Efficient verifier-based key agreement protocol for three parties without server's public key

So far, there have been several key agreement protocols for three-parties, in which two clients establish a common session key through a authentication server. Most of those protocols require to use server's public key to prevent password guessing attacks. However, because clients need to verify and safely keep the server's public key, the protocols may not be practical for some environments. This paper proposes a new efficient verifier-based key agreement protocol for three parties which does not require server's public key. The proposed protocol is resistant against various attacks and provides the perfect forward secrecy.