Three-party encrypted key exchange without server public-keys

Abstract

Three-party key-exchange protocols with password authentication-clients share an easy-to-remember password with a trusted server only-are very suitable for applications requiring secure communications between many light-weight clients (end users); it is simply impractical that every two clients share a common secret. Steiner, Tsudik and Waidner (1995) proposed a realization of such a three-party protocol based on the encrypted key exchange (EKE) protocols. However, their protocol was later demonstrated to be vulnerable to off-line and undetectable on-line guessing attacks. Lin, Sun and Hwang (see ACM Operating Syst. Rev., vol.34, no. 4, p.12-20, 2000) proposed a secure three-party protocol with server public-keys. However, the approach of using server public-keys is not always a satisfactory solution and is impractical for some environments. We propose a secure three-party EKE protocol without server public-keys.