A Proxy Re-Encryption with Keyword Search Scheme in Cloud Computing

With the widespread use of cloud computing technology,more and more users and enterprises decide to store their data in a cloud server by outsourcing.However,these huge amounts of data may contain personal privacy,business secrets and other sensitive information of the users and enterprises.Thus,at present,how to protect,retrieve,and legally use the sensitive information while preventing illegal accesses are security challenges of data storage in the cloud environment.A new proxy re-encryption with keyword search scheme is proposed in this paper in order to solve the problem of the low retrieval efficiency of the encrypted data in the cloud server.In this scheme,the user data are divided into files,file indexes and the keyword corresponding to the files,which are respectively encrypted to store.The improved scheme does not need to re-encrypt partial file cipher-text as in traditional schemes,but re-encrypt the cipher-text of keywords corresponding to the files.Therefore the scheme can improve the computational efficiency as well as resist chosen keyword attack.And the scheme is proven to be indistinguishable under Hash Diffie-Hellman assumption.Furthermore,the scheme does not need to use any secure channels,making it more effective in the cloud environment.

Policy-Based Group Signature Scheme from Lattice

Although the existing group signature schemes from lattice have been optimized for efficiency,the signing abilities of eachmember in the group are relatively single.It may not be suitable for complex applications.Inspired by the pioneering work of Bellare and Fuchsbauer,we present a primitive called policy-based group signature.In policy-based group signatures,group members can on behalf of the group to sign documents that meet their own policies,and the generated signatures will not leak the identity and policies of the signer.Moreover,the group administrator is allowed to reveal the identity of signer when a controversy occurs.Through the analysis of application scenarios,we concluded that the policy-based group signature needs to meet two essential security properties:simulatability and traceability.And we construct a scheme of policy-based group signature from lattice through techniques such as commitment,zero-knowledge proof,rejection sampling.The security of our scheme is proved to be reduced to the module short integer solution(MSIS)and module learning with errors(MLWE)hard assumptions.Furthermore,we make a performance comparison between our scheme and three lattice-based group signature schemes.The result shows that our scheme has more advantages in storage overhead and the sizes of key and signature are decreased roughly by 83.13%,46.01%,respectively,compared with other schemes.