Friday, September 26, 2014

Encrypting Disks With LUKS (RHEL 6 / CentOS 6)

LUKs a concept used to encrypt disks for securing data. Partitions will not be accessible without decrypting that device with an defined PASSPHRASE

How to setup encrypted disks with LUKs?

1) Install LUKs utilities

yum -y install crypt*

2) Load dm_crypt module

modprobe dm_crypt

3) Add dm_crypt in system, so that after reboot this should be loaded

cat > /etc/sysconfig/modules/dm_crypt.modules
modprobe dm_crypt

save and exit with  CTRL+D

chmod 755 /etc/sysconfig/modules/dm_crypt.modules

NOTE: dm_crypt.modules script created to loaod module

4) Lets say /dev/sdb is the disk to encrypt, First Create setup and format /dev/sdb with following command:

cryptsetup luksFormat /dev/sdb

This will ask for passphrase which will be used to decrypt/open this disk before using this disk

To mount or use /dev/sdb disk follow below given steps as at this point /dev/sdb will not be available to mount

5) Open LUKs disk/device by mapping/assigning an name, this will create and file/mapping in /dev/mapper

cryptsetup luksOpen /dev/sdb myluksdev_map

This will ask for passphrase to decrypt disk. Enter passphrase set in step number 4

NOTE : myluksdev_map given name can be anything as per your desire

6) As above command has opened/decrypted disk, now we can format with ext4

mkfs.ext4 /dev/mapper/myluksdev_map

7) Create an folder and mount /dev/sdb

mkdir /mnt/my_secret_dir

mount /dev/mapper/myluksdev_map /mnt/my_secret_dir

[Above /dev/mapper/myluksdev_map is name which is given at the time of opening/decrypting /dev/sdb device]

8) If we want to close encryption, have to follow given steps

umount /mnt/my_secret_dir
cryptsetup luksClose myluksdev_map

8) To make partition persistent or permanent after reboot we should add MOUNT entry in /etc/fstab but for mounting encrypted file system, we should decrypt disk/device. So, we should follow given steps to mount disks at the time of boot

    a) Create a file /etc/crypttab
    b) Update with given content

        MAPname         Device/path     ------------------- example

        In our case MAPname = myluksdev_map , Device Path = /dev/sdb

    c) Content should be

         cat /etc/crypttab
         myluksdev_map      /dev/sdb

   d) Now update /etc/fstab file with below content
       /dev/mapper/myluksdev_map                /mnt/my_secret_dir          ext4      defaults        0 0

Now reboot your server, this will ask for PASSPHRASE while mounting device /dev/mapper/myluksdev_map

To automatically unlock passphrase or avoiding asking password use below given steps:

    a) Create an file, lets say /root/cpasswd which will store password
         echo -n "password" > /root/cpasswd
         chmod 600 /root/cpasswd

   b) Now update /etc/crypttab like this


       So, in our case this should be

       myluksdev_map     /dev/sdb           /root/cpasswd

Now try rebooting your server, this should not ask for password.

Thats it!!!

Please comment with your feedback :-)


  1. Nice. I wanted to add that it seems with more attention to security I am seeing a lot more about enabling the FIPS standard for encryption. You can read about FIPS here:

    I wrote about enabling FIPS (and then using LUKS similar to you to encrypt a device)

    Hope this is helpful!