Encrypting Offline Files

Encrypting Offline Files
The offline files feature, introduced with Windows 2000, allows you to cache a copy of files from a network share on your local computer. This capability is particularly useful for a mobile computer because it allows you to continue working with your files even when your computer is not connected to the network. (When you reconnect to the network, Windows synchronizes the local and network versions of each file.) As we point out, however, mobile computers are the ones most vulnerable to theft, so it would be terrific to be able to encrypt the local versions of your offline files. With Windows XP (but not Windows 2000), you can.

To encrypt your offline files, do the following:

In Windows Explorer, choose Tools, Folder Options.
On the Offline Files tab, shown in Figure 18-2, select both Enable Offline Files and Encrypt Offline Files To Secure Data.

Figure 18-2. When you select this option, the local copy of your offline files is always encrypted, regardless of the files' setting in the network folder.
Using the Cipher Command
Cipher.exe provides a command-line alternative for encrypting and decrypting folders and files. To encrypt or decrypt a folder or file, include the path and the appropriate switches. Use the /E switch to encrypt the folders or files you specify or the /D switch to decrypt them. For example, to encrypt the My Documents folder, including its files and subfolders, type cipher /e /a /s:"%userprofile%\my documents" at a command prompt.

In the file specification, you can use wildcards. You can also specify multiple folders and files in a single instance of the command; simply separate each name with a space. Table 18-1 shows Cipher's command-line switches for basic encryption and decryption operations. Cipher can also generate file encryption keys for users, create file recovery certificates, wipe unused data areas, and perform other tasks. For a complete list, type cipher /? at a command prompt.

Table 18-1. Common Command-Line Switches for Cipher.exe
Switch Description
/E
Encrypts the specified folders

/D
Decrypts the specified folders

/S:folder
Performs the operation on folder and its subfolders (but not on files)

/A
Performs the operation on specified files and files in specified folders