C# CF: file encryption/decryption on the fly

Question

Hi, i've seen many article on encrypt/decrypt of file and typically a button is used to choose the file for encrypt and another button to decrypt the file.

i've seen some application like truecrypt and probably others which does file encryption on-the-fly with transparent. this means that when a encrypted file is clicked to access, it will automatically decrypt and play/open the file. then when the file is closed, it will automatically encrypt again.

some have said that the only way to detect file open is through file system filter.

but is there other ways to do this in c# compact framework?

Answer 1

You could give all the encrypted files a specific file extension which is handled by your decryption program, then when the user opens the file, your program would decrypt it and then open it in the correct application.

Answer 2

I think I understand your question. You don't control the programs which display the files, you want to just control the encryption anddecryption of the files behind the scenes without the program knowing it even happened (like a .docx file, would be encrypted and decrypted without Word knowing it). I think you should look into WMI. I haven't specifically used it to check for system events having to do with files being retrieved or saved but I have used it to hook into system events and set off code at certain times very effectively. Here is the MSDN reference:

WMI Reference

I would look into the __Instance Events. Like the __InstanceModificationEvent class for file save events to the IO:

__InstanceModificationEvent Reference

Hope this get you onto the right track!

Answer 3

I answered this in the MS Foums. You have to write a file system filter and that filter can only be written in C.