Sensitive data must be protected from breaches and unwanted access by stronger security measures due to the growing dependence on cloud storage services. The technology known as blockchain allows for the distributed storage of data. Data cannot be altered once it has been stored. Thus, we suggest a blockchain-based decentralized cloud storage system design. This study presents a blockchain system based on Java that integrates RSA encryption to improve cloud storage security. The objective of the suggested architecture is to guarantee data availability, secrecy, and integrity by fusing strong encryption methods with the immutable, decentralized nature of blockchain technology. The experimental findings demonstrate the efficient block creation, encryption/decryption, and data retrieval speeds of the suggested Java-based blockchain framework for cloud storage security utilizing RSA. We examine the implementation specifics, architectural elements, and performance assessments, offering a strong basis for upcoming advancements in safe cloud storage technologies.