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 ciphertexts. 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 his ciphertexts into more than n classes, user can register for additional key pairs. Each class is indexed by a two-level index and the number of classes is increased by n for each added key. For the approach, at most two aggregate keys are needed. This key extension approach can also be seen as a key update process. In case a secret value is compromised, user can replace compromised publickey with new publickey. Eventually the approach is flexible and effective.
展开▼
