An embodiment for securely accessing services of a service provider based on single sign on. The user device is authenticated by an authentication server if the computed hash of the first random number r is same as the received hash of the first random number r sent by a user device. Thereafter, the second random number y, the user id and an element Q are encrypted using a service provider password and send to the service provider. The user device computes a first discrete exponential function Z using the element Q and the second random number y and sends along with the user id to the service provider. The service provider computes a second discrete exponential function Z′ using the element Q and the second random number y received from the authentication server and provides the user device access to the services if Z is equal to Z′.