CertiGuide to A+ (A+ 4 Real)  9  Chapter 1: What are Operating Systems and How Do They Work?       9  File Management

Encryption? 1 2 Third Party Tools

Via NTFS 5, Windows 2000 and XP both support EFS – “Encrypting File System”. EFS use PKI certificates¹⁴ to allow each user of a computer to encrypt their own files. Until unencrypted, no one else may view the contents of the file (with one exception, covered shortly). Using encryption provides a huge security advantage over just using NTFS permissions to secure files. As discussed previously, it is possible to bypass NTFS permissions both by using specialist tools, and by installing the hard drive with the target files into a different computer, and using a parallel installation of Windows to access them. When a file is encrypted, it remains encrypted. To use EFS, simply locate the file you wish to encrypt ¹⁵and right click it. In this example we will encrypt a confidential text file, shown in Figure 162.

Select “Properties”, and click the “Advanced” button in the properties window that appears. The dialog in Figure 163 appears.

To encrypt the file, tick “Encrypt contents to secure data”, and click OK. You will be presented with the following warning.

The warning is self-explanatory, but very important. In this example, we only wish to encrypt a single file, so select “Encrypt the file only” and click OK. The file will be immediately encrypted and accessible only to the current user.

Locate the file in an Explorer window, and double click it. When the file opens, it will appear as though it was never encrypted.

This demonstrates that EFS operates “on the fly”, decrypting and encrypting files as they are accessed.

Encryption? 1 2 Third Party Tools