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Chapter 17. Encrypting block devices by using LUKS

You can protect the data on a block device by using the disk encryption. 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.

17.1. 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.
Important

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 has 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.

17.2. 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.

Important

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 some luksmeta metadata are detected.
  • A device is active. The device must be in an inactive state before any conversion is possible.

17.3. 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/<device_ID> command, where you can replace <device_ID> with the ID of your device.

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 the SIGTERM 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.
Manually
By using the cryptsetup repair /dev/<device_ID> command on the LUKS2 device.

17.4. 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.

    Warning

    You 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

  1. Unmount all file systems on the device that you plan to encrypt, for example: 

    # umount /dev/mapper/vg00-lv00
    Copy to Clipboard

  2. 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
      Copy to Clipboard
    • 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.

  3. 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.
    Copy to Clipboard

  4. Mount the device: 

    # mount /dev/mapper/lv00_encrypted /mnt/lv00_encrypted
    Copy to Clipboard

  5. Add an entry for a persistent mapping to the /etc/crypttab file:

    1. Find the luksUUID: 

      # cryptsetup luksUUID /dev/mapper/vg00-lv00

a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325
      Copy to Clipboard

    2. 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
      Copy to Clipboard

      Replace a52e2cc9-a5be-47b8-a95d-6bdf4f2d9325 with your device’s luksUUID.

    3. Refresh initramfs with dracut: 

      $ dracut -f --regenerate-all
      Copy to Clipboard
  6. Ensure that if an entry for this device exists in the /etc/fstab file, it is using the filesystem UUID and not the device name.

  7. 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
    Copy to Clipboard

Verification

  1. 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
[...]
    Copy to Clipboard

  2. 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
    Copy to Clipboard

17.5. 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.

  • Your data is backed up.

    Warning

    You 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

  1. Unmount all file systems on the device, for example: 

    # umount /dev/<nvme0n1p1>
    Copy to Clipboard

    Replace <nvme0n1p1> with the device identifier corresponding to the partition you want to unmount.

  2. 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.
    Copy to Clipboard

    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.
    • <nvme_encrypted> with the name of the device mapper that is created after encryption.

  3. Mount the device: 

    # mount /dev/mapper/<nvme_encrypted> /mnt/<nvme_encrypted>
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  4. Add an entry for a persistent mapping to the /etc/crypttab file: 

    # <nvme_encrypted> /dev/disk/by-id/<nvme-partition-id> none header=</home/header>
    Copy to Clipboard

    Replace <nvme-partition-id> with the identifier of the NVMe partition.

  5. Regenerate initramfs with dracut: 

    # dracut -f --regenerate-all -v
    Copy to Clipboard

  6. Add an entry for a persistent mounting to the /etc/fstab file:

    1. Find the file system’s UUID of the active LUKS block device: 

      $ blkid -p /dev/mapper/<nvme_encrypted>

/dev/mapper/<nvme_encrypted>: UUID="37bc2492-d8fa-4969-9d9b-bb64d3685aa9" BLOCK_SIZE="4096" TYPE="xfs" USAGE="filesystem"
      Copy to Clipboard

    2. Open /etc/fstab in a text editor and add a device in this file, for example: 

      $ vi /etc/fstab

UUID=<file_system_UUID> /home auto rw,user,auto 0
      Copy to Clipboard

      Replace <file_system_UUID> with your file system’s UUID.

  7. 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
    Copy to Clipboard

Verification

  1. 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]
[...]
    Copy to Clipboard

  2. View the status of the encrypted blank block device: 

    # cryptsetup status <nvme_encrypted> --header </home/header>

/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>
  sector size: 512
  offset: 0 sectors
  size: 10485760 sectors
  mode: read/write
    Copy to Clipboard

17.6. 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

  1. 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:
    Copy to Clipboard

  2. Open an encrypted LUKS partition: 

    # cryptsetup open /dev/nvme0n1p1 nvme0n1p1_encrypted

Enter passphrase for /dev/nvme0n1p1:
    Copy to Clipboard

    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.

  3. 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
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  4. Mount the device: 

    # mount /dev/mapper/nvme0n1p1_encrypted mount-point
    Copy to Clipboard

Verification

  1. 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]
[...]
    Copy to Clipboard

  2. 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
    Copy to Clipboard

17.7. 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 10 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

  1. Log in to the RHEL 10 web console.

    For details, see Logging in to the web console.

  2. In the panel, click Storage.
  3. In the Storage table, click the menu button ⋮ for the storage device you want to encrypt and click Format.
  4. In the Encryption field, select the encryption specification, LUKS1 or LUKS2.
  5. Set and confirm your new passphrase.
  6. Optional: Modify further encryption options.
  7. Finalize formatting settings.
  8. Click Format.

17.8. Changing the LUKS passphrase by using the command line

Change a LUKS passphrase on an encrypted disk or partition by using the command line. With the cryptsetup utility, you can control the encryption process with a variety of configuration options and functions, and integrate it in existing automation workflows.

Prerequisites

  • You have root privileges or permissions to enter administrative commands with sudo.

Procedure

  1. Change the existing passphrase on the LUKS encrypted device: 

    # cryptsetup luksChangeKey /dev/<device_ID>
    Copy to Clipboard

    Replace <device_ID> with the device designator, for example, sda.

    If you have multiple key slots configured, you can specify the slot to work with: 

    # cryptsetup luksChangeKey /dev/<device_ID> --key-slot <slot_number>
    Copy to Clipboard

    Replace <slot_number> with the number of the key slot you want to modify.

  2. Insert the current passphrase and the new passphrase: 

    Enter passphrase to be changed:
Enter new passphrase:
Verify passphrase:
    Copy to Clipboard

  3. Validate the new passphrase: 

    # cryptsetup --verbose open --test-passphrase /dev/<device_ID>
    Copy to Clipboard

Verification

  1. Verify that the new passphrase can unlock the device: 

    Enter passphrase for /dev/<device_ID>:
Key slot <slot_number> unlocked.
Command successful.
    Copy to Clipboard

17.9. Changing the LUKS passphrase in the web console

Change a LUKS passphrase on an encrypted disk or partition in the web console.

Prerequisites

Procedure

  1. Log in to the RHEL 10 web console.

    For details, see Logging in to the web console.

  2. In the panel, click Storage.
  3. In the Storage table, select the disk with encrypted data.
  4. On the disk page, scroll to the Keys section and click the edit button.

  5. In the Change passphrase dialog window:

    1. Enter your current passphrase.
    2. Enter your new passphrase.
    3. Confirm your new passphrase.
  6. Click Save.

17.10. 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

Procedure

  1. Store your sensitive variables in an encrypted file:

    1. Create the vault: 

      $ ansible-vault create ~/vault.yml
New Vault password: <vault_password>
Confirm New Vault password: <vault_password>
      Copy to Clipboard

    2. After the ansible-vault create command opens an editor, enter the sensitive data in the <key>: <value> format: 

      luks_password: <password>
      Copy to Clipboard
    3. Save the changes, and close the editor. Ansible encrypts the data in the vault.

  2. Create a playbook file, for example ~/playbook.yml, with the following content: 

    ---
- name: Manage local storage
  hosts: managed-node-01.example.com
  vars_files:
    - ~/vault.yml
  tasks:
    - name: Create and configure a volume encrypted with LUKS
      ansible.builtin.include_role:
        name: redhat.rhel_system_roles.storage
      vars:
        storage_volumes:
          - name: barefs
            type: disk
            disks:
              - sdb
            fs_type: xfs
            fs_label: <label>
            mount_point: /mnt/data
            encryption: true
            encryption_password: "{{ luks_password }}"
            encryption_cipher: <cipher>
            encryption_key_size: <key_size>
            encryption_luks_version: luks2
    Copy to Clipboard

    The settings specified in the example playbook include the following:

    encryption_cipher: <cipher>
    Specifies the LUKS cipher. Possible values are: twofish-xts-plain64, serpent-xts-plain64, and aes-xts-plain64 (default).
    encryption_key_size: <key_size>
    Specifies the LUKS key size. The default is 512 bit.
    encryption_luks_version: luks2
    Specifies the LUKS version. The default is luks2.

    For details about all variables used in the playbook, see the /usr/share/ansible/roles/rhel-system-roles.storage/README.md file on the control node.

  3. Validate the playbook syntax: 

    $ ansible-playbook --ask-vault-pass --syntax-check ~/playbook.yml
    Copy to Clipboard

    Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

  4. Run the playbook: 

    $ ansible-playbook --ask-vault-pass ~/playbook.yml
    Copy to Clipboard

Verification

  • Verify the created LUKS encrypted volume: 

    # ansible managed-node-01.example.com -m command -a 'cryptsetup luksDump /dev/sdb'

LUKS header information
Version: 2
Epoch: 3
Metadata area: 16384 [bytes]
Keyslots area: 16744448 [bytes]
UUID: bdf6463f-6b3f-4e55-a0a6-1a66f0152a46
Label: (no label)
Subsystem: (no subsystem)
Flags: (no flags)

Data segments:
0: crypt
offset: 16777216 [bytes]
length: (whole device)
cipher: aes-cbc-essiv:sha256
sector: 512 [bytes]

Keyslots:
0: luks2
Key: 256 bits
Priority: normal
Cipher: aes-cbc-essiv:sha256
Cipher key: 256 bits
    Copy to Clipboard
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