Cryptology ePrint Archive: Report 2008/537

A Secure Threshold Anonymous Password-Authenticated Key Exchange Protocol

SeongHan Shin and Kazukuni Kobara and Hideki Imai

Abstract: At Indocrypt 2005, Viet et al., [22] have proposed an anonymous password-authenticated key exchange (PAKE) protocol and its threshold construction both of which are designed for client's password-based authentication and anonymity against a passive server, who does not deviate the protocol. In this paper, we first point out that their threshold construction is completely insecure against off-line dictionary attacks. For the threshold t > 1, we propose a secure threshold anonymous PAKE (for short, TAP) protocol with the number of clients n upper-bounded, such that n \leq 2 \sqrt{N-1} -1, where N is a dictionary size of passwords. We rigorously prove that the TAP protocol has semantic security of session keys in the random oracle model by showing the reduction to the computational Diffie-Hellman problem. In addition, the TAP protocol provides unconditional anonymity against a passive server. For the threshold t=1, we propose an efficient anonymous PAKE protocol that significantly improves efficiency in terms of computation costs and communication bandwidth compared to the original (not threshold) anonymous PAKE protocol [22].

Category / Keywords: cryptographic protocols / password authentication, key exchange, PAKE, anonymity, provable security

Publication Info: This is the full version of IWSEC2007 paper.

Date: received 21 Dec 2008

Contact author: seonghan shin at aist go jp

Available format(s): PDF | BibTeX Citation

Note: In this paper, we added some comments (including an attack) on Yang and Zhang's Indocrypt2008 paper.

Version: 20081228:085732 (All versions of this report)

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