Interactive diffie-hellman assumptions with applications to password-based authentication

Abstract

Password-based authenticated key exchange are protocols that are designed to provide strong authentication for client-server applications, such as online banking, even when the users' secret keys are considered weak (e.g., a four-digit pin). In this paper, we address this problem in the three-party setting, in which the parties trying to authenticate each other and to establish a session key only share a password with a trusted server and not directly among themselves. This is the same setting used in the popular Kerberos network authentication system. More precisely, we introduce a new three-party password-based authenticated key exchange protocol. Our protocol is reasonably efficient and has a per-user computational cost that is comparable to that of the underlying two-party authenticated key exchange protocol. The proof of security is in the random oracle model and is based on new and apparently stronger variants of the decisional Diffie-Hellman problem which are of independent interest. © Springer-Verlag Berlin Heidelberg 2005.