Chapter 10. 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.

10.1. 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 partitions, which 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
LUKS performs the following operations
  • 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 allows users to 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.

Additional resources

10.2. 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. Red Hat Enterprise Linux 7 supports the LUKS2 format since version 7.6.

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:

  • Change the volume key

  • Change 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.

10.3. 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 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/sdx command on the LUKS2 device.

Additional resources

  • cryptsetup-reencrypt(8) and cryptsetup-repair(8) man pages

10.4. 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

  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
    • 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.

  4. Mount the device: 

    # mount /dev/mapper/lv00_encrypted /mnt/lv00_encrypted

  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

    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

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

    3. Refresh initramfs with dracut: 

      $ dracut -f --regenerate-all

  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/lv00_encrypted

/dev/mapper/lv00-encrypted: UUID="37bc2492-d8fa-4969-9d9b-bb64d3685aa9" BLOCK_SIZE="4096" TYPE="xfs" USAGE="filesystem"

    2. 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.

  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

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
[...]

  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

Additional resources

  • cryptsetup(8), cryptsetup-reencrypt(8), lvextend(8), resize2fs(8), and parted(8) man pages

10.5. 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.

    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

  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.

    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.

  3. Mount the device: 

    # mount /dev/mapper/nvme_encrypted /mnt/nvme_encrypted

  4. 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

  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]
[...]

  2. 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) and cryptsetup-reencrypt(8) man pages

10.6. 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:

  2. 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.

  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

  4. Mount the device: 

    # mount /dev/mapper/nvme0n1p1_encrypted mount-point

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]
[...]

  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

Additional resources

  • cryptsetup(8), cryptsetup-open (8), and cryptsetup-lusFormat(8) man pages

10.7. Creating a LUKS2 encrypted volume 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

  • Access and permissions to one or more managed nodes, which are systems you want to configure with the crypto_policies System Role.
  • An inventory file, which lists the managed nodes.
  • Access and permissions to a control node, which is a system from which Red Hat Ansible Core configures other systems. On the control node, the ansible-core and rhel-system-roles packages are installed.
Important

RHEL 8.0-8.5 provided access to a separate Ansible repository that contains Ansible Engine 2.9 for automation based on Ansible. Ansible Engine contains command-line utilities such as ansible, ansible-playbook, connectors such as docker and podman, and many plugins and modules. For information on how to obtain and install Ansible Engine, see the How to download and install Red Hat Ansible Engine Knowledgebase article.

RHEL 8.6 and 9.0 have introduced Ansible Core (provided as the ansible-core package), which contains the Ansible command-line utilities, commands, and a small set of built-in Ansible plugins. RHEL provides this package through the AppStream repository, and it has a limited scope of support. For more information, see the Scope of support for the Ansible Core package included in the RHEL 9 and RHEL 8.6 and later AppStream repositories Knowledgebase article.

Procedure

  1. Create a new playbook.yml file with the following content: 

    - hosts: all
  vars:
    storage_volumes:
      - name: barefs
        type: disk
        disks:
         - sdb
        fs_type: xfs
        fs_label: label-name
        mount_point: /mnt/data
        encryption: true
        encryption_password: your-password
  roles:
   - rhel-system-roles.storage

    You can also add the other encryption parameters such as encryption_key, encryption_cipher, encryption_key_size, and encryption_luks version in the playbook.yml file.

  2. Optional: Verify playbook syntax: 

    # ansible-playbook --syntax-check playbook.yml

  3. Run the playbook on your inventory file: 

    # ansible-playbook -i inventory.file /path/to/file/playbook.yml

Verification

  1. 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
[...]

  2. 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]
[...]

  3. View the cryptsetup parameters in the playbook.yml file, which the storage role supports: 

    # cat ~/playbook.yml

    - hosts: all
      vars:
        storage_volumes:
          - name: foo
            type: disk
            disks:
             - nvme0n1
            fs_type: xfs
            fs_label: label-name
            mount_point: /mnt/data
            encryption: true
            #encryption_password: passwdpasswd
            encryption_key: /home/passwd_key
            encryption_cipher: aes-xts-plain64
            encryption_key_size: 512
            encryption_luks_version: luks2

      roles:
       - rhel-system-roles.storage

Additional resources