A Secure Anti-Collusion Data Sharing Scheme for Dynamic Groups in the Cloud with Improved Mail Security System

Data sharing is an inevitable functionality in the cloud storage.The paper describes how to securely, efficiently, and flexibly share data in cloud storage. It describes new public-key cryptosystem which produce constant size ciphertexts such that efficient delegation of decryption rights for any set of ciphertexts are possible. The novelty is that one can aggregate any set of private keys and make it compact as a single key, but by encompassing the power of all the keys being aggregated or in other words, the secret key holder can release a constant-size aggregate key for flexible choices of cipher text set in cloud storage, but the other encrypted files outside the set remains confidential. The compact aggregate key can be conveniently sent to others or be stored in a smart card with a limited secure storage. Here it will provide formal security analysis of our schemes in the standard model. In particular, this schemes give the first public-key patient-controlled encryption for flexible hierarchy, which was yet to be known.