Cloud storage is a storage of data online in cloud which is accessible from multiple and connected resources. Cloud storage can provide good accessibility and reliability, strong protection, disaster recovery and lowest cost. Cloud storage having important functionality i.e. securely, efficiently, flexibly and sharing data with others. New public key encryption which is called as Key-Aggregate Cryptosystem (KAC) is introduced. Key-aggregate cryptosystem produce constant size cipher texts such that efficient delegation of decryption rights for any set of cipher text are possible.