Abstract
The session initiation protocol (SIP) is the most widely used signaling protocol for controlling communication on the Internet, establishing, maintaining, and terminating the sessions. To get secure communication, many authentication protocols for SIP have been proposed. Very recently, Zhang et al. proposed a new authenticated key agreement protocol for SIP using smart card. They also show their protocol could withstand various attacks. However, in this paper, we point out that their protocol is vulnerable to the impersonation attack. We also propose an improved protocol to overcome the weakness. Security analysis shows that our protocol could overcome the weaknesses in Zhang et al.’s protocol. Performance analysis shows that the computational cost in the authentication phase of our protocol is about 75 % of Zhang et al.’s protocol.