Protected Data Sharing scheme with Multi Ownership for Non Static Groups in the Cloud
Cloud computing offers an economical and efficient solution for sharing group resources among cloud users i.e. the individual can now run the application from anywhere in the world, as the server provides the processing power to the application and the server is also connected to a network via Internet or other connection platforms to be accessed from anywhere and with the character of low maintenance. But, due to frequent change of the membership, sharing data provided with multi ownership, while protecting data and identity privacy of users from an untrusted cloud is a challenging issue. To overcome this problem a protected multiowner data sharing scheme will be proposed for non static groups in the cloud. By leveraging group signature and dynamic broadcast encryption techniques, any cloud user can anonymously share data with others without revealing identity to untrusted cloud and the data owner will be given with the option of traceability to reveal the identity of any user at time of disputes. In the interim, the storage overhead and encryption computation cost of the proposed scheme are independent with the number of revoked users. Keywords Cloud Computing, Data Sharing, Access Control, Non Static groups, Group Signature, Dynamic Broadcast Encryption. INTRODUCTION Cloud computing is recognized as best alternative to traditional information technology [1] due to its resource sharing and low maintenance characteristics. In cloud computing, the cloud service providers, such as Amazon, are able to deliver various services to cloud users with the help of powerful datacenters. By migrating from local data management systems into cloud servers, users can enjoy high quality services and save significant investments on their local infrastructures. One of the most fundamental services offered by cloud providers is data storage. However, it also poses a significant risk to the confidentiality of the stored files. Specifically, the cloud servers managed by cloud providers are not fully trusted by users while the data files stored in the cloud may be sensitive and confidential, such as business plans. To preserve data privacy, a basic solution is to encrypt data files, and then upload the encrypted data into the cloud [2] Unfortunately, designing an efficient and secure data sharing scheme for groups in the cloud is not an easy task due to the following challenging issues. 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 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 multiple owner manner. Compared with the singleowner manner [3] 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. Lastly 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. Several security schemes for data sharing on untrusted servers have been proposed [4 6] In these approaches, data owners store the encrypted data files in untrusted storage and distribute the corresponding 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. However, the complexities of user participation and revocation in these schemes are linearly increasing with the number of data owners and the number of revoked users, respectively. By setting a group with a single attribute, Lu et al. [7] proposed a secure provenance scheme based on the ciphertext policy attribute based encryption technique [8] which allows any member in a group to share data with others. However, the issue of user revocation is not Chaitra C et al, (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 5 (3) 2014, 4608 4614