# Energy Efficient Dynamic Symmetric Key Based Protocol for Secure Traffic Exchanges in Smart Homes
## 1 Introduction  
The Internet of Things (IoT) devices offer a myriad of services, such as smart lighting, remote surveillance, and door locking. A smart home is part of IoT application scenarios which comprises sensors, actuators, home appliances, and controllers that are accessed and controlled remotely. In smart homes, users may utilize various applications or voice commands to turn appliances on or off [1] or monitor temperature and humidity at home [2]. In so doing, smart homes potentially boost user comfort and quality of life. A typical smart home consists of Indoor Smart Devices (ISDs), users, Home Gateways (HGs), and Registration Authority (RA) which acts as a controller [2, 3, 4]. Here, the controllers scrutinize sensor data before transmitting messages to home appliances for some action. Since smart home devices such as sensors are bandwidth, computational power, and memory constrained, remote users access sensor data via the home gateway. In essence, the HGoffers long and short-distance wireless connectivity between the ISDs and remote users. For remote monitoring and access to the ISDs, users deploy internet-enabled tablets and smartphones [5] while the ISDs communicate with each other via Radio Frequency (RF) channels [6]. Before the actual deployment of smart home networks, all ISDs, gateways, and users are registered at the RA. The goals of smart homes include a reduction in operational costs, increased energy efficiency, convenience, and comfort [2,5] through home systems automation. As such, massive information flows over smart home networks, which raises performance, privacy, and security issues [1,7]. This is because message exchanges take place over insecure public channels [1,2,8,9] and over longer distances, which increases latencies [7]. In addition, most ISDs do not incorporate security and privacy in their designs [10] or have weak embedded security [11]. Therefore, it becomes easy for attackers to tamper, eavesdrop and have unauthorized access to the transmitted data. It is also possible for adversaries to insert bogus messages and insert or delete exchanged data. Consequently, the preservation of perfect privacy and security in smart-phone, stored data, networks, and ISDs is paramount [9]. Unfortunately, much attention has only been paid to boosting the smartness of the devices and user comfort while little work is devoted to security and privacy issues [2]. Numerous security issues have been identified in smart home networks. These issues include a lack of proper user privacy, identity authentication, and access control [8,12,13,14]. These vulnerabilities have made it possible for attackers to deploy these networks to launch attacks such as Distributed Denial of Services (DDoS) [15] and spreading malware [11]. In addition, packet interception, deletion, modification, and bogus data injections are common [2]. To address the above security, performance, and privacy challenges, authentication of the communicating entities must be executed. This ensures that only authorized parties are able to establish connections to the smart home network [16,17,18]. It also helps in establishing the integrity of applications and devices. In addition, there is a need to preserve the confidentiality and availability of the exchanged messages [1]. Moreover, secure remote access can prevent disclosure of access privileges and private information [17] or illegal control of ISDs and subsequent illegitimate surveillance [19]. Therefore, many security solutions have been presented in literature based on techniques such as usernames and passwords and asymmetric and symmetric key crypto-systems. However, usernames and passwords are not effective for highly mobile IoT devices [17]. Similarly, most asymmetric and symmetric key techniques have high computational overheads, which are not ideal for ISDs [1]. Since the majority of the sensors deployed in smart homes are limited in terms of computation power [16,20], the authentication protocols need to be lightweight [2,19].