Decrypting a file before sending from the ftp server (vsftpd)
 

I am stucked on one point of my academic project, the situation is like:
The ftp server stores all the files in encrypted form.
Whenever there is ftp get from client to server for a file, the file will be decrypted
and the decrypted file will be sent to the client. The encryption & decryption
is done at the VFS layer of kernel (vfs_read(),vfs_write().....).
Please suggest any way to do so.

Surely the point of an academic project is to work it out yourself and come up with your own solution rather than just posting and letting other people do the work for you?