Ubuntu Manpage: cryptsetup - manage plain dm-crypt and LUKS encrypted volumes

Provided by: cryptsetup-bin_1.6.6-5ubuntu2.1_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 historic  loopaes  volumes
       and for TruerCrypt 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 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.

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), 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 of the underlying block device 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 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,  --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 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.

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 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.

The <device> parameter can be also specified by LUKS UUID in the format
UUID=<uuid>, which uses the symlinks in /dev/disk/by-uuid.

<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].

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]

WARNING: If you read the passphrase from stdin (without further argument or with
'-' as argument to --key-file), batch-mode (-q) will be implicitely 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].

luksKillSlot <device> <key slot number>

Wipe the key-slot number <key slot> from the LUKS device. 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].

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].

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.

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>

              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.

TCRYPT (TrueCrypt-compatible) EXTENSION

cryptsetup supports mapping of TrueCrypt or tcplay 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).

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 http://www.truecrypt.org 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.

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.

              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
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 spefification, 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>
Force the size of the underlying 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 no
use it.

A kernel version of 3.1 or later is needed. For earlier kernels this option is
ignored.

--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).

--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
has 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. if the key file is shorter than the key,
cryptsetup will quit with an error.

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 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.

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.

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 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).

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 © 2009-2012 Red Hat, Inc.
       Copyright © 2009-2014 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.