Data Sharing in Cloud Computing by Using Steganography

Abstract

The important use of cloud computing is data sharing. However, security is always an issue in cloud. So, in this paper we show the ways to share our data securely, efficiently, and flexibly in cloud storage. We create new public-key cryptosystems that produce constant-size ciphertexts such that efficient delegation of decryption rights for any set of ciphertexts are possible. One can aggregate any set of secret keys and make them as compact as a single key, but encompassing the power of all the keys being aggregated. The secret key holder can release a constant-size aggregate key for flexible choices of ciphertext set in cloud storage, but the other encrypted files outside the set remain confidential. This compact aggregate key can be conveniently sent to others or be stored in a smart card with very limited secure storage. We provide formal security analysis of our schemes in the standard model. We also describe other application of our schemes. In particular, our schemes give the first public-key patient-controlled encryption for flexible hierarchy, which was yet to be known.