Directory password protection (ESP on the assembler)

Course work for the assembler Protection directories (folders) password (password protection). Detail of the job:
In this course project should develop a program to protect against unauthorized access to directories located on floppy disks. Develop programs should be designed to work in the operating system DOS.
The program should provide a variety of directory to which nebhodimo deny access, and request the password for each access to this directory, as long as the code is entered correctly.
It must be a resident with the possibility of unloading and reloading of protection.
To deny access to the directory you want to prevent the reading of sectors in which a subdirectory is related to a given directory. Search sector through the file table. This project is designed for the file system FAT12, because it is used in the majority of floppy disks.
To disable the directory must be read to intercept interrupt 13h disk read and check whether there was an attempt to read the forbidden sector. If such an attempt took place, the password request. If the password is correct, control is returned to the old interrupt vector, or exits the interrupt handler.