## 2 Background and Related Studies  
### VMF Authentication Improvements Based on MIL-STD-2045-47001  
In the existing VMF standard applied to CNRs with TDL, the MIL-STD-2045-47001 standard defines the VMF network protocol and application header, security parameter information (SPI), and group parameter (GP). The purpose of the MIL-STD-2045-47001 standard is to stipulate the technical parameters and procedures, such as application header generation, message packaging and unpackaging, data segmentation, and assembly, which are essential for the message exchange and communication of digital tactical information between the digital message transfer (DMT) equipment and C4I systems in All-IP-based CNRs with limited bandwidth, resources, and device energy. It also presents the VMF message header, RSA-based encryption, and SHA-1-based DSA authentication rules. This determines the DSA-based authentication according to the SPI value in a VMF binary message header, which falls within the scope of this study. The existing protocols and authentication schemes in the VMF standard have several unique characteristics. * **Variability--**Variability minimizes message transmission and processing time by dynamically selecting only required real-time tactical messages and information when performing various operations in a limited resources-based network;
* **Bit-coded transmission--**Bit-coded transmission subdivides the transmission unit of a tactical message containing military operation information into bit and octet. It can maximize the transmission efficiency of the operational information and tactical data and ensure integrity;
* **Applicability of multiple layers--**The VMF standard is independent of arbitrary network structures applied in various types of military tactical networks. The MIL-STD-188-220 standard was applied for the physical and link layers, and the MIL-STD-6017 and MIL-STD-2045-47001 standards were applied in the application layer based on CNR networks. Therefore, the multi-layer applicability enables a configuration for the independence of the form of military tactical network and the handling of each squad's platooning behavior and related networks;
* **Integration and interoperability--**The integration of VMF is an essential feature in the design, development, testing, certification, and continuous operation of the automated tactical data system (that is, it satisfies the necessary requirements for promptly transmitting command and control information through joint boundaries). In addition, an integration is required to exchange tactical data and situation awareness information between heterogeneous weapon systems, and to exchange the command system within the allied operation in real-time through an interlocking of the joint tactical data link system (JTDLS). Currently, this is being applied, with a focus on FBCB2-based platooning networks in cell planning areas and mosaic warfare. However, these protocols and authentication systems used in the VMF standard can cause several issues and limitations. * **Weak authentication process by SHA-1 cryptographic hash function:** In the existing VMF military standard, the SHA-1-based DSA authentication and modification detection process is performed according to the SPI setting in a dynamic limited CNR network without additional encryption. However, SHA-1 currently has theoretical collision vulnerability and exploits a practical proof of concept (PoC). Thus, to protect confidential military information from leakage and theft in a tactical CNR network under the VMF standard, cryptographic hash-based authentication algorithms (e.g., SHA-2, SHA-3, and LSH of Korean cryptographic hash standard) that are more robust than SHA-1 are urgently required. In addition, although the SPI setting is immediately applied, it is only assumed that authentication in the current VMF-based CNR networks is safe from the perspective of the closed military network.