Non-Repudiable Proofs of Storage in Cloud

With the widespread use of cloud computing and cloud storage, how to ensure the authenticity of data in remote storage has become a severe problem. Provable data possession (PDP) and Proof of Retrievability (POR) are techniques for a client to verify whether an untrusted server possesses the original data entirely, and many PDP and POR schemes have been proposed to resolve above issue so far. But driven by profits, a malicious client may accuse an honest server and deny the correct verification in many circumstances. In this paper, we give a method to reform any private verification PDP/POR scheme into a non-repudiable PDP/POR scheme. And then we propose an instantiation, the Non-repudiable PDP (NRPDP) scheme of private verification, which can provide mutual proof to protect both the client and server. Based on homomorphic verifiable tags and commitment function, our solution allows both the client and the server to prove themselves and verify the other side respectively. To achieve better performance, we improve the NRPDP scheme to obtain an E-NRPDP scheme, which can save the storage cost of the server and reduce the I/O costs to raise efficiency. We prove the security of NRPDP scheme in the random oracle model, and implement a prototype based on our NRPDP scheme. Then we utilize data size as much as 10G to evaluate the performance in a realistic cloud platform. The experiments show our scheme can be executed efficiently as the original PDP/POR scheme and guarantee non-repudiation efficaciously. Our method is universal and practical, which means that it can be applied in any private PDP/POR schemes to guarantee nonrepudiation.