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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 his‐
       toric loopaes volumes and for TruerCrypt 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	Crypt‐
       setup  FAQ.  Read  it.  Nonetheless, some risks deserve to be mentioned

       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  vol‐

       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 crypt‐
       setup, 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 creat‐
       ing 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 individ‐
	      ual 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  ker‐
	      nel memory.

	      For  backward  compatibility  there  are	close command aliases:
	      remove, plainClose, luksClose,  loopaesClose,  tcryptClose  (all
	      behaves  exactly	the  same, device type is determined automati‐
	      cally 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	under‐
	      lying  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 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

       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  con‐
       tainer  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

	      <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-

	      <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

	      <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

	      <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,	--mas‐
	      ter-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 con‐
	      tainer. 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 over‐
	      write 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 inaccessi‐

	      <options>	 can be [--key-file, --keyfile-offset, --keyfile-size,
	      --new-keyfile-offset,	 --new-keyfile-size,	   --key-slot,

       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

	      <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 con‐
	      tainer. Removing the last passphrase makes  the  LUKS  container
	      permanently inaccessible.

       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  success‐
	      ful.'  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  mas‐
	      ter  key	cannot	be changed and can be used to decrypt the data
	      stored in the LUKS container without a passphrase and even with‐
	      out  the	LUKS header. This means that if the master key is com‐
	      promised, 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 sup‐
	      plied, either interactively or via --key-file.

	      <options> can be [--dump-master-key, --key-file,	--keyfile-off‐
	      set, --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.

       cryptsetup supports mapping loop-AES encrypted partition using  a  com‐
       patibility 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 param‐

	      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 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-

       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 algo‐
       rithms" in "Cryptographic API" section (CRYPTO_USER_API_SKCIPHER	 .con‐
       fig 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

       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].

	      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.

       tcryptDump <device>

	      Dump the header information of a TCRYPT device.

	      If  the --dump-master-key option is used, the TCRYPT device mas‐
	      ter 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 com‐
	      promised, the whole device has to be erased to  prevent  further
	      access. Use this option carefully.

	      <options>	 can  be [--dump-master-key, --key-file, --tcrypt-hid‐
	      den, --tcrypt-system, --tcrypt-backup].

	      The keyfile parameter allows combination of  file	 content  with
	      the passphrase and can be repeated.

       See  also for more information regarding True‐

       Please note that cryptsetup does not use TrueCrypt code, please	report
       all  problems  related  to  this	 compatibility extension to cryptsetup

       repair <device>

	      Tries to repair the device metadata if possible. Currently  sup‐
	      ported 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 informa‐
	      tive.  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 "Crypto‐
	      graphic API" section (CRYPTO_USER_API_SKCIPHER .config option).

	      <options> can be [--cipher, --key-size, --hash].

       --verbose, -v
	      Print more information on command execution.

	      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 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.

	      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

       --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 charac‐

	      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.

	      Use a master key stored in a file.

	      For luksFormat this allows creating a LUKS header with this spe‐
	      cific  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 compro‐
	      mise security.

	      For  luksAddKey this allows adding a new passphrase without hav‐
	      ing to know an exiting one.

	      For open this allows to open the LUKS device  without  giving  a

	      For  luksDump  this  option  includes the master key in the dis‐
	      played information. Use with care, as the master key can be used
	      to bypass the passphrases, see also option --master-key-file.


	      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

	      WARNING:	In  a  low-entropy situation (e.g. in an embedded sys‐
	      tem), 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

       --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

       --readonly, -r
	      set up a read-only mapping.

	      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 pro‐
	      cessing.	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 pro‐
	      vided by kernel for the underlying device to get optimal	align‐
	      ment.   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.

	      Use the provided UUID for the luksFormat command instead of gen‐
	      erating  new  one.  Changes the existing UUID when used with the
	      luksUUID command.

	      The UUID must be provided in  the	 standard  UUID	 format,  e.g.

	      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.

	      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 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.  luksAdd‐
	      Key),  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 speci‐
	      fied actually belongs to the header given. In fact you can spec‐
	      ify  an  arbitrary device as the ciphertext device for open with
	      the --header option. Use with care.

	      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

	      Show the program version.

	      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 maxi‐
       mum key file size and  can be overwritten using --keyfile-size option.

       The data read will be hashed with the default hash or the  hash	speci‐
       fied  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.

       LUKS uses PBKDF2 to protect against dictionary attacks and to give some
       protection  to low-entropy passphrases (see RFC 2898 and the cryptsetup

       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 new‐
       line character or the compiled-in maximum key file  length.  If	--key‐
       file-size is given, it is ignored.

       From key file: The complete keyfile is read up to the compiled-in maxi‐
       mum size. Newline characters do not terminate  the  input.  The	--key‐
       file-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  protec‐
       tion  for  low-entropy  passphrases,  but open will take longer to com‐
       plete. 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 automati‐
       cally). 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 <> 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 Christophe Saout <>
       The LUKS extensions and original man page were written by Clemens Fruh‐
       wirth <>.
       Man page extensions by Milan Broz <>.
       Man page rewrite and extension by Arno Wagner <>.

       Copyright © 2004 Christophe Saout
       Copyright © 2004-2006 Clemens Fruhwirth
       Copyright © 2009-2012 Red Hat, Inc.
       Copyright © 2009-2013 Milan Broz
       Copyright © 2012-2013 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

       The LUKS website at

       The cryptsetup FAQ, contained in the distribution package and online at

       The cryptsetup mailing list and list archive, see FAQ entry 1.6.

       The    LUKS    on-disk	 format	    specification     available	    at

cryptsetup			 December 2013			 CRYPTSETUP(8)

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