Cloud computing is employed to store and share knowledge by anyone from any place within the world. Cloud storage having important functionality i.e., securely, efficiently, flexibly share data with others. The authors explain new public-key cryptosystems which produce constant size cipher text. In this, they describe a cryptographic technique in which secret keys are combined to make them compact as a single key. Here, the functionality of all keys being aggregated. The owner of the secret key can provides the aggregate key to the second party on demand, then the receiver able to decrypt the files by using the aggregate key.