Overcome Weakness of a Password-Based Group Key Agreement Protocol

Recently, Kim et al. proposed a very efficient provably secure group key agreement protocol KLL, security of which relies on the computational Diffie-Hellman (CDH) assumption in the presence of random oracles. In our earlier work, we embed the protocol KLL into password-based environment -yielding the protocol DB-PWD. In this paper, we detect certain flaws in the protocol DB-PWD and take suitable measures to overcome these attacks. We introduce a protocol MDB-PWD -an improved variant of the protocol DB-PWD and analyze its security in the security framework formalized by Bellare et al. in both the ideal cipher model and the random oracle model under CDH assumption.