On Fly encryption File system filter driver

Hi,

I am developing a file system filter driver on windows 2000, which does on
fly encryption and decryption. I would like to know what is best method to
mark the file for encryption.

My plan is to add a header information to the encrypted file so that the
filter driver will use this information to identify the encrypted file
when it is read or written to the disk. Does this solution have any
side-effects ?

One more issue I have identifed is with temporary files that are created
by applications like MS-Word, Visual studio. For example, if an encrypted
word document is opened with MS-Word, it creates a temporary document with
the same contents and when the document is saved it deletes the original
document and renames the temporary document to the orignal name. Since the
temoprary document is not marked for encryption its contents will NOT be
in encrypted format and when it is renamed to orginal document it is still
unencrypted. But the user thinks that the original document is encrypted
and hence it is a bug. Is there any solution for this ?

Kedar.