## 3 Security Implications and Fundamental Approaches of Blockchain-Based Data Storage Methods
### Access Control Mechanisms in Relation to Blockchain Storage Types
\begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Access Control Mechanism** & **On-Chain** & **Off-Chain** & **Hybrid** & **Operational Characteristics of the Mechanisms** \\ \hline DAC (Discretionary Access Control) & \(\bigtimes\) & \(\bigvee\) & \(\bigvee\) & DAC allows users to flexibly modify access rights but cannot be implemented on-chain due to blockchain’s immutability. Off-chain systems are suitable as they provide user authorization without requiring a central authority. Hybrid models enhance security by managing authorization off-chain while maintaining access records on-chain. \\ \hline MAC (Mandatory Access Control) & \(\bigtimes\) & \(\bigtimes\) & MAC, which requires centralized authorization, aligns well with blockchain’s immutable and auditable structure. Off-chain solutions are unsuitable due to their decentralized nature. Hybrid models balance policy enforcement by storing access control rules on-chain while processing decision mechanisms off-chain for greater flexibility. \\ \hline RBAC (Role-Based Access Control) & \(\bigvee\) & \(\bigvee\) & Since roles can be stored immutably on the blockchain, on-chain implementation is feasible. However, for large-scale organizations, off-chain storage is preferable. Hybrid models provide flexible solutions by balancing security and scalability. \\ \hline ABAC (Attribute-Based Access Control) & \(\bigvee\) & \(\bigvee\) & On-chain storage is appropriate for immutable attributes, but off-chain solutions improve update speed for frequently changing attributes. Hybrid models ensure flexibility by keeping static attributes on-chain while dynamically managing updates off-chain. \\ \hline PBAC (Policy-Based Access Control) & \(\bigvee\) & \(\bigvee\) & For transparent policy recording, on-chain storage is ideal. Off-chain solutions enable quick responses to dynamic policy changes. Hybrid models maintain core policies on-chain while updating dynamic components off-chain to ensure balance. \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Classification of access control mechanisms compatible with on-chain, off-chain, and hybrid storage methods [44; 111; 113]. In off-chain systems, users have greater control over their own data. However, in large-scale blockchain systems, DAC operates efficiently when data are stored off-chain [44; 111; 156]. On-chain structures support MAC's high-security requirements, but its centralized and rigid nature limits flexibility in dynamic applications [59; 65]. In on-chain systems, roles and access permissions can be immutably recorded, ensuring tamper-proof access control [155]. Hybrid systems provide scalability by allowing dynamic role modifications [16; 37; 101]. Off-chain solutions can store large datasets related to roles, though this approach is less common [111; 161]. On-chain structures ensure transparency through immutable attribute records [44; 45; 111]. Off-chain applications enable fast attribute updates, improving real-time adaptability. Hybrid systems combine the security of on-chain storage with the flexibility of off-chain processing. For example, dynamic attributes like user age and location can be effectively managed within a hybrid system [16; 37; 101]. On-chain applications facilitate transparent policy recording, while off-chain systems enable rapid implementation of dynamic policy changes. Hybrid architectures optimize policy updates by balancing performance and security [111; 162; 163]. Context-Based Access Control (CBAC) dynamically manages context changes. On-chain implementations securely store immutable context data, while off-chain systems efficiently process real-time context variations. Hybrid approaches ensure flexibility and security in context-aware access con