## 3 Security Implications and Fundamental Approaches of Blockchain-Based Data Storage Methods
### Blockchain-Based Data Integrity and Traceability Solutions
#### 3.5.3 Achieving Flexibility with Hybrid Storage Solutions  
Hybrid approaches combine the advantages of on-chain and off-chain methods, providing a balanced solution between security and cost [26; 28; 37; 47]. These methods are especially practical for managing large datasets in healthcare and IoT applications [6; 33]. However, complex configuration requirements may limit their applicability and require technical expertise [24; 32]. The selection of blockchain-based data storage methods depends on data integrity requirements, cost constraints, and sector-specific needs [26; 35; 47]. On-chain methods are preferred in high-security environments, whereas off-chain solutions offer cost advantages [36]. Hybrid approaches, by integrating both methods, provide a broader range of applications [6; 32; 33]. These insights contribute to optimizing blockchain-based data storage systems across various industries [26; 28; 47]. Sectoral Applications and Perspectives Regarding On-Chain, Off-Chain, and Hybrid Data Storage Methods  
The adoption of blockchain-based data storage solutions has transformed how industries approach security, scalability, and efficiency in managing sensitive data. Depending on the industry, the choice of storage method (on-chain, off-chain, or hybrid) plays a critical role in addressing specific challenges and requirements. For instance, the healthcare sector prioritizes privacy and real-time access to patient records [151; 166; 167; 168; 169; 170], whereas the financial sector focuses on immutability and data integrity [43; 100]. Similarly, supply chain management requires traceability and logistical efficiency [103; 171; 172; 173], while IoT applications emphasize efficiency and high-speed data processing [50; 51]. Each of these sectors leverages the strengths of various data storage approaches while using blockchain technology to address unique challenges. Table 10 summarizes the applications, use cases, security requirements, advantages, and disadvantages of on-chain, off-chain, and hybrid data storage solutions across different industries. This comprehensive analysis provides valuable insights into how blockchain technology is adapted to meet industry-specific demands. The classification aims to illustrate how blockchain-based storage methods align with sectoral needs, offering perspectives on real-world applications, and future potential blockchain-based data storage solutions are being implemented through various methods tailored to the specific needs of different industries. Healthcare, finance, education, supply chain, government, and IoT each require different technologies based on data security requirements, transaction costs, integration demands, and scalability concerns. Table 10 evaluates blockchain-based data storage methods across different industries, identifying which technologies ensure the highest security and efficiency for each sector. Real-World Implementations of Blockchain Storage Solutions  
Blockchain storage solutions have been widely adopted across various industries, demonstrating their potential to enhance data security, transparency, and operational efficiency. In this section, real-world case studies are presented to illustrate how on-chain, off-chain, and hybrid blockchain storage models have been utilized in sectors such as healthcare, finance, education, supply chain management, public administration, and IoT applications. In healthcare, the secure and decentralized storage of patient data and electronic health records (EHRs) is essential [151; 166]. Hybrid solutions, combining blockchain with decentralized storage systems like IPFS, protect data integrity while preventing unauthorized access through encryption [168; 169]. Projects like MedRec and FHIRChain facilitate secure patient data sharing between healthcare institutions while ensuring immutability [167; 168; 169; 170]. For instance, FHIRChain has been piloted in major hospital networks, demonstrating its ability to provide tamper-proof patient records while complying with the HIPAA and the GDPR.