## 2 Background
### Limitations in Conventional IoT Protocols and Architectures  
Regarding the limitations of traditional IoT architectures, based on previous research findings in [4], these include the ability to transmit data collected by sensors to the Internet through an NB-IoT User Equipment (UE) of sensor hub, as shown in Figure 3. The data is sent using the Constrained Application Protocol (CoAP) transport protocol, and messages are exchanged through the Internet with the application cloud server [20]. CoAP, defined by the Internet Engineering Task Force (IETF) [21], is a lightweight transport protocol used for data exchange at the application layer of devices with constrained resources, such as IoT terminal devices. However, the CoAP protocol includes the ability to use Datagram Transport Layer Security (DTLS) for encrypted data transmission. However, this NB-IoT sensor hub utilizes a low-cost 8-bit micro-processor [22], with an operating frequency of only 16 MHz and a program storage capacity of only 64 Kbytes. In such resource-constrained device applications, achieving assured transmission security is indeed a challenge beyond mere transmission functionality. Accordingly, the highly demanding yet more challenging issues for developing the NB-IoT communication system are as follows:  
1. The first issue to address is the efficiency of the micro-processor's execution. Scholars in study [23] concluded the following: \"Applying our model, we identified the cryptographic operations being the main cost factor\". In other words, cryptographic operations, in the absence of hardware accelerator support, are the main performance cost that must be borne. This might be difficult for low-cost IoT devices to handle additional computational burdens and power consumption requirements, especially for achieving the desired continuous streaming data transmission functionality in this paper. 2. The second issue is the operation mode of CoAP, which is a client-server architecture. In other words, to achieve network transmission functionality between device endpoints, all data transmission processes must go through CoAP proxy servers. Moreover, all application layer data forwarded by the proxy must be received and decrypted by the server before being encrypted and sent out again. During these processes, numerous information security concerns arise. For example, plaintext data used when establishing connections between devices and servers may be intercepted. Furthermore, proxy servers are easily targeted for hacker attacks [24]. To provide security functionalities for IoT devices, manufacturers are increasingly aware of the need to begin investing in this area. However, due to the diverse types of  
Figure 3: NB-IoT sensor system employs CoAP as the IoT communication protocol. devices and varying security setup options, the lack of global standards for device and application-layer security poses significant challenges in securing the application layer of devices. This has left device manufacturers and IoT deployment companies confused and hesitant. To solve this problem, a leading cybersecurity company, Trend Micro, has introduced Trend Micro IoT Security (TMIS) 3.0, an IoT device protection software [25]. TMIS is a security solution that can run on Raspberry Pi [26], designed for embedded IoT devices communicating externally using Internet Protocol (IP). TMIS monitors and protects these devices to guard against various potential risks, including data theft and ransomware attacks. Given its system's hardware resource requirements, TMIS is clearly not suitable for running on our used NB-IoT UE Sensor Hub, as shown in Figure 3. Furthermore, upon further investigation, we understand that the TMIS solution provided by Trend Micro does not offer complementary hardware acceleration support. Therefore, careful consideration is needed regarding the computational resources of the micro-processor that the software requires to run on IoT devices, especially for routine data encryption and decryption operations that this paper addresses.