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Chapter 9. Encrypting block devices using LUKS
By using the disk encryption, you can protect the data on a block device by encrypting it. To access the device’s decrypted contents, enter a passphrase or key as authentication. This is important for mobile computers and removable media because it helps to protect the device’s contents even if it has been physically removed from the system. The LUKS format is a default implementation of block device encryption in Red Hat Enterprise Linux.
9.1. LUKS disk encryption
Linux Unified Key Setup-on-disk-format (LUKS) provides a set of tools that simplifies managing the encrypted devices. With LUKS, you can encrypt block devices and enable multiple user keys to decrypt a master key. For bulk encryption of the partition, use this master key.
Red Hat Enterprise Linux uses LUKS to perform block device encryption. By default, the option to encrypt the block device is unchecked during the installation. If you select the option to encrypt your disk, the system prompts you for a passphrase every time you boot the computer. This passphrase unlocks the bulk encryption key that decrypts your partition. If you want to modify the default partition table, you can select the partitions that you want to encrypt. This is set in the partition table settings.
Ciphers
The default cipher used for LUKS is aes-xts-plain64
. The default key size for LUKS is 512 bits. The default key size for LUKS with Anaconda XTS mode is 512 bits. The following are the available ciphers:
- Advanced Encryption Standard (AES)
- Twofish
- Serpent
Operations performed by LUKS
- LUKS encrypts entire block devices and is therefore well-suited for protecting contents of mobile devices such as removable storage media or laptop disk drives.
- The underlying contents of the encrypted block device are arbitrary, which makes it useful for encrypting swap devices. This can also be useful with certain databases that use specially formatted block devices for data storage.
- LUKS uses the existing device mapper kernel subsystem.
- LUKS provides passphrase strengthening, which protects against dictionary attacks.
- LUKS devices contain multiple key slots, which means you can add backup keys or passphrases.
LUKS is not recommended for the following scenarios:
- Disk-encryption solutions such as LUKS protect the data only when your system is off. After the system is on and LUKS has decrypted the disk, the files on that disk are available to anyone who have access to them.
- Scenarios that require multiple users to have distinct access keys to the same device. The LUKS1 format provides eight key slots and LUKS2 provides up to 32 key slots.
- Applications that require file-level encryption.
9.2. LUKS versions in RHEL
In Red Hat Enterprise Linux, the default format for LUKS encryption is LUKS2. The old LUKS1 format remains fully supported and it is provided as a format compatible with earlier Red Hat Enterprise Linux releases. LUKS2 re-encryption is considered more robust and safe to use as compared to LUKS1 re-encryption.
The LUKS2 format enables future updates of various parts without a need to modify binary structures. Internally it uses JSON text format for metadata, provides redundancy of metadata, detects metadata corruption, and automatically repairs from a metadata copy.
Do not use LUKS2 in systems that support only LUKS1.
Since Red Hat Enterprise Linux 9.2, you can use the cryptsetup reencrypt
command for both the LUKS versions to encrypt the disk.
Online re-encryption
The LUKS2 format supports re-encrypting encrypted devices while the devices are in use. For example, you do not have to unmount the file system on the device to perform the following tasks:
- Changing the volume key
Changing the encryption algorithm
When encrypting a non-encrypted device, you must still unmount the file system. You can remount the file system after a short initialization of the encryption.
The LUKS1 format does not support online re-encryption.
Conversion
In certain situations, you can convert LUKS1 to LUKS2. The conversion is not possible specifically in the following scenarios:
-
A LUKS1 device is marked as being used by a Policy-Based Decryption (PBD) Clevis solution. The
cryptsetup
tool does not convert the device when someluksmeta
metadata are detected. - A device is active. The device must be in an inactive state before any conversion is possible.
9.3. Options for data protection during LUKS2 re-encryption
LUKS2 provides several options that prioritize performance or data protection during the re-encryption process. It provides the following modes for the resilience
option, and you can select any of these modes by using the cryptsetup reencrypt --resilience resilience-mode /dev/sdx
command:
checksum
The default mode. It balances data protection and performance.
This mode stores individual checksums of the sectors in the re-encryption area, which the recovery process can detect for the sectors that were re-encrypted by LUKS2. The mode requires that the block device sector write is atomic.
journal
- The safest mode but also the slowest. Since this mode journals the re-encryption area in the binary area, the LUKS2 writes the data twice.
none
-
The
none
mode prioritizes performance and provides no data protection. It protects the data only against safe process termination, such as theSIGTERM
signal or the user pressing Ctrl+C key. Any unexpected system failure or application failure might result in data corruption.
If a LUKS2 re-encryption process terminates unexpectedly by force, LUKS2 can perform the recovery in one of the following ways:
- Automatically
By performing any one of the following actions triggers the automatic recovery action during the next LUKS2 device open action:
-
Executing the
cryptsetup open
command. -
Attaching the device with the
systemd-cryptsetup
command.
-
Executing the
- Manually
-
By using the
cryptsetup repair /dev/sdx
command on the LUKS2 device.
Additional resources
-
cryptsetup-reencrypt(8)
andcryptsetup-repair(8)
man pages on your system
9.4. Encrypting existing data on a block device using LUKS2
You can encrypt the existing data on a not yet encrypted device by using the LUKS2 format. A new LUKS header is stored in the head of the device.
Prerequisites
- The block device has a file system.
You have backed up your data.
WarningYou might lose your data during the encryption process due to a hardware, kernel, or human failure. Ensure that you have a reliable backup before you start encrypting the data.
Procedure
Unmount all file systems on the device that you plan to encrypt, for example:
# umount /dev/mapper/vg00-lv00
Make free space for storing a LUKS header. Use one of the following options that suits your scenario:
In the case of encrypting a logical volume, you can extend the logical volume without resizing the file system. For example:
# lvextend -L+32M /dev/mapper/vg00-lv00
-
Extend the partition by using partition management tools, such as
parted
. -
Shrink the file system on the device. You can use the
resize2fs
utility for the ext2, ext3, or ext4 file systems. Note that you cannot shrink the XFS file system.
Initialize the encryption:
# cryptsetup reencrypt --encrypt --init-only --reduce-device-size 32M /dev/mapper/vg00-lv00 lv00_encrypted /dev/mapper/lv00_encrypted is now active and ready for online encryption.
Mount the device:
# mount /dev/mapper/lv00_encrypted /mnt/lv00_encrypted
Add an entry for a persistent mapping to the
/etc/crypttab
file:Find the
luksUUID
:# cryptsetup luksUUID /dev/mapper/vg00-lv00 a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325
Open
/etc/crypttab
in a text editor of your choice and add a device in this file:$ vi /etc/crypttab lv00_encrypted UUID=a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325 none
Replace a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325 with your device’s
luksUUID
.Refresh initramfs with
dracut
:$ dracut -f --regenerate-all
Add an entry for a persistent mounting to the
/etc/fstab
file:Find the file system’s UUID of the active LUKS block device:
$ blkid -p /dev/mapper/lv00_encrypted /dev/mapper/lv00-encrypted: UUID="37bc2492-d8fa-4969-9d9b-bb64d3685aa9" BLOCK_SIZE="4096" TYPE="xfs" USAGE="filesystem"
Open
/etc/fstab
in a text editor of your choice and add a device in this file, for example:$ vi /etc/fstab UUID=37bc2492-d8fa-4969-9d9b-bb64d3685aa9 /home auto rw,user,auto 0
Replace 37bc2492-d8fa-4969-9d9b-bb64d3685aa9 with your file system’s UUID.
Resume the online encryption:
# cryptsetup reencrypt --resume-only /dev/mapper/vg00-lv00 Enter passphrase for /dev/mapper/vg00-lv00: Auto-detected active dm device 'lv00_encrypted' for data device /dev/mapper/vg00-lv00. Finished, time 00:31.130, 10272 MiB written, speed 330.0 MiB/s
Verification
Verify if the existing data was encrypted:
# cryptsetup luksDump /dev/mapper/vg00-lv00 LUKS header information Version: 2 Epoch: 4 Metadata area: 16384 [bytes] Keyslots area: 16744448 [bytes] UUID: a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325 Label: (no label) Subsystem: (no subsystem) Flags: (no flags) Data segments: 0: crypt offset: 33554432 [bytes] length: (whole device) cipher: aes-xts-plain64 [...]
View the status of the encrypted blank block device:
# cryptsetup status lv00_encrypted /dev/mapper/lv00_encrypted is active and is in use. type: LUKS2 cipher: aes-xts-plain64 keysize: 512 bits key location: keyring device: /dev/mapper/vg00-lv00
Additional resources
-
cryptsetup(8)
,cryptsetup-reencrypt(8)
,lvextend(8)
,resize2fs(8)
, andparted(8)
man pages on your system
9.5. Encrypting existing data on a block device using LUKS2 with a detached header
You can encrypt existing data on a block device without creating free space for storing a LUKS header. The header is stored in a detached location, which also serves as an additional layer of security. The procedure uses the LUKS2 encryption format.
Prerequisites
- The block device has a file system.
You have backed up your data.
WarningYou might lose your data during the encryption process due to a hardware, kernel, or human failure. Ensure that you have a reliable backup before you start encrypting the data.
Procedure
Unmount all file systems on the device, for example:
# umount /dev/nvme0n1p1
Initialize the encryption:
# cryptsetup reencrypt --encrypt --init-only --header /home/header /dev/nvme0n1p1 nvme_encrypted WARNING! ======== Header file does not exist, do you want to create it? Are you sure? (Type 'yes' in capital letters): YES Enter passphrase for /home/header: Verify passphrase: /dev/mapper/nvme_encrypted is now active and ready for online encryption.
Replace /home/header with a path to the file with a detached LUKS header. The detached LUKS header has to be accessible to unlock the encrypted device later.
Mount the device:
# mount /dev/mapper/nvme_encrypted /mnt/nvme_encrypted
Resume the online encryption:
# cryptsetup reencrypt --resume-only --header /home/header /dev/nvme0n1p1 Enter passphrase for /dev/nvme0n1p1: Auto-detected active dm device 'nvme_encrypted' for data device /dev/nvme0n1p1. Finished, time 00m51s, 10 GiB written, speed 198.2 MiB/s
Verification
Verify if the existing data on a block device using LUKS2 with a detached header is encrypted:
# cryptsetup luksDump /home/header LUKS header information Version: 2 Epoch: 88 Metadata area: 16384 [bytes] Keyslots area: 16744448 [bytes] UUID: c4f5d274-f4c0-41e3-ac36-22a917ab0386 Label: (no label) Subsystem: (no subsystem) Flags: (no flags) Data segments: 0: crypt offset: 0 [bytes] length: (whole device) cipher: aes-xts-plain64 sector: 512 [bytes] [...]
View the status of the encrypted blank block device:
# cryptsetup status nvme_encrypted /dev/mapper/nvme_encrypted is active and is in use. type: LUKS2 cipher: aes-xts-plain64 keysize: 512 bits key location: keyring device: /dev/nvme0n1p1
Additional resources
-
cryptsetup(8)
andcryptsetup-reencrypt(8)
man pages on your system
9.6. Encrypting a blank block device using LUKS2
You can encrypt a blank block device, which you can use for an encrypted storage by using the LUKS2 format.
Prerequisites
-
A blank block device. You can use commands such as
lsblk
to find if there is no real data on that device, for example, a file system.
Procedure
Setup a partition as an encrypted LUKS partition:
# cryptsetup luksFormat /dev/nvme0n1p1 WARNING! ======== This will overwrite data on /dev/nvme0n1p1 irrevocably. Are you sure? (Type 'yes' in capital letters): YES Enter passphrase for /dev/nvme0n1p1: Verify passphrase:
Open an encrypted LUKS partition:
# cryptsetup open /dev/nvme0n1p1 nvme0n1p1_encrypted Enter passphrase for /dev/nvme0n1p1:
This unlocks the partition and maps it to a new device by using the device mapper. To not overwrite the encrypted data, this command alerts the kernel that the device is an encrypted device and addressed through LUKS by using the
/dev/mapper/device_mapped_name
path.Create a file system to write encrypted data to the partition, which must be accessed through the device mapped name:
# mkfs -t ext4 /dev/mapper/nvme0n1p1_encrypted
Mount the device:
# mount /dev/mapper/nvme0n1p1_encrypted mount-point
Verification
Verify if the blank block device is encrypted:
# cryptsetup luksDump /dev/nvme0n1p1 LUKS header information Version: 2 Epoch: 3 Metadata area: 16384 [bytes] Keyslots area: 16744448 [bytes] UUID: 34ce4870-ffdf-467c-9a9e-345a53ed8a25 Label: (no label) Subsystem: (no subsystem) Flags: (no flags) Data segments: 0: crypt offset: 16777216 [bytes] length: (whole device) cipher: aes-xts-plain64 sector: 512 [bytes] [...]
View the status of the encrypted blank block device:
# cryptsetup status nvme0n1p1_encrypted /dev/mapper/nvme0n1p1_encrypted is active and is in use. type: LUKS2 cipher: aes-xts-plain64 keysize: 512 bits key location: keyring device: /dev/nvme0n1p1 sector size: 512 offset: 32768 sectors size: 20938752 sectors mode: read/write
Additional resources
-
cryptsetup(8)
,cryptsetup-open (8)
, andcryptsetup-lusFormat(8)
man pages on your system
9.7. Configuring the LUKS passphrase in the web console
If you want to add encryption to an existing logical volume on your system, you can only do so through formatting the volume.
Prerequisites
You have installed the RHEL 9 web console.
For instructions, see Installing and enabling the web console.
-
The
cockpit-storaged
package is installed on your system. - Available existing logical volume without encryption.
Procedure
Log in to the RHEL 9 web console.
For details, see Logging in to the web console.
- Click Storage.
- In the Storage table, click the menu button, , next to the storage device you want to encrypt.
- From the drop-down menu, select .
- In the Encryption field, select the encryption specification, LUKS1 or LUKS2.
- Set and confirm your new passphrase.
- Optional: Modify further encryption options.
- Finalize formatting settings.
- Click Format.
9.8. Changing the LUKS passphrase in the web console
Change a LUKS passphrase on an encrypted disk or partition in the web console.
Prerequisites
You have installed the RHEL 9 web console.
For instructions, see Installing and enabling the web console.
-
The
cockpit-storaged
package is installed on your system.
Procedure
Log in to the RHEL 9 web console.
For details, see Logging in to the web console.
- Click Storage
- In the Storage table, select the disk with encrypted data.
On the disk page, scroll to the Keys section and click the edit button.
In the Change passphrase dialog window:
- Enter your current passphrase.
- Enter your new passphrase.
Confirm your new passphrase.
- Click Save
9.9. Creating a LUKS2 encrypted volume by using the storage
RHEL system role
You can use the storage
role to create and configure a volume encrypted with LUKS by running an Ansible playbook.
Prerequisites
- You have prepared the control node and the managed nodes
- You are logged in to the control node as a user who can run playbooks on the managed nodes.
-
The account you use to connect to the managed nodes has
sudo
permissions on them.
Procedure
Create a playbook file, for example
~/playbook.yml
, with the following content:--- - name: Create and configure a volume encrypted with LUKS hosts: managed-node-01.example.com roles: - rhel-system-roles.storage vars: storage_volumes: - name: barefs type: disk disks: - sdb fs_type: xfs fs_label: label-name mount_point: /mnt/data encryption: true encryption_password: <password>
You can also add other encryption parameters, such as
encryption_key
,encryption_cipher
,encryption_key_size
, andencryption_luks
, to the playbook file.Validate the playbook syntax:
$ ansible-playbook --syntax-check ~/playbook.yml
Note that this command only validates the syntax and does not protect against a wrong but valid configuration.
Run the playbook:
$ ansible-playbook ~/playbook.yml
Verification
View the encryption status:
# cryptsetup status sdb /dev/mapper/sdb is active and is in use. type: LUKS2 cipher: aes-xts-plain64 keysize: 512 bits key location: keyring device: /dev/sdb ...
Verify the created LUKS encrypted volume:
# cryptsetup luksDump /dev/sdb Version: 2 Epoch: 6 Metadata area: 16384 [bytes] Keyslots area: 33521664 [bytes] UUID: a4c6be82-7347-4a91-a8ad-9479b72c9426 Label: (no label) Subsystem: (no subsystem) Flags: allow-discards Data segments: 0: crypt offset: 33554432 [bytes] length: (whole device) cipher: aes-xts-plain64 sector: 4096 [bytes] ...
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.storage/README.md
file -
/usr/share/doc/rhel-system-roles/storage/
directory - Encrypting block devices by using LUKS