This document proposes a system for secure cloud storage that uses data deduplication, integrity auditing by a third party auditor (TPA), and encryption to improve security, reduce storage usage, and verify data integrity. It compares different levels of data deduplication (byte-level, block-level, file-level) and proposes using a combination of SHA-512 hashing, Merkle hash trees, and AES-128 encryption. Performance analysis shows the proposed system requires less storage space than existing systems by removing duplicate data, and the third party auditor can verify data integrity more efficiently than the cloud service provider.