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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.

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.

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>.

       There are four operations:

       create <name> <device>

	      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   create  e1  /dev/sda10'	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.

       remove <name>

	      Removes the existing mapping <name> and wipes the key from  ker‐
	      nel memory.

       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.

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.

       luksOpen <device> <name>

	      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,  --allow-discards,  --header,	 --key-slot, --master-
	      key-file].

       luksClose <name>

	      identical to remove.

       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 luksClose 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.

       repair <device>

	      Tries to repair the LUKS device metadata if possible.

	      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.

loop-AES EXTENSION
       cryptsetup  supports  mapping loop-AES encrypted partition using a com‐
       patibility mode.

       loopaesOpen <device> <name> --key-file <keyfile>

	      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 --key-file-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].

       loopaesClose <name>

	      Identical to remove.

       See also section 7 of the FAQ and  http://loop-aes.sourceforge.net  for
       more information regarding loop-AES.

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 create and loopaesOpen.

	      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 create 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  luksOpen 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 luksOpen, 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 create 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 create 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 create and loopaesOpen actions.

       --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 create and loopaesOpen action.

	      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 create action. Use --offset, --size and --skip to spec‐
	      ify 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 create, luksOpen, 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 create, luksOpen, 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 create, luksOpen and loopaesOpen.

	      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.

       --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, luksOpen, 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 luksOpen
	      with the --header option. Use with care.

       --version
	      Show the program version.

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 luksOpen 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 © 2009-2011 Red Hat, Inc.
       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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