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As a special kind of public-key encryption, attribute-based encryption (ABE) is able to achieve fine-grained access control mechanism by offering one-to-many encryption. Due to such unique characteristic, this primitive is widely employed in the cloud computing environment to provide flexible and secure data sharing. However, how to revoke the access privilege of a user to access encrypted data stored in cloud servers is challenging. Furthermore, the complex operation of ABE may cause a huge computational cost and is usually considered to be a heavy burden for system users. Motivated by the practical needs, an ABE scheme called efficient and revocable storage CP-ABE scheme with outsourced decryption and constant-size ciphertexts and secret keys is proposed in this paper. Our scheme offers the following features: Chinese remainder theorem is utilized to achieve revocable storage. In detail, third party severs are allowed to update ciphertexts stored on them so that those revoked users cannot decrypt any ciphertexts any more. To minimize local operations, the concept of outsourced ABE system with constant-size ciphertexts and secret keys are introduced. More specifically, decryptor is able to outsource most of computing work to the outsourcing service providers. In addition, the scheme is provably secure against selectively chosen-ciphertext attack. At the end, we describe how to deploy the scheme in cloud computing environment. [ABSTRACT FROM AUTHOR]

Ciphertext-policy attribute-based encryption (CP-ABE) scheme can be deployed in a mobile cloud environment to ensure that data outsourced to the cloud will be protected from unauthorized access. Since mobile devices are generally resource-constrained, CP-ABE schemes designed for a mobile cloud deployment should have constant sizes for secret keys and ciphertexts. However, most existing CP-ABE schemes do not provide both constant size ciphertexts and secret keys. Thus, in this paper, we propose a new pairing-based CP-ABE scheme, which offers both constant size ciphertexts and secret keys (CSCTSK) with an expressive AND gate access structure. We then show that the proposed CP-ABE-CSCTSK scheme is secure against chosen-ciphertext adversary in the selective security model, and present a comparative summary to demonstrate the utility of the scheme. [ABSTRACT FROM AUTHOR]