Summary: Password-based authentication protocols are currently the conventional authentication protocols in many distributed systems. However, the security of these protocols is falling behind the times because more and more attacks can now break them. The security weaknesses of the Simple And Secure (SAS) protocol, the optimal strong-password authentication protocol, and the revised SAS protocols are examined in this paper. We then propose our RObust and SImple (ROSI) protocol to help raise security levels. The ROSI protocol can be easily implemented and has lower communication costs than most other protocols.