Encryption is the process of converting data into a format that cannot be read by others. You can use EFS to automatically encrypt your data when it is stored on the hard disk.You can encrypt files only on volumes that are formatted with the NTFS file system.EFS, the Encrypted File System, is a feature native to Windows XP that can be used to encrypt(or encode) sensitive files so that only you are able to see and access them. Encryption is the strongest form of protection that Windows provides.The EFS feature is not included in Microsoft Windows XP Home Edition.EFS does support file sharing between multiple users on a single file.
The use of EFS file sharing in Windows XP provides another opportunity for data recovery by adding additional users to an encrypted file.Although the use of additional users cannot be enforced through policy or other means, it is a useful and easy method for enabling recovery of encrypted files by multiple users without actually using groups, and without sharing private keys between users.
How to Encrypt a File
You can encrypt files only on volumes that are formatted with the NTFS file system. To encrypt a file: