Multi-authority scheme based CP-ABE with attribute revocation for cloud data storage

Security of the outsourced data has become the core problem of cloud computing. Many security models have been proposed, among which, CP-ABE has gained popularity in this research area. The Ciphertext-Policy Attribute Based Encryption (CP-ABE) is considered as a propitious tool for fine grained data access in the cloud storage system. The existing CP-ABE scheme with only one authority does not solve the trust issues as well as attribute revocation problem. Although many multi-authority CP-ABE schemes have been proposed and solved the trust problem to some extent but failed to provide efficient attribute revocation and solution for system failure. This paper proposes a multi-authority scheme which can solve the trust issues, attribute revocation problem, and system failure.

I. Introduction

With the popularity and amelioration of Internet, the data load on the network is expanding rapidly and these data requires a high computation. Cloud computing emerged as one of the promising solution for computation. It provides different facilities like data storage, multi-tenancy, scalability, and self-provisioning of resources. Cloud computing achieves better resource utilisation by virtualization and relocation of resources as per the demand. One of the most important service of cloud computing is data storage [1]. This service allows people to store their data and access it anytime and anywhere which reduces the cost of implementation and maintenance. Cloud storage services like Google Cloud Storage [2], Amazon Cloud Drive [3] and IBM system Storage [4] are very popular among users, as they provide dynamic scalability of storage space and pay as you use facility. Although Cloud computing solved many of the problem but also came up with issues of access control of outsourced data. One of the technique to secure data is encryption. The traditional method of encryption can provide data access control. However, when number of users in the system increases, key management becomes a challenging issue. Moreover, the data has to be encrypted for every user with their different key which increases the unnecessary computation overhead. Ciphertext Policy Attribute Based Encryption (popularly termed as CP-ABE), proposed by Brent Waters and Amit Sahai [5] is considered as the most suitable technique for data access control in cloud [6]–[9]. Access control based on CP-ABE is presented in [10]–[11]. In CP-ABE, ciphertext is associated with the access structure and when the users attribute satisfies the structure where the user is able to decrypt the data provided. However, this scheme considered single authority for management of all the attribute and private key generation for the authorised user. Once the Central Authority (CA) is compromised, it may disclose all the user's data. Hence this is not suitable for real world application. The recent trend of the research in CP-ABE focuses on multi authority model but the main challenge with this type of system is to group different secret keys more efficiently, so that the system is collusion resistant.