# A Survey on Cybersecurity in IoT
## 2 Device Authentication and Identity Management
While AES ensures strong encryption and efficiency, its reliance on secure key management remains a limitation in large-scale IoT networks. However, the challengewith symmetric key cryptography lies in the secure distribution and management of keys, particularly in large-scale IoT deployments [50]. Secure key distribution protocols, such as the Diffie-Hellman key exchange, have been adapted for IoT but these still face challenges related to scalability and the potential for man-in-the-middle attacks during the key exchange process [51; 52; 53]. Beyond cryptographic techniques, physical unclonable functions (PUFs) have gained attention as a novel approach to device authentication in IoT [54; 55]. PUFs exploit the inherent manufacturing variations in electronic circuits to generate unique, device-specific responses that can be used for authentication purposes. Since these responses are derived from the physical characteristics of the device, they are difficult to replicate or forge, providing a high level of security. PUF-based authentication is particularly appealing for IoT devices due to its low computational requirements and resistance to cloning attacks. PUFs generate unique responses based on inherent device variations, requiring minimal hardware operations like delay-based measurements. For example, ring oscillator PUFs consume a few hundred nanowatts of power and require only kilobytes of memory for challenge-response storage, making them suitable for resource-constrained IoT devices. These architectures are integrated into MCUs and FPGAs for lightweight authentication, with error-correction techniques ensuring reliability under environmental variations [56; 57]. While PUF-based authentication is highly effective, deploying it at scale presents challenges, such as the need for standardized interfaces and protocols to integrate PUFs into diverse IoT ecosystems [58; 59; 60]. Decentralized identity management systems, leveraging blockchain and distributed ledger technologies (DLTs), have been proposed as a solution to the challenges of scalability and trust in IoT networks. By using blockchain, IoT devices can register their identities in a tamper-proof ledger that is distributed across the network. This approach provides several advantages, including the elimination of single points of failure and the ability to audit identity transactions transparently [61; 62; 63]. Smart contracts, which are self-executing contracts with the terms of the agreement directly written into code, can be utilized within blockchain-based identity systems to automate identity verification processes and enforce access control policies [64]. However, the integration of blockchain with IoT also raises issues related to the overhead of consensus mechanisms, the latency of blockchain transactions, and the energy consumption associated with maintaining a distributed ledger [65]. Another emerging trend in IoT identity management is the use of federated identity models, which allow IoT devices to share identity credentials across multiple domains or organizations. Federated identity management can simplify the process of integrating IoT devices into diverse and multi-stakeholder environments, such as smart cities or industrial IoT systems, by enabling devices to authenticate across different networks without needing to re-establish their identities. This model, however, requires robust trust frameworks and interoperability standards to ensure that identity information can be securely shared and managed across different domains [66; 67; 68; 69]. Identity management also plays a crucial role in ensuring the secure decommissioning of IoT devices. When a device is retired or no longer trusted, its identity must be revoked to prevent it from being used as a vector for attacks. This process, known as identity revocation, must be carried out securely and efficiently to ensure that compromised or outdated devices do not remain a threat to the network [70].