[This is preliminary documentation and subject to change.]
Windows NT version 5.0 and later support the Encrypted File System (EFS), which provides cryptographic protection of files on NTFS volumes. EFS provides file encryption on an individual file basis using a public-key system. The following topics discuss NTFS file encryption:
Note EFS encryption and NTFS file compression are mutually exclusive; you cannot compress an encrypted file. However, encrypted files tend to be compressed already, due the nature of cryptographic algorithms.