# The Integration of Azure Sphere and Azure Cloud Services for Internet of Things
## 2 Related Work
### Azure Sphere  
In order to deal with this challenging problem, a novel class of price-sensitive application platform called Azure Sphere was released by Microsoft which integrates real-time processing capabilities with a secure, internet-connected operating system [32]. Along with the Azure Sphere MCU SDK tools for application development, the Azure Sphere Security Service is also included for secure cloud and web connection.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Solution** & **Application Area** & **IoT Layers** & **Security Considerations** \\ \hline
[12] & Industrial IoT & Cisco IoT Framework & Security threats in data mining and big data \\ \hline
[13] & Health care & Things and clouds layer & Signal monitoring in health care application \\ \hline
[14] & General & Sensing, network and application & Authentication, privacy encryption, packet forwarding \\ \hline
[15] & General & Perception, network and application & Security threats and strategies in \\  & & layer & three layers \\ \hline
[16] & General & Object, object abstraction, service & \\  & & management, application and & Security protocols in IoT \\  & & business layer & \\ \hline
[17] & General & Cisco IoT seven-layer model & Security threats and strategies in \\  & & & three layers \\ \hline \hline \end{tabular}
\end{table}
Table 1: A summary of security considerations for IoT solutions.  
The goal of the Azure Sphere is to enable IoT designers to incorporate high levels of security into every low-cost MCU device with network connectivity. Based on the extensive experience in software design for device security, seven necessary properties of highly secure, network-connected devices were identified by Microsoft, namely, hardware-based root of trust, small trusted computing base, defense in depth, compartmentalization, certificate-based authentication, security renewal and failure reporting [33]. Motivated by the referred goals, Azure Sphere MCU, Azure Sphere OS and Azure Sphere Security Service were designed to work together in a harmonious whole to reduce risks. The architecture of the Azure Sphere comprises the following three main components.  
* The Azure Sphere MCU is composed of multiple ARM Cortex cores, network connectivity subsystem, multiplexed I/O peripherals, integrated RAM and flash, hardware firewalls, and the Pluton security subsystem, which provide built-in security from a hardware perspective.
* The custom Linux-based kernel, the Security Monitor and OS services that host the application container add a four-layer defense, in-depth secure environment from a software perspective.
* The Azure Sphere Security Service that merges with certificate-based authentication, timely update and failure reporting renews security to confront with emerging threats from a service perspective [34].  
With the help of silicon partner MediaTek, the first Azure Sphere certified MCU MT3620 was released at the end of 2017 [35]. The price of MT3620 is less than 8.65 US dollars, which covers the physical MCU chip, licenses for the chip, the Azure Sphere OS and the Azure Sphere Security Service. MT3620 includes both ARM Cortex-A7 application processor and ARM Cortex-M4F I/O subsystems, which are designed for running Azure Sphere OS and real-time control requirements of on-chip peripherals, respectively. In addition to the high-performance ARM cores, the Pluton security subsystem and the on-board Wi-Fi subsystem are embedded in MT3620 to handle secure boot, secure system operation and high throughput network connectivity. For targeting a wide range of IoT applications, five serial interfaces, two I2S interfaces, eight ADC channels, twelve PWM outputs and seventy-two programmable GPIOs are included. Subsequently, in September 2018, the Azure Sphere MT3620 development kit was released by Seeed Studio to support rapid prototyping with Azure Sphere technology [36; 37].