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CRYPTSETUP(8)		     Maintenance Commands		 CRYPTSETUP(8)

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.

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 Crypt‐
       setup 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 vol‐
       ume.

       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.

BASIC COMMANDS
       The following are valid actions for all supported device types.

       open <name> <device> --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: open --type plain <device> <name> switched arguments)
	      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.

       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 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
       (created),  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)

	      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 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
	      mapped.

	      <options> can  be	 [--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].

	      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].

       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‐
	      ble.

	      <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
	      inaccessible.

	      <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.

loop-AES EXTENSION
       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‐
	      eter.

	      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	 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. Use the whole device not
       the system partition as the device parameter.

       To use hidden  header  (and  map	 hidden	 device,  if  available),  use
       --tcrypt-hidden option.

       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,
	      --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].

	      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 True‐
       Crypt.

       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  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].

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 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
	      both plain dm-crypt and LUKS.

	      For XTS mode (a possible future default), use "aes-xts-plain" or
	      better "aes-xts-plain64" as cipher specification and  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.
	      Ignores 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‐
	      ters.

	      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 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.

	      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
	      passphrase.

       --dump-master-key
	      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.

       --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 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
	      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>
	      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.

	      This  is different from the --offset options with respect to the
	      sector numbers used in  IV  calculation.	 Using	--offset  will
	      shift the IV calculation by the same negative amount.  Hence, if
	      --offset n, sector n will get a sector number of 0  for  the  IV
	      calculation.   Using --skip causes sector n to also be the first
	      sector of the mapped device, but with its number for IV  genera‐
	      tion is n.

       --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  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.

       --uuid=UUID
	      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.
	      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 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.

       --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 has 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.

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  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 --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 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 slow
       device.

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 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).

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 Christophe Saout <christophe@saout.de>
       The LUKS extensions and original man page were written by Clemens Fruh‐
       wirth <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 Christophe Saout
       Copyright © 2004-2006 Clemens Fruhwirth
       Copyright © 2009-2012 Red Hat, Inc.
       Copyright © 2009-2012 Milan Broz
       Copyright © 2012 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.

SEE ALSO
       The LUKS website at http://code.google.com/p/cryptsetup/

       The cryptsetup FAQ, contained in the distribution package and online at
       http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions

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

       The    LUKS    on-disk	 format	    specification     available	    at
       http://code.google.com/p/cryptsetup/wiki/Specification

cryptsetup			   May 2012			 CRYPTSETUP(8)
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