Abstract: Data sharing is an important functionality in cloud storage. Cloud computing technology is widely used so that the data can be outsourced on cloud can be accessed easily. But the user has no control over the outsourced data. A new public key encryption method is based on aggregate key is discuss here. Instead of sending large no of decryption keys, Sender can release a constant size aggregate key that can send via e-mail securely. In policy-based file assured deletion scheme that reliably deletes files with regard to revoked file access policies. The encrypted files can be securely deleted and remain permanently inaccessible after a predefined duration. The main idea is that a file is encrypted with a data key, and this data key is further encrypted with a control key that is maintained by a separate key manager service. The control key is time-based, meaning that it will be completely removed by the key manager, when an expiration time is reached. Without the control key, the data key and hence the data file remain encrypted and are deemed to be inaccessible. Thus, the main security property of file assured deletion is that even if a cloud provider does not remove expired file copies from its storage, those files remain encrypted and unrecoverable.
Keywords: Virtual machine, Key aggregate encryption, ciphertext , Attribute based Encryption, Aggregate key.