Encrypting File System
The Encrypting File System (EFS) on Microsoft Windows is a feature introduced in version 3.0 of NTFS that provides filesystem-level encryption. The technology enables files to be transparently encrypted to protect confidential data from attackers with physical access to the computer. EFS is available in all versions of Windows except the home versions (see Supported operating systems below) from Windows 2000 onwards. By default, no files are encrypted, but encryption can be enabled by users on a per-file, per-directory, or per-drive basis. Some EFS settings can also be mandated via Group Policy in Windows domain environments. Cryptographic file system implementations for other operating systems are available, but the Microsoft EFS is not compatible with any of them. See also the list of cryptographic file systems. Basic ideas When an operating system is running on a system without file encryption, access to files normally goes through OS-controlled user authentication and access control lists. However, if an attacker gains physical access to the computer, this barrier can be easily circumvented. One way, for example, would be to remove the disk and put it in another computer with an OS installed that can read the filesystem; another, would be to simply reboot the