Public Auditing on Shared Data in the Cloud Using Ring Signature Mechanism

Cloud computing is the long dreamed vision of computing as a utility, where users can remotely store their data into the cloud so as to enjoy the on-demand high quality applications and services from a shared pool of configurable computing resources. By data outsourcing, users can be relieved from the burden of local data storage and maintenance. Thus, enabling public auditability for cloud data storage security is of critical importance so that users can resort to an external audit party to check the integrity of outsourced data when needed. To securely introduce an effective third party auditor (TPA), the following two fundamental requirements have to be met: 1) TPA should be able to efficiently audit the cloud data storage without demanding the local copy of data, and introduce no additional on-line burden to the cloud user. Specifically, our contribution in this work can be summarized as the following three aspects: 1) We motivate the public auditing system of data storage security in Cloud Computing and provide a homomorphic authenticable ring signature mechanism for Public Auditing on shared data in the Cloud, i.e., our scheme supports an external auditor to audit user’s outsourced data in the cloud without learning knowledge on the data content. 2) To the best of our knowledge, our scheme is the first to support scalable and efficient public auditing in the Cloud Computing. In particular, our scheme achieves batch auditing where multiple delegated auditing tasks from different users can be performed simultaneously by the TPA. INTRODUCTION: Cloud service providers manage an enterprise-class infrastructure that offers a scalable, secure and reliable environment for users, at a much lower marginal cost due to the sharing nature of resources. It is routine for users to use cloud storage services to share data with others in a team, as data sharing becomes a standard feature in most cloud storage offerings, including Drop box and Google Docs. The integrity of data in cloud storage, however, is subject to skepticism and scrutiny, as data stored in an untrusted cloud can easily be lost or corrupted, due to hardware failures and human errors. To protect the integrity of cloud data, it is best to perform public auditing by introducing a third party auditor (TPA), who offers its auditing service with more powerful computation and communication abilities than regular users. The first provable data possession (PDP) mechanism to perform public auditing is designed to check the correctness of data stored in an untrusted server, without retrieving the entire data. Moving a step forward, Wang et al. (referred to as WWRL) is designed to construct a public auditing mechanism for cloud data, so that during public auditing, the content of private data belonging to a personal user is not disclosed to the third party auditor. We believe that sharing data among multiple users is perhaps one of the most engaging features that motivates cloud storage. A unique problem introduced during the process of public auditing for shared data in the cloud is how to preserve identity privacy from the TPA, because the identities of signers on shared data may indicate that a particular user in the group or a special block in shared data is a higher valuable target than others. For example, Alice and Bob work together as a group and share a file in the cloud. The shared file is divided into a number of small blocks, which are independently signed by users. Once a block in this shared file is modified by a user, this user needs to sign the new block using her public/private key pair. The TPA needs to know the identity of the signer on each block in this shared file, so that it is able to audit the integrity of the whole file based on requests from Alice or Bob. We propose the system, a new privacy preserving public auditing mechanism for shared data in an untrusted cloud. In this system, we utilize ring signatures to construct homomorphic authenticators, so that the third party auditor is able to verify the integrity of shared data for a group of users without retrieving the entire data — while the identity of the signer on each block in shared data is kept private from the TPA. In addition, we further extend our mechanism to support batch auditing, which can audit multiple shared data simultaneously in a single auditing task. Meanwhile, it continues to use random masking to support data privacy during public auditing, and leverage index hash tables to support fully dynamic operations on shared data. A dynamic operation indicates an insert, delete or update operation on a single block in shared data. A high-level comparison between this system and existing mechanisms in the literature is shown. To our best knowledge, this represents the first attempt towards designing an effective privacy preserving public auditing mechanism for shared data in the cloud. 1. EXISTING SYSTEM Many mechanisms have been proposed to allow not only a data owner itself but also a public verifier to efficiently perform integrity checking without downloading the entire data from the cloud, which is referred to as public auditing . In these mechanisms, data is divided into many small blocks, where each block is independently signed by the owner; and a random combination of all the blocks instead Gayatri D Patwardhan et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 7 (4) , 2016, 1940-1946