17.5. Encrypting existing data on a block device using LUKS2 with a detached header

Procedure

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

   # umount /dev/<nvme0n1p1>

   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.

   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>

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>

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

5. Regenerate initramfs with dracut:

   # dracut -f --regenerate-all -v

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"

   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

      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

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> --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