## 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  
A hash chain is a cryptographic hash function-based one-way chain structure originally devised by the mathematician [PERSON]. By continuously calculating the hash value using a one-time password and a random value as the initial seed determined by the client, the cryptographic hash function has a preimage resistance. Therefore, it is impossible to recover the original message from the arbitrary hash value of a given message. Because one hash-based password contains both the actual data value and the hash value for the next hash-based password, it is used in the authentication process, which utilizes the continuity and sequentiality of the passwords formed in the chain structure. Therefore, by the comparative analysis of various prior authentication studies using this hash chain structure with the security requirements presented in Section 3.1, its applicability in a VMF-based CNR network in a pre-built cell planning area is determined as follows. The functional satisfaction scores in each study, presented in Table 4, are the key points required in VMF standards. In particular, to logically distinguish the satisfaction of these qualitative requirements, it is necessary to express them as relative indexes, such as weak, slightly weak, slightly strong, and strong, compared to the proposed research method. First, [PERSON] et al. [12] proposed \"S/Key,\" an authentication scheme that uses an exclusive OR and a one-way chain structure based on a cryptographic hash function. This technique makes it difficult for attackers to use old message exchange information, despite the existence of all previous communications and related messages between the client and server. Moreover, because this scheme does not allow for duplicate hash values in the chain and establishes overall security based on the preimage resistance, it is suitable for lightweight authentication environments. In the S/Key standard, however, because all hash values in the one-way chain are sequential, unless a random one-time hash value is used, the hash value is valid for an indefinite amount of time and is also vulnerable to theft, abuse, race condition, loop, MITM, and small-n attacks. Therefore, the widespread use of other cryptographic protocols that can secure an entire session, and not only the password, can render S/Key insignificant if mainly used by itself. Despite these limitations, applying such features of the S/Key standard to the authentication process in VMF-based CNR networks will achieve the following:  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **CKP (\(\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\  
* The basic verification and re-authentication processes can be standardized using only one S/Key structure-based hash chain without needing multiple independent keys to periodically identify normal nodes in a resource-limited tactical network;
* S/Key has an extensible structure that is easiest to employ in multi-factor authentication without duplication for a randomly exposed key or hash value;
* To transit to a joint operation front with other squads during a combined operation, interoperability is achieved by applying the S/Key-based one-way chain structure used in the previous squad unit to the new squad unit, and based on the sequential hashing process, a rapidly lightweight tactical message transmission and authentication scheme can be secured according to the VMF-based information control. Thus, the existing authentication schemes and related parameters presented in VMF standards can be satisfied and further strengthened based on S/Key as an initial interface for the construction of a lightweight authentication scheme. Next, [PERSON] et al. [15] proposed \"TESLA\", based on the S/Key standard.