ISSN : 1796-203X
Volume : 2    Issue : 8    Date : October 2007

Converting Group Key Agreement Protocol into Password-Based Setting – Case Study
Ratna Dutta
Page(s): 26-33
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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