International Journal of Innovative Research in Science, Engineering and Technology (IJIRSET)
Emerging new computing technology cloud offers storage services. Data sharing with others in secure and efficient manner is important function in cloud storage. For this the new expandable public-key cryptosystems which derives fixed-size cipher texts. Using expandable public-key cryptosystems transform the multiple keys of the classes as single secret key. The generated single secret key sent to others or be stored in a smart card with very limited secure storage. If a user needs to classify their cipher texts into more than n classes, user can register for additional key pairs.