Provided by: cryptsetup-bin_2.2.2-3ubuntu2.4_amd64 
NAME
cryptsetup - manage plain dm-crypt and LUKS encrypted volumes
SYNOPSIS
cryptsetup <options> <action> <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 and for
TrueCrypt compatible volumes.
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". 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.
BASIC COMMANDS
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>.
Device type can be plain, luks (default), luks1, luks2, loopaes or tcrypt.
For backward compatibility there are open command aliases:
create (argument-order <name> <device>): open --type plain
plainOpen: open --type plain
luksOpen: open --type luks
loopaesOpen: open --type loopaes
tcryptOpen: open --type tcrypt
<options> are type specific and are described below for individual device types.
For create, the order of the <name> and <device> options is inverted for historical
reasons, all other aliases use the standard <device> <name> order.
close <name>
Removes the existing mapping <name> and wipes the key from kernel memory.
For backward compatibility there are close command aliases: remove, plainClose,
luksClose, loopaesClose, tcryptClose (all behaves exactly the same, device type is
determined automatically from active device).
<options> can be [--deferred]
status <name>
Reports the status for the mapping <name>.
resize <name>
Resizes an active mapping <name>.
If --size (in 512-bytes sectors) or --device-size are not specified, the size is
computed from the underlying device. For LUKS it is the size of the underlying
device without the area reserved for LUKS header (see data payload offset in
luksDump command). For plain crypt device, the whole device size is used.
Note that this does not change the raw device geometry, it just changes how many
sectors of the raw device are represented in the mapped device.
If cryptsetup detected volume key for active device loaded in kernel keyring
service, resize action would first try to retrieve the key using a token and only
if it failed it'd ask for a passphrase to unlock a keyslot (LUKS) or to derive a
volume key again (plain mode). The kernel keyring is used by default for LUKS2
devices.
With LUKS2 device additional <options> can be [--token-id, --token-only,
--key-slot, --key-file, --keyfile-size, --keyfile-offset, --timeout,
--disable-locks, --disable-keyring].
refresh <name>
Refreshes parameters of active mapping <name>.
Updates parameters of active device <name> without need to deactivate the device
(and umount filesystem). Currently it supports parameters refresh on following
devices: LUKS1, LUKS2 (including authenticated encryption), plain crypt and
loopaes.
Mandatory parametrs are identical to those of an open action for respective device
type.
You may change following parameters on all devices --perf-same_cpu_crypt,
--perf-submit_from_crypt_cpus and --allow-discards.
Refreshing device without any optional parameter will refresh the device with
default setting (respective to device type).
LUKS2 only:
--integrity-no-journal parameter affects only LUKS2 devices with underlying dm-
integrity device.
Adding option --persistent stores any combination of device parameters above in
LUKS2 metadata (only after successful refresh operation).
--disable-keyring parameter refreshes a device with volume key passed in dm-crypt
driver.
reencrypt <device> or --active-name <name> [<new_name>]
Run resilient reencryption (LUKS2 device only).
There are 3 basic modes of operation:
• device reencryption (reencrypt)
• device encryption (reencrypt --encrypt)
• device decryption (reencrypt --decrypt)
<device> or --active-name <name> is mandatory parameter.
With <device> parameter cryptsetup looks up active <device> dm mapping. If no
active mapping is detected, it starts offline reencryption otherwise online
reencryption takes place.
Reencryption process may be safely interrupted by a user via SIGTERM signal
(ctrl+c).
To resume already initialized or interrupted reencryption, just run the cryptsetup
reencrypt command again to continue the reencryption operation. Reencryption may
be resumed with different --resilience or --hotzone-size unless implicit datashift
resilience mode is used (reencrypt --encrypt with --reduce-device-size option).
If the reencryption process was interrupted abruptly (reencryption process crash,
system crash, poweroff) it may require recovery. The recovery is currently run
automatically on next activation (action open) when needed.
Optional parameter <new_name> takes effect only with --encrypt option and it
activates device <new_name> immediately after encryption initialization gets
finished. That's useful when device needs to be ready as soon as possible and
mounted (used) before full data area encryption is completed.
Action supports following additional <options> [--encrypt, --decrypt,
--device-size, --resilience, --resilience-hash, --hotzone-size, --init-only,
--resume-only, --reduce-device-size].
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 --type plain <device> <name>
create <name> <device> (OBSOLETE syntax)
Opens (creates a mapping with) <name> backed by device <device>.
<options> can be [--hash, --cipher, --verify-passphrase, --sector-size, --key-file,
--keyfile-offset, --key-size, --offset, --skip, --size, --readonly, --shared,
--allow-discards, --refresh]
Example: 'cryptsetup open --type plain /dev/sda10 e1' maps the raw encrypted device
/dev/sda10 to the mapped (decrypted) device /dev/mapper/e1, which can then be
mounted, fsck-ed or have a filesystem created on it.
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 PBKDF2, which
implements hash iteration and salting in one function.
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),
either via prompting or via <key file>. Note that if the second argument is
present, then the passphrase is taken from the file given there, without the need
to use the --key-file option. Also note that for both forms of reading the
passphrase from a file you can give '-' as file name, which results in the
passphrase being read from stdin and the safety-question being skipped.
You can only call luksFormat on a LUKS device that is not mapped.
To use LUKS2, specify --type luks2.
<options> can be [--hash, --cipher, --verify-passphrase, --key-size, --key-slot,
--key-file (takes precedence over optional second argument), --keyfile-offset,
--keyfile-size, --use-random | --use-urandom, --uuid, --master-key-file,
--iter-time, --header, --pbkdf-force-iterations, --force-password, --disable-
locks].
For LUKS2, additional <options> can be [--integrity, --integrity-no-wipe,
--sector-size, --label, --subsystem, --pbkdf, --pbkdf-memory, --pbkdf-parallel,
--disable-locks, --disable-keyring, --luks2-metadata-size, --luks2-keyslots-size,
--keyslot-cipher, --keyslot-key-size].
WARNING: Doing a luksFormat on an existing LUKS container will make all data the
old container permanently irretrievable unless you have a header backup.
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.
First, the passphrase is searched in LUKS tokens. If it's not found in any token
and also the passphrase is not supplied via --key-file, the command prompts for it
interactively.
<options> can be [--key-file, --keyfile-offset, --keyfile-size, --readonly,
--test-passphrase, --allow-discards, --header, --key-slot, --master-key-file,
--token-id, --token-only, --disable-keyring, --disable-locks, --type, --refresh,
--serialize-memory-hard-pbkdf].
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. Needs
kernel 2.6.19 or later.
After this operation you have to use luksResume to reinstate the encryption key and
unblock the device or close to remove the mapped device.
WARNING: never suspend the device on which the cryptsetup binary resides.
<options> can be [--header, --disable-locks].
luksResume <name>
Resumes a suspended device and reinstates the encryption key. Prompts
interactively for a passphrase if --key-file is not given.
<options> can be [--key-file, --keyfile-size, --header, --disable-keyring,
--disable-locks, --type]
luksAddKey <device> [<key file with new key>]
Adds a new passphrase. An existing passphrase must be supplied interactively or via
--key-file. The new passphrase to be added can be specified interactively or read
from the file given as positional argument.
NOTE: with --unbound option the action creates new unbound LUKS2 keyslot. The
keyslot cannot be used for device activation. If you don't pass new key via
--master-key-file option, new random key is generated. Existing passphrase for any
active keyslot is not required.
<options> can be [--key-file, --keyfile-offset, --keyfile-size,
--new-keyfile-offset, --new-keyfile-size, --key-slot, --master-key-file,
--force-password, --header, --disable-locks, --iter-time, --pbkdf,
--pbkdf-force-iterations, --unbound, --type, --keyslot-cipher, --keyslot-key-size].
luksRemoveKey <device> [<key file with passphrase to be removed>]
Removes the supplied passphrase from the LUKS device. The passphrase to be removed
can be specified interactively, as the positional argument or via --key-file.
<options> can be [--key-file, --keyfile-offset, --keyfile-size, --header,
--disable-locks, --type]
WARNING: If you read the passphrase from stdin (without further argument or with
'-' as an argument to --key-file), batch-mode (-q) will be implicitly switched on
and no warning will be given when you remove the last remaining passphrase from a
LUKS container. Removing the last passphrase makes the LUKS container permanently
inaccessible.
luksChangeKey <device> [<new key file>]
Changes an existing passphrase. The passphrase to be changed must be supplied
interactively or via --key-file. The new passphrase can be supplied interactively
or in a file given as positional argument.
If a key-slot is specified (via --key-slot), the passphrase for that key-slot must
be given and the new passphrase will overwrite the specified key-slot. If no key-
slot is specified and there is still a free key-slot, then the new passphrase will
be put into a free key-slot before the key-slot containing the old passphrase is
purged. If there is no free key-slot, then the key-slot with the old passphrase is
overwritten directly.
WARNING: If a key-slot is overwritten, a media failure during this operation can
cause the overwrite to fail after the old passphrase has been wiped and make the
LUKS container inaccessible.
<options> can be [--key-file, --keyfile-offset, --keyfile-size,
--new-keyfile-offset, --iter-time, --pbkdf, --pbkdf-force-iterations,
--new-keyfile-size, --key-slot, --force-password, --header, --disable-locks,
--type, --keyslot-cipher, --keyslot-key-size].
luksConvertKey <device>
Converts an existing LUKS2 keyslot to new pbkdf parameters. The passphrase for
keyslot to be converted must be supplied interactively or via --key-file. If no
--pbkdf parameters are specified LUKS2 default pbkdf values will apply.
If a keyslot is specified (via --key-slot), the passphrase for that keyslot must be
given. If no keyslot is specified and there is still a free keyslot, then the new
parameters will be put into a free keyslot before the keyslot containing the old
parameters is purged. If there is no free keyslot, then the keyslot with the old
parameters is overwritten directly.
WARNING: If a keyslot is overwritten, a media failure during this operation can
cause the overwrite to fail after the old parameters have been wiped and make the
LUKS container inaccessible.
<options> can be [--key-file, --keyfile-offset, --keyfile-size, --key-slot,
--header, --disable-locks, --iter-time, --pbkdf, --pbkdf-force-iterations,
--pbkdf-memory, --pbkdf-parallel, --keyslot-cipher, --keyslot-key-size].
luksKillSlot <device> <key slot number>
Wipe the key-slot number <key slot> from the LUKS device. Except running in batch-
mode (-q) a remaining passphrase must be supplied, either interactively or via
--key-file. This command can remove the last remaining key-slot, but requires an
interactive confirmation when doing so. Removing the last passphrase makes a LUKS
container permanently inaccessible.
<options> can be [--key-file, --keyfile-offset, --keyfile-size, --header,
--disable-locks, --type].
WARNING: If you read the passphrase from stdin (without further argument or with
'-' as an argument to --key-file), batch-mode (-q) will be implicitly switched on
and no warning will be given when you remove the last remaining passphrase from a
LUKS container. Removing the last passphrase makes the LUKS container permanently
inaccessible.
NOTE: If there is no passphrase provided (on stdin or through --key-file argument)
and batch-mode (-q) is active, the key-slot is removed without any other warning.
erase <device>
luksErase <device>
Erase all keyslots and make the LUKS container permanently inaccessible. You do
not need to provide any password for this operation.
WARNING: This operation is irreversible.
luksUUID <device>
Print the UUID of a LUKS device.
Set new UUID if --uuid option is specified.
isLuks <device>
Returns true, if <device> is a LUKS device, false otherwise. Use option -v to get
human-readable feedback. 'Command successful.' means the device is a LUKS device.
By specifying --type you may query for specific LUKS version.
luksDump <device>
Dump the header information of a LUKS device.
If the --dump-master-key option is used, the LUKS device master key is dumped
instead of the keyslot info. Together with --master-key-file option, master key is
dumped to a file instead of standard output. Beware that the master key cannot be
changed without reencryption and can be used to decrypt the data stored in the LUKS
container without a passphrase and even without the LUKS header. This means that if
the master key is compromised, the whole device has to be erased to prevent further
access. Use this option carefully.
To dump the master key, a passphrase has to be supplied, either interactively or
via --key-file.
<options> can be [--dump-master-key, --key-file, --keyfile-offset, --keyfile-size,
--header, --disable-locks, --master-key-file, --type].
WARNING: If --dump-master-key is used with --key-file and the argument to
--key-file is '-', no validation question will be asked and no warning given.
luksHeaderBackup <device> --header-backup-file <file>
Stores a binary backup of the LUKS header and keyslot area.
Note: Using '-' as filename writes the header backup to a file named '-'.
WARNING: This backup file and a passphrase valid at the time of backup allows
decryption of the LUKS data area, even if the passphrase was later changed or
removed from the LUKS device. Also note that with a header backup you lose the
ability to securely wipe the LUKS device by just overwriting the header and key-
slots. You either need to securely erase all header backups in addition or
overwrite the encrypted data area as well. The second option is less secure, as
some sectors can survive, e.g. due to defect management.
luksHeaderRestore <device> --header-backup-file <file>
Restores a binary backup of the LUKS header and keyslot area from the specified
file.
Note: Using '-' as filename reads the header backup from a file named '-'.
WARNING: Header and keyslots will be replaced, only the passphrases from the backup
will work afterward.
This command requires that the master key size and data offset of the LUKS header
already on the device and of the header backup match. Alternatively, if there is no
LUKS header on the device, the backup will also be written to it.
token <add|remove|import|export> <device>
Action add creates new keyring token to enable auto-activation of the device. For
the auto-activation, the passphrase must be stored in keyring with the specified
description. Usually, the passphrase should be stored in user or user-session
keyring. The token command is supported only for LUKS2.
For adding new keyring token, option --key-description is mandatory. Also, new
token is assigned to key slot specified with --key-slot option or to all active key
slots in the case --key-slot option is omitted.
To remove existing token, specify the token ID which should be removed with
--token-id option.
WARNING: The action token remove removes any token type, not just keyring type from
token slot specified by --token-id option.
Action import can store arbitrary valid token json in LUKS2 header. It may be
passed via standard input or via file passed in --json-file option. If you specify
--key-slot then successfully imported token is also assigned to the key slot.
Action export writes requested token json to a file passed with --json-file or to
standard output.
<options> can be [--header, --token-id, --key-slot, --key-description,
--disable-locks, --disable-keyring, --json-file].
convert <device> --type <format>
Converts the device between LUKS1 and LUKS2 format (if possible). The conversion
will not be performed if there is an additional LUKS2 feature or LUKS1 has
unsupported header size.
Conversion (both directions) must be performed on inactive device. There must not
be active dm-crypt mapping established for LUKS header requested for conversion.
--type option is mandatory with following accepted values: luks1 or luks2.
WARNING: The convert action can destroy the LUKS header in the case of a crash
during conversion or if a media error occurs. Always create a header backup before
performing this operation!
<options> can be [--header, --type].
config <device>
Set permanent configuration options (store to LUKS header). The config command is
supported only for LUKS2.
The permanent options can be --priority to set priority (normal, prefer, ignore)
for keyslot (specified by --key-slot) or --label and --subsystem.
<options> can be [--priority, --label, --subsystem, --key-slot, --header].
loop-AES EXTENSION
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>.
If the key file is encrypted with GnuPG, then you have to use --key-file=- and
decrypt it before use, e.g. like this:
gpg --decrypt <keyfile> | cryptsetup loopaesOpen --key-file=- <device> <name>
WARNING: The loop-AES extension cannot use the direct input of key file on real
terminal because the keys are separated by end-of-line and only part of the multi-
key file would be read.
If you need it in script, just use the pipe redirection:
echo $keyfile | cryptsetup loopaesOpen --key-file=- <device> <name>
Use --keyfile-size to specify the proper key length if needed.
Use --offset to specify device offset. Note that the units need to be specified in
number of 512 byte sectors.
Use --skip to specify the IV offset. If the original device used an offset and but
did not use it in IV sector calculations, you have to explicitly use --skip 0 in
addition to the offset parameter.
Use --hash to override the default hash function for passphrase hashing (otherwise
it is detected according to key size).
<options> can be [--key-file, --key-size, --offset, --skip, --hash, --readonly,
--allow-discards, --refresh].
See also section 7 of the FAQ and http://loop-aes.sourceforge.net for more information
regarding loop-AES.
TCRYPT (TrueCrypt-compatible and VeraCrypt) EXTENSION
cryptsetup supports mapping of TrueCrypt, tcplay or VeraCrypt (with --veracrypt option)
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).
To recognize a VeraCrypt device use the --veracrypt option. VeraCrypt is just extension
of TrueCrypt header with increased iteration count so unlocking can take quite a lot of
time (in comparison with TCRYPT device).
To open a VeraCrypt device with a custom Personal Iteration Multiplier (PIM) value,
additionally to --veracrypt 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 for
more detailed information.
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>.
<options> can be [--key-file, --tcrypt-hidden, --tcrypt-system, --tcrypt-backup,
--readonly, --test-passphrase, --allow-discards, --veracrypt, --veracrypt-pim,
--veracrypt-query-pim].
The keyfile parameter allows a combination of file content with the passphrase and
can be repeated. Note that using keyfiles is compatible with TCRYPT and is
different from LUKS keyfile logic.
WARNING: Option --allow-discards cannot be combined with option --tcrypt-hidden.
For normal mapping, it can cause the destruction of hidden volume (hidden volume
appears as unused space for outer volume so this space can be discarded).
tcryptDump <device>
Dump the header information of a TCRYPT device.
If the --dump-master-key option is used, the TCRYPT device master key is dumped
instead of TCRYPT header info. Beware that the master key (or concatenated master
keys if cipher chain is used) can be used to decrypt the data stored in the TCRYPT
container without a passphrase. This means that if the master key is compromised,
the whole device has to be erased to prevent further access. Use this option
carefully.
<options> can be [--dump-master-key, --key-file, --tcrypt-hidden, --tcrypt-system,
--tcrypt-backup].
The keyfile parameter allows a combination of file content with the passphrase and
can be repeated.
See also https://en.wikipedia.org/wiki/TrueCrypt for more information regarding TrueCrypt.
Please note that cryptsetup does not use TrueCrypt code, please report all problems
related to this compatibility extension to the cryptsetup project.
MISCELLANEOUS
repair <device>
Tries to repair the device metadata if possible. Currently supported only for LUKS
device type.
This command is useful to fix some known benign LUKS metadata header corruptions.
Only basic corruptions of unused keyslot are fixable. This command will only change
the LUKS header, not any key-slot data. You may enforce LUKS version by adding
--type option.
WARNING: Always create a binary backup of the original header before calling this
command.
benchmark <options>
Benchmarks ciphers and KDF (key derivation function). Without parameters, it tries
to measure few common configurations.
To benchmark other ciphers or modes, you need to specify --cipher and --key-size
options or --hash for KDF test.
NOTE: This benchmark is using memory only and is only informative. You cannot
directly predict real storage encryption speed from it.
For testing block ciphers, this benchmark 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).
<options> can be [--cipher, --key-size, --hash].
OPTIONS
--verbose, -v
Print more information on command execution.
--debug or --debug-json
Run in debug mode with full diagnostic logs. Debug output lines are always prefixed
by '#'. If --debug-json is used, additional LUKS2 JSON data structures are
printed.
--type <device-type>
Specifies required device type, for more info read BASIC COMMANDS section.
--hash, -h <hash-spec>
Specifies the passphrase hash for open (for plain and loopaes device types).
Specifies the hash used in the LUKS key setup scheme and volume key digest for
luksFormat. The specified hash is used as hash-parameter for PBKDF2 and for the AF
splitter.
The specified hash name is passed to the compiled-in crypto backend. Different
backends may support different hashes. For luksFormat, the hash algorithm must
provide at least 160 bits of output, which excludes, e.g., MD5. Do not use a non-
crypto hash like "crc32" as this breaks security.
Values compatible with old version of cryptsetup are "ripemd160" for open --type
plain and "sha1" for luksFormat.
Use cryptsetup --help to show the defaults.
--cipher, -c <cipher-spec>
Set the cipher specification string.
cryptsetup --help shows the compiled-in defaults. The current default in the
distributed sources is "aes-cbc-essiv:sha256" for plain dm-crypt and "aes-xts-
plain64" for LUKS.
If a hash is part of the cipher specification, then it is used as part of the IV
generation. For example, ESSIV needs a hash function, while "plain64" does not and
hence none is specified.
For XTS mode you can optionally set a key size of 512 bits with the -s option. Key
size for XTS mode is twice that for other modes for the same security level.
XTS mode requires kernel 2.6.24 or later and plain64 requires kernel 2.6.33 or
later. More information can be found in the FAQ.
--verify-passphrase, -y
When interactively asking for a passphrase, ask for it twice and complain if both
inputs do not match. Advised when creating a regular mapping for the first time, or
when running luksFormat. Ignored on input from file or stdin.
--key-file, -d name
Read the passphrase from file.
If the name given is "-", then the passphrase will be read from stdin. In this
case, reading will not stop at newline characters.
With LUKS, passphrases supplied via --key-file are always the existing passphrases
requested by a command, except in the case of luksFormat where --key-file is
equivalent to the positional key file argument.
If you want to set a new passphrase via key file, you have to use a positional
argument to luksAddKey.
See section NOTES ON PASSPHRASE PROCESSING for more information.
--keyfile-offset value
Skip value bytes at the beginning of the key file. Works with all commands that
accept key files.
--keyfile-size, -l value
Read a maximum of value bytes from the key file. The default is to read the whole
file up to the compiled-in maximum that can be queried with --help. Supplying more
data than the compiled-in maximum aborts the operation.
This option is useful to cut trailing newlines, for example. If --keyfile-offset is
also given, the size count starts after the offset. Works with all commands that
accept key files.
--new-keyfile-offset value
Skip value bytes at the start when adding a new passphrase from key file with
luksAddKey.
--new-keyfile-size value
Read a maximum of value bytes when adding a new passphrase from key file with
luksAddKey. The default is to read the whole file up to the compiled-in maximum
length that can be queried with --help. Supplying more than the compiled in
maximum aborts the operation. When --new-keyfile-offset is also given, reading
starts after the offset.
--master-key-file
Use a master key stored in a file.
For luksFormat this allows creating a LUKS header with this specific master key. If
the master key was taken from an existing LUKS header and all other parameters are
the same, then the new header decrypts the data encrypted with the header the
master key was taken from.
Action luksDump together with --dump-master-key option: The volume (master) key is
stored in a file instead of being printed out to standard output.
WARNING: If you create your own master key, you need to make sure to do it right.
Otherwise, you can end up with a low-entropy or otherwise partially predictable
master key which will compromise security.
For luksAddKey this allows adding a new passphrase without having to know an
existing one.
For open this allows one to open the LUKS device without giving a passphrase.
--dump-master-key
For luksDump this option includes the master key in the displayed information. Use
with care, as the master key can be used to bypass the passphrases, see also option
--master-key-file.
--json-file
Read token json from a file or write token to it. See token action for more
information. --json-file=- reads json from standard input or writes it to standard
output respectively.
--use-random
--use-urandom
For luksFormat these options define which kernel random number generator will be
used to create the master key (which is a long-term key).
See NOTES ON RANDOM NUMBER GENERATORS for more information. Use cryptsetup --help
to show the compiled-in default random number generator.
WARNING: In a low-entropy situation (e.g. in an embedded system), both selections
are problematic. Using /dev/urandom can lead to weak keys. Using /dev/random can
block a long time, potentially forever, if not enough entropy can be harvested by
the kernel.
--key-slot, -S <0-7>
For LUKS operations that add key material, this options allows you to specify which
key slot is selected for the new key. This option can be used for luksFormat, and
luksAddKey.
In addition, for open, this option selects a specific key-slot to compare the
passphrase against. If the given passphrase would only match a different key-slot,
the operation fails.
--key-size, -s <bits>
Sets 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.
See /proc/crypto for more information. Note that key-size in /proc/crypto is stated
in bytes.
This option can be used for open --type plain or luksFormat. All other LUKS
actions will use the key-size specified in the LUKS header. Use cryptsetup --help
to show the compiled-in defaults.
--size, -b <number of 512 byte sectors>
Set the size of the device in sectors of 512 bytes. This option is only relevant
for the open and resize actions.
--offset, -o <number of 512 byte sectors>
Start offset in the backend device in 512-byte sectors. This option is only
relevant for the open action with plain or loopaes device types or for LUKS devices
in luksFormat.
For LUKS, the --offset option sets the data offset (payload) of data device and
must be be aligned to 4096-byte sectors (must be multiple of 8). This option
cannot be combined with --align-payload option.
--skip, -p <number of 512 byte sectors>
Start offset used in IV calculation in 512-byte sectors (how many sectors of the
encrypted data to skip at the beginning). This option is only relevant for the
open action with plain or loopaes device types.
Hence, if --offset n, and --skip s, sector n (the first sector of the encrypted
device) will get a sector number of s for the IV calculation.
--device-size size[units]
Instead of real device size, use specified value.
With reencrypt action it means that only specified area (from the start of the
device to the specified size) will be reencrypted.
With resize action it sets new size of the device.
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 when used with reencrypt command.
--readonly, -r
set up a read-only mapping.
--shared
Creates an additional mapping for one common ciphertext device. Arbitrary mappings
are supported. This option is only relevant for the open --type plain action. Use
--offset, --size and --skip to specify the mapped area.
--pbkdf <PBKDF spec>
Set Password-Based Key Derivation Function (PBKDF) algorithm for LUKS keyslot. The
PBKDF can be: pbkdf2 (for PBKDF2 according to RFC2898), argon2i for Argon2i or
argon2id for Argon2id (see https://www.cryptolux.org/index.php/Argon2 for more
info).
For LUKS1, only PBKDF2 is accepted (no need to use this option). The default
PBKDF2 for LUKS2 is set during compilation time and is available in cryptsetup
--help output.
A PBKDF is used for increasing dictionary and brute-force attack cost for keyslot
passwords. The parameters can be time, memory and parallel cost.
For PBKDF2, only time cost (number of iterations) applies. For Argon2i/id, there
is also memory cost (memory required during the process of key derivation) and
parallel cost (number of threads that run in parallel during the key derivation.
Note that increasing memory cost also increases time, so the final parameter values
are measured by a benchmark. The benchmark tries to find iteration time
(--iter-time) with required memory cost --pbkdf-memory. If it is not possible, the
memory cost is decreased as well. The parallel cost --pbkdf-parallel is constant,
is is checked against available CPU cores (if not available, it is decreased) and
the maximum parallel cost is 4.
You can see all PBKDF parameters for particular LUKS2 keyslot with luksDump
command.
NOTE: If you do not want to use benchmark and want to specify all parameters
directly, use --pbkdf-force-iterations with --pbkdf-memory and --pbkdf-parallel.
This will override the values without benchmarking. Note it can cause extremely
long unlocking time. Use only is specified cases, for example, if you know that the
formatted device will be used on some small embedded system. In this case, the
LUKS PBKDF2 digest will be set to the minimum iteration count.
--iter-time, -i <number of milliseconds>
The number of milliseconds to spend with PBKDF passphrase processing. This option
is only relevant for LUKS operations that set or change passphrases, such as
luksFormat or luksAddKey. Specifying 0 as parameter selects the compiled-in
default.
--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
decrease 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
maximal value, it is decreased automatically if CPU online count is lower. This
option is not available for PBKDF2.
--pbkdf-force-iterations <num>
Avoid PBKDF benchmark and set time cost (iterations) directly. It can be used for
LUKS/LUKS2 device only. See --pbkdf option for more info.
--batch-mode, -q
Suppresses all confirmation questions. Use with care!
If the -y option is not specified, this option also switches off the passphrase
verification for luksFormat.
--progress-frequency <seconds>
Print separate line every <seconds> with wipe progress.
--timeout, -t <number of seconds>
The number of seconds to wait before timeout on passphrase input via terminal. It
is relevant every time a passphrase is asked, for example for open, luksFormat or
luksAddKey. It has no effect if used in conjunction with --key-file.
This option is useful when the system should not stall if the user does not input a
passphrase, e.g. during boot. The default is a value of 0 seconds, which means to
wait forever.
--tries, -T
How often the input of the passphrase shall be retried. This option is relevant
every time a passphrase is asked, for example for open, luksFormat or luksAddKey.
The default is 3 tries.
--align-payload <number of 512 byte sectors>
Align payload at a boundary of value 512-byte sectors. This option is relevant for
luksFormat.
If not specified, cryptsetup tries to use the topology info provided by the kernel
for the underlying device to get the optimal alignment. If not available (or the
calculated value is a multiple of the default) data is by default aligned to a 1MiB
boundary (i.e. 2048 512-byte sectors).
For a detached LUKS header, this option specifies the offset on the data device.
See also the --header option.
WARNING: This option is DEPRECATED and has often unexpected impact to the data
offset and keyslot area size (for LUKS2) due to the complex rounding. For fixed
data device offset use --offset option instead.
--uuid=UUID
Use the provided UUID for the luksFormat command instead of generating a new one.
Changes the existing UUID when used with the luksUUID command.
The UUID must be provided in the standard UUID format, e.g.
12345678-1234-1234-1234-123456789abc.
--allow-discards
Allow the use of discard (TRIM) requests for the device. This option is only
relevant for open action.
WARNING: This command can have a negative security impact because it can make
filesystem-level operations visible on the physical device. For example,
information leaking filesystem type, used space, etc. may be extractable from the
physical device if the discarded blocks can be located later. If in doubt, do not
use it.
A kernel version of 3.1 or later is needed. For earlier kernels, this option is
ignored.
--perf-same_cpu_crypt
Perform encryption using the same cpu that IO was submitted on. The default is to
use an unbound workqueue so that encryption work is automatically balanced between
available CPUs. This option is only relevant for open action.
NOTE: This option is available only for low-level dm-crypt performance tuning, use
only if you need a change to default dm-crypt behaviour. Needs kernel 4.0 or later.
--perf-submit_from_crypt_cpus
Disable offloading writes to a separate thread after encryption. There are some
situations where offloading write bios from the encryption threads to a single
thread degrades performance significantly. The default is to offload write bios to
the same thread. This option is only relevant for open action.
NOTE: This option is available only for low-level dm-crypt performance tuning, use
only if you need a change to default dm-crypt behaviour. Needs kernel 4.0 or later.
--test-passphrase
Do not activate the device, just verify passphrase. This option is only relevant
for open action (the device mapping name is not mandatory if this option is used).
--header <device or file storing the LUKS header>
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.
This option is only relevant for LUKS devices and can be used with the luksFormat,
open, luksSuspend, luksResume, status and resize commands.
For luksFormat with a file name as the argument to --header, the file will be
automatically created if it does not exist. See the cryptsetup FAQ for header size
calculation.
For other commands that change the LUKS header (e.g. luksAddKey), specify the
device or file with the LUKS header directly as the LUKS device.
If used with luksFormat, the --align-payload option is taken as absolute sector
alignment on ciphertext device and can be zero.
WARNING: There is no check whether the ciphertext device specified actually belongs
to the header given. In fact, you can specify an arbitrary device as the ciphertext
device for open with the --header option. Use with care.
--header-backup-file <file>
Specify file with header backup for luksHeaderBackup or luksHeaderRestore actions.
--force-password
Do not use password quality checking for new LUKS passwords.
This option applies only to luksFormat, luksAddKey and luksChangeKey and is ignored
if cryptsetup is built without password quality checking support.
For more info about password quality check, see the manual page for
pwquality.conf(5) and passwdqc.conf(5).
--deferred
Defers device removal in close command until the last user closes it.
--disable-locks
Disable lock protection for metadata on disk. This option is valid only for LUKS2
and ignored for other formats.
WARNING: Do not use this option unless you run cryptsetup in a restricted
environment where locking is impossible to perform (where /run directory cannot be
used).
--disable-keyring
Do not load volume key in kernel keyring and store it directly in the dm-crypt
target instead. This option is supported only for the LUKS2 format.
--key-description <text>
Set key description in keyring for use with token command.
--priority <normal|prefer|ignore>
Set a priority for LUKS2 keyslot. The prefer priority marked slots are tried
before normal priority. The ignored priority means, that slot is never used, if
not explicitly requested by --key-slot option.
--token-id
Specify what token to use in actions token, open or resize. If omitted, all
available tokens will be checked before proceeding further with passphrase prompt.
--token-only
Do not proceed further with action (any of token, open or resize) if token
activation failed. Without the option, action asks for passphrase to proceed
further.
--sector-size <bytes>
Set sector size for use with disk encryption. It must be power of two and in range
512 - 4096 bytes. The default is 512 bytes sectors. This option is available only
in the LUKS2 mode.
Note that if sector size is higher than underlying device hardware sector and there
is not integrity protection that uses data journal, using this option can increase
risk on incomplete sector writes during a power fail.
If used together with --integrity option and dm-integrity journal, the atomicity of
writes is guaranteed in all cases (but it cost write performance - data has to be
written twice).
Increasing sector size from 512 bytes to 4096 bytes can provide better performance
on most of the modern storage devices and also with some hw encryption
accelerators.
--persistent
If used with LUKS2 devices and activation commands like open, the specified
activation flags are persistently written into metadata and used next time
automatically even for normal activation. (No need to use cryptab or other system
configuration files.) Only --allow-discards, --perf-same_cpu_crypt,
--perf-submit_from_crypt_cpus and --integrity-no-journal can be stored
persistently.
--refresh
Refreshes an active device with new set of parameters. See action refresh
description for more details.
--label <LABEL>
--subsystem <SUBSYSTEM> Set label and subsystem description for LUKS2 device, can
be used in config and format actions. The label and subsystem are optional fields
and can be later used in udev scripts for triggering user actions once device
marked by these labels is detected.
--integrity <integrity algorithm>
Specify integrity algorithm to be used for authenticated disk encryption in LUKS2.
WARNING: This extension is EXPERIMENTAL and requires dm-integrity kernel target
(available since kernel version 4.12). For native AEAD modes, also enable "User-
space interface for AEAD cipher algorithms" in "Cryptographic API" section
(CONFIG_CRYPTO_USER_API_AEAD .config option).
For more info, see AUTHENTICATED DISK ENCRYPTION section.
--luks2-metadata-size <size>
This option can be used to enlarge the LUKS2 metadata (JSON) area. The size
includes 4096 bytes for binary metadata (usable JSON area is smaller of the binary
area). According to LUKS2 specification, only these values are valid: 16, 32, 64,
128, 256, 512, 1024, 2048 and 4096 kB The <size> can be specified with unit suffix
(for example 128k).
--luks2-keyslots-size <size>
This option can be used to set specific size of the LUKS2 binary keyslot area (key
material is encrypted there). The value must be aligned to multiple of 4096 bytes
with maximum size 128MB. The <size> can be specified with unit suffix (for example
128k).
--keyslot-cipher <cipher-spec>
This option can be used to set specific cipher encryption for the LUKS2 keyslot
area.
--keyslot-key-size <bits>
This option can be used to set specific key size for the LUKS2 keyslot area.
--integrity-no-journal
Activate device with integrity protection without using data journal (direct write
of data and integrity tags). Note that without journal power fail can cause non-
atomic write and data corruption. Use only if journalling is performed on a
different storage layer.
--integrity-no-wipe
Skip wiping of device authentication (integrity) tags. If you skip this step,
sectors will report invalid integrity tag until an application write to the sector.
NOTE: Even some writes to the device can fail if the write is not aligned to page
size and page-cache initiates read of a sector with invalid integrity tag.
--unbound
Creates new LUKS2 unbound keyslot. See luksAddKey action for more details.
--tcrypt-hidden
--tcrypt-system --tcrypt-backup Specify which TrueCrypt on-disk header will be used
to open the device. See TCRYPT section for more info.
--veracrypt
Allow VeraCrypt compatible mode. Only for TCRYPT extension. See TCRYPT section for
more info.
--veracrypt-pim
--veracrypt-query-pim Use a custom Personal Iteration Multiplier (PIM) for
VeraCrypt device. See TCRYPT section for more info.
--serialize-memory-hard-pbkdf
Use a global lock to serialize unlocking of keyslots using memory-hard PBKDF.
NOTE: This is (ugly) workaround for a specific situation when multiple devices are
activated in parallel and system instead of reporting out of memory starts
unconditionally stop processes using out-of-memory killer.
DO NOT USE this switch until you are implementing boot environment with parallel
devices activation!
--encrypt
Initialize (and run) device encryption (reencrypt action parameter)
--decrypt
Initialize (and run) device decryption (reencrypt action parameter)
--init-only
Initialize reencryption (any variant) operation in LUKS2 metadata only and exit. If
any reencrypt operation is already initialized in metadata, the command with
--init-only parameter fails.
--resume-only
Resume reencryption (any variant) operation already described in LUKS2 metadata. If
no reencrypt operation is initialized, the command with --resume-only parameter
fails. Useful for resuming reencrypt operation without accidentally triggering new
reencryption operation.
--resilience <mode>
Reencryption resilience mode can be one of checksum, journal or none.
checksum: default mode, where individual checksums of ciphertext hotzone sectors
are stored, so the recovery process can detect which sectors where already
reencrypted. It requires that the device sector write is atomic.
journal: the hotzone is journaled in the binary area (so the data are written
twice).
none: performance mode. There is no protection and the only way it's safe to
interrupt the reencryption is similar to old offline reencryption utility.
(ctrl+c).
The option is ignored if reencryption with datashift mode is in progress.
--resilience-hash <hash>
The hash algorithm used with "--resilience checksum" only. The default hash is
sha256. With other resilience modes, the hash parameter is ignored.
--hotzone-size <size>
This option can be used to set an upper limit on the size of reencryption area
(hotzone). The <size> can be specified with unit suffix (for example 50M). Note
that actual hotzone size may be less than specified <size> due to other limitations
(free space in keyslots area or available memory).
--reduce-device-size <size>
Initialize LUKS2 reencryption with data device size reduction (currently only
--encrypt variant is supported).
Last <size> sectors of <device> will be used to properly initialize device
reencryption. That means any data at last <size> sectors will be lost.
It could be useful if you added some space to underlying partition or logical
volume (so last <size> sectors contains no data).
Recommended minimal size is twice the default LUKS2 header size
(--reduce-device-size 32M) for --encrypt use case. Be sure to have enough (at least
--reduce-device-size value of free space at the end of <device>).
WARNING: This is a destructive operation and cannot be reverted. Use with extreme
care - accidentally overwritten filesystems are usually unrecoverable.
--version
Show the program version.
--usage
Show short option help.
--help, -?
Show help text and default parameters.
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 ON 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.
NOTES ON PASSPHRASE PROCESSING FOR LUKS
LUKS uses PBKDF2 to protect against dictionary attacks and to give some protection to low-
entropy passphrases (see RFC 2898 and the 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.
NOTES ON 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 (master) 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.
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.
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/lock/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.
DEPRECATED ACTIONS
The reload action is no longer supported. Please use dmsetup(8) if you need to directly
manipulate with the device mapping table.
The luksDelKey was replaced with luksKillSlot.
REPORTING BUGS
Report bugs, including ones in the documentation, on the cryptsetup mailing list at <dm-
crypt@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 originally written by Jana Saout <jana@saout.de>
The LUKS extensions and original man page were written by Clemens Fruhwirth
<clemens@endorphin.org>.
Man page extensions by Milan Broz <gmazyland@gmail.com>.
Man page rewrite and extension by Arno Wagner <arno@wagner.name>.
COPYRIGHT
Copyright © 2004 Jana Saout
Copyright © 2004-2006 Clemens Fruhwirth
Copyright © 2012-2014 Arno Wagner
Copyright © 2009-2019 Red Hat, Inc.
Copyright © 2009-2019 Milan Broz
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 LUKS website at https://gitlab.com/cryptsetup/cryptsetup/
The cryptsetup FAQ, contained in the distribution package and online at
https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions
The cryptsetup mailing list and list archive, see FAQ entry 1.6.
The LUKS on-disk format specification available at
https://gitlab.com/cryptsetup/cryptsetup/wikis/Specification