEEE Comm. Letters 13 (5) (2009) Presenter: Yu-Chi Chen

2. Outline Introduction Huang and Cao’s scheme Conclusions

3. Introduction A secret handshakes scheme – affiliation-hiding authentication – firstly introduced by Balfanz et al. – For example, two FBI agents, Alice and Bob, want to discover and communicates with other agents, but they don’t want to reveal their affiliations to non-agents.

4. Introduction An unlinkable secret handshakes scheme – provide unlinkability – an adversary cannot link any two different instances of same party. Given C, to guess C is AB, A’B’, or other. (blind signature) unlinkability has been widely considered in many applications.

5. Introduction Jarecki et al.’s scheme – an unlinkable secret handshakes scheme – not efficient, but secure at present Huang and Cao presented an unlinkable secret handshakes scheme – novel and efficient – Simple, so it can be published in IEEE-CL.

6. Outline Introduction Huang and Cao’s scheme Conclusions

7. Bilinear pairing Referred to as “bilinear maps” e: G 1 × G 2 →G 3 G 1, G 2 : (+, q) G 3 : (×, q)

8. Bilinear pairing Properties: – Computation: given P 1 (P 2 ) in G 1 (G 2 ), we can obtain e(P 1, P 2 ) in G 3 – Bilinear: given xP 1 and bP 2, where a, b in Z q, then e(aP 1, bP 2 ) = e(P 1, P 2 ) ab – Non-degenerate: P 1 (P 2 ) is a generator of G 1 (G 2 ), then e(P 1, P 2 ) ≠ 1. (or e(P 1, P 2 ) is a generator of G 3 )

9. Huang and Cao’s scheme This figure is copied from IEEE Comm. Letters 13 (9) (2009), page 731

10. Conclusions Huang and Cao analyzed this scheme can provide authenticated key exchange security, affiliation-hiding, and unlinkability. The scheme is more efficient than Jarecki et al.’s.

11. On the security of a novel and efficient unlinkable secret handshakes scheme Author: Renwang Su (PR China) Source: IEEE Comm. Letters 13 (9) (2009)

12. Su found Huang and Cao’s scheme is not secure. – Cannot provide authenticated key exchange security.

13. This figure is copied from IEEE Comm. Letters 13 (9) (2009), page 731

14. Security analysis of an unlinkable secret handshakes scheme Author: T.-Y. Youn and Y.-H. Park (Korea) Source: IEEE Comm. Letters 14 (1) (2009)

15. Youn and Park also found Huang and Cao’s scheme is not secure. – Cannot provide authenticated key exchange security and affiliation-hiding.

16. Receiving v B, then try find PK where v B =H 1 (K A, (PK, E A, E B ), resp)