Research On Secure Protection Of Documents And File Contents In NTFS

Computer files have security issues such as file stealing,tampering,forgery and infringement,while most operating system's own file protection functions are based on driver encryption and user management,which can not meet multiple application scenarios for file protection,and the need for special file security protection tools arised.Most government and individual platforms used for file operations are Windows.Considering that most existing Windows systems support NTFS(New Technology File System),this thesis studied three mechanisms about data encryption,digital signature and data steganography based on characteristics of files structure in Windows NTFS.The protection tool implemented includes file encryption,file signature and file steganography.The main research contents are summarized as follows.(1)After analyzing symmetric cryptosystem and selecting the block cipher mode,the protection tool implemented autonomous security of file encryption by replacing the S-box of standard AES with a better and controllable one.Operating file attributes and clearing files completely can enhance security.Besides,changing the round function of deformed AES to pre-calculated table improved the efficiency of file encryption.(2)After analyzing the public key cryptosystem and selecting the ECDSA and SHA-256 algorithm,the tool implemented file signature by using OpenSSL involving ECDSA and ECC.Besides supporting standard key pair generation of ECDSA,the fixed key pair generation also be supported,which can enhance flexibility and usability.(3)After analyzing steganography algorithms and selecting the spatial LSB steganography method with large capacity in image file,the protection tool selects pixels randomly to embed data into BMP file to overcome shortcomings of simple LSB replacement,while guaranteeing the capacity and solving the security problems.(4)Correctness and performance of file encryption,signature and steganography were tested.Pre-calculation processing and different file buffer size to file encryption or decryption efficiency were tested,the average efficiency reached 200MB/S,the file buffer is set by 128 KB.File signature efficiency is guaranteed by OpenSSL.Invisibility is guaranteed when the number of steganographic bits is half of BMP picture pixels.