¹Cryptography and Security Department, Institute for Infocomm Research 21 Heng Mui Keng Terrace, Singapore 119613

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Abstract—Converting a secure group key agreement protocol into password-based setting is not a trivial task. The security of a password-based scheme hinges on preventing dictionary attack that enables an adversary to take advantage of the low entropy of human memorable passwords. In this paper, we make a case study considering the constant round group key agreement protocol DB proposed by Dutta- Barua, which is a simple variant of Burmester-Desmedt protocol BD. We present a simple and elegant contributory group key agreement in password-based setting derived from the protocol DB. We discuss several issues regarding the difficulties of converting this DB protocol into password-based setting. We have made several modifications in the protocol DB and then enhance it to password-based setting. The security of the proposed scheme against dictionary attacks is in the ideal cipher model under Decision Diffie-Hellman (DDH) assumption. We analyze our protocol in the security framework formalized by Bellare et al. Our proposed scheme achieves efficiency over the work of Bresson et al. in terms of both computation and communication power.

Index Terms—password-based group key agreement, DDH problem, dictionary attack

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Cite: Ratna Dutta, "Converting Group Key Agreement Protocol into Password-Based Setting – Case Study," Journal of Computers vol. 2, no. 8, pp.26-33, 2007.