Research On Revocable Attribute-based Encryption

With the rapid development of Internet technology and the arrival of the cloud computing time,more and more sensitive data is being transmitted and stored over the Internet.How to guarantee the safety and controllability of all kinds of data in the network has become a research hotspot in cryptography.By using the access structure,the attribute-based encryption(ABE)mechanism can solve the security problem and access control problem of sensitive data.In an ABE system,it is inevitable that the user key will be lost,expired or attribute changed.Therefore,it is a necessary function of ABE system to revoke user and attribute effectively.On the basisi of analyzing and summarizing the various revocation techniques of attribute-based encryption,this thesis focuses on the deep and systematic study on the scheme design and security proof of revocable ABE system.The main contributions can be summarized as follows:(1)Using the direct way to realize revocation in ABE system,there are some shortages existing in the length of system parameters and ciphertext which are growing linearly with the total number of attributes and the number of attributes in ciphertext respectively,and the rough control of attribute revocation.To solve these problems,with dual system encryption technology,a new directly revocable key-policy ABE scheme is proposed,which is provably secure under the static assumptions in the standard model.Analysis demonstrates that the length of system parameters of proposed scheme is constant.Besides,the proposed scheme supports fine-grained revocation of user's attribute in the direct way and reduces communication cost.(2)Using the indirect way to realize revocation in ABE system has the problem of low efficiency.To solve this problem,with bilinear pairing,a new indirectly revocable and proxy-based ciphertext-policy ABE scheme is proposed,which is provably secure under the Decisional Bilinear Diffie-Hellman assumption in the random oracle model.Analysis demonstrates that the length of system parameters and master key of proposed scheme is constant.Besides,the proposed scheme supports efficient revocation of system attribute and user identity,solves the on-line problem of authority and reduces system cost of authority and revocation cost of third party at the same time.