file system filter driver

**mayuradatia** · 28-01-2009

1) I want to encrypt all my .doc files before saving and decrypt before opening so that they open fine in Word. Should I be writing a file system filter driver for such a task? Is there any other way, I can do this?
2) Can I use WDK or DDK to develop a file system filter driver?
3) Do I need to use IFS kit for writing a file system filter driver?
4) Will one filter driver work across various file systems supported by Windows XP & Vista?
5) Will such a filter driver work on machine which has antivirus software installed?

**Mutilda** · 28-01-2009

How to encrypt and decrypt using the Encrypting File System
The following steps encrypt and decrypt a file or folder using the Encrypting File System.

Note These guidelines apply to Windows 2000 and Windows XP.
Encrypting a folder
Although you can encrypt files individually, we strongly recommend that you designate a specific folder for storing encrypted data.

Encrypt a folder and its contents

Although you can encrypt files individually, generally it is a good idea to designate a specific folder where you will store your encrypted files, and to encrypt that folder. If you do this, all files that are created in or moved to this folder will automatically obtain the encrypted attribute.

To encrypt a folder and its current contents, follow these steps:

1. Right-click the folder that you want to encrypt, and then click Properties.
2. In the Properties dialog box, click Advanced.
3. The Advanced Attributes dialog box displays attribute options for compression and encryption. This dialog box also includes archive and indexing attributes.

Note Although the NTFS file system supports both compression and encryption, it does not support both at the same time. This means that you can only select one or the other. A file or folder cannot be both encrypted and compressed at the same time.

To encrypt the folder, click to select the Encrypt contents to secure data check box, and then click OK.
4. Click OK to close the Advanced Attributes dialog box.
5. If the folder you chose to encrypt in steps 1 to 3 already contains files, a Confirm Attribute Changes dialog box will appear.

You can choose to encrypt only the folder so that all files subsequently moved to the folder or created in this folder will be encrypted. If you want to also encrypt all the contents of this folder, click Apply changes to this folder, subfolders, and files, and then click OK.

Decrypting a folder
To decrypt a folder, use basically the same process but in reverse order:

1. Right-click the folder that you want to decrypt, and then click Properties.
2. Click Advanced.
3. Click to clear the Encrypt contents to secure data check box to decrypt the data.
4. Click OK to close the Advanced Attributes dialog box.
5. Click OK to close the Properties dialog box.
6. If the folder has files in it, the Confirm Attribute Changes dialog box appears. You can choose to decrypt only the folder. However, this will not decrypt any files currently contained in the folder.

If you want to decrypt all the contents of this folder, click Apply changes to this folder, subfolders, and files, and then click OK.

For more details: Microsoft