Abstract: Cloud storage is a storage of information on-line in cloud that is accessible from multiple and connected resources. Cloud storage is the storage that offers smart accessibility and dependability, sturdy protection, disaster recovery, and lowest price. Cloud storage definitely has important practicality i.e. securely, sharing information with others, with great efficiency. New public–key cryptography is introduced that is termed as Key aggregate cryptosystem (KAC). Key-aggregate cryptosystem yield constant size ciphertexts so that trustworthy relinquishment of decryption rights for a prepared bunch of ciphertexts is feasible. Any set of secret keys may be mass composed and form a single key that encompasses power of all the keys being mass composed. This combination key may be sent to the others over a secured channel, and remaining encrypted files are untouched and remain confidential. The system has great potential to leverage secured use of cloud system.

Keywords: Cloud storage, Data sharing, Ciphertext, Key-aggregate, Encryption.