SECURITY ENHANCEMENT OF GROUP SHARING AND PUBLIC AUDITING FOR DATA STORAGE IN CLOUD

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1 SECURITY ENHANCEMENT OF GROUP SHARING AND PUBLIC AUDITING FOR DATA STORAGE IN CLOUD S.REVATHI B.HASEENA M.NOORUL IZZATH PG Student PG Student PG Student II- ME CSE II- ME CSE II- ME CSE Al-Ameen Engineering College, Al-Ameen Engineering College, Al-Ameen Engineering College, Karundevanpalayam, Tamilnadu. Karundevanpalayam, Tamilnadu. Karundevanpalayam, Tamilnadu. ABSTRACT In the cloud data services, users can simply change and distribute data as a group. But here for security consideration, create a group and the users in the group are called group members and there is one group manager. To ensure data integrity can be audited publicly, users need to compute signatures on all the blocks in shared data. The straightforward method, which allows an existing user to download the equivalent part of shared data. Here, propose a novel public auditing system for the integrity of shared data with efficient user revocation in mind. A public verifier is always able to audit the integrity of shared data without retrieving the whole data from the cloud, even if some part of shared data has been re-signed by the cloud. Public auditing technique uses four methods: Keygen, Signgen, Genproof and verify proof. In addition, providing an extra level security for the cloud data using Blow Fish Encryption and setting a group signature for data sharing. Blowfish is a symmetric block encryption algorithm designed in consideration with fast, compact, Simple and Secure. INTRODUCTION 1.1. Cloud Storage Cloud storage is a model of networked enterprise storage where data is stored in virtualized pools of storage which are generally hosted by third parties. Hosting companies operate large data centers, and people who require their data to be hosted buy or lease storage capacity from them. The data center operators, in the background, virtualized the resources according to the requirements of the customer and expose them as storage pools, which the customers can themselves 14 use to store files or data objects. Physically, the resource may span across multiple servers and multiple locations. The basic services presented in cloud providers is data storage that means the data can be stored in cloud by user(i.e., Cloud Storage).Cloud storage means "the storage of data online in the cloud," wherein a company's data is stored in and accessible from multiple distributed and connected resources that comprise a cloud. Cloud storage can provide the benefits of greater accessibility and reliability. But the security of cloud storage is still in a challenging issue, In previous work

2 followed Encryption and decryption technique to the user. Encryption is the process of translating plain text data (plaintext) into something that appears to be random and meaningless (ciphertext). Decryption is the process of converting ciphertext back to plaintext. One of the most fundamental services offered by cloud providers is data storage. Let us consider a practical data application. A company allows its staffs in the same group or department to store and share files in the cloud. By utilizing the cloud, the staffs can be completely released from the troublesome local data storage and maintenance. To encrypt more than a small amount of data, symmetric encryption is used. A symmetric key is used during both the encryption and decryption processes. To decrypt a particular piece of ciphertext, the key that was used to encrypt the data must be used. The goal of every encryption algorithm is to make it as difficult as possible to decrypt the generated ciphertext without using the key. If a really good encryption algorithm is used, there is no technique significantly better than methodically trying every possible key. For such an algorithm, the longer the key, the more difficult it is to decrypt a piece of ciphertext without possessing the key. It is mainly focused on group signature and dynamic data encryption for data security. Because of this an authorized person only can access the data unauthorized user cannot access any data. First, identity privacy is one of the most significant obstacles for the wide deployment of cloud computing. Without the guarantee of identity privacy, users may be unwilling to join in cloud computing systems because their real identities could be easily 15 disclosed to cloud providers and attackers. On the other hand, unconditional identity privacy may incur the abuse of privacy. For example, a misbehaved staff can deceive others in the company by sharing false files without being traceable. Therefore traceability, which enables the group manager (e.g., a company manager) to reveal the real identity of a user, is also highly desirable. Second, it is highly recommended that any member in a group should be able to fully enjoy the data storing and sharing services provided by the cloud, which is defined as the multipleowner manner. Compared with the singleowner manner, where only the group manager can store and modify data in the cloud, the multiple owner manner is more flexible in practical applications. More concretely, each user in the group is able to not only read data, but also modify his/her part of data in the entire data file shared by the company. Last but not least, groups are normally dynamic in practice, e.g., new staff participation and current employee revocation in a company. The changes of membership make secure data sharing extremely difficult. On one hand, the anonymous system challenges new granted users to learn the content of data files stored before their participation, because it is impossible for new granted users to contact with anonymous data owners, and obtain the corresponding decryption keys. On the other hand, an efficient membership revocation mechanism without updating the secret keys of the remaining users is also desired to minimize the complexity of key management. In these approaches, data owners store the encrypted data files in untrusted storage and distribute the corresponding

3 decryption keys only to authorized users. Thus, unauthorized users as well as storage servers cannot learn the content of the data files because they have no knowledge of the decryption keys. 1.2 Auditing scheme It is very essential that cloud that allows investigation from a audit the outsource data to ensure the data security and save the user s computation and data storage. it is very important to provide public auditing service for cloud data storage, so that the user trust an independent third party auditor (TPA). TPA checks the integrity of data on the cloud on the behalf of the users,and it provides the reasonable way for the users to check the validity of data in the cloud. On the whole, enabling public auditing services plays a vital role in establishing cloud economy, where by users need way to assess to risk and gain faith in the cloud. Public auditing in addition to user provides the external party to verify the correctness of stored data against the external attacks. However these schemes don t involve the privacy protection of the data. It is a main disadvantage which affect the security of the protocols in cloud computing. So the users who depend on TPA only for their security storage want their data to be protected from the external auditors. i.e. they focus that there is no leakage of data security. Algorithms Blowfish is a symmetric-key block cipher, designed in 1993 by Bruce Schneier and included in a large number of cipher suites and encryption products. Blowfish provides a good encryption rate in software.blowfish is a fast block cipher, except when changing keys. Each new key requires pre-processing equivalent to encrypting about 4 kilobytes of text, which is very slow compared to other block ciphers. This prevents its use in certain applications, but is not a problem in others. 2. RELATED WORKS 2.1 Scalable and Efficient Provable Data Possession Storage outsourcing is a rising trend which prompts a number of interesting security issues, many of which have been extensively investigated in the past. However, Provable Data Possession (PDP) is a topic that has only recently appeared in the research literature. The main issue is how to frequently, efficiently and securely verify that a storage server is faithfully storing its client s (potentially very large) outsourced data. The storage server is assumed to be untrusted in terms of both security and reliability. (In other words, it might maliciously or accidentally erase hosted data; it might also relegate it to slow or off-line storage.) The problem is exacerbated by the client being a small computing device with limited resources. Prior work has addressed this problem using either public key cryptography or requiring the client to outsource its data in encrypted form. Construct a highly efficient and provably secure PDP technique based entirely on symmetric key cryptography, while not requiring any bulk encryption. Also, in contrast with its predecessors, our PDP technique allows outsourcing of dynamic data, i.e, it efficiently supports operations, such as block modification, deletion and append. 16

4 More recently, however, the problem of Provable Data Possession (PDP) is also sometimes referred to as Proof of Data Retrivability (POR) has popped up in the research literature. 2.2 Provable Data Possession at Untrusted Stores Introduce a model for provable data possession (PDP) that allows a client that has stored data at an untrusted server to verify that the server possesses the original data without retrieving it. The model generates probabilistic proofs of possession by sampling random sets of blocks from the server, which drastically reduces I/O costs. The client maintains a constant amount of metadata to verify the proof. The challenge/response protocol transmits a small, constant amount of data, which minimizes network communication. Thus, the PDP model for remote data checking supports large data sets in widely-distributed storage systems. Present two provably-secure PDP schemes that are more efficient than previous solutions, even when compared with schemes that achieve weaker guarantees. In particular, the overhead at the server is low (or even constant), as opposed to linear in the size of the data. Experiments using our implementation verify the practicality of PDP and reveal that the performance of PDP is bounded by disk I/O and not by cryptographic computation. 2.3 TPA Auditing Third-party auditor (TPA) is introduced into a public auditing mechanism in the cloud, both the content 17 of data and the identities of signers are private information to users, and should be preserved from the TPA. Multiple auditing tasks from different users efficiently, they also extended their mechanism to support auditing. a mechanism for public auditing shared data in the cloud for a group of users. With ring signature-based homomorphic authenticators, the TPA can verify the integrity of shared data but is not able to reveal the identity of the signer on each block. The auditing mechanism in is designed to preserve identity privacy for a large number of users. 2.4 File storage in cloud server After auditing process if the file is verified correct then only member can store the file in cloud server. Cloud storage is a model of data storage where the file is stored in cloud server, the physical storage spans multiple servers and the physical environment is typically owned and managed by a Cloud admin. These cloud storage providers are responsible for keeping the data available and accessible, and the physical environment protected and running. Only the registered user can only store the file 2.5 Group member revocation The user revocation is secure because only existing users are able to sign the blocks in shared data. The cloud cannot generate a valid signature for an arbitrary block on behalf of an existing user. In addition, after being revoked from the group, a revoked user is no longer in the user list, and can no longer generate valid signatures on shared data.

5 CONCLUSION Proposed a new public auditing mechanism for shared data with efficient user revocation in the cloud. When a user in the group is revoked, we allow the semitrusted cloud to re-sign blocks that were signed by the revoked user with proxy resignatures. Experimental results show that the cloud can improve the efficiency of user revocation, and existing users in the group can save a significant amount of computation and communication resources during user revocation REFERENCES 1. B. Wang, B. Li, and H. Li, Public Auditing for Shared Data with Efficient User Revoation in the Cloud, in the Proceedings of IEEE INFOCOM 2013, 2013, pp M. Armbrust, A. Fox, R. Griffith, A. D. Joseph, R. H. Katz, A. Konwinski, G. Lee, D. A. Patterson, A. Rabkin, I. Stoica, and M. Zaharia, A View of Cloud Computing, Communications of the ACM, vol. 53, no. 4, pp , Apirl G. Ateniese, R. Burns, R. Curtmola, J. Herring, L. Kissner, Z. Peterson, and D. Song, Provable Data Possession at Untrusted Stores, in the Proceedings of ACM CCS 2007, 2007, pp H. Shacham and B. Waters, Compact Proofs of Retrievability, in the Proceedings of ASIACRYPT Springer-Verlag,2008,pp C. Wang, Q. Wang, K. Ren, and W. Lou, Ensuring Data Storage Security in Cloud Computing, in the Proceedings of ACM/IEEE IWQoS 2009, 2009, pp