Researches On Proxy ReEncryption In Cloud Computing

With the rapid development of the cloud computing,the productivity and social progress had been greatly promoted.However,the information share and its corresponding security issues of the different clouds had become more and more serious.Fortunately,the technology of proxy reencryption had solved these issues at the technical level.The proxy reencryption(PRE)is a conversion mechanism of the ciphertext,the semi-trusted proxy can convert the delegater's ciphertext into the delegatee's without decrypting the delegater's ciphertext.The delegatee can decrypt the converted ciphertext by his private key.It makes the information share be more efficient and secure in the cloud computing.The proxy reencryption is one of cryptography primitives,it has been proposed by Blaze et al.in 1998.From then on,a large number of scholars have devoted themself to research PRE.PRE has already been widely applied in many fields,such as encrypted e-mail forwarding,spam filtering and digital copyright protection,and so on.Unfortunately,the existed PRE schemes had some faultiness,such as the private key of the delegate should be submitted to the delegater to generate the reencryption key.This maybe bring about the hidden security danger;the decryption condition of conditional proxy reencryption scheme should be presetted at the beginning of the system establishment.It was inflexible in the practical application;there needed a large amount of computational overhead in many PRE schemes.This thesis made a deep research on how to better realize the information share by the PRE technology in the cloud computing environment and the corresponding PRE schemes were proposed.The proposed PRE schemes have overcome the faultiness of the exsited PRE schemes.The main works and the innovation points of this thesis are illustrated by the following three aspects:1.Heterogeneous conditional proxy reencryption schemes in cloud computing.The existed CPRE schemes required the delegater and delegatee belong to the same cryptosystem,delegatee's private key was used to generate reencryption key,and the decryption condition was set before the first level ciphertext.It is unreasonable in cloud computing environment.To overcome those limitations,two heterogeneous conditional proxy reencryption schemes were proposed in this thesis.In the proposed schemes,the delegater and delegatee came from different cryptosystems,the reencryption key was generated by the delegatee's private key and the delegater's public key,and the decryption condition can be changed according to the different delegater.This made the proposed schemes be more efficient and reasonable in cloud computing environment.Under the complexity assumption of DHIP problem,the proposed schemes were proved to be CCA secure in random oracle model.2.Certificateless proxy reencryption scheme in cloud computing.In order to solve the problem of key escrow and the generation of reencryption key in the ID-based PRE schemes,this thesis proposed a novel certificateless proxy reencryption scheme.In the proposed scheme,the first level ciphertexts and the second level ciphertexts have the same form;There does not need the delegatee's private key to generate the reencryption key.Under the mCDH assumption,the proposed CPRE scheme was proved to be CCA secure in the random oracle model.Compared with other certificateless PRE schemes,the proposed CPRE scheme was more efficient.3.Proxy reencryption scheme without bilinear pairings in cloud computing.In the cloud computing environment,it is much more reasonable that to deal with the massive data with the more efficient nonbilinear pairing PRE scheme.A novel proxy reencryption without bilinear pairing scheme was proposed in this thesis.Under the CDH assumption,the proposed scheme was proved to be CCA secure in random oracle model.Compared with other PRE scheme without bilinear pairing,the proposed scheme has the higher efficiency and the generation of the reencryption key is more reasonable.