###### Abstract
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Device Specification**} & \multicolumn{2}{c}{**CPU**} & \multicolumn{2}{c}{**Storage**} & \multicolumn{2}{c}{**Networking**} \\ \cline{2-7}  & **Arch (Bits)** & **Clock (MHz)** & **RAM (KB)** & **ROM (KB)** & **Standard** & **Radio Interface** & **BW (kbps)** \\ \hline Sky-Mote [24] & 16 & 8 & 10 & 48 & 6 LoWPAN & IEEE 802.15.4 & 250 \\ \hline Z1-Mote [23] & 32 & 32 & 32 & 512 & 6 LoWPAN & IEEE 802.15.4 & 250 \\ \hline Opennote [26] & 32 & 32 & 32 & 512 & 6 LoWPAN & IEEE 802.15.4 & 250 \\ \hline Waspmote [27] & 8 & 16 & 8 & 128 & Zigbee & IEEE 802.15.4 & 250 \\ \hline Arduino Uno [28] & 8 & 16 & 2 & 32 & 6 LoWPAN & IEEE 802.15.4 & 250 \\ \hline Mbed [29] & 32 & 96 & 32 & 512 & CAN & CAN Bus & 320 \\ \hline Weptech [30] & 32 & 32 & 32 & 512 & 6 LoWPAN & IEEE 802.15.4 & 250 \\ \hline KNX Stacks [31] & 32 & 32 & 32 & 512 & KNX & KNX Radio & 16.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Specifications of some representative devices used for IoT applications. Figure 1: Security issues with commercialized IoT devices [9]. An IoT device may not respond to a real-time request if it spends most of its assigned time slots for serving a request on exchanging security messages. * IoT devices use lightweight operating systems, such as Contiki [32] and RIoT [33], due to their resource-constrained natures. As such, the protocol stack of IoT operating systems requires a resource-efficient version of contemporary security modules, such as IPSec [34] and DTLS [35], to run on IoT devices. * IoT software has to be updated regularly to mitigate potential security vulnerabilities. However, the real-time and lightweight operating systems that run on IoT devices may not have the capability to receive and integrate new codes or libraries to keep the system software updated. * IoT networks are expected to experience abrupt changes in network topologies because mobile IoT devices may join a network without prior configuration or leave the network abruptly. The sudden changes in the network topologies may affect various performances of the existing security methods, such as re-distribution of shared credentials in the pre-shared key-based authentication methods. As a result, conventional security schemes may not be suitable for mobile IoT-based systems. * A wide range of wireless protocols are used for communications in the IoT systems, which include WiFi [36], ZigBee [37], Z-Wave [38], and NFC [39]. A smart device can use proprietary networking protocols for device-to-device communications and standard protocols for Internet communications. The conventional security methods may not be comprehensive enough for the entire set of properties of each communication protocol. The above constraints suggest that the utilization of IoT-based systems without appropriate security measures puts the success of the evolving IoT paradigm at risk, which would downgrade or even destroy the whole IoT business. We must be careful to investigate and determine priorities for IoT security solutions. Accordingly, security solutions and guidlines used in designing IoT elements, systems, and protocols should be customized for the context of use. In this paper, we survey contemporary IoT security issues and perform an in-depth critical analysis of them with the aim of educating learners and practitioners in IoT security implications.