In a pervasive computing environment, users interact with many smart devices or service providers (SPs) to obtain some useful services from them. These SPs can be either genuine or malicious. As a result, users privacy is at a greater risk, as they are prone to revealing their location, identity and transactions information to such SPs. On the other hand, user authentication is also required for SPs to provide service access control to only authorized users. In order to protect users privacy, they must be allowed to have anonymous interactions with SPs. But, authenticating and authorizing an anonymous user becomes a challenging task. In this paper, we propose a simple and efficient scheme that allows users to anonymously interact with SPs and the SPs can effectively authenticate and authorize the users based on the anonymous information submitted by the users.