cryptsetup/man/cryptsetup.8.adoc

= cryptsetup(8)
:doctype: manpage
:manmanual: Maintenance Commands
:mansource: cryptsetup {release-version}
:man-linkstyle: pass:[blue R < >]

== Name

cryptsetup - manage plain dm-crypt, LUKS, and other encrypted volumes

== SYNOPSIS

*cryptsetup <action> [<options>] <action args>*

== DESCRIPTION

cryptsetup is used to conveniently setup dm-crypt managed device-mapper
mappings. These include plain dm-crypt volumes and LUKS volumes. The
difference is that LUKS uses a metadata header and can hence offer more
features than plain dm-crypt. On the other hand, the header is visible
and vulnerable to damage.

In addition, cryptsetup provides limited support for the use of loop-AES
volumes, TrueCrypt, VeraCrypt, BitLocker and FileVault2 compatible volumes,
and for hardware-based encryption on OPAL capable drives.

For more information about specific cryptsetup action see
*cryptsetup-<action>*(8), where *<action>* is the name of the
cryptsetup action.

== BASIC ACTIONS

The following are valid actions for all supported device types.

=== OPEN
*open <device> <name> --type <device_type>*

Opens (creates a mapping with) <name> backed by device <device>. +
See *cryptsetup-open*(8).

=== CLOSE
*close <name>*

Removes the existing mapping <name> and wipes the key from kernel memory. +
See *cryptsetup-close*(8).

=== STATUS
*status <name>*

Reports the status for the mapping <name>. +
See *cryptsetup-status*(8).

=== RESIZE
*resize <name>*

Resizes an active mapping <name>. +
See *cryptsetup-resize*(8).

=== REFRESH
*refresh <name>*

Refreshes parameters of active mapping <name>. +
See *cryptsetup-refresh*(8).

=== REENCRYPT
*reencrypt <device> or --active-name <name> [<new_name>]*

Run LUKS device reencryption. +
See *cryptsetup-reencrypt*(8).

== PLAIN MODE

Plain dm-crypt encrypts the device sector-by-sector with a single,
non-salted hash of the passphrase. No checks are performed, no metadata
is used. There is no formatting operation. When the raw device is mapped
(opened), the usual device operations can be used on the mapped device,
including filesystem creation. Mapped devices usually reside in
/dev/mapper/<name>.

The following are valid plain device type actions:

=== OPEN
*open --type plain <device> <name>* +
create <name> <device> (*OBSOLETE syntax*)

Opens (creates a mapping with) <name> backed by device <device>. +
See *cryptsetup-open*(8).

== LUKS EXTENSION

LUKS, the Linux Unified Key Setup, is a standard for disk encryption. It
adds a standardized header at the start of the device, a key-slot area
directly behind the header and the bulk data area behind that. The whole
set is called a 'LUKS container'. The device that a LUKS container
resides on is called a 'LUKS device'. For most purposes, both terms can
be used interchangeably. But note that when the LUKS header is at a
nonzero offset in a device, then the device is not a LUKS device
anymore, but has a LUKS container stored in it at an offset.

LUKS can manage multiple passphrases that can be individually revoked or
changed and that can be securely scrubbed from persistent media due to
the use of anti-forensic stripes. Passphrases are protected against
brute-force and dictionary attacks by Password-Based Key Derivation
Function (PBKDF).

LUKS2 is a new version of header format that allows additional
extensions like different PBKDF algorithm or authenticated encryption.
You can format device with LUKS2 header if you specify *--type luks2* in
*luksFormat* command. For activation, the format is already recognized
automatically.

Each passphrase, also called a *key* in this document, is associated
with one of 8 key-slots. Key operations that do not specify a slot
affect the first slot that matches the supplied passphrase or the first
empty slot if a new passphrase is added.

The *<device>* parameter can also be specified by a LUKS UUID in the
format UUID=<uuid>. Translation to real device name uses symlinks in
/dev/disk/by-uuid directory.

To specify a detached header, the *--header* parameter can be used in
all LUKS commands and always takes precedence over the positional
*<device>* parameter.

The following are valid LUKS actions:

=== FORMAT
*luksFormat <device> [<key file>]*

Initializes a LUKS partition and sets the initial passphrase (for key-slot 0). +
See *cryptsetup-luksFormat*(8).

=== OPEN
*open --type luks <device> <name>* +
luksOpen <device> <name> (*old syntax*)

Opens the LUKS device <device> and sets up a mapping <name> after
successful verification of the supplied passphrase. +
See *cryptsetup-open*(8).

=== SUSPEND
*luksSuspend <name>*

Suspends an active device (all IO operations will block and accesses to
the device will wait indefinitely) and wipes the encryption key from
kernel memory. +
See *cryptsetup-luksSuspend*(8).

=== RESUME
*luksResume <name>*

Resumes a suspended device and reinstates the encryption key. +
See *cryptsetup-luksResume*(8).

=== ADD KEY
*luksAddKey <device> [<key file with new key>]*

Adds a new passphrase using an existing passphrase. +
See *cryptsetup-luksAddKey*(8).

=== REMOVE KEY
*luksRemoveKey <device> [<key file with passphrase to be removed>]*

Removes the supplied passphrase from the LUKS device. +
See *cryptsetup-luksRemoveKey*(8).

=== CHANGE KEY
*luksChangeKey <device> [<new key file>]*

Changes an existing passphrase. +
See *cryptsetup-luksChangeKey*(8).

=== CONVERT KEY
*luksConvertKey <device>*

Converts an existing LUKS2 keyslot to new PBKDF parameters. +
See *cryptsetup-luksConvertKey*(8).

=== KILL SLOT
*luksKillSlot <device> <key slot number>*

Wipe the key-slot number <key slot> from the LUKS device. +
See *cryptsetup-luksKillSlot*(8).

=== ERASE
*erase <device>* +
luksErase <device> (*old syntax*)

Erase all keyslots and make the LUKS container permanently inaccessible. +
See *cryptsetup-erase*(8).

=== UUID
*luksUUID <device>*

Print or set the UUID of a LUKS device. +
See *cryptsetup-luksUUID*(8).

=== IS LUKS
*isLuks <device>*

Returns true, if <device> is a LUKS device, false otherwise. +
See *cryptsetup-isLuks*(8).

=== DUMP
*luksDump <device>*

Dump the header information of a LUKS device. +
See *cryptsetup-luksDump*(8).

=== HEADER BACKUP
*luksHeaderBackup <device> --header-backup-file <file>*

Stores a binary backup of the LUKS header and keyslot area. +
See *cryptsetup-luksHeaderBackup*(8).

=== HEADER RESTORE
*luksHeaderRestore <device> --header-backup-file <file>*

Restores a binary backup of the LUKS header and keyslot area from the
specified file. +
See *cryptsetup-luksHeaderRestore*(8).

=== TOKEN
*token <add|remove|import|export> <device>*

Manipulate token objects used for obtaining passphrases. +
See *cryptsetup-token*(8).

=== CONVERT
*convert <device> --type <format>*

Converts the device between LUKS1 and LUKS2 format (if possible). +
See *cryptsetup-convert*(8).

=== CONFIG
*config <device>*

Set permanent configuration options (store to LUKS header). +
See *cryptsetup-config*(8).

== loop-AES EXTENSION

cryptsetup supports mapping loop-AES encrypted partition using a
compatibility mode.

=== OPEN
*open --type loopaes <device> <name> --key-file <keyfile>* +
loopaesOpen <device> <name> --key-file <keyfile> (*old syntax*)

Opens the loop-AES <device> and sets up a mapping <name>. +
See *cryptsetup-open*(8).

See also section 7 of the FAQ and http://loop-aes.sourceforge.net[loop-AES]
for more information regarding loop-AES.

== TCRYPT (TrueCrypt and VeraCrypt compatible) EXTENSION

cryptsetup supports mapping of TrueCrypt, tcplay or VeraCrypt encrypted
partition using a native Linux kernel API. Header formatting and TCRYPT
header change is not supported, cryptsetup never changes TCRYPT header
on-device.

TCRYPT extension requires kernel userspace crypto API to be available
(introduced in Linux kernel 2.6.38). If you are configuring kernel
yourself, enable "User-space interface for symmetric key cipher
algorithms" in "Cryptographic API" section
(CRYPTO_USER_API_SKCIPHER .config option).

Because TCRYPT header is encrypted, you have to always provide valid
passphrase and keyfiles.

Cryptsetup should recognize all header variants, except legacy cipher
chains using LRW encryption mode with 64 bits encryption block (namely
Blowfish in LRW mode is not recognized, this is limitation of kernel
crypto API).

VeraCrypt is extension of TrueCrypt header with increased iteration
count so unlocking can take quite a lot of time.

To open a VeraCrypt device with a custom Personal Iteration Multiplier
(PIM) value, use either the *--veracrypt-pim=<PIM>* option to directly
specify the PIM on the command- line or use *--veracrypt-query-pim* to
be prompted for the PIM.

The PIM value affects the number of iterations applied during key
derivation. Please refer to
https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html[PIM]
for more detailed information.

If you need to disable VeraCrypt device support, use
*--disable-veracrypt* option.

*NOTE:* Activation with *tcryptOpen* is supported only for cipher chains
using LRW or XTS encryption modes.

The *tcryptDump* command should work for all recognized TCRYPT devices
and doesn't require superuser privilege.

To map system device (device with boot loader where the whole encrypted
system resides) use *--tcrypt-system* option. You can use partition
device as the parameter (parameter must be real partition device, not an
image in a file), then only this partition is mapped.

If you have the whole TCRYPT device as a file image and you want to map
multiple partition encrypted with system encryption, please create
loopback mapping with partitions first (*losetup -P*, see *losetup(8)*
man page for more info), and use loop partition as the device parameter.

If you use the whole base device as a parameter, one device for the
whole system encryption is mapped. This mode is available only for
backward compatibility with older cryptsetup versions which mapped
TCRYPT system encryption using the whole device.

To use hidden header (and map hidden device, if available), use
*--tcrypt-hidden* option.

To explicitly use backup (secondary) header, use *--tcrypt-backup*
option.

*NOTE:* There is no protection for a hidden volume if the outer volume
is mounted. The reason is that if there were any protection, it would
require some metadata describing what to protect in the outer volume and
the hidden volume would become detectable.

=== OPEN
*open --type tcrypt <device> <name>* +
tcryptOpen_ <device> <name> (*old syntax*)

Opens the TCRYPT (a TrueCrypt-compatible) <device> and sets up a mapping
<name>. +
See *cryptsetup-open*(8).

=== DUMP
*tcryptDump <device>*

Dump the header information of a TCRYPT device. +
See *cryptsetup-tcryptDump*(8).

See also https://en.wikipedia.org/wiki/TrueCrypt[*TrueCrypt*] and
https://en.wikipedia.org/wiki/VeraCrypt[*VeraCrypt*] pages for more information.

Please note that cryptsetup does not use TrueCrypt or VeraCrypt code, please
report all problems related to this compatibility extension to the cryptsetup
project.

== BITLK (Windows BitLocker compatible) EXTENSION

cryptsetup supports mapping of BitLocker and BitLocker to Go encrypted
partition using a native Linux kernel API. Header formatting and BITLK
header changes are not supported, cryptsetup never changes BITLK header
on-device.

BITLK extension requires kernel userspace crypto API to be available
(for details see TCRYPT section).

Cryptsetup should recognize all BITLK header variants, except legacy
header used in Windows Vista systems and partially decrypted BitLocker
devices. Activation of legacy devices encrypted in CBC mode requires at
least Linux kernel version 5.3 and for devices using Elephant diffuser
kernel 5.6.

The *bitlkDump* command should work for all recognized BITLK devices and
doesn't require superuser privilege.

For unlocking with the *open* a password or a recovery passphrase or a
startup key must be provided.

Additionally unlocking using volume key is supported. You must provide
BitLocker Full Volume Encryption Key (FVEK) using the --volume-key-file
option. The key must be decrypted and without the header (only
128/256/512 bits of key data depending on used cipher and mode).

Other unlocking methods (TPM, SmartCard) are not supported.

=== OPEN
*open --type bitlk <device> <name>* +
bitlkOpen <device> <name> (*old syntax*)

Opens the BITLK (a BitLocker-compatible) <device> and sets up a mapping
<name>. +
See *cryptsetup-open*(8).

=== DUMP
*bitlkDump <device>*

Dump the header information of a BITLK device. +
See *cryptsetup-bitlkDump*(8).

Please note that cryptsetup does not use any Windows BitLocker code,
please report all problems related to this compatibility extension to
the cryptsetup project.

== FVAULT2 (Apple macOS FileVault2 compatible) EXTENSION

cryptsetup supports the mapping of FileVault2 (FileVault2 full-disk
encryption) by Apple for the macOS operating system using a native Linux
kernel API.

*NOTE:* cryptsetup supports only FileVault2 based on Core Storage and HFS+
filesystem (introduced in MacOS X 10.7 Lion).
It does NOT support the new version of FileVault based on the APFS
filesystem used in recent macOS versions.

Header formatting and FVAULT2 header changes are not supported;
cryptsetup never changes the FVAULT2 header on-device.

FVAULT2 extension requires kernel userspace crypto API to be available
(for details, see TCRYPT section) and kernel driver for HFS+ (hfsplus)
filesystem.

Cryptsetup should recognize the basic configuration for portable drives.

The *fvault2Dump* command should work for all recognized FVAULT2 devices
and doesn't require superuser privilege.

For unlocking with the *open*, a password must be provided.
Other unlocking methods are not supported.

=== OPEN
*open --type fvault2 <device> <name>* +
fvault2Open <device> <name> (*old syntax*)

Opens the FVAULT2 (a FileVault2-compatible) <device> (usually the second
partition on the device) and sets up a mapping <name>. +
See *cryptsetup-open*(8).

== SED (Self Encrypting Drive) OPAL EXTENSION

cryptsetup supports using native hardware encryption on drives that provide an
*OPAL* interface, both nested with *dm-crypt* and standalone. Passphrases,
tokens and metadata are stored using the LUKS2 header format, and are thus
compatible with any software or system that uses LUKS2 (e.g.: tokens).

*WARNING:* this support is new and experimental, and requires at least kernel
v6.4. Resizing devices is not supported.

*--hw-opal* can be specified for OPAL + dm-crypt, and
*--hw-opal-only* can be specified to use OPAL only, without a dm-crypt layer.

Opening, closing and enrolling tokens work in the same way as with LUKS2 and
dm-crypt. The new parameters are only necessary when formatting, the LUKS2
metadata will ensure the right setup is performed when opening or closing. If
no *subsystem* is specified, it will be automatically set to *HW-OPAL* so that
it is immediately apparent when a device uses OPAL.

=== FORMAT
*luksFormat --type luks2 --hw-opal <device> [<key file>]*

Additionally specify *--hw-opal-only* instead of *--hw-opal* to avoid the
dm-crypt layer. Other than the usual passphrase, an admin password will have
to be specified when formatting the first partition of the drive, and will have
to be re-supplied when formatting any other partition until a factory reset
is performed.

=== ERASE
*erase <device>*

Securely erase a partition or device. Requires admin password.
Additionally specify *--hw-opal-factory-reset* for a FULL factory reset of the
drive, using the drive's *PSID* (typically printed on the label) instead of the
admin password.
*WARNING*: a factory reset will cause ALL data on the device to be lost,
regardless of the partition it is ran on, if any, and regardless of any LUKS2
header backup.

== MISCELLANEOUS ACTIONS

=== REPAIR
*repair <device>*

Tries to repair the device metadata if possible. Currently supported
only for LUKS device type. +
See *cryptsetup-repair*(8).

=== BENCHMARK
*benchmark <options>*

Benchmarks ciphers and KDF (key derivation function). +
See *cryptsetup-benchmark*(8).

== PLAIN DM-CRYPT OR LUKS?

Unless you understand the cryptographic background well, use LUKS. With
plain dm-crypt there are a number of possible user errors that massively
decrease security. While LUKS cannot fix them all, it can lessen the
impact for many of them.

== WARNINGS

A lot of good information on the risks of using encrypted storage, on
handling problems and on security aspects can be found in the
Cryptsetup FAQ. Read it. Nonetheless, some risks deserve to be
mentioned here.

*Backup:* Storage media die. Encryption has no influence on that. Backup
is mandatory for encrypted data as well, if the data has any worth. See
the Cryptsetup FAQ for advice on how to do a backup of an encrypted
volume.

*Character encoding:* If you enter a passphrase with special symbols,
the passphrase can change depending on character encoding. Keyboard
settings can also change, which can make blind input hard or impossible.
For example, switching from some ASCII 8-bit variant to UTF-8 can lead
to a different binary encoding and hence different passphrase seen by
cryptsetup, even if what you see on the terminal is exactly the same. It
is therefore highly recommended to select passphrase characters only
from 7-bit ASCII, as the encoding for 7-bit ASCII stays the same for all
ASCII variants and UTF-8.

*LUKS header:* If the header of a LUKS volume gets damaged, all data is
permanently lost unless you have a header-backup. If a key-slot is
damaged, it can only be restored from a header-backup or if another
active key-slot with known passphrase is undamaged. Damaging the LUKS
header is something people manage to do with surprising frequency. This
risk is the result of a trade-off between security and safety, as LUKS
is designed for fast and secure wiping by just overwriting header and
key-slot area.

*Previously used partitions:* If a partition was previously used, it is
a very good idea to wipe filesystem signatures, data, etc. before
creating a LUKS or plain dm-crypt container on it. For a quick removal
of filesystem signatures, use *wipefs*(8). Take care though that this may
not remove everything. In particular, MD RAID signatures at the end of a
device may survive. It also does not remove data. For a full wipe,
overwrite the whole partition before container creation. If you do not
know how to do that, the cryptsetup FAQ describes several options.

== EXAMPLES

Example 1: Create LUKS 2 container on block device /dev/sdX.::
  sudo cryptsetup --type luks2 luksFormat /dev/sdX
Example 2: Add an additional passphrase to key slot 5.::
  sudo cryptsetup luksAddKey --key-slot 5 /dev/sdX
Example 3: Create LUKS header backup and save it to file.::
  sudo cryptsetup luksHeaderBackup /dev/sdX --header-backup-file
  /var/tmp/NameOfBackupFile
Example 4: Open LUKS container on /dev/sdX and map it to sdX_crypt.::
  sudo cryptsetup open /dev/sdX sdX_crypt
*WARNING: The command in example 5 will erase all key slots.*::
  Your cannot use your LUKS container afterward anymore unless you have
  a backup to restore.
Example 5: Erase all key slots on /dev/sdX.::
  sudo cryptsetup erase /dev/sdX
Example 6: Restore LUKS header from backup file.::
  sudo cryptsetup luksHeaderRestore /dev/sdX --header-backup-file
  /var/tmp/NameOfBackupFile

== RETURN CODES

Cryptsetup returns *0* on success and a non-zero value on error.

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

== NOTES

=== Passphrase processing for PLAIN mode

Note that no iterated hashing or salting is done in plain mode. If
hashing is done, it is a single direct hash. This means that low-entropy
passphrases are easy to attack in plain mode.

*From a terminal*: The passphrase is read until the first newline, i.e.
'\n'. The input without the newline character is processed with the
default hash or the hash specified with --hash. The hash result will be
truncated to the key size of the used cipher, or the size specified with
-s.

*From stdin*: Reading will continue until a newline (or until the
maximum input size is reached), with the trailing newline stripped. The
maximum input size is defined by the same compiled-in default as for the
maximum key file size and can be overwritten using --keyfile-size
option.

The data read will be hashed with the default hash or the hash specified
with --hash. The hash result will be truncated to the key size of the
used cipher, or the size specified with -s.

Note that if --key-file=- is used for reading the key from stdin,
trailing newlines are not stripped from the input.

If "plain" is used as argument to --hash, the input data will not be
hashed. Instead, it will be zero padded (if shorter than the key size)
or truncated (if longer than the key size) and used directly as the
binary key. This is useful for directly specifying a binary key. No
warning will be given if the amount of data read from stdin is less than
the key size.

*From a key file*: It will be truncated to the key size of the used
cipher or the size given by -s and directly used as a binary key.

*WARNING*: The --hash argument is being ignored. The --hash option is
usable only for stdin input in plain mode.

If the key file is shorter than the key, cryptsetup will quit with an
error. The maximum input size is defined by the same compiled-in default
as for the maximum key file size and can be overwritten using
--keyfile-size option.

=== Passphrase processing for LUKS

LUKS uses PBKDF to protect against dictionary attacks and to give some
protection to low-entropy passphrases (see cryptsetup FAQ).

*From a terminal*: The passphrase is read until the first newline and
then processed by PBKDF2 without the newline character.

*From stdin*: LUKS will read passphrases from stdin up to the first
newline character or the compiled-in maximum key file length. If
--keyfile-size is given, it is ignored.

*From key file*: The complete keyfile is read up to the compiled-in
maximum size. Newline characters do not terminate the input. The
--keyfile-size option can be used to limit what is read.

*Passphrase processing*: Whenever a passphrase is added to a LUKS header
(luksAddKey, luksFormat), the user may specify how much the time the
passphrase processing should consume. The time is used to determine the
iteration count for PBKDF2 and higher times will offer better protection
for low-entropy passphrases, but open will take longer to complete. For
passphrases that have entropy higher than the used key length, higher
iteration times will not increase security.

The default setting of one or two seconds is sufficient for most
practical cases. The only exception is a low-entropy passphrase used on
a device with a slow CPU, as this will result in a low iteration count.
On a slow device, it may be advisable to increase the iteration time
using the --iter-time option in order to obtain a higher iteration
count. This does slow down all later luksOpen operations accordingly.

=== Incoherent behavior for invalid passphrases/keys

LUKS checks for a valid passphrase when an encrypted partition is
unlocked. The behavior of plain dm-crypt is different. It will always
decrypt with the passphrase given. If the given passphrase is wrong, the
device mapped by plain dm-crypt will essentially still contain encrypted
data and will be unreadable.

=== Supported ciphers, modes, hashes and key sizes

The available combinations of ciphers, modes, hashes and key sizes
depend on kernel support. See /proc/crypto for a list of available
options. You might need to load additional kernel crypto modules in
order to get more options.

For the --hash option, if the crypto backend is libgcrypt, then all
algorithms supported by the gcrypt library are available. For other
crypto backends, some algorithms may be missing.

=== Notes on passphrases

Mathematics can't be bribed. Make sure you keep your passphrases safe.
There are a few nice tricks for constructing a fallback, when suddenly
out of the blue, your brain refuses to cooperate. These fallbacks need
LUKS, as it's only possible with LUKS to have multiple passphrases.
Still, if your attacker model does not prevent it, storing your
passphrase in a sealed envelope somewhere may be a good idea as well.

=== Notes on Random Number Generators

Random Number Generators (RNG) used in cryptsetup are always the kernel
RNGs without any modifications or additions to data stream produced.

There are two types of randomness cryptsetup/LUKS needs. One type (which
always uses /dev/urandom) is used for salts, the AF splitter and for
wiping deleted keyslots.

The second type is used for the volume key. You can switch between using
/dev/random and /dev/urandom here, see *--use-random* and
*--use-urandom* options. Using /dev/random on a system without enough
entropy sources can cause *luksFormat* to block until the requested
amount of random data is gathered. In a low-entropy situation (embedded
system), this can take a very long time and potentially forever. At the
same time, using /dev/urandom in a low-entropy situation will produce
low-quality keys. This is a serious problem, but solving it is out of
scope for a mere man-page. See *urandom(4)* for more information.

=== Authenticated disk encryption (EXPERIMENTAL)

Since Linux kernel version 4.12 dm-crypt supports authenticated disk
encryption.

Normal disk encryption modes are length-preserving (plaintext sector is
of the same size as a ciphertext sector) and can provide only
confidentiality protection, but not cryptographically sound data
integrity protection.

Authenticated modes require additional space per-sector for
authentication tag and use Authenticated Encryption with Additional Data
(AEAD) algorithms.

If you configure LUKS2 device with data integrity protection, there will
be an underlying dm-integrity device, which provides additional
per-sector metadata space and also provide data journal protection to
ensure atomicity of data and metadata update. Because there must be
additional space for metadata and journal, the available space for the
device will be smaller than for length-preserving modes.

The dm-crypt device then resides on top of such a dm-integrity device.
All activation and deactivation of this device stack is performed by
cryptsetup, there is no difference in using *luksOpen* for integrity
protected devices. If you want to format LUKS2 device with data
integrity protection, use *--integrity* option (see *cryptsetup-luksFormat(8)*).

Albeit Linux kernel 5.7 added TRIM support for standalone dm-integrity devices,
*cryptsetup(8)* can't offer support for discards (TRIM) in authenticated
encryption mode, because the underlying dm-crypt kernel module does not support
this functionality when dm-integrity is used as auth tag space allocator
(see *--allow-discards* in *cryptsetup-luksFormat(8)*).

Some integrity modes requires two independent keys (key for encryption
and for authentication). Both these keys are stored in one LUKS keyslot.

*WARNING:* All support for authenticated modes is experimental and there
are only some modes available for now. Note that there are a very few
authenticated encryption algorithms that are suitable for disk
encryption. You also cannot use CRC32 or any other non-cryptographic
checksums (other than the special integrity mode "none"). If for some
reason you want to have integrity control without using authentication
mode, then you should separately configure dm-integrity independently of
LUKS2.

=== Notes on loopback device use

Cryptsetup is usually used directly on a block device (disk partition or
LVM volume). However, if the device argument is a file, cryptsetup tries
to allocate a loopback device and map it into this file. This mode
requires Linux kernel 2.6.25 or more recent which supports the loop
autoclear flag (loop device is cleared on the last close automatically).
Of course, you can always map a file to a loop-device manually. See the
cryptsetup FAQ for an example.

When device mapping is active, you can see the loop backing file in the
status command output. Also see losetup(8).

=== LUKS2 header locking

The LUKS2 on-disk metadata is updated in several steps and to achieve
proper atomic update, there is a locking mechanism. For an image in
file, code uses *flock(2)* system call. For a block device, lock is
performed over a special file stored in a locking directory (by default
*/run/cryptsetup*). The locking directory should be created with the
proper security context by the distribution during the boot-up phase.
Only LUKS2 uses locks, other formats do not use this mechanism.

=== LUKS on-disk format specification

For LUKS on-disk metadata specification see
https://gitlab.com/cryptsetup/cryptsetup/wikis/Specification[*LUKS1*] and
https://gitlab.com/cryptsetup/LUKS2-docs[*LUKS2*].

== AUTHORS

Cryptsetup is originally written by mailto:jana@saout.de[Jana Saout]. +
The LUKS extensions and original man page were written by
mailto:clemens@endorphin.org[Clemens Fruhwirth]. +
Man page extensions by mailto:gmazyland@gmail.com[Milan Broz]. +
Man page rewrite and extension by mailto:arno@wagner.name[Arno Wagner].

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