trusty (8) cryptsetup.8.gz

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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 Cryptsetup FAQ. Read it. Nonetheless, some  risks  deserve  to  be  mentioned
       here.

       Backup:  Storage  media die. Encryption has no influence on that.  Backup is mandatory for encrypted data
       as well, if the data has any worth. See the Cryptsetup FAQ for advice on how to do backup of an encrypted
       volume.

       Character  encoding:  If you enter a passphrase with special symbols, the passphrase can change depending
       character encoding. Keyboard settings can also change, which can make blind input hard or impossible. For
       example,  switching  from  some  ASCII 8-bit variant to UTF-8 can lead to a different binary encoding and
       hence different passphrase seen by cryptsetup, even if what you see on the terminal is exactly the  same.
       It is therefore highly recommended to select passphrase characters only from 7-bit ASCII, as the encoding
       for 7-bit ASCII stays the same for all ASCII variants and UTF-8.

       LUKS header: If the header of a LUKS volume gets damaged, all data is permanently lost unless you have  a
       header-backup.   If  a  key-slot  is  damaged, it can only be restored from a header-backup or if another
       active key-slot with known passphrase is undamaged.  Damaging the LUKS header is something people  manage
       to  do  with surprising frequency. This risk is the result of a trade-off between security and safety, as
       LUKS is designed for fast and secure wiping by just overwriting header and key-slot area.

       Previously used partitions: If a partition was previously used, it is a very good idea to wipe filesystem
       signatures,  data, etc. before creating a LUKS or plain dm-crypt container on it.  For a quick removal of
       filesystem signatures, use "wipefs". Take care though that this may not remove everything. In  particular
       md  (RAID)  signatures at the end of a device may survive. It also does not remove data. For a full wipe,
       overwrite the whole partition before container creation.  If  you  do  not  know  how  to  to  that,  the
       cryptsetup FAQ describes several options.

BASIC COMMANDS

       The following are valid actions for all supported device types.

       open <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 individual device types.

       close <name>

              Removes the existing mapping <name> and wipes the key from kernel memory.

              For  backward  compatibility  there  are  close  command  aliases:  remove, plainClose, luksClose,
              loopaesClose, tcryptClose (all behaves exactly the same, device type is  determined  automatically
              from active device).

       status <name>

              Reports the status for the mapping <name>.

       resize <name>

              Resizes an active mapping <name>.

              If  --size  (in  sectors)  is not specified, the size of the underlying block device is used. Note
              that this does not change the raw device geometry, it just changes how many  sectors  of  the  raw
              device are represented in the mapped device.

PLAIN MODE

       Plain  dm-crypt encrypts the device sector-by-sector with a single, non-salted hash of the passphrase. No
       checks are performed, no metadata is used. There is no formatting operation.   When  the  raw  device  is
       mapped  (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 container resides on is called a
       'LUKS device'.  For most purposes both terms can be used interchangeably. But note  that  when  the  LUKS
       header  is  at a nonzero offset in a device, then the device is not a LUKS device anymore, but has a LUKS
       container stored in it at an offset.

       LUKS can manage multiple passphrases that can be individually revoked or changed and that can be securely
       scrubbed from persistent media due to the use of anti-forensic stripes. Passphrases are protected against
       brute-force and dictionary attacks by  PBKDF2,  which  implements  hash  iteration  and  salting  in  one
       function.

       Each  passphrase,  also  called  a  key  in  this  document,  is associated with one of 8 key-slots.  Key
       operations that do not specify a slot affect the first slot that matches the supplied passphrase  or  the
       first empty slot if a new passphrase is added.

       The following are valid LUKS actions:

       luksFormat <device> [<key file>]

              Initializes  a  LUKS  partition  and  sets  the  initial  passphrase  (for key-slot 0), either via
              prompting or via <key file>. Note that if the second argument is present, then the  passphrase  is
              taken from the file given there, without the need to use the --key-file option. Also note that for
              both forms of reading the passphrase from file you can give '-' as file name, which results in the
              passphrase being read from stdin and the safety-question being skipped.

              You can only call luksFormat on a LUKS device that is not mapped.

              <options>  can  be  [--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 container. Removing the last passphrase makes
              the LUKS container permanently inaccessible.

       luksChangeKey <device> [<new key file>]

              Changes an existing passphrase. The passphrase to be changed must be supplied interactively or via
              --key-file.   The  new  passphrase  can be supplied interactively or in a file given as positional
              argument.

              If a key-slot is specified (via --key-slot), the passphrase for that key-slot must  be  given  and
              the new passphrase will overwrite the specified key-slot. If no key-slot is specified and there is
              still a free key-slot, then the new passphrase will be put into a free key-slot  before  the  key-
              slot containing the old passphrase is purged. If there is no free key-slot, then the key-slot with
              the old passphrase is overwritten directly.

              WARNING: If a key-slot is overwritten, a  media  failure  during  this  operation  can  cause  the
              overwrite  to  fail  after  the  old  passphrase  has  been  wiped  and  make  the  LUKS container
              inaccessible.

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

       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 container. 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 successful.'  means the device is a LUKS device.

       luksDump <device>

              Dump the header information of a LUKS device.

              If the --dump-master-key option is used, the LUKS device master  key  is  dumped  instead  of  the
              keyslot  info.  Beware  that  the master key cannot be changed and can be used to decrypt the data
              stored in the LUKS container without a passphrase and even without the  LUKS  header.  This  means
              that  if  the  master  key  is  compromised,  the whole device has to be erased to prevent further
              access. Use this option carefully.

              In order to dump the master key, a passphrase has to be  supplied,  either  interactively  or  via
              --key-file.

              <options> can be [--dump-master-key, --key-file, --keyfile-offset, --keyfile-size].

              WARNING:  If  --dump-master-key  is used with --key-file and the argument to --key-file is '-', no
              validation question will be asked and no warning given.

       luksHeaderBackup <device> --header-backup-file <file>

              Stores a binary backup of the LUKS header and keyslot area.
              Note: Using '-' as filename writes the header backup to a file named '-'.

              WARNING: This backup file and a passphrase valid at the time of backup allows  decryption  of  the
              LUKS  data  area,  even  if the passphrase was later changed or removed from the LUKS device. Also
              note that with a header backup you lose the ability to securely  wipe  the  LUKS  device  by  just
              overwriting  the  header  and  key-slots.  You either need to securely erase all header backups in
              addition or overwrite the encrypted data area as well.  The second option is less secure, as  some
              sectors can survive, e.g. due to defect management.

       luksHeaderRestore <device> --header-backup-file <file>

              Restores a binary backup of the LUKS header and keyslot area from the specified file.
              Note: Using '-' as filename reads the header backup from a file named '-'.

              WARNING:  Header  and  keyslots  will  be replaced, only the passphrases from the backup will work
              afterwards.

              This command requires that the master key size and data offset of the LUKS header already  on  the
              device  and  of  the header backup match. Alternatively, if there is no LUKS header on the device,
              the backup will also be written to it.

loop-AES EXTENSION

       cryptsetup supports mapping loop-AES encrypted partition using a compatibility mode.

       open --type loopaes <device> <name> --key-file <keyfile>
       loopaesOpen <device> <name> --key-file <keyfile>  (old syntax)

              Opens the loop-AES <device> and sets up a mapping <name>.

              If the key file is encrypted with GnuPG, then you have to use --key-file=- and decrypt  it  before
              use, e.g. like this:
              gpg --decrypt <keyfile> | cryptsetup loopaesOpen --key-file=- <device> <name>

              Use --keyfile-size to specify the proper key length if needed.

              Use  --offset  to specify device offset. Note that the units need to be specified in number of 512
              byte sectors.

              Use --skip to specify the IV offset. If the original device used an offset and but did not use  it
              in  IV  sector  calculations,  you  have  to  explicitly  use  --skip  0 in addition to the offset
              parameter.

              Use --hash to override the default hash function for passphrase hashing (otherwise it is  detected
              according to key size).

              <options> can be [--key-file, --key-size, --offset, --skip, --hash, --readonly, --allow-discards].

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

TCRYPT (TrueCrypt-compatible) EXTENSION

       cryptsetup supports mapping of TrueCrypt or tcplay encrypted partition using a native Linux  kernel  API.
       Header  formatting  and TCRYPT header change is not supported, cryptsetup never changes TCRYPT header on-
       device.

       TCRYPT extension requires kernel userspace crypto  API  to  be  available  (introduced  in  Linux  kernel
       2.6.38).   If  you are configuring kernel yourself, enable "User-space interface for symmetric key cipher
       algorithms" in "Cryptographic API" section (CRYPTO_USER_API_SKCIPHER .config option).

       Because TCRYPT header is encrypted, you have to always provide valid passphrase and keyfiles.

       Cryptsetup should recognize all header variants, except legacy cipher chains using  LRW  encryption  mode
       with  64  bits  encryption  block  (namely  Blowfish in LRW mode is not recognized, this is limitation of
       kernel crypto API).

       NOTE: Activation with tcryptOpen is supported only for cipher chains using LRW or XTS encryption modes.

       The tcryptDump command should work for all  recognized  TCRYPT  devices  and  doesn't  require  superuser
       privilege.

       To  map  system  device  (device with boot loader where the whole encrypted system resides) use --tcrypt-
       system option. 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 master key is dumped instead of TCRYPT
              header info. Beware that the master key (or concatenated master keys if cipher chain is used)  can
              be  used to decrypt the data stored in the TCRYPT container without a passphrase.  This means that
              if the master key is compromised, the whole device has to be erased to prevent further access. Use
              this option carefully.

              <options> can be [--dump-master-key, --key-file, --tcrypt-hidden, --tcrypt-system].

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

       See also http://www.truecrypt.org for more information regarding TrueCrypt.

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

MISCELLANEOUS

       repair <device>

              Tries to repair the device metadata if possible. Currently supported only for LUKS device type.

              This command is useful to fix some known benign  LUKS  metadata  header  corruptions.  Only  basic
              corruptions  of unused keyslot are fixable. This command will only change the LUKS header, not any
              key-slot data.

              WARNING: Always create a binary backup of the original header before calling this command.

       benchmark <options>

              Benchmarks ciphers and KDF (key derivation function).  Without parameters it tries to measure  few
              common configurations.

              To benchmark other ciphers or modes, you need to specify --cipher and --key-size options or --hash
              for KDF test.

              NOTE: This benchmark is using memory only and is only informative.  You  cannot  directly  predict
              real storage encryption speed from it.

              For  testing  block  ciphers,  this benchmark requires kernel userspace crypto API to be available
              (introduced in Linux kernel 2.6.38).  If you are configuring kernel yourself,  enable  "User-space
              interface    for    symmetric    key   cipher   algorithms"   in   "Cryptographic   API"   section
              (CRYPTO_USER_API_SKCIPHER .config option).

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

OPTIONS

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

       --debug
              Run in debug mode with full diagnostic logs. Debug output lines are always prefixed by '#'.

       --hash, -h <hash-spec>
              Specifies the passphrase hash for open (for plain and loopaes device types).

              Specifies the hash used in the LUKS key setup scheme and volume key digest for luksFormat.

              The specified hash 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 characters.

              With  LUKS, passphrases supplied via --key-file are always the existing passphrases requested by a
              command, except in the case of luksFormat where --key-file is equivalent  to  the  positional  key
              file argument.

              If  you  want  to  set  a  new  passphrase  via key file, you have to use a positional argument to
              luksAddKey.

              See section NOTES ON PASSPHRASE PROCESSING for more information.

       --keyfile-offset value
              Skip value bytes at the beginning of the key file.  Works  with  all  commands  that  accepts  key
              files.

       --keyfile-size, -l value
              Read  a  maximum  of  value  bytes from the key file.  Default is to read the whole file up to the
              compiled-in maximum that can be queried with --help. Supplying  more  data  than  the  compiled-in
              maximum aborts the operation.

              This  option  is  useful to cut trailing newlines, for example. If --keyfile-offset is also given,
              the size count starts after the offset.  Works with all commands that accepts key files.

       --new-keyfile-offset value
              Skip value bytes at the start when adding a new passphrase from key file with luksAddKey.

       --new-keyfile-size  value
              Read a maximum of value bytes when adding a new passphrase from key file with luksAddKey.  Default
              is  to  read  the whole file up to the compiled-in maximum length that can be queried with --help.
              Supplying more than the compiled in maximum aborts the operation.   When  --new-keyfile-offset  is
              also given, reading starts after the offset.

       --master-key-file
              Use a master key stored in a file.

              For luksFormat this allows creating a LUKS header with this specific master key. If the master key
              was taken from an existing LUKS header and all other parameters are the same, then the new  header
              decrypts the data encrypted with the header the master key was taken from.

              For luksAddKey this allows adding a new passphrase without having 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 displayed information. Use with care, as
              the master key can be used to bypass the passphrases, see also option --master-key-file.

       --use-random

       --use-urandom
              For luksFormat these options define which kernel random number generator will be  used  to  create
              the master key (which is a long-term key).

              See  NOTES  ON  RANDOM  NUMBER  GENERATORS for more information. Use cryptsetup --help to show the
              compiled-in default random number generator.

              WARNING: In a low-entropy situation (e.g. in an embedded system), both selections are problematic.
              Using  /dev/urandom  can  lead to weak keys.  Using /dev/random can block a long time, potentially
              forever, if not enough entropy can be harvested by the kernel.

       --key-slot, -S <0-7>
              For LUKS operations that add key material, this options allows you to specify which  key  slot  is
              selected for the new key.  This option can be used for luksFormat, and luksAddKey.
              In  addition, for open, this option selects a specific key-slot to compare the passphrase against.
              If the given passphrase would only match a different key-slot, the operation fails.

       --key-size, -s <bits>
              Sets key size in bits. The argument has to be a multiple of 8. The possible key-sizes are  limited
              by the cipher and mode used.

              See /proc/crypto for more information. Note that key-size in /proc/crypto is stated in bytes.

              This  option can be used for open --type plain or luksFormat.  All other LUKS actions will use the
              key-size specified in the LUKS header.  Use cryptsetup --help to show the compiled-in defaults.

       --size, -b <number of 512 byte sectors>
              Force the size of the underlying device in sectors of 512 bytes.  This option is only relevant for
              the open and resize actions.

       --offset, -o <number of 512 byte sectors>
              Start offset in the backend device in 512-byte sectors.  This option is only relevant for the open
              action with plain or loopaes device types.

       --skip, -p <number of 512 byte sectors>
              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  generation
              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 processing.  This option is only
              relevant for LUKS operations that set or change passphrases, such  as  luksFormat  or  luksAddKey.
              Specifying 0 as parameter selects the compiled-in default.

       --batch-mode, -q
              Suppresses all confirmation questions. Use with care!

              If  the  -y option is not specified, this option also switches off the passphrase verification for
              luksFormat.

       --timeout, -t <number of seconds>
              The number of seconds to wait before timeout on passphrase input  via  terminal.  It  is  relevant
              every  time  a  passphrase  is  asked,  for example for open, luksFormat or luksAddKey.  It has no
              effect if used in conjunction with --key-file.
              This option is useful when the system should not stall if the user does not  input  a  passphrase,
              e.g. during boot. The default is a value of 0 seconds, which means to wait forever.

       --tries, -T
              How  often  the  input  of  the passphrase shall be retried.  This option is relevant every time a
              passphrase is asked, for example for open, luksFormat or luksAddKey.  The default is 3 tries.

       --align-payload <number of 512 byte sectors>
              Align payload at a boundary of value 512-byte sectors.  This option is relevant for luksFormat.

              If not specified, cryptsetup tries to use the topology info provided by kernel for the  underlying
              device  to  get optimal alignment.  If not available (or the calculated value is a multiple of the
              default) data is by default aligned to a 1MiB boundary (i.e. 2048 512-byte sectors).

              For a detached LUKS header this option specifies the offset on  the  data  device.  See  also  the
              --header option.

       --uuid=UUID
              Use  the  provided  UUID  for  the  luksFormat  command instead of generating new one. Changes the
              existing UUID when used with the luksUUID command.

              The UUID must be provided in the standard UUID format, e.g. 12345678-1234-1234-1234-123456789abc.

       --allow-discards
              Allow the use of discard (TRIM) requests for device.   This  option  is  only  relevant  for  open
              action.

              WARNING:  This  command  can  have a negative security impact because it can make filesystem-level
              operations visible on the physical device. For example, information leaking filesystem type,  used
              space,  etc.  may  be  extractable from the physical device if the discarded blocks can be located
              later. If in doubt, do no use it.

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

       --test-passphrase
              Do not activate device, just verify passphrase.  This option is only relevant for open action (the
              device mapping name is not mandatory if this option is used).

       --header <device or file storing the LUKS header>
              Use  a  detached (separated) metadata device or file where the LUKS header is stored. This options
              allows to store ciphertext and LUKS header on different devices.

              This option is only relevant for  LUKS  devices  and  can  be  used  with  the  luksFormat,  open,
              luksSuspend, luksResume, status and resize commands.

              For  luksFormat  with  a file name as argument to --header, it has to exist and be large enough to
              contain the LUKS header.  See the cryptsetup FAQ for header size calculation.

              For other commands that change the LUKS header (e.g. luksAddKey), specify the device or file  with
              the LUKS header directly as the LUKS device.

              If  used  with  luksFormat,  the  --align-payload  option is taken as absolute sector alignment on
              ciphertext device and can be zero.

              WARNING: There is no check whether the ciphertext device specified actually belongs to the  header
              given.  In  fact  you  can  specify an arbitrary device as the ciphertext device for open with the
              --header option. Use with care.

       --force-password
              Do not use password quality checking for new LUKS passwords.

              This option applies only to luksFormat, luksAddKey and luksChangeKey and is ignored if  cryptsetup
              is built without password quality checking support.

              For more info about password quality check, see manual page for pwquality.conf(5).

       --version
              Show the program version.

       --usage
              Show short option help.

       --help, -?
              Show help text and default parameters.

RETURN CODES

       Cryptsetup returns 0 on success and a non-zero value on error.

       Error  codes  are:  1 wrong parameters, 2 no permission (bad passphrase), 3 out of memory, 4 wrong device
       specified, 5 device already exists or device is busy.

NOTES ON PASSPHRASE PROCESSING FOR PLAIN MODE

       Note that no iterated hashing or salting is done in plain mode.  If hashing  is  done,  it  is  a  single
       direct hash. This means that low-entropy passphrases are easy to attack in plain mode.

       From  a  terminal:  The  passphrase  is  read  until the first newline, i.e. '\n'.  The input without the
       newline character is processed with the default hash or the hash specified with --hash.  The  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
       maximum key file size and  can be overwritten using --keyfile-size option.

       The  data  read  will  be hashed with the default hash or the hash specified with --hash.  The has result
       will be truncated to the key size of the used cipher, or the size specified with -s.

       Note that if --key-file=- is used for reading the key from stdin, trailing newlines are not stripped from
       the input.

       If  "plain"  is  used  as argument to --hash, the input data will not be hashed. Instead, it will be zero
       padded (if shorter than the key size) or truncated (if longer than the key size) and used directly as the
       binary  key. This is useful for directly specifying a binary key.  No warning will be given if the amount
       of data read from stdin is less than the key size.

       From a key file: It will be truncated to the key size of the used cipher or the  size  given  by  -s  and
       directly  used  as  binary  key.   if  the key file is shorter than the key, cryptsetup will quit with an
       error.

NOTES ON PASSPHRASE PROCESSING FOR LUKS

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

       From  a terminal: The passphrase is read until the first newline and then processed by PBKDF2 without the
       newline character.

       From stdin: LUKS will read passphrases from stdin up to the first newline character  or  the  compiled-in
       maximum key file length. If --keyfile-size is given, it is ignored.

       From key file: The complete keyfile is read up to the compiled-in maximum size. Newline characters do not
       terminate the input. The --keyfile-size option can be used to limit what is read.

       Passphrase processing: Whenever a passphrase is added to a LUKS header (luksAddKey, luksFormat), the user
       may specify how much the time the passphrase processing should consume. The time is used to determine the
       iteration count for PBKDF2 and higher times will offer better protection for low-entropy passphrases, but
       open  will  take  longer  to complete. For passphrases that have entropy higher than the used key length,
       higher iteration times will not increase security.

       The default setting of one second is sufficient for most practical cases. The only exception  is  a  low-
       entropy passphrase used on a 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 automatically). Of course, you can always map a file to a loop-device manually. See
       the cryptsetup FAQ for an example.

       When  device  mapping is active, you can see the loop backing file in the status command output. Also see
       losetup(8).

DEPRECATED ACTIONS

       The reload action is no longer supported.  Please use dmsetup(8) if you need to directly manipulate  with
       the device mapping table.

       The luksDelKey was replaced with luksKillSlot.

REPORTING BUGS

       Report  bugs,  including ones in the documentation, on the cryptsetup mailing list at <dm-crypt@saout.de>
       or in the 'Issues' section on LUKS website.  Please attach the output of  the  failed  command  with  the
       --debug option added.

AUTHORS

       cryptsetup originally written by Christophe Saout <christophe@saout.de>
       The LUKS extensions and original man page were written by Clemens Fruhwirth <clemens@endorphin.org>.
       Man page extensions by Milan Broz <gmazyland@gmail.com>.
       Man page rewrite and extension by Arno Wagner <arno@wagner.name>.

       Copyright © 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