Research On Partially Hidden Access Structure CP-ABE

Data stored in the cloud should be encrypted for security,and Ciphertext-Policy Attribute-Based Encryption(CP-ABE)is best suited for Encryption in the cloud at present.CP-ABE has a flexible access structure,in which the ciphertext can be decrypted successfully only when the user's attributes meet the access structure of the data.However,in CP-ABE,the access policy may leak risk information,so we consider to hide part of the access policy that contains risk information.The time required for data encryption and decryption is related to the complexity of the access structure,so we also consider reducing the amount of computation of the encryption and decryption stage.This thesis mainly does the following research work:1.Hiding the access structure is an effective security measure to prevent the disclosure of risk information contained in the access structure of CP-ABE.The existing CP-ABE schemes with tree access structure either completely expose or completely hide the access structure,resulting in either poor policy confidentiality or heavy computation overhead of both encryption and decryption.We propose a CP-ABE scheme with selectively-hidden tree access structure.It uses the mutual information to extract partial attributes,which contain almost all information that the original attributes in the access structure hold,from the access structure,and hides these extracted attributes.This scheme has nearly the same policy privacy as fully hiding,meanwhile effectively reduces the computational burden of both the encryption and decryption.Compared to the scheme of open access structure,the confidentiality of policy is improved.2.Considering that the user's decryption ability to data can't be judged in advance due to partial concealment of attributes,this paper analyzes the user's decryption ability with the least matching cost in two cases,so that users without decryption ability give up trying to decrypt as early as possible.