Research On Security Enhancement Of Time-release Encryption Technology

Timed-release encryption(TRE)is a cryptographic primitive which is decrypted at a future time by the sender.TRE combined with other cryptographic technologies is suitable for many scenarios,such as the storage and access of electronic medical files,online bidding,online voting,broadcast of film and TV series,etc.Therefore,TRE will play an essential role in real life.In view of the current security problems of TRE,this thesis starts with the latest research development of TRE technology,carries out the research on protecting the private key of time server to enhance the security of TRE and enhancing the security of any time decryption.The specific work is as follows:(1)Research on the latest development of TRE technology.This thesis first introduces the research history since the emergence of TRE,and summarizes the TRE schemes proposed from 2015 to 2018.Secondly,three basic methods of constructing TRE are described: mathematical,physical and network methods.Finally,this thesis conducts in-depth classification from the perspective of whether there is time server or not,and briefly introduce the advantages and disadvantages of each model and the construction scheme of each model.(2)Research on protecting private key of time server to enhance TRE security.In this thesis,we design a time release encryption security enhancement scheme based on random oracle model.In the scheme designed in this thesis,the time server will store the random numbers generated in advance in the order of generation time.To generate time trapdoor of time T,the time server needs to select random number corresponding to time sequence position of time T and private key of time server to generate time trapdoor together,which realizes one-time-pad of time trapdoors and greatly enhances the safety of TRE.In this thesis,the specific construction and general construction of the scheme are given.In the specific construction scheme,the construction process of the scheme is described in detail,and the simple security proof is given.Compared with the most efficient scheme based on random oracle model,the time efficiency of the scheme is improved by 24%.In the general construction scheme,the formal definition,general construction and the simple safety analysis are carried out.(3)Research on security enhancement of decryption at any time.Taking advantage of the powerful computing power of the cloud computing,this thesis designs an ATRE scheme which is realized by thetime server and the cloud server.The security of the scheme is based on BDH problem in the random oracle model and q-DBDHI problem in the standard model.On the premise of decryption at any time,the scheme can not only prevent the cloud server from colluding with the attacker to decrypt the ciphertext in advance,on the other hand,but also resist the denial of service attack.In this thesis,the model and specific scheme of the ATRE scheme are given.In the scheme model,the formal definition of the scheme and the security game model based on q-DBDH I problem are described.In the specific scheme,the detailed construction process of the scheme is given,and the security proof process of the scheme to solve q-DBDHI problem is mainly given.