Radio Frequency IDentification (RFID) has gathered a lot of interest as a good wireless technology in pervasive computing. However, the security challenge should be addressed for secure and reliable communication in RFID environment. The main goal of this paper is exploring a way to authenticate the RFID users with the cost efficiency and secure estimation advantages. The proposed mechanism inherits the benefits of existing positioning and authenticating technologies and applies a dynamic authentication method with a random generated node to help the reader estimates the distance and authenticates the user simultaneously. Our design focuses on determining the secure location of user extension by relying on RFID reader and computes distance deviation between time-based and coordinate-base estimation method.