Research On Ciphertext Policy Attribute-based Encryption In Cloud Environment

With the rapid development of cloud computing and big data,cloud server attracts more and more users and enterprises to outsource their data to the cloud,due to its powerful computing and storage capabilities.However,the remote storage of users' data in the cloud environment will result in the separation of data ownership,management,and usage right.Since the cloud server cannot be fully trusted,it poses a great threat to the privacy of outsourced data.Ciphertext Policy Attribute-Based Encryption(CP-ABE),as a one-to-many public key encryption method,has attracted extensive attention in the academic world.Because this technique can protect data security,as well as provide fine-grained access control.Although some research achievements have been made in this field,there still exist some obstacles towards practical applications,including the aspects of functionality,efficiency and anti-quantum security.This dissertation takes it as the research object and conducts researches from those three aspects.This dissertation is committed to constructing several CP-ABE schemes to meet different requirements.The main contributions of this work are given as follows.(1)Aiming at the policy requirements that shared data are sensitive to access time and access location,this dissertation proposes a CP-ABE scheme with temporal-spatial constraint policy based on composite order groups.Firstly,a new access structure tree is designed,which can flexibly express access policy with multiple spatial-temporal constraints.For time range constraint,the multi-dimensional range derivative function is applied to process the comparable attribute.By means of the proxy re-encryption mechanism,the ciphertext obtained by users are organically combined with current access time.For spatial region constraint,users can obtain corresponding tokens to deal with the location trapdoor information.To reduce the decryption overhead imposed on users,this dissertation further proposes an extension scheme to support outsourcing decryption.Security analysis shows that our scheme is selectively CPA secure under random oracle model.Finally,the performance of our scheme is analyzed theoretically and the effectiveness of the proposed method is verified by experiments.(2)In order to deal with the frequent changes of user's attribute and access policy,this dissertation proposes a CP-ABE scheme that supports attribute revocation and policy update based on prime order groups.The solution can realize immediate changes to user's access right or access policy,ensuring forward security and backward security of shared data.Compared with user revocation,the KEK tree structure is introduced to maintain the frequent changes of the members in the attribute group,so as to support more fine-grained revocation.To meet the requirement of policy update,our scheme updates ciphertext efficiently based on the policy comparison algorithm and the proxy re-encryption mechanism.In addition,our scheme can support multiple attribute authorities and large universe attributes,which makes it more suitable for practical applications.Security analysis shows that the proposed scheme is statically(non-adaptively)secure under the selective security model.Finally,the performance of our scheme is analyzed theoretically and the experimental results are evaluated.(3)To solve the problem of insufficient computing capacity of physical devices in attribute-based encryption schemes,this dissertation proposed a CP-ABE scheme that supports offline/online operations and verifiable outsourcing computation based on prime order groups.Our scheme can support offline/online key generation,offline/online encryption and verifiable outsourcing decryption.As most of the operations are executed during the offline phase,the online response time can be significantly reduced for key generation and data encryption.By outsourcing decryption,the amount of final decryption imposed on user is reduced to a constant.In addition,our scheme has the property of verifiability for the outsourcing calculations.This dissertation describes the schemes OOCP-ABKEM,OO-CP-ABE and OO-VO-CPABE successively.Security analysis shows that all these three schemes are CPA secure under standard model.Finally,the performance of our scheme is analyzed theoretically.Simulation results show that our schemes can effectively reduce the computational cost imposed on resource-constrained devices.(4)In view of the fact that most CP-ABE schemes are constructed on elliptic curve bilinear groups and can not resist quantum attack,this dissertation proposes two multiauthority CP-ABE schemes based on ideal lattice,whose security can be reduced to the decisional R-LWE assumption.This dissertation firstly constructs trapdoor generation algorithm,sampling preimage algorithm,sampling left algorithm and sampling right algorithm on ideal lattice.By using the above algorithms and the full rank differences function,two multi-authority CP-ABE schemes are proposed,supporting boolean attributes and multi-valued attributes respectively.By means of the coefficient vector of polynomial ring element on the ideal lattice,both of the two schemes can encrypt n bits per time.In addition,by adding virtual attributes to the attribute authorities,these two schemes can support flexible threshold access policies.Security analysis shows that the proposed schemes are CPA secure under standard model.Finally,compared with other lattice-based related works,our schemes have better functional characteristics.