## 2 Background and Related Studies
### Related Research and Improvements for Introduction of Hash Chain-Based Authentication in VMF
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Octet** & **Field Identification** & **Value** \\ \hline
1 & Block Number: Identifies specific data block. & 15 \\ \hline
2 &
\begin{tabular}{c} Length: Indicates the length of the Address \\ Designation Parameters block in octets. \\ \end{tabular} & Variable length: 13 + size of Digital Signature \\ \hline
3 & Hash Algorithm: Used to produce the hash. & 0 = MD5 \\  & & 1 = SHA-1 \\ \hline
4 &
\begin{tabular}{c} Crypto Algorithm: Identification of the \\ crypto algorithm used to encrypt the hash to \\ produce the digital signature. \\ \end{tabular} & 0 = Not encrypted \\
2-255 User defined \\ \hline
5-13 & Key ID: signer’s public key. & 8 octet binary field \\ \hline
14-Length field & Digital Signature: Authentication of the \\  & sender of the message. \\ \end{tabular}
\end{table} 
Table 3: Digital signature. management of the finite hash chain length, the complexity of computation according to the hash chain length, the lack of a self-reinitialization scheme, and security problems dependent on the hash chain length, related to the efficiency of T-OTP generation and verification in T/Key. Consequently, it was possible to use less storage than T/Key, lower network transactions, and maximize the efficiency of OTP generation and verification time [27]. However, despite these unique features and advantages, previous studies related to hash chain-based authentication have not presented specific exception handling concepts at an algorithmic level for functional problems that potentially arise in a rapidly changing limited battlefield network, such as VMF-based CNRs. In particular, in a low-resource wireless CNR network, where the bandwidth varies according to the layers because of dynamic operational environments, a method for specialized authentication has not been clearly described. An existing hash chain authentication approach in poor communication environments causes several restrictions to network-centric operations, and the performance of the entire network potentially deteriorates when the traffic increases rapidly, such as during wartime. In addition, these naive hash chain-based authentications have a limitation in that their parameters do not consider the structure or functional aspects under such limited tactical circumstances. In particular, when topology update messages are periodically transmitted to prevent VMF-based CNR networks from disconnecting when the squad commander and related members perform combined platooning operations, poor communication environments may increase the corruption of the authentication status of each squad member, causing network overhead owing to transactions that are required to establish authentication. Therefore, rather than utilizing the same existing hash chain-related authentication scheme in this military ad hoc network that focuses on cell planning areas and mosaic warfare networks, an alternative approach is necessary to identify and analyze unique features that can be optimized for All-IP or non-All-IP-based CNRs. Accordingly, a comparative analysis of the pros and cons of existing hash chain-based approaches is required.