File ciphering method and its device

TLDR: In this paper, the ordinary text file is divided by n to the smallest data size at which data transaction between the data region on a memory to be used by the application program and a disk buffer is possible, by which n-pieces of ordinary text blocks 101 to 103 are formed.

Abstract: PURPOSE:To adequately cipher a file to be written into a memory device without depending on the kind of an application program by which the file is formed. CONSTITUTION:The ordinary text file 100 is divided by n to the smallest data size at which data transaction between the data region on a memory to be used by the application program and a disk buffer is possible, by which n-pieces of ordinary text blocks 101 to 103 are formed. Next, n-pieces of these ordinary text blocks 101 to 103 are respectively separately ciphered by a user key 104 and n-pieces of cipher text blocks 105 to 107 are formed. Finally, the formed n-pieces of these cipher text blocks 105 to 107 are connected to obtain a cipher text file 108. Then, the application program ciphers the ordinary text file by each of the smallest data size at which a partial operation, such as superscription, of the file is possible and, therefore, the correct diciphering to the original ordinary text file is possible at any time even if any operation is executed by the application program.