## 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
Despite a recipient knowing the specific signature, the signature for the next sequence cannot be computed in advance until it is disclosed in the next time interval; therefore, malicious nodes in the network are prevented from sending packets after they have been declared false through packet theft and abuse. Thus, by applying the loosely time synchronization concept, this process handles situations in which a specific hash value for authentication is valid for an indefinite period, while reducing the overhead in generating and verifying authentication information, as compared to S/Key (aspects of network transactions and computations), expanding the recipient nodes, and preparing for a packet loss [16]. However, the TESLA authentication has limitations, including the non-guaranteed problem of non-repudiation, and the problem of storage space if packets transmitted during a specific time interval before the release of a random secret key must be continuously buffered in the receiver. Other limitations include the delayed authentication of buffered packets until the secret key is disclosed, the use of the same cryptographic hash function as that in the S/Key, and the inadequate exception handling of malicious nodes. Despite these limitations, applying the features of the TESLA standard to the authentication process in VMF-based CNR networks will achieve the following:  
* TESLA is an authentication method for adding the calculated message authentication code (MAC), including a secret key generated through a hash function, to a packet based on a one-way chain. Therefore, based on the act of revealing the hash value owing to the loose time synchronization between the sender and the receiver, it is possible to minimize the exposure of information to the attacker and block false packet attacks. In addition, when there are multiple recipients in a multicast environment, quick and accurate individual authentication for each recipient can also be performed;
* The TESLA standard that was first proposed did not support non-repudiation, but TESLA++, an improved version, can secure a higher non-repudiation function than the elliptic curve digital signature algorithm (ECDSA). Through the TESLA-based VAST combined with the existing ECDSA, it is possible to derive specialization for authentication in military ad hoc networks such as VMF-based CNRs, including MANET and VANET [50];
* In addition to protection from valid authentication values that have not been used for long periods of time in VMF-based CNRs, a system can be established to monitor and identify spoofed nodes using such valid authentication keys. Moreover, hash chain-based authentication schemes can be constructed for an update and expansion of the squad member authorization list for long-term operations. [PERSON] et al. [19] proposed \"LHAP\", which uses a TESLA-based bootstrap trust structure and a one-way chain for traffic and device authentication. As a protocol concept specialized in ad hoc networks based on MANET, this study implemented a network access control scheme while preventing unauthorized nodes from injecting traffic into a given MANET. To implement this process, each node in the network applied token-based hop-by-hop authentication before specific neighboring nodes one hop away transmitted a random packet, thereby deleting abnormal packets. To achieve this, a structure was adopted that combined one-way chain-based authentication and trust management between nodes. Based on this lightweight structure, issues with a buffering-based authentication delay and a large-capacity storage demand owing to delayed key disclosure and loose time synchronization in the existing TESLA could be addressed. Moreover, issues related to securing independence and transparency for multiple routing protocols, increasing the authentication and computational efficiencies compared to those of TESLA, and abnormal node exception handling that was not well defined in TESLA could be addressed through a standardization based on a trust relationship.