A Secure Re-encryption Scheme for Data Sharing in Unreliable Cloud Environment

To share encrypted data in cloud storage, data owner provides decryption keys to authorised users. When such a user is revoked, the encrypted data related to revoked user is re-encrypted and new decryption keys are re-distributed among the non-revoked users. In this paper, an efficient and secure re-encryption scheme has been proposed for data sharing in unreliable cloud environment. The scheme is built on top of Ciphertext-Policy based Attribute-Based Encryption (CP-ABE), which will provide fine-grained access control to share data. The scheme can achieve user revocation without whole ciphertexts re-encryption and key re-distributions. In addition, re-encryption is not performed until a user requests for that data, which reduces overheads. Further, it does not need any clock synchronization. Moreover, the scheme is proven to be secured under Computational Bilinear Diffie-Hellman (CBDH) assumption. A comparison with the other notable work in this area shows that the performance is better in terms of functionality, computational and communication overheads.