cryptsetup-reencrypt(8) - phpMan

CRYPTSETUP-REENCRYPT(8) Maintenance Commands CRYPTSETUP-REENCRYPT(8)

NAME
cryptsetup-reencrypt - tool for offline LUKS device re-encryption

SYNOPSIS
cryptsetup-reencrypt <options> <device>

DESCRIPTION
Cryptsetup-reencrypt can be used to change reencryption parameters which otherwise require
full on-disk data change (re-encryption).

You can regenerate volume key (the real key used in on-disk encryption unclocked by
passphrase), cipher, cipher mode.

Cryptsetup-reencrypt reencrypts data on LUKS device in-place. During reencryption process
the LUKS device is marked unavailable.

NOTE: If you're looking for LUKS2 online reencryption manual please read cryptsetup(8) man
page instead (see reencrypt action). This page is for legacy offline reencryption utility
only.

WARNING: The cryptsetup-reencrypt program is not resistant to hardware or kernel failures
during reencryption (you can lose your data in this case).

ALWAYS BE SURE YOU HAVE RELIABLE BACKUP BEFORE USING THIS TOOL.
The reencryption can be temporarily suspended (by TERM signal or by using ctrl+c) but you
need to retain temporary files named LUKS-<uuid>.[log|org|new]. LUKS device is unavail-
able until reencryption is finished though.

Current working directory must be writable and temporary files created during reencryption
must be present.

For more info about LUKS see cryptsetup(8).

OPTIONS
To start (or continue) re-encryption for <device> use:

cryptsetup-reencrypt <device>

<options> can be [--batch-mode, --block-size, --cipher | --keep-key, --debug, --device-
size, --hash, --header, --iter-time | --pbkdf-force-iterations, --key-file, --key-size,
--key-slot, --keyfile-offset, --keyfile-size, --master-key-file, --tries, --pbkdf,
--pbkdf-memory, --pbkdf-parallel, --progress-frequency, --use-directio, --use-random |
--use-urandom, --use-fsync, --uuid, --verbose, --write-log]

To encrypt data on (not yet encrypted) device, use --new in combination with --reduce-de-
vice-size or with --header option for detached header.

To remove encryption from device, use --decrypt.

For detailed description of encryption and key file options see cryptsetup(8) man page.

--batch-mode, -q
Suppresses all warnings and reencryption progress output.

--block-size, -B value
Use re-encryption block size of <value> in MiB.

Values can be between 1 and 64 MiB.

--cipher, -c <cipher-spec>
Set the cipher specification string.

--debug
Run in debug mode with full diagnostic logs. Debug output lines are always prefixed
by '#'.

--decrypt
Remove encryption (decrypt already encrypted device and remove LUKS header).

WARNING: This is destructive operation and cannot be reverted.

--device-size size[units]
Instead of real device size, use specified value.

It means that only specified area (from the start of the device to the specified
size) will be reencrypted.

If no unit suffix is specified, the size is in bytes.

Unit suffix can be S for 512 byte sectors, K/M/G/T (or KiB,MiB,GiB,TiB) for units
with 1024 base or KB/MB/GB/TB for 1000 base (SI scale).

WARNING: This is destructive operation.

--hash, -h <hash-spec>
Specifies the hash used in the LUKS1 key setup scheme and volume key digest.

NOTE: if this parameter is not specified, default hash algorithm is always used for
new LUKS1 device header.

NOTE: with LUKS2 format this option is only relevant when new keyslot pbkdf algo-
rithm is set to PBKDF2 (see --pbkdf).

--header <LUKS header file>
Use a detached (separated) metadata device or file where the LUKS header is stored.
This option allows one to store ciphertext and LUKS header on different devices.

WARNING: There is no check whether the ciphertext device specified actually belongs
to the header given. If used with --new option, the header file will created (or
overwritten). Use with care.

--iter-time, -i <milliseconds>
The number of milliseconds to spend with PBKDF2 passphrase processing for the new
LUKS header.

--keep-key
Do not change encryption key, just reencrypt the LUKS header and keyslots.

This option can be combined only with --hash, --iter-time, --pbkdf-force-itera-
tions, --pbkdf (LUKS2 only), --pbkdf-memory (Argon2i/id and LUKS2 only) and
--pbkdf-parallel (Argon2i/id and LUKS2 only) options.

--key-file, -d name
Read the passphrase from file.

WARNING: --key-file option can be used only if there is only one active keyslot, or
alternatively, also if --key-slot option is specified (then all other keyslots will
be disabled in new LUKS device).

If this option is not used, cryptsetup-reencrypt will ask for all active keyslot
passphrases.

--key-size, -s <bits>
Set key size in bits. The argument has to be a multiple of 8.

The possible key-sizes are limited by the cipher and mode used.

If you are increasing key size, there must be enough space in the LUKS header for
enlarged keyslots (data offset must be large enough) or reencryption cannot be per-
formed.

If there is not enough space for keyslots with new key size, you can destructively
shrink device with --reduce-device-size option.

--key-slot, -S <0-MAX>
Specify which key slot is used. For LUKS1, max keyslot number is 7. For LUKS2, it's
31.

WARNING: All other keyslots will be disabled if this option is used.

--keyfile-offset value
Skip value bytes at the beginning of the key file.

--keyfile-size, -l
Read a maximum of value bytes from the key file. Default is to read the whole file
up to the compiled-in maximum.

--master-key-file
Use new volume (master) key stored in a file.

--new, -N
Create new header (encrypt not yet encrypted device).

This option must be used together with --reduce-device-size.

WARNING: This is destructive operation and cannot be reverted.

--pbkdf
Set Password-Based Key Derivation Function (PBKDF) algorithm for LUKS keyslot. The
PBKDF can be: pbkdf2, argon2i for Argon2i or argon2id for Argon2id.

For LUKS1, only pbkdf2 is accepted (no need to use this option).

--pbkdf-force-iterations <num>
Avoid PBKDF benchmark and set time cost (iterations) directly.

--pbkdf-memory <number>
Set the memory cost for PBKDF (for Argon2i/id the number represents kilobytes).
Note that it is maximal value, PBKDF benchmark or available physical memory can de-
crease it. This option is not available for PBKDF2.

--pbkdf-parallel <number>
Set the parallel cost for PBKDF (number of threads, up to 4). Note that it is max-
imal value, it is decreased automatically if CPU online count is lower. This op-
tion is not available for PBKDF2.

--progress-frequency <seconds>
Print separate line every <seconds> with reencryption progress.

--reduce-device-size size[units]
Enlarge data offset to specified value by shrinking device size.

This means that last sectors on the original device will be lost, ciphertext data
will be effectively shifted by specified number of sectors.

It can be useful if you e.g. added some space to underlying partition (so last sec-
tors contains no data).

For units suffix see --device-size parameter description.

You cannot shrink device more than by 64 MiB (131072 sectors).

WARNING: This is destructive operation and cannot be reverted. Use with extreme
care - shrunk filesystems are usually unrecoverable.

--tries, -T
Number of retries for invalid passphrase entry.

--type <type>
Use only while encrypting not yet encrypted device (see --new).

Specify LUKS version when performing in-place encryption. If the parameter is omit-
ted default value (LUKS1) is used. Type may be one of: luks (default), luks1 or
luks2.

--use-directio
Use direct-io (O_DIRECT) for all read/write data operations related to block device
undergoing reencryption.

Useful if direct-io operations perform better than normal buffered operations (e.g.
in virtual environments).

--use-fsync
Use fsync call after every written block. This applies for reencryption log files
as well.

--use-random

--use-urandom
Define which kernel random number generator will be used to create the volume key.

--uuid <uuid>
Use only while resuming an interrupted decryption process (see --decrypt).

To find out what <uuid> to pass look for temporary files LUKS-<uuid>.[|log|org|new]
of the interrupted decryption process.

--verbose, -v
Print more information on command execution.

--version
Show the program version.

--write-log
Update log file after every block write. This can slow down reencryption but will
minimize data loss in the case of system crash.

RETURN CODES
Cryptsetup-reencrypt returns 0 on success and a non-zero value on error.

Error codes are: 1 wrong parameters, 2 no permission, 3 out of memory, 4 wrong device
specified, 5 device already exists or device is busy.

EXAMPLES
Reencrypt /dev/sdb1 (change volume key)
cryptsetup-reencrypt /dev/sdb1

Reencrypt and also change cipher and cipher mode
cryptsetup-reencrypt /dev/sdb1 -c aes-xts-plain64

Add LUKS encryption to not yet encrypted device

First, be sure you have space added to disk.

Or alternatively shrink filesystem in advance.
Here we need 4096 512-bytes sectors (enough for 2x128 bit key).

fdisk -u /dev/sdb # move sdb1 partition end + 4096 sectors (or use resize2fs or
tool for your filesystem and shrink it)

cryptsetup-reencrypt /dev/sdb1 --new --reduce-device-size 4096S

Remove LUKS encryption completely

cryptsetup-reencrypt /dev/sdb1 --decrypt

REPORTING BUGS
Report bugs, including ones in the documentation, on the cryptsetup mailing list at <dm-
crypt AT saout.de> or in the 'Issues' section on LUKS website. Please attach the output of
the failed command with the --debug option added.

AUTHORS
Cryptsetup-reencrypt was written by Milan Broz <gmazyland AT gmail.com>.

This is free software; see the source for copying conditions. There is NO warranty; not
even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
The project website at https://gitlab.com/cryptsetup/cryptsetup

cryptsetup-reencrypt January 2019 CRYPTSETUP-REENCRYPT(8)

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