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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.

       erase <device>
       luksErase <device>

	      Erase all keyslots and make the LUKS container permanently inac‐
	      cessible.	 You do not need to  provide  any  password  for  this

	      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  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,  --allow-dis‐

	      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 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 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

       --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 © 2009-2014 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

       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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