## 3 Background and Related Works
### Authentication Goals in IoT
#### 3.1.2 Existing M2M-IoT Mutual Authentication Solutions  
We detail, in this section, existing IoT solutions that are not based on HIP protocol. The authors of [24] propose a new mutual authentication protocol, based on public-key encryption, for IoT. They demonstrate that the emulated solution is efficient on computational cost and applies to device-to-device communication and device-to-server communication for Smart City applications. The efficiency of the lightweight public-key encryption scheme is studied only for communication cost, while evaluating the computation overhead for resource-constrained IoT devices is a crucial criterion that must be considered for such solutions. Besides, the authors conducted their evaluation with a 112-bits security level when comparing with ECC solutions. Nevertheless, for a high level of security with an ECC authentication solution, the recommended NIST curve is NIST P-256 [25]. The work in [26] presents an Identity-Based Cross-Domain Authentication Scheme for the Internet of Things (IRBA ). IRBA is an identity-based cross-domain authentication scheme for the Internet of Things. Authors replace the traditional certificate of authority with the Blockchain as a decentralized trust anchor and use the identity-based self-authentication algorithm to replace the traditional PKI. Their evaluation is done separately for two scenarios: intra-domain access and inter-domain access. For authenticating the user, authors define an algorithm based on identity and without the need of a trusted third party. IRBA is an IoT authentication solution that is not suitable for communications in an architecture based only on constrained devices since its implementation involves powerful servers (PC with Intel-Core i5 6300 HQ CPU (2.30 GHz), 16 GB). Relating to Industrial IoT (IIoT), the contribution in [27] defines an IoT mutual authentication solution for smart devices in IIoT applications. The smart device must register on the server, as a first step. The second step is mutual authentication between the smart device and the router. During these two steps, five messages must be exchanged between the involved components (the smart device, the authentication server, and the router). This high number of exchanged messages increases the communication overhead. In addition, the smart sensor sends a pre-shared key set to each router on the network, but authors do not define any mechanism to verify the identity of the smart device by the router such as the implementation of Access Control Lists. The same problem is posed when the smart device sends its unique ID to the server. This solution is not resistant against node capture of the router, flooding attack, or data freshness attack. Besides, the authors do not give an overview of the communication and computation costs for different values of the setting parameters (only evaluation for a fixed 128 value for all the parameters) and there is not any comparison with related works. Remaining in IIoT, the proposed authentication protocol Lightweight Authentication and Key Distribution (LAKD) for M2M communication [28] minimizes the number of exchanged messages from five to four, comparing with [29]. LKAD is strong against many network attacks and performs better costs in terms of communication and computation comparing with previous works. IIoT is out of the scope of this paper.