For nine certificateless signature schemes proposed by Y L Tang， et al. （TANG Y L， WANG F F， YE Q， et al. Improved provably secure certificateless signature scheme. Journal of Beijing University of Posts and Telecommunications， 2016， 39（1）： 112-116）， firstly， the linearized equation analysis method was used. It was found that there was a linear relationship between the public keys in all schemes. This defect was exploited to complete a signature forgery attack on all schemes. Secondly， in order to break the linear relationship between the public keys， the method of modifying the parameters of hash function was used to improve the scheme， and the security of the improved scheme was proved under the random oracle model. Thirdly， a public key construction format of certificateless signature scheme was proposed. The signature scheme constructed by this format could not be attacked by adversaries using public key replacement. Finally， the efficiency of the improved scheme was compared with those of the existing certificateless signature schemes through simulation. Experimental results show that the improved scheme promotes the security without reducing the computational efficiency.

Aiming at the problems that there is no unified registration of files, the whereabouts of files are not tracked, and the process of circulation is not standardized in the circulation of electronic files under the Internet ecology, a blockchain-based electronic file circulation scheme was proposed. Firstly, the design goals and design architecture of the electronic file circulation system based on blockchain were proposed using the multi-centralized system of the consortium blockchain in the blockchain. Secondly, blockchain-based electronic file circulation system was implemented by using a cloud storage platform to upload files for electronic file storage and adding time-stamps of the ownership transfer data of files to make the circulation process continuous, relevant, traceable, honest and credible. The data synchronization and tracing of the blockchain-based electronic file circulation system was achieved through using database calls to realize the data access. Finally, a smart contract for electronic file ownership transfer and query to verify and protect the contents of the files by reading the file identification. The security analysis and performance tests show that compared to the original one, the proposed scheme is more secure and enhances the credibility of the circulation information, at the same time, the shorter execution time of the smart contract makes the system have better reliability and traceability.