## 2 Background and Related Studies
### VMF Authentication Improvements Based on MIL-STD-2045-47001
Therefore, it is difficult to protect consistent security in CNR networks from parameter tampering because no separate encryption process in the modification detection and authentication scheme is applied (RSA public encryption may be applied in a separate protocol header area for tactical message encryption, but this may cause additional overhead on network performance and calculation). * **Lack of factor robustness:** The existing VMF standard includes variables from a rapidly changing battlefield environment (e.g., information loss from environmental changes, latency, jitter, and authentication delay), enemy types (e.g., active and passive internal and external attackers and masqueraders), and operational environments (e.g., bandwidth, energy, frequency, squad, and resources by limited CNRs) that are not well defined. Therefore, it is necessary to introduce additional requirements and establish parameter-based measures. * **Undefined re-authentication and revocation scheme**: The existing VMF standard does not suggest a continuous authentication scheme when it is necessary to re-establish the reliability of the participating nodes because it takes a certain amount of time after the initial authentication for the operation of the squad to be completed. In addition, processes related to authentication rejection and exclusion as well as the elimination of hostilities are not considered. Therefore, to support a consistent authentication system in a rapidly changing VMF-based CNR network, definitions of re-authentication and revocation schemes for all nodes are urgently required. * **Non-existent exception process:** The existing VMF standard does not provide any method for the detection, tolerance, and attenuation of node malfunctioning caused by dynamic changes in the network or enemy nodes corrupting operational data and stealing confidential information. Therefore, it is necessary to establish a variety of exception handling methods to satisfy the unique information exchange demand in the battlefield, and support both functional and structural stability. This can also be related to the following challenges: low speed and low bandwidth in real-time VMF-based CNR, the deployment of military base stations for constructing the cell planning area, guaranteeing the availability of authentication for low-spec networks, and the network delay and tolerance related to the establishment of the initial FBCB2-based CNR in mosaic warfare networks, which requires rapidity. As described above, SHA-1 was proposed by the National Security Agency (NSA) based on message digest 4 (MD4) and adopted in DSA. However, concerns regarding the collision attack vulnerabilities of the SHA-1-based cryptographic hash function were raised in 2005. In 2017, the PoC for generating collision pairs for the SHA-1 hash function was fully released, thereby verifying its theoretical and practical vulnerabilities. As such, owing to the existing vulnerabilities of SHA-1, the VMF standard for executing the authentication scheme between terminals through the SHA-1-based DSA in CNR networks also has limitations. Applying this method to the VMF authentication scheme without overcoming these vulnerabilities can result in the exposure of operational information and the exchange of tactical data to unauthorized nodes in real-time. Even during normal confidential operations, indiscriminate intrusions by enemy forces related to authentication in a tactical network can occur without preventative and detective measures. Thus, the cryptographic hash function must be transitioned into a function with guaranteed robustness, such as SHA-2, SHA-3, or LSH, the Korean cryptographic hash standard [6]. As indicated in Table 1, when the SPI is 0, the data in the VMF-based communication channel do not go through separate one-way encryption types in the authentication and transmission processes, but do undergo one-way encryption based on the weak cryptographic hash function standard, SHA-1. This aspect can also be observed in Tables 2 and 3.