# IoT-Enabled Smart Cities: Evolution and Outlook
## 3 Key Technologies Developed
### Security  
A smart city is composed of diverse and complex digital IoT systems and devices. As IoT devices used in numerous services are being connected to various networks, security threats to all elements comprising the smart city pose potential risks to the entire smart city. In fact, attackers can exploit a vulnerability in the network to infect an IoT device with malware, and subsequently cause mass infection of other IoT devices and systems connected to the smart city [87]. Various security technologies have been developed for IoT-based smart cities. This section discusses secure network, authentication, secure booting, and data privacy technologies among the developed security technologies. * **Secure booting:** When malware infects the boot sector of the system, it may not be detected by the security system present in the operating system. In particular, if malware infects a system on which a smart city IoT platform operates, a threat may be posed to the entire smart city infrastructure. To solve this problem, secure booting technology is implemented, thereby preemptively preventing operating systems and software that are not authorized. This security procedure technology serves as the first wall against various malicious attacks that can target a smart city. Secure booting technology checks the encrypted boot loader, kernel, and system software in authorized hardware. To this end, hardware is manufactured with authentication keys embedded in it. Secure booting technology checks such encrypted signatures before the operating system reads the kernel and system images, and only then the authenticated files are booted. * **Secure networks:** IoT devices in a smart city use various network technologies to access the cloud-based IoT platform. To prevent exposing important information because of security threats occurring during data transmission, messages are encrypted and transmitted using encryption algorithms. For example, devices using Bluetooth versions prior to BLE 4.0/4.1 use encrypted authentication pairing, while BLE 4.2 devices use encrypted low-power security connection authentication feature. In the case of ZigBee, it defines security based on a 128-bit AES encryption algorithm, and uses three types of security keys (master, network, and link) for network security. The 3 GPP 5G technology has additional security features to securely process network access volume increased by over ten times because of IoT devices. For this, the 3 GPP uses international mobile subscriber identity (IMSI) encryption to protect subscriber information, security edge protection proxy (SEPP) that resolves the roaming domain security issue (Signaling System No. 7 [88]) and implements security between application layers among different carriers, and an integrated authentication framework feature that enables the use of the same authentication method for access to 3 GPP and non-3 GPP components. * **Authentication and access control:** Devices and users connected to a smart city are managed using existing authentication and access control technologies. However, lightweight IoT-based devices are not powerful enough for using such technologies, hence, manual access control technologies are used. Various ways to resolve this issue are being proposed, including more detailed log and event monitoring, isolation of suspected devices, and role-based access control policies. * **Data protection:** Ensuring the integrity of data constituting a smart city is an important task. If the integrity of key data is compromised, it may cause attacks on the overall smart city services and infrastructure. System settings information, log files, system libraries, and binary execution files are examples of data that must be protected in a smart city platform. Traditional cyclic redundancy check (CRC) and hash functions for SHA-2 and above are used to verify data integrity.