cryptsetup - manage plain dm-crypt, LUKS, and other encrypted volumes
cryptsetup <action> [<options>] <action args>
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.
For more information about specific cryptsetup action see
cryptsetup-<action>(8), where
<action> is the name
of the cryptsetup action.
The following are valid actions for all supported device types.
open <device> <name> --type <device_type>
Opens (creates a mapping with) <name> backed by device <device>.
See
cryptsetup-open(8).
close <name>
Removes the existing mapping <name> and wipes the key from kernel memory.
See
cryptsetup-close(8).
status <name>
Reports the status for the mapping <name>.
See
cryptsetup-status(8).
resize <name>
Resizes an active mapping <name>.
See
cryptsetup-resize(8).
refresh <name>
Refreshes parameters of active mapping <name>.
See
cryptsetup-refresh(8).
reencrypt <device> or --active-name <name> [<new_name>]
Run LUKS device reencryption.
See
cryptsetup-reencrypt(8).
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 --type plain <device> <name>
create <name> <device> (
OBSOLETE syntax)
Opens (creates a mapping with) <name> backed by device <device>.
See
cryptsetup-open(8).
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:
luksFormat <device> [<key file>]
Initializes a LUKS partition and sets the initial passphrase (for key-slot 0).
See
cryptsetup-luksFormat(8).
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).
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).
luksResume <name>
Resumes a suspended device and reinstates the encryption key.
See
cryptsetup-luksResume(8).
luksAddKey <device> [<key file with new key>]
Adds a new passphrase using an existing passphrase.
See
cryptsetup-luksAddKey(8).
luksRemoveKey <device> [<key file with passphrase to be
removed>]
Removes the supplied passphrase from the LUKS device.
See
cryptsetup-luksRemoveKey(8).
luksChangeKey <device> [<new key file>]
Changes an existing passphrase.
See
cryptsetup-luksChangeKey(8).
luksConvertKey <device>
Converts an existing LUKS2 keyslot to new PBKDF parameters.
See
cryptsetup-luksConvertKey(8).
luksKillSlot <device> <key slot number>
Wipe the key-slot number <key slot> from the LUKS device.
See
cryptsetup-luksKillSlot(8).
erase <device>
luksErase <device> (
old syntax)
Erase all keyslots and make the LUKS container permanently inaccessible.
See
cryptsetup-erase(8).
luksUUID <device>
Print or set the UUID of a LUKS device.
See
cryptsetup-luksUUID(8).
isLuks <device>
Returns true, if <device> is a LUKS device, false otherwise.
See
cryptsetup-isLuks(8).
luksDump <device>
Dump the header information of a LUKS device.
See
cryptsetup-luksDump(8).
luksHeaderBackup <device> --header-backup-file <file>
Stores a binary backup of the LUKS header and keyslot area.
See
cryptsetup-luksHeaderBackup(8).
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 <add|remove|import|export> <device>
Manipulate token objects used for obtaining passphrases.
See
cryptsetup-token(8).
convert <device> --type <format>
Converts the device between LUKS1 and LUKS2 format (if possible).
See
cryptsetup-convert(8).
config <device>
Set permanent configuration options (store to LUKS header).
See
cryptsetup-config(8).
cryptsetup supports mapping loop-AES encrypted partition using a compatibility
mode.
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
loop-AES
<
http://loop-aes.sourceforge.net> for more information regarding
loop-AES.
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
PIM
<
https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html>
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 --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).
tcryptDump <device>
Dump the header information of a TCRYPT device.
See
cryptsetup-tcryptDump(8).
See also
TrueCrypt
<https://en.wikipedia.org/wiki/TrueCrypt> and
VeraCrypt
<https://en.wikipedia.org/wiki/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.
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 --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).
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.
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 --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).
fvault2Dump <device>
Dump the header information of an FVAULT2 device.
See
cryptsetup-fvault2Dump(8).
Note that cryptsetup does not use any macOS code or proprietary specifications.
Please report all problems related to this compatibility extension to the
cryptsetup project.
repair <device>
Tries to repair the device metadata if possible. Currently supported only for
LUKS device type.
See
cryptsetup-repair(8).
benchmark <options>
Benchmarks ciphers and KDF (key derivation function).
See
cryptsetup-benchmark(8).
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
Since dm-integrity doesn’t support discards (TRIM), dm-crypt device on
top of it inherits this, so integrity protection mode doesn’t support
discards either.
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.
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).
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.
For LUKS on-disk metadata specification see
LUKS1
<https://gitlab.com/cryptsetup/cryptsetup/wikis/Specification>
and LUKS2
<https://gitlab.com/cryptsetup/LUKS2-docs>.
Cryptsetup is originally written by
Jana <
[email protected]>Saout
The LUKS extensions and original man page were written by
Clemens
<
[email protected]>Fruhwirth
Man page extensions by
Milan <
[email protected]>Broz
Man page rewrite and extension by
Arno <
[email protected]>Wagner
Report bugs at
cryptsetup
<[email protected]>mailing or in
Issues project section
<https://gitlab.com/cryptsetup/cryptsetup/-/issues/new>.
Please attach output of the failed command with --debug option added.
Cryptsetup FAQ
<https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions>
,
integritysetup(8) and
veritysetup(8)
Part of
cryptsetup project
<https://gitlab.com/cryptsetup/cryptsetup/>.