DYNAMIC DELAY TIME DECISION METHOD FOR ENHANCING SECURITY OF THE FORCED LATENCY INTERLOCK PROTOCOL IN INTERNET OF THINGS

Most devices in the Internet of Things (IoT) utilize WiMAX communication, and Femtocells are used to provide reliable communication by eliminating shaded areas where wireless signals become weaker with distance and underground facilities. One downfall of this method is the possibility of eavesdropping through Man-in-the-Middle attacks. Forced latency interlock protocol is used to detect these attacks. This protocol uses a fixed latency value and does not consider packet size and distance. In this paper, we propose a dynamic delay time decision method for reducing the fixed delay time of the forced latency interlock protocol in wireless communications based on the IoT. The evaluation function considers the distance between the device, the packet size


INTRODUCTION
The Internet of Things (IoT) is the interaction of the state with or without user intervention between people/things and things. Many IoT devices configured on the IoT environment can suffer from the shaded area problem or signal weakness due to distance and underground communications in existing networks (WiMAX). When shaded areas cause door lock, refrigerators, washing machines, lighting, and electronic devices such as IoT devices may deteriorate the internet service [1]. This problem can be solved by installing base station (BS) in the shaded area; however, installing them over many shaded areas may expand the area where service is affected. Femtocells are a cost-effective method of countering the effect of shaded areas [2] and provide reliable communication in IoT. The femtocell is capable of optimal power settings [3] because it uses existing wide area networks in small-output compact mobile communication BS, which are used indoors in areas such as homes and offices. Femtocells also provide service in areas of smaller coverage.

Figure 1: Femtocell
Interlock protocol has been proposed to detect Man-in-the-Middle attacks in wireless communications [4]. However, Bellovin and Merritt prove the vulnerability of the interlock protocol by demonstrating Man-in-the-Middle attacks [5]. Then, forced latency interlock protocol has been proposed. However, Forced latency interlock protocol uses a fixed forced delay [6] and has been proposed to improve the Man-in-the-Middle attack detection.
This paper proposes a method for adjusting the forced delay time depending upon the actual distance of the devices. We use the evaluation function in order to determine this delay. The evaluation function must consider the distance and packet size of the two devices within the range of WiMAX femtocells; the delay time is proportional to the distance and packet size.
The rest of the paper is structured as follows. Section 2 introduces the interlock and forced latency interlock protocols, a proposed method overview is presented in Section 3, and Section 4 provides the experimental results. Conclusions and areas for future work are presented at the end of this paper.

2.1.INTERLOCK PROTOCOL
Interlock protocol is based on wireless communication and is applicable in WiMAX femtocells [4]. Interlock protocol compensates for the public key cryptosystem and provides secure communication for normal wireless communication; this protocol has been proposed to expose eavesdropping generated from Man-in-the-Middle attacks. The data transmission method of this protocol is shown below.  The process of the interlock protocol is shown in Figure 2. The Client and Server each have their own secret key, as follows: a) The Client sends his public key to the Server. b) The Server sends his public key to the Client. c) The Client is encrypted with the Server's public key and sends half of the encrypted data to the Server. d) The Server is encrypted with the Client's public key and sends half of the encrypted data to the Client. e) The Client sends the other half to the Server. f) The Server gathers the two parts of the data received from the Client and decrypts them using its private key. The Server sends the other half to the Client. Finally, the Client gathers the two parts of the data received from the Server, and decrypts it with his private key. In this protocol, each step is performed after receiving the information transmitted in the previous step.

2.2.FORCED LATENCY INTERLOCK PROTOCOL
In their work, Bellovin and Merritt presented a case of successful Man-in-the-Middle attacks on the interlock protocol.  The successful Man-in-the-Middle attack scenario is shown in Figure 3. The attacker is involved when the client and the server exchange public keys. After the client and server's public keys are intercepted to hand out the attacker's public key, the subsequent procedure is: a. The Client sends half of the encrypted data to the Server, but the attacker intercepts it. b. The attacker encrypts the data with the Client's public key and transmits half of the encrypted data to the Client. c. The Client cannot properly check the values. The Client sends the other half to the Server, but the attacker intercepts it.
The attacker then combines the two data received from the client with his private key to decrypt and re-encrypt using the Server's public key divided in half.
d. The Attacker sends half of the encrypted data to the Server. e. The Server sends half of the encrypted data to the Client, but the Attacker intercepts it. f. The Attacker sends the other half to the Server. g. The Server sends the other half to the Client, but the Attacker intercepts it.
The attacker is capable of normal communications with the server and alerts the client of network errors or exceptions. In this way, it is possible to mitigate the client's doubts. The attacker then sends the data received from the client to the server and he can authenticate both the server and the client. A forced latency interlock protocol has been proposed to address these problems [7,8].

PROPOSED METHOD
In the conventional technique using a fixed delay time, the packet transmission time may be less efficient than the interlock protocol that does not use delay time. This paper proposes a method for determining the dynamic delay time using the evaluation function and efficient delivery to shorten the delay time [9,10]. The proposed evaluation function takes three input values: Distance: This value is the distance between the devices. The maximum value is within the average range of the femtocell. In the evaluation function, longer distances will increase the delay time. Packet Size: This value is the size of data to transmit. In the evaluation function, longer distances will increase the delay time. Bit Rate: This value is the rate of the broadband internet network. The maximum value is within the average bit rate of WiMAX.
The evaluation function of the proposed method is as follows: Where d is the Distance, p is the Packet Size, and H(d, p) is an algorithm used in the session. For example, if the Distance is 1000 m and the Packet Size is 100 kb, then the Bit rate is 70 mbit/s and the delay time is 3.72 nanoseconds. The proposed method can be applied flexibly and at a rapid rate.

EXPERIMENTAL RESULTS
This section provides the experimental results. The initial parameters are discussed in Section 4.1, and the results are presented in Section 4.2.

Figure 5: Delay Time versus the Distance
Conventional techniques utilize fixed delay time within a radial range; however, the proposed method increases the delay time versus the distance and is faster than existing techniques, as shown in Figure 5. As shown in Figure 6, the attack occurred a million times per meter. The number of detected attacks drops sharply with distance in the conventional technique, and slowly in the proposed technique.

CONCLUSION
Man-in-the-Middle attacks can be used on WiMAX femtocell to eavesdrop data between two devices. In the past, forced latency interlock protocol was proposed to counter these attacks using a fixed delay time. The proposed method dynamically changes the delay time according to the packet size and distance, and is shown to more efficiently reduce the delay time compared to conventional techniques. We also observed improved attack detection using our method. In order to further improve our method in the future, we will increase the distance accuracy of wireless communication devices.