In a distributed system, authentication protocols are the basis of security to ensure that these protocols function properly. Passwords are one of the most common authentication protocol used nowadays. Because of low entropy of passwords make the systems vulnerable to password guessing attacks. This paper presents a simple scheme that strengthens password-based authentication protocols and helps prevent dictionary attacks, replay attacks and man in the middle attacks etc. The proposed scheme presents a new password authentication protocol by using the user and server system identification/serial number. Here there is no possibility to store the user passwords so an attacker who gets the password cannot use it directly to gain immediate access and compromise security.