If you selected the Encrypt System option, the installer prompts you for a passphrase with which to encrypt the partitions on the system.
Figure 9.27. Enter passphrase for encrypted partition
Choose a passphrase and type it into each of the two fields in the dialog box. You must provide this passphrase every time that the system boots.
If you lose this passphrase, any encrypted partitions and the data on them will become completely inaccessible. There is no way to recover a lost passphrase.