# A Proposal for a Zero-Trust-Based Multi-Level Security Model and Its Security Controls
## 2 Related Works and Their Analysis  
### Multi-Level Security  
Multi-Level Security is defined as a concept of processing information with different classifications and categories that simultaneously permits access to users with different security clearances and denies access to users who lack authorisation [18]. Based on this conceptual definition, the MLS model can be considered a security model that hierarchically classifies an organisation's information assets according to their data sensitivity and risk impact and applies appropriate security controls and policies to each layer. Furthermore, this clause seeks to compare and analyse the MLS models in the United States and Korea. The Multi-Level Security in the United States and the Republic of Korea reflects each country's unique environments and security requirements, adopting a differentiated approach based on the sensitivity of information and the criticality of systems. Both countries enhance their overall security levels by applying classification criteria aligned with their respective security objectives. The United States federal government employs FIPS 199 (Federal Information Processing Standards Publication 199) [19] as a standard for assessing the security level of information systems. FIPS 199 establishes confidentiality, integrity, and availability as the core security objectives and categorises information into the following three levels: Low, Moderate, and High. This framework evaluates the potential impact of each classification, systematically managing the sensitivity of information assets and the potential consequences of system loss or compromise. The method of assessing the impact of breaches on an organisation for each security objective is determined by comprehensively considering factors such as the sensitivity of information, threat elements, and the scale of potential damages. For instance, if information leakage has minimal impact on the organisation's mission, assets, or citizens, it is classified as Low Impact. If it significantly disrupts organisational operations, it is considered Moderate Impact, and if it poses severe risks to national security or human lives, it is classified as High Impact. This approach focuses on setting an appropriate security level for each system and applying security controls tailored to each classification. In essence, the classification of information systems in the United States independently evaluates the sensitivity of information and the potential impact of breaches. This serves as the basis for adopting a detailed approach to security, enabling the implementation of granular security measures aligned with each classification. Since 2006, the Republic of Korea has implemented and operated a network segregation system, primarily in government and public institutions. This system has playeda critical role in protecting the systems of government, public institutions, and financial companies from security threats and risks such as hacking [3]. However, with the accelerating pace of digital transformation and the advancement of cutting-edge technologies, such as cloud computing and artificial intelligence (AI), the network segregation system has become a limiting factor in leveraging these technologies. In response, the Republic of Korea is transitioning from its traditional physical and logical network segregation system towards a more flexible approach. This involves adopting an MLS framework based on the classification of data sensitivity, aiming to strike a balance between the usability of data and the security level. The Republic of Korea's MLS framework classifies data into two broad categories based on disclosure status: non-public and public data. Non-public data are further subdivided into Classified and Sensitive data, resulting in the following three classifications: Classified, Sensitive, and Open.