Research On Public Key Encryption With Equality Test In Cloud Environment

With the improvement of technology standards in the Internet of Things(IOT)and continuous breakthroughs in key technologies,the data explosion era will be getting closer.The conception of cloud computing is presented for processing massive data efficiently.Cloud computing is essentially a new type of computing model.It is a derivative of distributed computing and widely used for its efficient and fast service.Now,an increasing number of enterprises and individuals prefer to outsource data to cloud servers for storage,so as to reduce the storage space of local computers.However,for users,the cloud server is uncontrollable,and the data stored in the cloud server will face the risk of privacy leakage.Therefore,the privacy protection of data and the protection of user identity information are becoming increasingly prominent and urgently need to be further addressed.While enjoying the convenient services brought by the cloud server,we usually encrypt the data and then outsource it to the cloud server in order to protect the data privacy,but this also causes some obstacles for data users.In other words,how can users easily apply these encrypted data?The traditional way is to download all encrypted data to the local.And then,users search the data they needed in decrypted data,but it will cause a large bandwidth and local storage space.Therefore,it is not applicable.In this case,the keyword search over encrypted data is a critical technology to solve this problem.This dissertation studies public key encryption with keyword search,and concentrates on the problem of public key encryption with equality test under multi-user environment.The main contents are as follows:(1)Research on the verifiability of the public key encryption with equality test under the cloud environment.We analyzed and summarized the existing public key encryption with equality test schemes.It is found that in order to protect user's data privacy,the cloud server must be authorized before perform the equality test operation between ciphertexts.Also,the existing schemes assume that the cloud server is semi-trusted and do not verify the correctness of equality test results returned by the cloud server.In this dissertation,assuming that the cloud server is probably malicious,a verifiable public key encryption with equality test scheme is designed under the malicious cloud model.The scheme implements a variety of authorization types,from coarse-grained to fine-grained,and users can flexibly choose the type of authorization according to their needs.Furthermore,users generate the supplementary information and upload it to the cloud server,and then,the cloud server generates a proof for equality test using supplementary information,after equality test,the cloud server returns the proof and results to the user.Employing these results,the user can verify whether the cloud server has implemented the protocol honestly.Finally,it is proved that the scheme satisfies OW-CCA authorized security and IND-CCA unauthorized security using provable security theory.(2)Research on identity-based encryption with equality test against off-line keyword guessing attacks under the cloud environment.Due to the keyword space is much less than the secret key space,and users usually retrieve only some common keywords,attackers can launch keyword guessing attacks.The existing public key encryption with equality test schemes cannot resist the off-line keyword guessing attacks.In this dissertation,we use identity-based encryption and blind signature.Firstly,transform keywords using blind signature with the help of a server-aided.Secondly,encrypt keywords using identity-based encryption.Finally,perform the equality test between ciphertexts.When the server-aided is offline,attackers cannot transform keywords,so they cannot generate legitimate ciphertext and launch off-line keyword guessing attacks.It is proved that the scheme satisfies OW-ID-CCA authorized security using provable security theory.