## 3 Security Implications and Fundamental Approaches of Blockchain-Based Data Storage Methods
### Access Control Mechanisms in Relation to Blockchain Storage Types  
In blockchain-based data storage systems, access control mechanisms provide decentralized and secure methods to ensure that only authorized individuals can access sensitive data while preserving data confidentiality. Access control is particularly critical in industries handling sensitive data, such as healthcare, financial services, and government sectors, where strong security measures are required to prevent unauthorized access [40; 41; 44]. Access control mechanisms are closely linked to the fundamental data storage methods used in blockchain systems. On-chain storage ensures immutability and transparency for access control records, enabling auditable and tamper-proof access management. In contrast, off-chain storage allows for the scalable processing of large datasets, requiring additional security layers for access control enforcement [16; 37; 46]. Figure 5 shows the use of data storage systems with access control mechanisms. It plays a critical role in protecting sensitive data, particularly in the healthcare, finance, and public sectors [39; 151; 152]. Hybrid approaches, such as IPFS and blockchain integration, ensure high security while optimizing transaction costs [32; 37; 46; 113]. The transparency and immutability of blockchain enhance the traceability of access operations, making it easier to detect unauthorized access attempts [1; 104; 153]. For instance, in Ethereum-based systems, access logs are stored on-chain, while large datasets are processed off-chain, balancing security and cost efficiency [43; 53]. On-chain access control mechanisms enhance security by storing access policies immutably on the blockchain. Mandatory Access Control (MAC) enforces strict policies to limit access [154]. Role-Based Access Control (RBAC) grants role-based permissions [44; 155; 156]. Identity-Based Access Control (IBAC) enhances security by managing access based on user identities [44; 45; 154]. Lattice-Based Access Control (LBAC) provides hierarchical authorization, commonly used in defense industries [44; 154]. Figure 5: Use of data storage systems with access control mechanisms. Blockchain-based storage systems integrate access control to regulate data access. Authentication ensure only authorized users can retrieve or modify data. Smart contracts enforce access policies, while cryptographic techniques enhance security and integrity. Off-chain solutions improve scalability for large data processing while relying on blockchain references for security. Discretionary Access Control (DAC) allows data owners to manage access rights [44; 111; 156]. Capability-Based Access Control (CapBAC) provides flexibility with token-based authentication mechanisms, frequently used in distributed cloud systems [157; 158; 159; 160; 161]. Hybrid systems combine on-chain security with off-chain flexibility, enabling dynamic access control. Attribute-Based Access Control (ABAC) and Policy-Based Access Control (PBAC) manage access rights through on-chain policies and off-chain dynamic updates [40; 45; 111; 162]. Context-Based Access Control (CBAC) regulates access based on factors such as device, location, or time [111; 162]. Organization-Based Access Control (OBAC) optimizes access permissions within an organization [44]. The integration of these access control mechanisms with blockchain systems ensures high security and scalability across domains such as finance, healthcare, IoT, and supply chain management [150; 151; 104; 152]. Table 8 summarizes the integration of blockchain-based access control mechanisms with different storage strategies.