Cloud storage has become essential for data management, yet ensuring data integrity across multiple Cloud Service Providers (CSPs) remains challenging due to potential data corruption, unauthorized modifications, or service failures. Traditional verification methods rely on Third-Party Auditors (TPAs), introducing trust issues, single points of failure, and high computational overhead. This project proposes a blockchain-based data integrity verification scheme for multi-cloud storage that eliminates the need for a TPA. The system employs AES and RSA encryption for secure file uploads, stores cryptographic hashes on a private Ethereum blockchain (using Ganache and Truffle), and performs both overall and local verification to detect and localize corrupted CSPs efficiently. Smart contracts automate verification, ensuring transparency and immutability. The solution achieves high efficiency by reducing on-chain computation while maintaining security through cryptographic techniques. Experimental results demonstrate improved performance compared to traditional blockchain methods, making it suitable for practical multi-cloud environments. The system supports two roles: Data Owners (DOs) for file upload/verification and CSPs for storage management and user approval.

Keywords: Blockchain, Multi-Cloud Storage, Data Integrity Verification, AES-RSA Encryption, Smart Contracts, Ganache, Truffle, Third-Party Auditor Elimination, Local Verification, Cloud Security.