Method and system for user authentication are described. The method comprises receiving an authentication code from an application server seeking authentication of the user. Further, a private key of the user is computed in real time based on a user identity (ID) of the user and a master secret key of the PKG. The method further comprises, ascertaining a verification code based on the private key of the user and a verification timestamp, wherein the verification timestamp indicates a time at which the ascertaining of the verification code was initiated. Further, the authentication code is compared with the verification code. Further, the method comprises authenticating the user based on the comparison.