Research On Digital Watermarking And Digital Fingerprinting Algorithm For Important Electronic File Protection

With the development of computer and internet technologies,the electronic files have been widely used in the e-government network and the enterprise intranet.Since the electronic files are easily to be copied and spread without any trace,the poor file management will lead to leakage of secret information.Therefore,how to prevent users from copying and transmitting electronic files without authorization has become an important information security problem in intranet.Traditional security technologies can not meet the demands of protecting the electronic files in intranet.So there is theoretical significance and practical value on the research of protecting the important electronic files by introducing digital watermarking and digital fingerprinting technologies.The digital watermarking technology is used to embed security mark in the files in order to describe the importance of files and provide basis for cascade protection.It requires watermarking algorithm with high embedding capacity and good robustness.By improving the current image correction method,we propose a CDMA(Code Division Multiple Access) watermarking algorithm based on wavelet packet transform and discrete cosine transform.The algorithm employs the CDMA technology to increase the embedding capacity of watermark.After the host image is decomposed by the wavelet package transform,the algorithm embeds the watermark in the low and middle frequency bands of the image to improve the invisibility and robustness.We employ the image correction method based on SIFT(Scale Invariant Feature Transform) feature points to correct image geometric distortions for good robustness against geometric attack.The digital fingerprinting technology is used to defense collusive attack,so the fingerprinting algorithm should be able to trace all colluders when the collusion size is two.By employing concatenated codes,we propose a digital fingerprint coding and tracing algorithm based on IPP(Identifiable Parent Property) code.The algorithm first constructs a 2-frameproof code and a 2-secure code.Then it constructs a two-user collusion secure code as inner code,by combining the 2-secure code with chaotic sequence.The IPP code is used as outer code,which analyzes the decoding results of the inner code and trace two colluders with a high probability without accusing any innocent users.When more than two users collude,the fingerprinting algorithm should trace one colluder at least.By employing concatenated codes,a digital fingerprint coding and tracing algorithm based on Turbo code is proposed.TheГ₀(n,d) code is used as inner code,and the Turbo code is used as outer code.The decoding algorithm of Turbo code is improved to utilize the decoding results of the inner code,and can trace one of the colluders accurately.Compared with other algorithms based on theГ₀(n,d) code,under the same collusion size and error probability,the proposed algorithm has a shorter fingerprint length.The study on digital watermarking and digital fingerprinting technologies has reached some theoretical and practical achievements,which are significant for protecting the important electronic files and improving the information security in the intranet.