Weakness in a Mutual Authentication Scheme for Session Initiation   Protocol using Elliptic Curve Cryptography
  The session initiation protocol (SIP) is a powerful signaling protocol that controls communication on the Internet, establishing, maintaining, and terminating the sessions. The services that are enabled by SIP are equally applicable in the world of mobile and ubiquitous computing. In 2009, Tsai proposed an authenticated key agreement scheme as an enhancement to SIP. Very recently, Arshad et al. demonstrated that Tsai's scheme was vulnerable to offline password guessing attack and stolen-verifier attack. They also pointed that Tsai's scheme did not provide known-key secrecy and perfect forward secrecy. In order to overcome the weaknesses, Arshad et al. also proposed an improved mutual authentication scheme based on elliptic curve discrete logarithm problem for SIP and claimed that their scheme can withstand various attacks. In this paper, we do a cryptanalysis of Arshad et al.'s scheme and show that Arshad et al.'s scheme is vulnerable to the password guessing attack. 
Debiao He
cs.CR