CRYPTSETUP(8) Maintenance Commands CRYPTSETUP(8)
cryptsetup - manage plain dm-crypt and LUKS encrypted volumes
cryptsetup <options> <action> <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
historic loopaes volumes and for TrueCrypt compatible volumes.
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 backup of an
encrypted volume.
Character encoding: If you enter a passphrase with special symbols,
the passphrase can change depending 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 to that, the cryptsetup FAQ describes
several options.
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), 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).
status <name>
Reports the status for the mapping <name>.
resize <name>
Resizes an active mapping <name>.
If --size (in sectors) is 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.
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,
--key-file, --keyfile-offset, --key-size, --offset, --skip,
--size, --readonly, --shared, --allow-discards]
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, 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.
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 be also 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 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 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.
<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, --force-password].
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. If
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].
luksSuspend <name>
Suspends an active device (all IO operations will blocked 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].
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]
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.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size, --new-keyfile-offset, --new-keyfile-size,
--key-slot, --master-key-file, --iter-time, --force-password,
--header].
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
positional argument or via --key-file.
<options> can be [--key-file, --keyfile-offset,
--keyfile-size, --header]
WARNING: If you read the passphrase from stdin (without
further argument or with '-' as 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, --new-keyfile-size,
--key-slot, --force-password, --header].
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].
WARNING: If you read the passphrase from stdin (without
further argument or with '-' as 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.
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. Beware that
the master key cannot be changed 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.
In order 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].
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 afterwards.
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.
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 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].
See also section 7 of the FAQ and http://loop-aes.sourceforge.net for
more information regarding loop-AES.
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://veracrypt.codeplex.com/wikipage?title=Personal%20Iterations%20Multiplier%20(PIM)
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 image in file), then only this partition is mapped.
If you have 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 whole base device as 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 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].
The keyfile parameter allows 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
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 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
cryptsetup project.
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.
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].
--verbose, -v
Print more information on command execution.
--debug
Run in debug mode with full diagnostic logs. Debug output
lines are always prefixed by '#'.
--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 accepts key files.
--keyfile-size, -l value
Read a maximum of value bytes from the key file. 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 accepts 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. 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.
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 exiting 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.
--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.
--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 encrypted device) will get a sector number of s for the IV
calculation.
--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.
--iter-time, -i <number of milliseconds>
The number of milliseconds to spend with PBKDF2 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.
--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.
--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 kernel for the underlying device to get 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.
--uuid=UUID
Use the provided UUID for the luksFormat command instead of
generating 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 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 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 options 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 argument to --header, it
has to exist and be large enough to contain the LUKS header.
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.
--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 manual page
for pwquality.conf(5) and passwdqc.conf(5).
--deferred
Defers device removal in close command until the last user
closes it.
--version
Show the program version.
--usage
Show short option help.
--help, -?
Show help text and default parameters.
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 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 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 second 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 (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.
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 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 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.
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.
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 © 2004 Jana Saout
Copyright © 2004-2006 Clemens Fruhwirth
Copyright © 2009-2017 Red Hat, Inc.
Copyright © 2009-2017 Milan Broz
Copyright © 2012-2014 Arno Wagner
This is free software; see the source for copying conditions. There
is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
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
This page is part of the Cryptsetup ((open-source disk encryption))
project. Information about the project can be found at
⟨https://gitlab.com/cryptsetup/cryptsetup⟩. If you have a bug report
for this manual page, send it to dm-crypt@saout.de. This page was
obtained from the project's upstream Git repository
⟨https://gitlab.com/cryptsetup/cryptsetup.git⟩ on 2017-07-05. If you
discover any rendering problems in this HTML version of the page, or
you believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
cryptsetup March 2017 CRYPTSETUP(8)
Pages that refer to this page: cryptsetup-reencrypt(8), systemd-gpt-auto-generator(8)