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Windows Vista Security: Praxisorientierte Sicherheit für Profis by Marcus Nasarek

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Using Compression and Encryption
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You can expand a file or folder by completing these steps:
1. In Windows Explorer, right-click the file or folder that you want to expand and
then select Properties.
2. On the General tab of the related property dialog box, click Advanced.
3. In the Advanced Attributes dialog box, clear the “Compress contents to save
disk space” checkbox and click OK twice.
4. For a file, Windows Vista removes compression and expands the file. For a
folder, Windows Vista expands all the files within the folder. If the folder con-
tains subfolders, Windows Vista displays the Confirm Attribute Changes dialog
box, shown in Figure 19-19:
To expand only the folder and the files it contains, select “Apply changes to
this folder only” and then click OK.
To expand the folder, subfolders, and all related files, select “Apply changes
to this folder, subfolders and files” and then click OK.
Encrypting Files and Folders
You can use encryption to protect your files and folders so that only you can access
them regardless of the NTFS permissions assigned to those files or folders. The first
time you encrypt a file or folder, Windows Vista creates a personal certificate contain-
ing your encryption key. A personal certificate is similar to other types of certificates
used by computers in that it contains both private key and public key encryption
data. The certificate is extremely important. If it is damaged or removed from your
computer, you won’t be able to access your encrypted data.
Unlike NTFS compression, you can’t encrypt entire drives. You can’t encrypt com-
pressed files, system files, or read-only files either. If you try to encrypt compressed
Figure 19-18. Choosing the compression options
688
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Chapter 19: Managing Disks and Drives
files, they are automatically uncompressed and then encrypted. If you try to encrypt
system files, you’ll get an error message.
The Windows Vista component that handles encryption is called the Encrypting File
System (EFS). EFS encrypts files and folders using an encryption key that is automat-
ically generated and unique for each person that uses encryption on your computer.
When you encrypt a file or folder, the associated data is converted to an encrypted
format so that only you can access the file or folder.
By default, you are the only person who can access your encrypted files and folders.
However, as you might expect there are some caveats. If your computer has any
assigned recovery agents, those recovery agents have the authority to decrypt any
encrypted files and folders on your computer. You can think of a recovery agent as
having a master key. Additionally, you can grant a person the right to access your
encrypted files and folders. When you do this, this person’s encryption key is added
to the file or folder’s encryption data, allowing the person to access the file or folder
just like you can.
Encrypting a file or folder
You can encrypt a file or folder by completing these steps:
1. In Windows Explorer, right-click the file or folder that you want to encrypt and
then select Properties.
2. On the General tab of the related property dialog box, click Advanced.
3. In the Advanced Attributes dialog box, select the “Encrypt contents to secure
data” checkbox and then click OK.
4. For an individual file, Windows Vista marks the file as encrypted and then
encrypts it. If the file is in a folder that is not encrypted, Windows Vista displays
the Confirm Attribute Changes dialog box:
Figure 19-19. Choosing the uncompress options

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