## 3 Comparative Analysis of the Existing Hash Chain-Based Authentication Approaches
### Applicability Analysis of VMF-Based CNRs in Previous Studies on Hash Chain-Based Authentication
However, the limitations of the LHAP must be considered, including a central management problem in which all nodes in the network had to share the secret key in advance, a limited key maintenance package, and the increased complexity of the authentication process owing to a larger number of keys, latency caused by one node performing duplicate hashing for verification of abnormal packets and nodes, and authentication delays that could not be fully resolved owing to vulnerabilities to basic intrusion attacks such as wormhole and MITM [20; 21]. Despite these limitations, applying the features of the LHAP to the authentication process in VMF-based CNR networks will achieve the following:  
* LHAP was proposed to overcome the vulnerability of basic TESLA standards applied to multi-hop ad hoc networks such as MANET. Therefore, the network and computational overhead can be reduced by reducing the number and capacity of requests for nonce and hash values for initial authentication and re-initialization, and removing authentication information based on each node participating in or leaving the VMF-based ad hoc network. * The concept of hop-by-hop access control can be realized for the behavior of malicious nodes and collaborative hostile nodes that have personal channels. In addition, the issues of exception processing for authentication delay and disconnection according to changes in the ad hoc network can be alleviated by generating a separate control packet. Furthermore, an additional lightweight authentication for distributed VMF-based WSNs can be calculated. * Beyond filtering invalid authentication keys and packets at the authentication algorithm level, by establishing a system to authenticate and identify legitimate squad nodes and punish enemy nodes, a small-scale VMF-based CNR network specialized for more realistic battlefield environments can be constructed. Establishing trust relationships through specific keys will mitigate issues with authentication delays and network disconnections that arise in limited tactical networks and low-spec military wireless terminals. Various studies supplementing the weaknesses of the hash chain-based authentication, including the T-OTP value, must also be analyzed, including the problems of the server-side re-registration and initialization after the hash values in the hash chain are exhausted [22], and the client-side overhead based on multiple hash calculations when the hash values are stored beforehand. [PERSON] et al. [23] proposed an \"SRHC\" that does not require a separate re-registration, despite all hash chains being exhausted after registering the root value of the first hash chain in the Lamport's OTP. Here, during the authentication process, the bits constituting the root value of the new hash chain are transmitted to the server in advance, whereas a random hash value is transmitted through the OTP. A one-time signature (OTS) based on a cryptographic hash function standard is also applied as a secondary modification detection and authentication technique for protection against abnormal nodes and attackers during this transmission process. Consequently, all hash values in the current hash chain are exhausted, and the root value of the new hash chain is automatically registered based on a four-way protocol. However, further strategies to improve the SRHC are required owing to other limitations, such as a lack of exception handling in the case of mismatches between specific hash values of the client and server, and the computational and network overhead caused by the increasing length of the transmitted messages.