Encipherment in existing OS(Operating Systems) has typically used the techniques which encrypt and decrypt entirely a secret file at the application level with keys chosen by user In this mechanism it causes much overhead on the performance. However when a security-classified user-process writes a secret file, our proposed mechanism encrypts and stores automatically and efficiently the file by providing transparency to the user at the kernel level of Linux. Also when the user modifies the encrypted secret file, this mechanism decrypts partially the file and encrypts partially the file for restoring. When user reads only the part of the encrypted file, this mechanism decrypts automatically and partially the file. Therefore our proposed mechanism provides user much faster enciphering speed than that of the existing techniques at the application level.