‘s scheme. We verify that the proposed scheme is secure against possible attacks. We also analyze the performance of the proposed scheme by comparing its computation cost and communication cost with those of other schemes.The remainder of the paper is organized as follows. Section 2 presents a review of Vaidya et al.’s scheme. Section 3 is devoted to analyzing the security of Vaidya et al.’s scheme. Section 4 proposes the improved scheme. Section 5 analyzes the security of the proposed scheme against possible attacks. Section 6 is devoted to analyzing the performance of the proposed scheme and Section 7 concludes this paper.2.?Review of Vaidya et al.’s SchemeThere are three communication parties in Vaidya et al.’s scheme [12]: a user, a gateway node, and a sensor node.

This scheme is composed of four phases: registration phase, login phase, authentication-key agreement phase, and password change phase. We describe each phase in detail in Sections 2.1�C2.4, and Table 1 shows the notations used in the remainder of the paper.Table 1.Notations [12].Registration phase begins when the user sends a registration request with his/her identity and a hashed password to the gateway node. Then, the gateway node personalizes a smart card for the user and sends it to him/her as a response to the registration request. In the registration phase, all these communication messages are transmitted in secure channels.Login phase begins when the user inserts his/her smart card into the terminal and inputs his/her identity and password.

After the verification of the user’s input value, the smart card computes and sends the authentication request to the gateway node. When the gateway node receives the authentication request from the user side, the authentication-key agreement phase begins. The gateway node verifies whether the authentication request comes from a legitimate user. If the verification is successful, the gateway node sends the authentication request to a sensor node which can respond to a request or a query from the user. In this phase, three authentication requests are transmitted. The first request is from the gateway node to the sensor node, the second is from the sensor node to the gateway node, and the final is from the gateway node to the user. As stated, when one party receives an authentication request, the party verifies its validity and sends a new authentication request to Anacetrapib the other party.

In login phase and authentication-key agreement phase, these request messages are transmitted in insecure channels. If all verifications are passed successfully, the user and the sensor node then share the session key for communication. The password change phase begins whenever the user wants to change his/her password. In the password change phase, the user side does not have to communicate with other parties.2.1.