Abstract: Cloud storage is a model of data storage where the digital data is stored. Cloud provides a suitable infrastructure for storing and accessing our sensitive data. It also facilitates the service for storing and managing the data remotely through internet. The data can be effectively shared with other users over the cloud. The public-key cryptosystem is uses asymmetric key cryptography and also provides a better way of sharing of files. The secret key is the one which is kept as secret by the data owner. These secret keys can be aggregated to form a single key, called as aggregate key. We can say that, the data owner can release the constant-size aggregate key for the set of cipher text classes. User can have access to those set of files by using a single aggregate key. The files, which are outside the set, will remain confidential.

Keywords: Data sharing, public-key cryptosystem, Aggregate key.