An optimized certificate-based protocol for mobile network with authentication and security has been proposed
by Yi et al. This protocol allows efficient computation and less storage requirement in the mobile device. As a result,
less power is consumed in the mobile device. However, in 1999, 2002, and 2003, Martin et al., Wong, and Laih et al. respectively showed that Yi et al.’s scheme is vulnerable to some attacks, but did not remedy these attacks. In this paper, we propose an improved protocol to remedy these attacks. Using the new protocol, the protection against attacks can be assured. The security of the key distribution on the mobile network is enhanced as well.