Note on Robust and Simple Authentication Protocol

The password-based authentication protocol is the conventional authentication protocol in many distributed systems to authenticate the remote users. However, a passwordbased protocol is vulnerable to the guessing attack, the replay attack, the stolen-verifier problem and the forgery attack [1]. These attacks bother the SAS protocol [2], the revised SAS-1 [3], the revised SAS-2 [3] and the OSPA protocol [4]. Based on low-cost smart cards that support only simple hashing operations, ROSI [5] is a highly efficient password-based authentication protocol. Its simplicity, resistance to existing known attacks and high performance make it much more attractive than its counterparts [2, 3, 4]. However, the protocol requires state synchronization between the client and the server, and we shall exploit this property to launch the DOS attack on the ROSI protocol. We shall also propose an improved scheme that conquers the weakness and extends its key agreement function, and improves the server’s performance.