Cloud computing is one of the most exciting technologies due to its ability to increase flexibility and scalability for computer processes, while reducing cost associated with computing. It is important to share the data securely, efficiently, and flexibly in cloud storage. Existing data protection mechanisms such as symmetric encryption techniques are unsuccessful in preventing data sharing securely. This article suggests Key aggregate cryptosystem which produce constant size ciphertexts in order to delegate decryption rights for any set of ciphertexts. The uniqueness is that one can aggregate any number of secret keys and make them as compact as a single key. This compact aggregate key can be easily sent to others with very limited secure storage.