1. Iniciamos la partición para el cifrado con LUKS:

[#] cryptsetup luksFormat /dev/hda4
Are you sure? (Type uppercase yes): YES
Enter LUKS passphrase:
Verify passphrase:
Command successful.

2. Preparamos el dispositivo Device-Mapper:

[#] cryptsetup luksOpen /dev/hda4 testfs
Enter LUKS passphrase:
key slot 0 unlocked.
Command successful.

3. Formateamos la partición cifrada:

[#] mke2fs -j -L Test /dev/mapper/testfs

4. Montamos y escribimos los datos:

[#] mount /dev/mapper/testfs /mnt/testfs

6. Desmontamos la partición:

[#] umount /mnt/testfs

[#] cryptsetup luksClose /dev/mapper/testfs

7. Para volver a utilizar la partición:

[#] cryptsetup luksOpen /dev/hda4 testfs
Enter LUKS passphrase:
key slot 0 unlocked.
Command successful.

[#] mount /dev/mapper/testfs

Y listo.

Robado de aqui:

Howto use Cryptsetup with LUKS support.