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Earlier I had shared an article to encrypt, decrypt and sign a file using GPG key in Linux. In this article I will show you the steps to create an encrypted block device using LUKS. By default if somebody connects your hard disk to their computer, it can be mounted automatically, even without entering any user credentials, and that is why we should always encrypt hard disk.
If your hard disk was encrypted then in order to mount an encrypted device, you need to enter a passphrase, without passphrase, nobody can mount it. So this will protect your hard disk, or your server, hard disk from being lost or stolen or whatever, after which data can be accessed easily.
To create encrypted devices in Linux we use LUKS. LUKS is the Linux encryption layer.
Below are some more articles on LUKS based Disk Encryption
- How to Encrypt Hard Disk (partition) using LUKS in Linux
- How to auto mount LUKS encrypted partition using fstab at boot in Linux
- How to encrypt root partition and entire file system using LUKS in Linux
- How to resize LUKS partition (shrink or extend encrypted luks volume) in Linux
- Configure LUKS Network Bound Disk Encryption with clevis & tang server to boot without password
dm-crypt and cryptsetup vs LUKS
dm-crypt and cryptsetup
- Device-mapper is a part of the Linux kernel that provides a generic way to create virtual layers of block devices, most commonly LVM logical volumes. The device-mapper crypt target (dm-crypt) provides transparent encryption of block devices using the kernel crypto API.
- In Red Hat Enterprise Linux, userspace interaction with dm-crypt is managed by a tool called cryptsetup, which uses the device-mapper infrastructure to setup and operate on encrypted block devices.
LUKS
- With modern versions of cryptsetup (i.e., since ~2006), encrypted block devices can be created in two main formats, plain dm-crypt format or the extended LUKS (Linux Unified Key Setup-on-disk-format) format.
- LUKS provides a standard on-disk-format for hard disk encryption, which facilitates compatibility among Linux distributions and provides secure management of multiple user passwords.
- In contrast to previous Linux disk-encryption solutions, LUKS stores all necessary setup information in the partition header, enabling the user to more easily transport or migrate their data.
- The advantages of LUKS over plain dm-crypt are the obvious higher usability: automatic configuration of non-default crypto parameters, the ability to add, change, and remove multiple passphrases.
- Additionally, LUKS offers defenses against low-entropy passphrases like salting and iterated PBKDF2 passphrase hashing
Attach new hard disk (optional)
So to start with, you need an empty device. I have added a new virtual disk to my virtual machine as /dev/sdb
[root@node1 ~]# cat /proc/partitions
major minor #blocks name
11 0 1048575 sr0
8 0 31457280 sda
8 1 524288 sda1
8 2 28844032 sda2
8 16 5242880 sdb
253 0 26738688 dm-0
253 1 2097152 dm-1
Create new partition
We will create a new partition /dev/sdb1 on this disk
[root@node1 ~]# fdisk /dev/sdb Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table Building a new DOS disklabel with disk identifier 0xa12bdd47. Command (m for help): n Partition type: p primary (0 primary, 0 extended, 4 free) e extended Select (default p): Using default response p Partition number (1-4, default 1): First sector (2048-10485759, default 2048): Using default value 2048 Last sector, +sectors or +size{K,M,G} (2048-10485759, default 10485759): Using default value 10485759 Partition 1 of type Linux and of size 5 GiB is set Command (m for help): p Disk /dev/sdb: 5368 MB, 5368709120 bytes, 10485760 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0xa12bdd47 Device Boot Start End Blocks Id System /dev/sdb1 2048 10485759 5241856 83 Linux Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.
So our partition is successfully created.
[root@node1 ~]# partprobe
So our partition is successfully created.
[root@node1 ~]# cat /proc/partitions
major minor #blocks name
11 0 1048575 sr0
8 0 31457280 sda
8 1 524288 sda1
8 2 28844032 sda2
8 16 5242880 sdb
8 17 5241856 sdb1
253 0 26738688 dm-0
253 1 2097152 dm-1
Format the partition using luksFormat
So you would do luksFormat on the device, and the luksFormat command is going to create the encryption layer. This is the passphrase that needs to be entered by anyone who wants to access the device. In real life of course, you wanna have something that really is secure because devices are not mounted that often. (computer keys tapping and clicking)
[root@node1 ~]# cryptsetup luksFormat /dev/sdb1
WARNING!
========
This will overwrite data on /dev/sdb1 irrevocably.
Are you sure? (Type uppercase yes): YES
Enter passphrase for /dev/sdb1:
Verify passphrase:
Initialise LUKS device
Next, you need to do luksOpen, and that brings you to a different level where you are going to work with the encrypted device. So this will create a new device, and this new device is managed by the device mapper, so let's call it /dev/mapper/secret.
[root@node1 ~]# cryptsetup luksOpen /dev/sdb1 secret Enter passphrase for /dev/sdb1:
As we will see when you are using the cryptsetup, luksOpen command, a new device is created, and you will provide the name for the device. In this example, the name for the device is /dev/mapper/secret
[root@node1 ~]# cd /dev/mapper/
[root@node1 mapper]# ls -l total 0 lrwxrwxrwx. 1 root root 7 Feb 25 21:11 centos-root -> ../dm-0 lrwxrwxrwx. 1 root root 7 Feb 25 21:11 centos-swap -> ../dm-1 crw-------. 1 root root 10, 236 Feb 25 21:09 control lrwxrwxrwx. 1 root root 7 Feb 25 21:14 secret -> ../dm-2
Create file system on LUKS device
Now the important step is that you need to create a file system on the encrypted device, and that means that the file system is going to be created here.
[root@node1 mapper]# mkfs.ext4 /dev/mapper/secret
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
327680 inodes, 1309952 blocks
65497 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1342177280
40 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
Mount the LUKS partition
Once a file system has been created on the LUKS device, you can move on, you can create a mount point and mount it.
[root@node1 mapper]# mkdir /secret [root@node1 mapper]# cd [root@node1 ~]# mount /dev/mapper/secret /secret/
Once we can verify using the mount command, you can see that from the mount command perspective, there's nothing visible about the device being encrypted, we just see a device that is encrypted.
[root@node1 ~]# mount | grep secret /dev/mapper/secret on /secret type ext4 (rw,relatime,seclabel,data=ordered)
So we can create files on top of it. (computer keys tapping and clicking) And these files will be safely stored on the encrypted device.
Dis-connect the encrypted partition
let me also show you how to disconnect the encrypted device.
[root@node1 ~]# umount /secret
[root@node1 ~]# cryptsetup luksClose /dev/mapper/secret [root@node1 ~]# mount | grep secret
Lastly I hope the steps from the article to encrypt hard disk (partition) using LUKS on Linux was helpful. So, let me know your suggestions and feedback using the comment section.
In the next article I will share the steps to automatically decrypt and mount the encrypted partition at booting stage using key file on Linux
