<p>In today’s cloud ecosystem, cloud storage is a significant factor. Most of the users wish to save their data on the cloud. Even though cloud storage has numerous advantages like scalability, data security, redundancy and accessibility, it has a main drawback for preserving the data integrity. Auditing methods are used in the cloud to verify the integrity of data. Sometimes, the user’s data may be permanently lost by the Cloud Service Provider (CSP). So, public auditing is necessary to ensure data integrity. Third-Party Auditor (TPA)-based auditing is one of the existing methods for auditing, as it has some benefits, like fairness and effectiveness. But it cannot prevent malicious auditors. Security bottleneck issues are affecting the TPA-based public auditing mechanism. This paper introduces a blockchain-based public auditing mechanism for cloud storage, aimed at guaranteeing data security and integrity while mitigating the concerns of malicious activity. The mechanism employs Fully Homomorphic Encryption (FHE) to protect the sensitive data, allowing the computations to be performed on encrypted data without decryption. Optimizing the encryption process requires the use of an Optimal Key-Assisted Fully Homomorphic Encryption (OK-FHE) method and the Modified Future Search Algorithm (M-FSA) to choose the encryption key. Further, the data is securely stored on a blockchain, guaranteeing tamper-proof auditing and transparency. A Divide and Conquer Table (D-CT) is employed to effectively organize the data for auditing, allowing the public auditors to validate the integrity of the stored data without accessing the original plaintext. The proposed model is compared in the end with some baseline models, demonstrating security, efficiency, and resistance to malicious auditing behavior.</p>