Administrators can use Cipher.exe to encrypt and decrypt data on drives that use the NTFS file system and to view the encryption status of files and folders from a command prompt. An updated version of the Cipher tool has been released for Windows 2000, and is included with Windows XP. The updated version adds another security option. This new option is the ability to overwrite data that you have deleted so that it cannot be recovered and accessed.
When you delete files or folders, the data is not initially removed from the hard disk. Instead, the space on the disk that was occupied by the deleted data is "deallocated." After it is deallocated, the space is available for use when new data is written to the disk. Until the space is overwritten, it is possible to recover the deleted data by using a low-level disk editor or data-recovery software.
If you create files in plain text and then encrypt them, Encrypting File System (EFS) makes a backup copy of the file so that, if an error occurs during the encryption process, the data is not lost. After the encryption is complete, the backup copy is deleted. As with other deleted files, the data is not completely removed until it has been overwritten. The new version of the Cipher utility is designed to prevent unauthorized recovery of such data.
For Windows 2000 users, the new Cipher.exe tool is part of Windows 2000 Security Rollup Package 1. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
311401 Windows 2000 Security Rollup Package 1 (SRP1), January 2002
The Cipher.exe utility that is included with Windows XP provides the ability to overwrite deleted data.
How to Use the Cipher Security Tool to Overwrite Deleted Data
To overwrite deleted data on a volume by using Cipher.exe, use the /w switch with the cipher command. Use the following steps:
Quit all programs.
Click Start, click Run, type cmd, and then press ENTER.
Type cipher /w:driveletter:\foldername, and then press ENTER. Specify the drive and the folder that identifies the volume that contains the deleted data that you want to overwrite. Data that is not allocated to files or folders will be overwritten. This permanently removes the data. This can take a long time if you are overwriting a large space.
Note With mount points in Windows 2000, you can mount a volume on any empty folder on an NTFS volume. When you do this, the mounted volume does not have a drive letter of its own. The only way to address that volume is by using the path where you created the mount point. Therefore, the /w switch requests a path of a folder, and from that, it determines the associated volume to wipe. Because of the way the file system works, the whole volume must be wiped. A file can be written anywhere on the volume at any time. A folder does not address a specific physical location on disk but is a logical container for file entries in the volume's table of contents (MFT or FAT). To make sure that there is no leftover data in unallocated space, all unallocated space on the volume must be wiped.